Meridian Gyrocompass

S G BrownA Division of TSS (UK) Limited Meridian Gyrocompass System Manual SG Brown 1 Garnett Close Greycaine Industrial Estate Watford Hertfordshire WD2 4JL UK The information in this Manual is subject to change without notice and does not represent Telephone +44 (0)1923 470800 Facsimile +44 (0)1923 470838 a commitment on the part of SG Brown Document P/N 060070 Issue 2.0 © SG Brown May 2000 Abcdef Contents CAUTIONARY NOTICES Your attention is drawn to the following cautionary notices that apply throughout this Manual. WARNING The Meridian Gyrocompass weighs 15.5kg. To avoid personal injury, take proper precautions if you lift or move the equipment. CAUTION The Meridian Gyrocompass includes precision components and bearings. To avoid causing damage to any part of the System, handle all items with care. Retain the original transit cases so that you can use them to transport the system when necessary. You will void the warranty if you use improper packing during transportation. CAUTION Severe damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation. Note that the gyro rotor continues to spin for approximately ten minutes after you power-off the system. To avoid potential damage to the Meridian Gyrocompass, always allow a period of ten minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass. CAUTION During operation, the gyrocompass must remain level to within ±45°. If it experiences tilt greater than 45° in any direction, it will ‘topple’. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. To restore normal operation, establish a level operating attitude and then power-on the gyrocompass normally. Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocompass initialisation procedure. Note that the gyro rotor continues to spin for approximately ten minutes after you power-off the System. CAUTION If you install the gyrocompass in an enclosed space, make certain there is sufficient ventilation and circulation of free air to allow effective cooling. CAUTION Do not make any connections to the gyrocompass with power on the supply cable. DPN 060070 Issue 2.0C © SGBrown Page 1 of 6 Meridian Gyrocompass CAUTION You will void the warranty if you make any modifications to this equipment without prior permission from SG Brown. DO NOT modify this equipment in any way without obtaining permission from SG Brown. Page 2 of 6 © SGBrown Issue 2.0C DPN 060070 . 1.1 Power Requirements 4.1 Control Features 3.2.3 Auxiliary Inputs 1.1.2.4 Environment 4.2 Loss of speed log 3.2 Remote Control Unit 1.5 Signal Inputs 4.4.1 Specifications 4.2 Gyrocompass installation 2.2.2 Operating Considerations for High Speed Craft 3–1 3–2 3–3 3–4 3–4 3–4 3–5 3–5 3–5 3–6 3–6 3–8 3–8 3–8 4 TECHNICAL DATA 4.8 Standards 4.2 Speed correction 3.5.1.1.3.2 Principle of Operation 1–1 1–3 1–3 1–4 1–5 1–5 1–5 2 INSTALLATION 2.1 Unpacking and Inspection 2.4 Set the Gyrocompass DIP Switches 2.3.1.1.3 External Remote Control Unit 2.2.0C © SGBrown Page 3 of 6 .1 Latitude correction 3.5.2 Physical and Electrical Installation 2.2 Performance (definitions as in ISO 8728) 4.3.2 Data Formats 4.2.4.4 Error Modes 3.2 Initial Power-on 3.Contents CONTENTS 1 INTRODUCTION 1.2.1.7 Dimensions and Weight 4.1 Gyrocompass 1.1.1.4.1 NMEA 0183 Serial Data Formats – General information 4.1 System Description 1.1 Selecting a location 2.4 Heading Outputs 1.4 Final Gyrocompass Installation Tests 2.2 Inputs 4–1 4–1 4–1 4–1 4–1 4–1 4–1 4–2 4–2 4–2 4–3 4–4 4–5 DPN 060070 Issue 2.1.5 Installation Drawings 2–1 2–2 2–3 2–3 2–4 2–9 2–10 2–12 2–13 2–14 3 OPERATING INSTRUCTIONS 3.1.3 Alignment 2.3 DG operating mode 3.3 Compensation 4.1 General Operating Considerations 3.6 Signal outputs 4.3 Operating Procedure 3.5 Operating Considerations 3.1 Loss of GPS 3.3 Gyrocompass failure 3.1. 1 Built-in Test Equipment 5.1 NMEA output signals 4.3 Outputs 4.1 North-seeking Gyroscope A.5 NMEA 0183 sentence with Checksum 4.2.Meridian Gyrocompass 4.6.2.4 Rate of Turn 4–5 4–9 4–10 4–10 4–14 4–15 4–15 4–15 4–15 4–16 4–16 5 MAINTENANCE 5.2 Gyro Damping A.2 Azimuth Bias Adjustment 5.3.1 NMEA 0183 input signals 4.6.2.2.2.3 Summary A–1 A–2 A–5 A–5 A–5 A–6 A–7 Page 4 of 6 © SGBrown Issue 2.2 Resolver Output 4.2.3 Speed Error A.2 Test Connector 5–1 5–2 5–3 5–3 5–4 A OPERATING THEORY A.1.2.2 Gyrocompass Corrections A.1 Synchro Output 4.6.6 Other Output Formats 4.0C DPN 060070 .4 Course Recorder Output 4.2 Pulsed input 4.2.2.2.1.2.2.1 Latitude Correction A.3 Stepper S-Code 4.1 Azimuth Drift Adjustment 5.2.2.2.2.6. Add notification to avoid product modifications. Issue 2.0B 2.0C © SGBrown Page 5 of 6 .0A 2. Corrected identification of Azimuth Bias potentiometer and other details.Contents TABLE OF AMENDMENTS Old Issue New Issue Date – 2.0C 11 May 2000 12 Dec 2000 1 Mar 2001 23 Apr 2001 DPN 060070 Details New release.0 2. Modify power connection details. Include DIP switch default settings. Meridian Gyrocompass Page 6 of 6 © SGBrown Issue 2.0C DPN 060070 . The Meridian Gyrocompass specification makes the System ideal for installation and operation on board vessels of almost any size and in a wide range of applications.0C © SG Brown Page 1 of 6 . However. For your convenience.1 – Introduction 1 INTRODUCTION The Meridian Gyrocompass is a master heading reference instrument that applies the characteristics of a dynamically tuned gyroscope and the effects of gravity and earth rotation to provide a true north reference. Throughout this Manual all measurements conform to the SI standard of units unless otherwise indicated. It describes the System and contains full installation and operating instructions. WARNINGS Where appropriate. For your convenience. Among the standard features of the Meridian Gyrocompass are: ❐ A short settling time ❐ Operation from a 24V DC electrical supply This Manual is an important part of the Meridian Gyrocompass. CAUTION instructions alert you to the potential risk of damage to the System. this Manual includes several sections. This section includes full instructions to install the System and connect it to external equipment. DPN 060070 Issue 2. You should retain the Manual with the System for use by personnel who will install and operate it. You must obey these instructions: WARNING instructions alert you to a potential risk of death or injury to users of the System. Installation and operation of the Meridian Gyrocompass are not complex tasks. this Manual includes important safety information highlighted as WARNING and CAUTION instructions. the Table of Contents section includes copies of all the WARNING and CAUTION instructions included in this Manual. each of which describes specific features of the Meridian Gyrocompass: You should read sections 1 and 2 before you attempt to install the System: Section 1 contains introductory notes and describes those items supplied as standard. Section 2 describes how to select a suitable location for the gyrocompass. you should spend time to familiarise yourself with the contents of this Manual before you start to install or use the System. Time spent in identifying the task sequence now will ensure your System is operational in the minimum of time. Page 2 of 6 © SG Brown Issue 2. You should read sections 5 if you suspect a fault on the System: Section 5 describes how to use the internal 60-way test connector and explains how to conduct simple adjustments with the gyrocompass housing removed. DO NOT modify this equipment in any way without obtaining permission from SG Brown.Meridian Gyrocompass You should read sections 3 and 4 before you use the System: Section 3 describes how to operate the Meridian Gyrocompass. CAUTION You will void the warranty if you make any modifications to this equipment without prior permission from SG Brown. This Manual also contains the following appendices: Appendix A explains how a gyroscope can be made north seeking for use in a gyrocompass. Section 4 includes the System specifications and descriptions of the data formats.0C DPN 060070 . 1.1 Gyrocompass Figure 1–1: Gyrocompass housing with integral RCU Figure 1–1 shows the gyrocompass housing. the Meridian Gyrocompass uses information supplied by external equipment. ❐ RFI filter and distribution board. note that the gyrocompass weighs 15. achievable accuracy depends on the operating latitude and the vessel dynamics. The care that you take when you align the gyrocompass housing with the surveyed fore-aft axis of the vessel will have a direct impact on the accuracy of heading measurements delivered by the System. The Meridian Gyrocompass applies dynamic tuning to settle automatically to within 0.5kg and you must take due care when you lift and move it. However. Due to the physical principles of a north-seeking gyrocompass. the accu- DPN 060070 Issue 2.7° of the meridian within 45 minutes of power-on. ❐ Power supply board. To optimise its performance. such as radars and satellite communication antennas. Since the Meridian Gyrocompass is an ideal source of heading information for use by other systems on board.1.1 – Introduction 1. It is a relatively simple operation to install the gyrocompass and you should be able to accomplish this quickly without the need for specialised personnel or equipment.0C © SG Brown Page 3 of 6 . ❐ Digital and analogue control boards. which contains the following items: ❐ True north seeking dynamically tuned precision gyroscope and gimbal suspension assembly. for example a GPS receiver and a speed log. Refer to Appendix A for a simplified explanation of the gyrocompass theory of operation. to apply latitude and speed corrections.1 SYSTEM DESCRIPTION The Meridian Gyrocompass comprises two sub-assemblies: ❐ The gyrocompass housing ❐ The Remote Control Unit (RCU) Figure 1–1 shows the combined gyrocompass housing with the RCU included as an integral unit. Meridian Gyrocompass racy of its heading measurements will have a wide impact throughout the vessel.1. The four-character LED can show a range of information: ❐ Heading information. refer to Section 5 for instructions to renew this fuse and check the PSU board supplies. for example 012.3 when in the READY mode ❐ Source of speed signal when in SPEED mode ❐ Value of manually set speed when in SPEED mode with manual speed selected ❐ Source of latitude signal when in LAT mode ❐ Value of manually set latitude when in LAT mode with manual latitude selected ❐ Status of gyro when in ALARM mode ❐ Status of GPS when in ALARM mode ❐ Status of ship’s log when in ALARM mode ❐ Software version when in SOFTWARE VERSION mode Refer to Section 3 for instructions to operate the Meridian Gyrocompass. The only component available for user servicing is a 3A line fuse inside the gyrocompass housing. connect and align the Meridian Gyrocompass. Refer to Section 2 for full instructions to install. 1. Page 4 of 6 © SG Brown Issue 2. You should therefore take care when you install and align the gyrocompass. In case of failure.0C DPN 060070 .2 Remote Control Unit Figure 1–2: Remote Control Unit The Remote Control Unit (RCU) provides all the functions and indicators necessary to control and operate the Meridian Gyrocompass. However. 1. the true north direction. Ideally.1.3 Auxiliary Inputs Auxiliary inputs may be used for the Meridian Gyrocompass to apply latitude and speed corrections. Refer to Appendix A for the general theory of gyrocompass operation.0C © SG Brown Page 5 of 6 .4 Heading Outputs The Meridian Gyrocompass is a self-contained precision navigation instrument that is capable of supplying heading reference information simultaneously to a wide range of equipment on board the vessel. the Meridian Gyrocompass can supply heading information simultaneously through multiple channels using any of the common transmission formats. The advantage of using GPS or a speed log to provide correction signals is that they allow the Meridian Gyrocompass to apply corrections automatically. The Meridian Gyrocompass exploits this property and uses gravity control and earth rotation to align the gyroscope spin axis with the meridian. Throughout a typical vessel. i. DPN 060070 Issue 2.2 PRINCIPLE OF OPERATION In the absence of external influences. applications that can use information supplied by the Meridian Gyrocompass include: ❐ Autopilot ❐ Radars ❐ GPS ❐ Radio direction finder ❐ Course plotter and recorder ❐ Satellite communication systems ❐ Satellite television To support this wide range of equipment types.1 – Introduction 1. Section 2 includes instructions to connect and configure the external sources of latitude and speed information.1. Section 3 includes instructions to set the latitude and speed manually. 1.e. a free-spinning gyroscope will try to maintain a fixed orientation in space. Refer to Section 3 for a description of the available output channels and their data formats. you may supply this information manually if external sources are not available. the Meridian Gyrocompass should accept latitude and speed information from external sources such as a GPS receiver or a speed log. Meridian Gyrocompass Page 6 of 6 © SG Brown Issue 2.0C DPN 060070 . 2. 2.1 Unpacking and Inspection Page 2 Explains the inspection checks that you should perform as you unpack the Meridian Gyrocompass. Connect the system to an electrical supply and to external equipment. You should read this section carefully and understand the important instructions that it contains before you begin to install or connect the equipment. 2.2 – Installation 2 INSTALLATION To obtain the best performance from the Meridian Gyrocompass you must take care when you install and connect it.2 Physical and Electrical Installation Page 3 Choose a suitable location to install the Meridian Gyrocompass. This section includes all the information and instructions you will need to complete these tasks. DPN 060070 Issue 2.0C © SG Brown Page 1 of 18 .3 Alignment Page 12 The care that you take as you align the Meridian Gyrocompass with the fore-aft datum on the vessel will have a direct influence upon its accuracy. 0C DPN 060070 . always allow a period of ten minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass.1 UNPACKING AND INSPECTION WARNING The Meridian Gyrocompass weighs 15. Retain the original transit cases so that you can use them to transport the system when necessary. The packing case has a special design to protect the contents against shock during transit so that the equipment should arrive without damage or defect. To avoid loss or damage to any components of the system. Note that the gyro rotor continues to spin for approximately ten minutes after you power-off the system. To avoid potential damage to the Meridian Gyrocompass. You will void the warranty if you use improper packing during transportation. handle all items with care. take proper precautions if you lift or move the equipment. Notify SG Brown immediately if there are any components missing from the shipment. Obey the storage temperature limits listed in Section 4. Page 2 of 18 © SG Brown Issue 2. The Meridian Gyrocompass undergoes a full series of electrical and mechanical tests during manufacture and before dispatch. To avoid personal injury. The title page of this Manual lists the contact details for SG Brown.5kg. If you see any damage file a claim with the carrier and immediately notify SG Brown. As soon as possible after you have received the system. CAUTION The Meridian Gyrocompass includes precision components and bearings. CAUTION Severe damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation. Inspect all sub-assemblies carefully to check for any damage that may have occurred during transportation. check all items against the shipping documents.Meridian Gyrocompass 2. To avoid causing damage to any part of the System. store all sub-assemblies safely in the transit case until you need to install them. or enclosed within a cabinet.2 PHYSICAL AND ELECTRICAL INSTALLATION 2.2 – Installation 2. or in a location susceptible to vibration or shock. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. as on a chart table.5kg. Note that the gyro rotor continues to spin for approximately ten minutes after you power-off the System. ❐ Do not install the Meridian Gyrocompass close to strong mechanical or electrical noise sources. Choose a mounting location that is level. the gyrocompass must remain level to within ±45°. To restore normal operation. ❐ Allow a minimum distance of 1. connect and service the Meridian Gyrocompass. Refer to Figure 2–6 for clearance dimensions. it will ‘topple’.0C © SG Brown Page 3 of 18 . DPN 060070 Issue 2. CAUTION If you install the gyrocompass in an enclosed space. ❐ The gyrocompass weighs 15.3m between the gyrocompass housing and any standard magnetic compasses.2. ❐ Choose a location that allows convenient access to install. make certain there is sufficient ventilation and circulation of free air to allow effective cooling. ❐ Choose a location that protects the Meridian Gyrocompass from damage. Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocompass initialisation procedure. If it experiences tilt greater than 45° in any direction. The mounting location can be open. establish a level operating attitude and then power-on the gyrocompass normally. flat and sufficiently strong to support the unit without flexing or experiencing extreme vibration.1 Selecting a location There are certain guidelines that you should follow to install the Meridian Gyrocompass successfully: CAUTION During operation. ❐ Do not install or operate the Meridian Gyrocompass where the ambient temperature could fall below 0°C or rise above +45°C. or where rapid changes of temperature can occur. 2 Gyrocompass installation You must align the Meridian Gyrocompass so that its fore-aft axis is parallel to the foreaft datum on the vessel. During installation you must align the Meridian Gyrocompass so that its fore-aft axis is parallel with the fore-aft datum on the vessel. Refer to Figures 2–5 and 2–6 for dimensions.4mm (1.Meridian Gyrocompass 2. Three elongated securing holes machined into the gyrocompass base allow you to make fine adjustments to alignment after installation.5mm (1. There should be no need to remove the gyrocompass cover during installation. There is a removable panel on the top of the gyrocompass that allows access to the internal DIP switches and a 60-way test connector. comprising the Gland Plate and the Distribution Board.0C DPN 060070 .0mm2) butyl or EP rubber insulated. Serial data heading output Serial data speed input Serial data latitude input 1/0. butyl or EP rubber insulated. With the gyrocompass positioned accurately. You may gain access to make power and signal connections by removing the gland plate assembly. wire braided and CSP oversheathed. 1.2. CSP sheathed.6mm2) twisted pair. mark the supporting surface with the centre positions for the three securing holes.85mm (0. 2. There are alignment marks on the base of the Meridian Gyrocompass to help you achieve the correct alignment. Any misalignment between the gyrocompass housing and the vessel will have a direct effect on the accuracy of heading measurements delivered by the system.5mm × 150mm ❐ Screwdriver 3mm × 75mm ❐ Nut spinner 5.5mm2) HOFR sheathed to BS6883 Synchro heading output Resolver heading output Stepper S-code output 7/0. wire braided and CSP oversheathed. CSP sheathed. Table 2–1: Suitable cable types Purpose Suitable cable Power supply 7/0. It is not necessary for the gyrocompass to be on the vessel centre line.5mm ❐ Combination spanner 10mm ❐ Hexagon key 2mm ❐ Adjustable spanner opening to at least 33mm ❐ Suitable cables for the installation as indicated in Table 2–1. To install the Meridian Gyrocompass you will need the following tools: ❐ Screwdriver 5. Page 4 of 18 © SG Brown Issue 2. 6. Figure 2–1 shows the Gland Plate. Connect a 24V electrical supply (acceptable range 18V to 36V DC) to the Meridian Gyrocompass at J1.2 – Installation 3. Remove the gyrocompass and drill three 8. m CAUTION Do not make any connections to the gyrocompass with power on the supply cable. 5. Use three M8 bolts with washers and nuts to secure the gyrocompass in position. The Distribution Board accepts open tails for all connections.5mm diameter holes. England. D. Make all necessary signal connections to the Meridian Gyrocompass at the Distribution Board. Glands A. Connect the ship’s safety ground to the earthing stud adjacent to the power connector. the three-pin power inlet on the Gland Plate. E. 7. Figure 2–1: Gyrocompass gland plate CAUTION Gland plate release screws Cover plate release screws Before removing the cover or the RCU unit. Safe Dist. 4. Deburr the holes and remove any swarf. Compass Min. F and J (identified in Figure 2–5) DPN 060070 Issue 2.15AF Mfg. using the marks you have just made on the supporting surface as hole centres.0C © SG Brown Page 5 of 18 . Fuse 3. remove the gland plate and disconnect the RCU cable (TB1/17-22) from the distribution board. Build Standard No. Serial No. Reposition the gyrocompass and align it to the fore-aft datum. Date Watford. Pass cables through available glands in the Gland Plate. and Tables 2–3 and 2–4 for cable connection details. connect all the wire braiding on the cables to the grounding posts on the inside surface of the Gland Plate as shown in Figure 2–2. To maintain EMC compliance.Meridian Gyrocompass accept cables up to 18mm diameter. Refit the Gland Plate. while all other glands accept cables up to 14mm diameter. 8. making certain there are no trapped wires or cables. Refer to Figure 2–3. Figure 2–3: Gyrocompass distribution board Page 6 of 18 © SG Brown Issue 2. Figure 2–2: Termination of wire braided cables 9.0C DPN 060070 . 2 – Installation Table 2–2: J1 – Power supply input pin details Pin Description 1 Protective ground 2 +24V DC 3 0V Table 2–3: Input signals Signal description Signal type DG Distribution Board connector TB1/1 TB1/2 (0V) GPS input NMEA 0183 RS232 TB1/3 TB1/4 (0V) GPS input NMEA 0183 RS422 TB1/5 (+) TB1/6 (–) Log input NMEA 0183 RS232 TB1/7 TB1/8 (0V) Log input NMEA 0183 RS422 TB1/9 (+) TB1/10 (–) TB1/11 TB1/12 (0V) TTL pulses TB1/13 (+) TB1/14 (0V) Voltage free contact close TB1/15 (+) TB1/16 (0V) RCU in TB1/17 (+) TB1/18 (–) RCU On/Off TB1/19 (–) TB1/20 (+) TB1/21 (A) TB1/22 (B) TB1/23 TB1/24 Log OK Log Log relay RCU Communications Spare DPN 060070 RS422 – Issue 2.0C © SG Brown Page 7 of 18 . Meridian Gyrocompass Table 2–4: Output signals Signal description Signal type Distribution Board connector Channel 2 NMEA 0183 RS232 (all data) TB2/1 TB2/2 (0V) Channel 1 NMEA 0183 RS232 (all data) TB2/3 TB2/4 (0V Channel 2 NMEA 0183 RS422 (all data) TB2/5 (+) TB2/6 (–) Channel 1 NMEA 0183 RS422 (all data) TB2/7 (+) TB2/8 (–) TB2/9 (5V) TB2/11 (L2) TB2/13 (0V) TB2/10 (L1) TB2/12 (L3) Heading TTL S-type Heading Synchro/resolver Gyro fail Voltage free contact closure TB2/14 (36V) res TB2/15 (26V) syn TB2/16 (0V) syn/res TB2/17 (S1) syn TB2/18 (S1) res TB2/19 (S2) syn/res TB2/20 (S3) syn/res TB2/21 (S4) res TB2/22 (CC) TB2/23 (NO) TB2/24 (NC) System Fail TTL Gyro ready Voltage free contact closure Gyro ready TTL TB2/30 TB2/31 (0V) Channel 2 NMEA 0183 RS232 TB3/1 TB3/2 (0V) Channel 2 NMEA 0183 RS232 TB3/3 TB3/4 (0V) Channel 2 NMEA 0183 RS232 TB3/5 TB3/6 (0V) Channel 2 NMEA 0183 RS422 TB3/7 (+) TB3/8 (–) Channel 2 NMEA 0183 RS422 TB3/9 (+) TB3/10 (–) Channel 2 NMEA 0183 RS422 TB3/11 (+) TB3/12 (–) Channel 2 NMEA 0183 RS422 TB3/13 (+) TB3/14 (–) Channel 2 NMEA 0183 RS422 TB3/15 (+) TB3/16 (–) Channel 2 NMEA 0183 RS422 TB3/17 (+) TB3/18 (–) Channel 2 NMEA 0183 RS422 TB3/19 (+) TB3/20 (–) Channel 2 NMEA 0183 RS422 TB3/21 (+) TB3/22 (–) Channel 2 NMEA 0183 RS422 TB3/23 (+) TB3/24 (–) Rate of turn Analogue ±10V TB3/25 TB3/26 (0V) NMEA 0183 RS232 TB3/27 TB3/28 (0V) Course recorder Page 8 of 18 © SG Brown TB2/25 TB2/26 (0V) TB2/27 (CC) TB2/28 (NO) TB2/29 (NC) Issue 2.0C DPN 060070 . 2 – Installation 2. 8. 7. There may be applications where you prefer to install the RCU at some distance from the gyrocompass unit.2.3 External Remote Control Unit The standard Meridian Gyrocompass has the Remote Control Unit (RCU) mounted integrally and available for immediate operation. The cable run between the RCU and the remote location must not exceed 100 metres. Use the two star knobs supplied to fit the RCU into the mounting bracket. The kit includes the following items: ❐ RCU housing ❐ Mounting bracket ❐ Blanking plate for the gyrocompass housing There is no need to remove the gyrocompass cover to install the RCU externally: 1. A mounting kit. 9. Refit the Gland Plate and secure it in place using the seven release screws. 6. Remove the seven Gland Plate release screws marked ! in Figure 2–1. DPN 060070 Issue 2.Route the cable through a vacant cable gland on the Gland Plate and make the correct connections to the TB1 terminals. You may also flush mount the RCU in a panel. Choose a suitable location to mount the RCU: ❐ The mounting surface can be vertical or horizontal according to requirements. ❐ Avoid installing the RCU where it might experience severe shock or vibration. Remove the Gland Plate. Supply and fit a cable to connect the RCU to TB1/17–22 on the Distribution Board . 2. 3. Fit the blanking plate to fill the gap left in the cover by the RCU. Lift the RCU away from the gyrocompass and install it at the remote location. Tilt the unit to a convenient viewing and operating angle and then lock it in place by tightening both star knobs. part number 929190. ❐ Choose a location for the RCU that allows a clear view of the display in all conditions. Note the connection sequence of the RCU cable at TB1/17–22 so that you can restore the same connections through the extension cable. 5. Release and remove the four M3 screws at the corners of the RCU that secure it to the gyrocompass housing. Disconnect the RCU cable at TB1/17–22 . The cable must have three screened twisted pairs and should not exceed 100 metres in length. Use the bracket with the mounting kit to fix the RCU to a desk or to a bulkhead. 4.0C © SG Brown Page 9 of 18 . is available to use in these circumstances. Meridian Gyrocompass 2. 4.4 Set the Gyrocompass DIP Switches 1. Power-off the gyrocompass before you make any changes to the DIP switch settings.2. There is a removable panel on top of the gyrocompass that allows access to the two internal DIP switches (shown in Figure 2–4) without the need to remove the main gyrocompass cover. Do not adjust the settings of other preset controls inside the gyrocompass.0C DPN 060070 . 3. Release and remove the three securing screws to lift off the panel. Refer to Tables 2–5 and 2–6 set the DIP switches carefully for the specific requirements of your installation. 2. Refit the access panel to the top of the gyrocompass cover Figure 2–4: Location of DIP switches. Azimuth bias potentiometer Tilt bias potentiometer DIP switches Page 10 of 18 © SG Brown Issue 2. 0C © SG Brown Page 11 of 18 . 2. Factory default settings appear in bold and are marked with an asterisk in this table.2 – Installation Table 2–5: SW1 DIP switch settings Switch number and setting 1 = on. DPN 060070 Issue 2. If you set a 10Hz update rate. the heading output defaults to HDT + ROT format only. 0 = off Function 1 1 0 1 0* Speed Log Input 100 pulses per nautical mile 200 pulses per nautical mile 400 pulses per nautical mile LOG NMEA* 2 1 1 0 0* 3 1* 0 Channel 1 Baud rate 4800* 9600 4 1* 0 Channel 2 Baud rate 4800* 9600 5 1 0* Channel 1 update rate 10 Hz 1 Hz* 6 1 0* Channel 2 update rate 10 Hz 1 Hz* 7 1* 0 NMEA sentence format for heading output HDT* VHW 8 1* 0 Directional gyro mode DG mode not selected* DG mode selected Notes: 1. The marks on the gyrocompass base plate are precision indicators of the gyrocompass alignment orientation. Any misalignment between the housing and the vessel will appear directly as a fixed error in heading measurements. There are several methods you may use to align the gyrocompass to the vessel fore-aft datum: ❐ Align the gyrocompass to the fore-aft datum using a known reference line. Remove any residual misalignment by making minuscule adjustments to the gyrocompass mounting plate.Meridian Gyrocompass Table 2–6: SW2 DIP switch settings Switch number and setting 1 = on. such as a surveyed bulkhead or frame member. tighten the securing bolts fully to lock the gyrocompass in position.3 ALIGNMENT It is important to align the gyrocompass to the vessel accurately.0C DPN 060070 . ❐ Use the services of a marine surveyor to align the gyrocompass precisely with the fore-aft datum. any misalignment between the gyrocompass and the fore-aft datum might have a significant impact in many other areas of application. When you have achieved perfect alignment. Page 12 of 18 © SG Brown Issue 2. 0 = off Function 1 1* 0 Execute software version Operational software* Illegal setting 2 1 0* Heading output resolution Two decimal places One decimal place* 3 1 0* Checksum selector Checksum NOT selected Checksum selected* 4 1 0* Channel 2 output selector NMEA 0183 HDT only NMEA 0183 all data* Switches 5 to 7 8 1 0* Not used Test mode Factory test mode selected Normal operational mode* 2. Because measurements from the Meridian Gyrocompass are available for use by diverse systems around the vessel. 0C © SG Brown Page 13 of 18 . 3. Alternatively. Power-on the gyrocompass by following the instructions in sub-section 3. Typically this could be the alongside position of the fitting-out dock.5°. accurately survey an object at least five kilometres ahead of the vessel using the fore-aft line as a datum.2 – Installation 2. If there is an error larger than ±0. 2. Wait for three hours before you perform the following tests.4 FINAL GYROCOMPASS INSTALLATION TESTS After you have installed the gyrocompass and power supplies are available to it. re-check the vessel fore-aft datum to confirm that it is correct. 4. perform the following installation tests: 1. Check the displayed gyrocompass heading at intervals to make certain it is consistent with the surveyed vessel heading. 5.2. DPN 060070 Issue 2. Check that all the repeaters are accurately aligned with the gyrocompass heading and make certain they maintain their alignment at all times while the gyrocompass is powered-on. Check the vessel heading against a known reference mark on a chart. Build Standard No. Serial No. Safe Dist.15AF Mfg. Compass Min.Issue 2. remove the gland plate and disconnect the RCU cable (TB1/17-22) from the distribution board.5 INSTALLATION DRAWINGS Meridian Gyrocompass . England. Date Watford.0C DPN 060070 0 14 150 160 170 180 190 200 210 S 22 0 0 23 240 SW SE 13 0 © SG Brown W 260 270 280 290 250 300 31 0 NE N 350 0 10 20 50 NW 340 330 60 E 80 90 100 110 70 120 Page 14 of 18 0 32 40 30 CAUTION Before removing the cover or the RCU unit. 24VDC Fuse 3. m Figure 2–5: Gyrocompass installation – Sheet 1 2. © SG Brown Page 15 of 18 0 14 150 170 180 190 200 160 210 S 22 0 0 23 NW NE N 350 0 340 10 20 60 260 270 280 290 250 300 240 W 31 0 SW SE E 80 90 100 110 120 13 0 Issue 2. England. Fuse 3. Serial No. Build Standard No. Date Watford. remove the gland plate and disconnect the RCU cable (TB1/17-22) from the distribution board. m Figure 2–6: Gyrocompass installation – Sheet 2 2 – Installation . Compass Min. Safe Dist.0C 70 330 50 DPN 060070 0 32 40 30 CAUTION Before removing the cover or the RCU unit.15AF 24VDC Mfg. Meridian Gyrocompass Figure 2–7: RCU installation – Table mount Page 16 of 18 © SG Brown Issue 2.0C DPN 060070 . 2 – Installation Figure 2–8: RCU installation – Flush mount DPN 060070 Issue 2.0C © SG Brown Page 17 of 18 . 0C DPN 060070 .Meridian Gyrocompass Page 18 of 18 © SG Brown Issue 2. Refer to Section 4 for an explanation of the data formats relevant to the System.3 Operating Procedure Page 4 Explains how to select the latitude and speed correction sources. It also includes a four-character display panel that shows the heading indication and any alarm messages and error codes.0C © SG Brown Page 1 of 10 . 3. and how to set the latitude and speed manually if necessary.4 Error Modes Page 5 Identifies the system error modes.1 Control Features Page 2 The RCU provides all the controls you will need to operate the Meridian Gyrocompass. 3. DPN 060070 Issue 2.3 – Operating Instructions 3 OPERATING INSTRUCTIONS This section explains how to power-on and configure the Meridian Gyrocompass after installation. Use these indicators to identify a possible fault condition. 3.5 Operating Considerations Page 8 Includes general advice for operating the Meridian Gyrocompass on a vessel and on high speed craft.2 Initial Power-on Page 3 Explains how to power-on the Meridian Gyrocompass after installation and describes the initialisation sequence. 3. 3. release-to-break button. This is a press-to-make.0C DPN 060070 . Use this button. together with the increase and decrease selection buttons to apply speed correction manually. " Selection button – Up. % Speed selection button. press-to-break switch. This is a press-to-make. Use this button. release-to-break button.Meridian Gyrocompass 3. © SG Brown Issue 2. Use this button to cancel an audible alarm. This is a press-to-make. Indicates that the Meridian Gyrocompass has settled to indicate the true heading. release-to-break button $ Latitude selection button. release-to-break button.1 CONTROL FEATURES Figure 3–1: RCU front panel features The RCU front panel includes all the operator controls for the Meridian Gyrocompass: Table 3–1: RCU Control and Indicator functions Control Function ! Power switch. This is a press-to-make. together with the increase and decrease selection buttons to apply latitude correction manually. recessed to prevent accidental operation. This is a press-to-make. & Alarm. release-to-break button. # Selection button – Down. Indicates 24V DC nominal power received by the Meridian Gyrocompass.3 Power lamp (red) Ready lamp (green) Page 2 of 10 Four-character display to indicate heading and system status. 012. This is a press-to-make. The display will continue to toggle for a further six seconds after you release the buttons and will then return to the heading indication.3. 7. The gyrocompass draws 3A from the DC supply during start-up.Y. 3. Wait for the gyrocompass to settle. This will occur automatically and will take between 24 and 45 minutes to complete. the alarm will silence and the display will flash the heading until the gyrocompass provides a stable north reference. Use the increase and decrease selection buttons to adjust the RCU illumination level to a comfortable setting.O.R. To ensure continuous operation. Check that the red ‘Power’ lamp on the RCU illuminates.3 – Operating Instructions 3. + . Set the source of speed information by following the instructions in sub-section 3. . 1. Set the source of latitude information by following the instructions in sub-section 3. 6. The display will toggle between indications of the main processor software version (with prefix ‘M’) and the control panel software (with prefix ‘R’). All operator controls are on the RCU. The Meridian Gyrocompass signifies its settled condition by illuminating the green ‘Ready’ lamp and by showing a stable heading on the RCU display. 8. In the following instruction sequence.2 INITIAL POWER-ON The Meridian Gyrocompass starting cycle is fully automatic after power-on. The acceptable supply range is 18V to 36V DC.2. If necessary. means that the four-character display alternates between showing ‘G. 9.Y. 2. On successful completion of the self-tests.O.1. 5.O. Check that there is a nominal 24V DC electrical supply available to the gyrocompass.N. for example.N. the instrument illumination may be difficult to see in bright ambient lighting. the power supply for this unit must have a 200W power rating. 4.’. The RCU will sound an alarm briefly and the display indicates ‘TEST’ while the system performs a series of self tests. This lamp indicates only that the Meridian Gyrocompass is receiving power and does NOT indicate a settled condition. you can view the software versions of the main and the control panel processors by pressing both the Up and the Down selection buttons simultaneously. .O. the display description ‘G.3.R.’ and ‘ .0C © SG Brown Page 3 of 10 . DPN 060070 Issue 2. Even at its maximum setting. Check that the instrument illumination is at maximum during the initialisation sequence.’. To start the Meridian Gyrocompass press the power switch on the RCU. 0C DPN 060070 . the Meridian Gyrocompass should accept latitude and speed information from external sources such as a GPS receiver or a speed log. 2. the display will flash and the Meridian Gyrocompass will not accept the selection as an input source. which sets the directional gyrocompass operating mode explained in subsection 3.2 Speed correction 1. Page 4 of 10 © SG Brown Issue 2. ❐ To select automatic speed compensation from a GPS receiver or a speed log. Press and hold the Latitude selection button. remember to change the setting when necessary. Release both buttons to set the latitude to the displayed value or to set the gyrocompass to use GPS as the source of automatic latitude correction.LOG.70.3. 2.Meridian Gyrocompass 3. If you input the operating latitude manually.3°.GPS or S. Note that.3. the display will flash and the Meridian Gyrocompass will not accept the selection as an input source. 3.GPS.1 Latitude correction 1. Use the up and down selection buttons "# to set the local latitude manually. Disregard the DG setting. use the up or down selection buttons "# to scroll beyond 80°N or 80°S until the display shows L. Release both buttons to set the speed to the displayed value or to set the gyrocompass to use GPS or a speed log as the source of automatic speed correction. The display will indicate the latitude source for a further three seconds and will then return to the normal heading display. Ideally. for example L. If there is no valid input available from a GPS receiver.3 OPERATING PROCEDURE The Meridian Gyrocompass will settle automatically after power-on. taking a maximum of 45 minutes to provide a true north reference. in medium latitudes. The display will indicate the latitude setting for a further three seconds and will then return to the normal heading display. to perform to the specified accuracy. If there is no valid input available from a speed log or GPS receiver. 3. The display will show the latitude in one-degree increments in the range 80°N to 80°S. a 10° error in setting the operating latitude will result in a compass error of approximately 0. The system requires only latitude and speed correction.N. use the up selection button " to scroll beyond 90 knots until the display shows S. applied manually or from external sources. Use the up and down selection buttons "# to set the speed manually in the range zero to 90 knots. which allow the System to apply corrections automatically. 3.3. 3.3. ❐ To select automatic latitude compensation from a GPS receiver. Press and hold the Speed selection button. 3 – Operating Instructions If you input the vessel speed manually, remember to set the average vessel speed and to change the setting when necessary. Return the setting to zero on completion of the voyage. For a vessel steaming in a northerly direction, a 5-knot error in speed setting will generate an error of approximately 0.5°. 3.3.3 DG operating mode Follow the instructions in sub-section 3.3.1 to set the latitude correction to the Directional Gyro (DG) mode. In this mode you can use the Meridian Gyrocompass as a direction indicating instrument all the way up to the poles. If the gyrocompass has settled on north immediately prior to entering the DG mode, it will continue to provide a useful indication of the northerly direction for a period, but will not continue to seek north. The length of time that the direction indication remains valid depends entirely on the gyro drift characteristics. Note that the gyrocompass will not north seek while operating in the DG mode. 3.4 ERROR MODES The Meridian Gyrocompass has three possible Error modes: 1. Loss or corruption of GPS signal 2. Loss or corruption of speed log signal 3. Gyrocompass failure 3.4.1 Loss of GPS This failure mode can occur when you have selected GPS as the source of speed or latitude information and the signal corrupts or becomes lost for a period of two minutes. You can recognise this condition by the following indications: ❐ The display flashes S.GPS + FAIL or L.GPS + FAIL at one-second intervals. ❐ An audible alarm will sound. Press the Alarm button to cancel the audible alarm. This will have two effects: 1. The audible alarm will cancel. 2. The RCU will automatically select the manual source for its speed or latitude input signal. It will use the most recent valid value supplied by the GPS source for the initial setting, although you can adjust this if necessary. If a signal is available from a speed log, you may set this as the speed source. DPN 060070 Issue 2.0C © SG Brown Page 5 of 10 Meridian Gyrocompass 3.4.2 Loss of speed log This failure mode can occur when you have selected the speed log as the source of speed information and the signal corrupts or becomes lost for a period of two minutes. You can recognise this condition by the following indications: ❐ The display flashes S.LOG + FAIL at one-second intervals. ❐ An audible alarm will sound. Press the Alarm button to cancel the alarm. This will have two effects: 1. The audible alarm will cancel. 2. The RCU will automatically select the manual source for its speed input signal. It will use the most recent valid value supplied by the speed log for the initial setting, although you can adjust this if necessary. If speed information is available from a GPS receiver, you may set this as the speed source. 3.4.3 Gyrocompass failure The Meridian Gyrocompass has a built-in system that monitors operation of the gyrocompass. If it detects a fault condition, it will use three methods to alert you: ❐ The display flashes GYRO + FAIL at one-second intervals. ❐ An audible alarm will sound. ❐ The ‘Ready’ lamp will extinguish. Press the Alarm button to cancel the audible alarm. The RCU uses the decimal points at each display character position to identify the cause of the failure. Figure 3–2: Gyrocompass failure codes Page 6 of 10 © SG Brown Issue 2.0C DPN 060070 3 – Operating Instructions If your system develops a fault condition as indicated by the display, refer to sub-section 5.1 for some simple checks that you can make. If necessary, contact SG Brown or an approved local service agent for assistance. DPN 060070 Issue 2.0C © SG Brown Page 7 of 10 the heading error in latitudes up to 60° and for speeds up to 25 knots will normally be less than 0. which generates an electrical signal related to the tilt of the gyro spin axis. When functioning correctly. ❐ The precession in tilt that arises from the damping component of gravity control is called ballistic tilt. 3. This effect. ❐ Never move the gyrocompass with the gyro rotor spinning unless you leave the servos operational.1 General Operating Considerations ❐ You should leave the Meridian Gyrocompass running continuously. The heading indication will be accurate when the RCU ‘Ready’ lamp is on.5. ❐ In the Meridian Gyrocompass. called ballistic deflection. you should arrange to run the gyrocompass for a period of at least thirty minutes at intervals of six months or less. The combined effects of ballistic tilt and ballistic deflection cause the gyrocompass to tilt downwards. Note that the gyro rotor continues to spin for a period of approximately ten minutes after you power-off the gyrocompass. the gyro spin axis will return to the settled position by the normal anticlockwise spiral after the acceleration has ceased.0C DPN 060070 . Power-off the system only during long periods of lay-up. The use of accelerometer damping by the Meridian Gyrocompass is of prime importance in the reduction of a particularly serious form of ballistic error called inter cardinal rolling error. The gyro rotor will take approximately ten minutes to come to rest. Page 8 of 10 © SG Brown Issue 2.2 Operating Considerations for High Speed Craft ❐ The gyrocompass gravity control gives rise to errors whenever the gyrocompass accelerates or decelerates along the north-south line.Meridian Gyrocompass 3.5. it is heavily damped and the range of output is restricted to a small angle. ❐ The Meridian Gyrocompass has full protection against interruption of its electrical supply. ❐ If you intend to leave the system powered-off for an extended period.75° regardless of the vessel manoeuvres.5 OPERATING CONSIDERATIONS 3. To power-off the Meridian Gyrocompass. which produces a torque about the horizontal axis and therefore a precession in azimuth. gravity control comes from an accelerometer (pendulum). It will re-start and align itself automatically on restoration of electrical power. for example during vessel dry-docking. This type of error occurs most noticeably when the vessel steams on an inter cardinal heading while rolling simultaneously through a significant angle. ❐ Monitor the Meridian Gyrocompass performance regularly. causes an increase in error during acceleration. press the ‘Power’ button. Because of the factors that guide the behaviour of a damped gyroscope. This devices has two important design features. The heading display will go blank and the front panel lamps will switch off. that is whenever the northerly speed or course changes. These errors are caused by the inertia of the pendulous element of the gyro. and provided the correct Speed and Latitude compensations are applied. ❐ It is also possible to eliminate the effects of acceleration by operating the gyrocompass temporarily in the directional gyro (DG) mode. by damping the accelerometer using a time constant several times larger than the vessel rolling period. ❐ Another form of ballistic error arises from north-south accelerations generated by vessel manoeuvres. the Meridian Gyrocompass reduces the error potential typically to less than one degree. the gyrocompass uses gravity control for tilt corrections only. If the effect persists for long enough.821(19). By limiting the angular output of the accelerometer. However.0C © SG Brown Page 9 of 10 .3 – Operating Instructions If the gyrocompass is installed at some distance above the vessel centre of roll rotation. so that ballistic effects would cause negligible heading error during short-term periods of acceleration. In this mode. The alarm will activate if the accelerometer signal exceeds the threshold setting for more than 30 minutes. Such accelerations can arise from changes in speed and/or course. inter cardinal rolling errors are significantly reduced. as is usually the case on commercial vessels. The gyrocompass will automatically set the DG mode if the accelerometer signal exceeds a pre-set threshold. DPN 060070 Issue 2. this error might become as large as several degrees. the resulting lateral acceleration components along the east-west and north-south axes of the gyrocompass combine to build an error in the northerly settle point. ❐ The Meridian Gyrocompass complies with all requirements of IMO Resolution A. Performance Standards for Gyrocompasses for High-Speed Craft. You can set the DG mode manually from the RCU. The gyrocompass will remain in the DG mode until the accelerometer signal falls below the threshold value for more than 30 seconds. 0C DPN 060070 .Meridian Gyrocompass Page 10 of 10 © SG Brown Issue 2. NMEA 0183 via RS232 or RS422 from GPS or speed log DPN 060070 Issue 2.2 Performance (definitions as in ISO 8728) Settle point error 0.1.821(19).4 Environment Operating environment EN 6095:1997 designated category ‘weather protected’ Operating temperature 0°C to +45°C (to ISO 8728) –15°C to +55°C (with reduced accuracy) Storage temperature –25°C to +80°C 4. 4. power to the gyrocompass should be delivered by an uninterruptable power supply.1 Power Requirements Voltage 24V DC (acceptable range 18V to 36V DC) Maximum power consumption 3A at power-on (The power supply capacity should exceed 200W) To comply with the requirements of IMO Resolution A.5 Signal Inputs Latitude NMEA 0183 via RS232 or RS422 from GPS Speed Pulse or contact closure at 100.7° Less than 45 minutes 4.1.25° sec latitude Follow up speed 200°/s Time to settle within 0.1 SPECIFICATIONS 4.3 Compensation Latitude compensation range 80°N to 80°S Speed compensation range 0 to 90 knots 4. for example the SGBrown UPS part number 929128.1° sec latitude RMS Dynamic accuracy 0.6° sec latitude (Scorsby and Intercardinal motion tests) Settle point repeatability 0.1.1.0C © SG Brown Page 1 of 16 .1. Performance Standards for Gyrocompasses for High Speed Craft. 200 or 400 per nautical mile from speed log.25° sec latitude Static error 0.4 – Technical Data 4 TECHNICAL DATA 4. time) Status/alarm 5V TTL power/gyro failure Voltage free power/gyro failure contacts 5V TTL system ready Voltage free system ready contacts 4.8V maximum line-to-line). 6 steps per degree (TTL level) Synchro heading 1 × 26V 400Hz (11.8 Standards The Meridian Gyrocompass is designed to meet the requirements of the following: ❐ IMO Resolution A.Meridian Gyrocompass 4.1.7 Dimensions and Weight Dimensions 344mm (H) × 267mm (W) × 440mm (D) Weight 15.6 Signal outputs S-type heading 1 × step-by-step. Performance Standards for Gyrocompasses for High Speed Craft ❐ BS EN 60945 (January 1997).0C DPN 060070 .5kg RCU size (when mounted externally) 96mm (H) × 192mm (W) × 108mm (D)0 RCU weight 0.1.821 (19). date. Graphical Symbols for use on Electrical Equipment ❐ CE marking ❐ Electromagnetic Compatibility (EMC) Directive ❐ The Marine Equipment Directive 96/98/EC Page 2 of 16 © SG Brown Issue 2. Performance Standards for Gyrocompasses ❐ IMO Resolution A. General Requirements .1.75 kg 4.424 (XI). sector value 360° Resolver heading 1 × 36V 400Hz (8V maximum per phase). sector value 360° Analogue rate of turn 1 × rate of turn ±20°/s (±10V) Serial data outputs 6 × RS232 11 × RS422 Serial data formats NMEA 0183 (all data) at 1Hz or 10Hz.Methods of testing and required test results ❐ BS EN ISO 8728:1999. Course recorder outputNMEA 0183 (heading. Shipbuilding – Marine Gyrocompasses ❐ BS 6217:1981. ❐ Rate of turn using the ROT sentence format. The sentences can contain speed information using knots and/or km/h.2 DATA FORMATS Set the DIP switches according to your specific input and output requirements.2. GGA or RMC sentences. Inputs – Refer to sub-section 4. with updates occurring at 1Hz or 10Hz as defined by the setting of the DIP switches. Outputs – Refer to sub-section 4. VHW or RMC sentences. Refer to Figures 4–10 and 4–9 respectively for a description of these formats. ❐ Speed using VTG. ❐ Latitude using GLL. and will calculate the speed in knots if the sentence contains only speed in km/h. Refer to Figure 4–17 for a description of this format Other output formats: ❐ Synchro Heading Output ❐ Resolver Heading Output ❐ Stepper S-code Heading Output ❐ Rate of turn using a bipolar analogue voltage in the range ±10V DPN 060070 Issue 2. the Meridian Gyrocompass makes its selection in the stated preference order. Refer to Figures 4–8. GGA or RMC sentences determined by the available input format.2.4 – Technical Data 4. ❐ TTL-compatible pulsed speed input with a TTL-level signal on contact closure. 4–3 and 4–4 respectively for a description of these formats.2 Acceptable input formats: ❐ Latitude information using serial NMEA 0183 GLL. 4–3 and 4–4 respectively for a description of these formats. Refer to Figures 4–2. The Meridian Gyrocompass will use the speed in knots if available. The serial output contains all available NMEA sentences transmitted consecutively and in the following order: ❐ Heading using either HDT or VHW sentence formats as selected by the DIP switches. Refer to Figures 4–8.2.4.3 Serial output formats: The Meridian Gyrocompass transmits all available information through RS232 and RS422 serial lines using the NMEA 0183 format. 4–9 and 4–4 respectively for a description of these formats. The serial transmission rate can be either 4800 or 9600 baud. ❐ Data and time using the ZDA sentence format. 4–9 and 4–4 respectively for a description of these formats.0C © SG Brown Page 3 of 16 . Refer to Figures 4–2. Refer to Figure 4–12 for a description of this format. If more than one of these formats is available. You will find the instructions to do this in sub-section 2. ❐ Speed information using serial NMEA 0183 VTG. VHW or RMC sentences determined by the available input format. The absolute value of the checksum is transmitted in ASCII characters representing the value in HEX. the checksum occurs as an additional field immediately before the carriage return line-feed characters. 4. The data bits occur in each packet with the least significant bit first. For circumstances where the Meridian Gyrocompass retransmits serial data using the same NMEA sentence format supplied by an external source. including null fields. The outputs are grouped into two channels that can be set independently to either 1Hz or 10Hz updates. NMEA sentences are usually transmitted once per second. All fields. are separated by commas. it will recalculate any checksum and insert the new value into the output sentence.0C DPN 060070 . Page 4 of 16 © SG Brown Issue 2. however you can set a DIP switch to select a transmission rate of 10 per second. in the sentence. The most significant bit of the 8-bit character will always be zero. but excluding the $ symbol.1 NMEA 0183 Serial Data Formats – General information The Meridian Gyrocompass accepts and transmits asynchronous serial data using 8 data bits. The NMEA format supports an optional checksum – if included.2. one stop bit and no parity through RS232 and RS422 transmit-only lines. It consists of an asterisk (*) followed by a checksum derived by exclusive OR-ing the eight data bits of each valid character preceding the asterisk. Figure 4–1: Serial data format All data is interpreted as ASCII characters that form NMEA sentences split into individual fields.Meridian Gyrocompass The following sub-sections describe each of the formats supported by the Meridian Gyrocompass. the Meridian Gyrocompass uses the data fields marked ‘XXX’ in the NMEA sentence. GPS Interface (see Table 2–3 for connection details) The Meridian Gyrocompass can accept speed. date and time inputs at the GPS interface in NMEA 0183 format using GLL. RMC.2 Inputs 4. VTG. VHW and ZDA sentences. Figure 4–2: NMEA 0183 GLL sentence structure DPN 060070 Issue 2. The gyrocompass will recognise the arriving sentence format and will extract the required data from it automatically.1 NMEA 0183 input signals In the following descriptions of input sentences.2. The system does not use the fields marked ‘???’ and their descriptions are included here for completeness only. latitude.0C © SG Brown Page 5 of 16 . GGA.2.2.4 – Technical Data 4. fix valid Note 2: Geoidal Separation – The difference between the WGS-84 earth ellipsoid and mean sea level (geoid).0C DPN 060070 . Note 3: Time in seconds since the last SC104 Type 1 or Type 9 update. A negative character precedes the value if the mean sea level is below the ellipsoid. fix valid 2 = Differential GPS. Null field when DGPS is not in use. Page 6 of 16 © SG Brown Issue 2. fix valid 3 = GPS PPS mode.Meridian Gyrocompass Figure 4–3: NMEA 0183 GGA sentence structure Notes for the NMEA 0183 GGA sentence: Note 1: GPS quality indicator: 0 = Fix not available or is invalid 1 = GPS SPS mode. SPS mode. 4 – Technical Data Figure 4–4: NMEA 0183 RMC sentence structure Notes for the NMEA 0183 RMC sentence: Note 1: Easterly variation (E) subtracts from true course. Note 2: The positioning system mode indicator field supplements the positioning system status field (see Note 3). Note 3: Positioning system mode indicator: A = Autonomous mode D = Differential mode E = Estimated (dead reckoning) mode M = Manual mode S = Simulator mode N = Data not valid Figure 4–5: NMEA 0183 VTG sentence structure DPN 060070 Issue 2.0C © SG Brown Page 7 of 16 . These fields will never be empty. which will be set to V = invalid for all values of mode indicator except for A = Autonomous and D = Differential. Westerly variation (W) add to true course. 0C DPN 060070 .Meridian Gyrocompass Figure 4–6: NMEA 0183 VHW sentence structure Figure 4–7: NMEA 0183 ZDA sentence structure Page 8 of 16 © SG Brown Issue 2. 4 – Technical Data Log Interface (see Table 2–3 for connection details) The Meridian Gyrocompass can accept speed inputs at the Log interface in NMEA 0183 format using VTG and VHW sentences only. although they should be TTL-level.0C © SG Brown Page 9 of 16 .2. Figure 4–8: NMEA 0183 VTG sentence structure Figure 4–9: NMEA 0183 VHW sentence structure 4. 200 or 400 per nautical mile as selected by a DIP switch. DPN 060070 Issue 2.2. Contact closures should be of good quality and electrically floating. The speed pulses do not need to have a particular mark/space ratio.2 Pulsed input The Meridian Gyrocompass can accept a speed input as a series of pulses or contact closures occurring at a frequency of 100. The gyrocompass determines the vessel speed by reference against the microprocessor timing circuits. Refer to Figures 4–14 and 4– 16 respectively for a description of the NMEA 0183 RMC and GGA output formats.3 Outputs 4. described in Figure 4–13.1 NMEA output signals The Meridian Gyrocompass can output serial data through RS232 and RS422 transmit-only serial lines using the NMEA 0183 format. modifying the sentence to include the talker identifier ‘HE’.3. the Meridian Gyrocompass inserts the heading information into the received sentence so that it transmits only one sentence containing both heading and speed. Page 10 of 16 © SG Brown Issue 2. if the gyrocompass is configured for a manual latitude input or if the GPS source uses this sentence format. the gyrocompass will transmit the NMEA 0183 ZDA output sentence with empty data fields. Note that the heading output will default to the NMEA 0183 HDT format if you set a 10Hz update rate for either Channel 1 or Channel 2. ❐ Latitude output uses the NMEA 0183 GLL sentence format. or if this sentence is supplied by the external speed source. If there is no valid date and time information from an external source.0C DPN 060070 . Refer to Figure 4–12 for a description of this output format. Optionally you can set Channel 2 to transmit NMEA 0183 HDT only. The output includes all the following information in the order stated: ❐ Heading information uses can use either the NMEA 0183 HDT or the VHW sentence format as determined by the setting of a DIP switch. Refer to Figures 4–11 and 4–14 respectively for a description of these formats. modifying the sentence to include the talker identifier ‘HE’. ❐ Rate of turn uses the NMEA 0183 ROT sentence format. if the gyrocompass is configured for a manual or a pulsed log speed input.2. If this information is available from a GPS source. modifying the sentence to include the talker identifier ‘HE’. ❐ Speed uses the NMEA 0183 VTG sentence format. If speed information arrives at the gyrocompass using either the NMEA 0183 VHW or the RMC format then the gyrocompass will retransmit this format.Meridian Gyrocompass 4. ❐ Date and Time output uses the NMEA 0183 ZDA sentence format described in Figure 4– 17.2. The resolution of the heading output can be set to one or two decimal places at the DIP switches. If you set a 10Hz update rate for either Channel 1 or Channel 2. the output format on that channel will default to NMEA 0183 HDT + ROT only. If you have selected NMEA 0183 VHW as the heading output sentence and a valid NMEA 0183 VHW format sentence is available from a GPS or speed log source. If latitude information arrives at the gyrocompass using either the NMEA 0183 RMC or the GGA format then the gyrocompass will retransmit this format. described in Figure 4–15. then the gyrocompass will retransmit this format. Refer to Figures 4–10 and 4–11 respectively for a description of these output formats. but the ‘M’ character is still transmitted.4 – Technical Data Figure 4–10: NMEA 0183 HDT output sentence structure Figure 4–11: NMEA 0183 VHW output sentence structure Note: The field before ‘M’ is reserved for magnetic heading information. Magnetic heading is not used.0C © SG Brown Page 11 of 16 . Figure 4–12: NMEA 0183 ROT output sentence structure DPN 060070 Issue 2. Westerly variation (W) add to true course. which will be set to V = invalid for all values of mode indicator except for A = Autonomous and D = Differential.0C DPN 060070 . Note 2: The positioning system mode indicator field supplements the positioning system status field (see Note 3). Note 3: Positioning system mode indicator: A = Autonomous mode D = Differential mode E = Estimated (dead reckoning) mode M = Manual mode S = Simulator mode N = Data not valid Page 12 of 16 © SG Brown Issue 2.Meridian Gyrocompass Figure 4–13: NMEA 0183 VTG output sentence structure Figure 4–14: NMEA 0183 RMC output sentence structure Notes for the NMEA 0183 RMC output sentence: Note 1: Easterly variation (E) subtracts from true course. These fields will never be empty. Note 3: Time in seconds since the last SC104 Type 1 or Type 9 update. fix valid 2 = Differential GPS. Null field when DGPS is not in use. fix valid Note 2: Geoidal Separation – The difference between the WGS-84 earth ellipsoid and mean sea level (geoid). fix valid 3 = GPS PPS mode.0C © SG Brown Page 13 of 16 . A negative character precedes the value if the mean sea level is below the ellipsoid. DPN 060070 Issue 2.4 – Technical Data Figure 4–15: NMEA 0183 GLL output sentence structure Figure 4–16: NMEA 0183 GGA output sentence structure Notes for the NMEA 0183 GGA output sentence: Note 1: GPS quality indicator: 0 = Fix not available or is invalid 1 = GPS SPS mode. SPS mode. ❐ Date and Time – Transmitted in the NMEA 0183 ZDA format defined in Figure 4–17. then the Meridian Gyrocompass retransmits the information with the talker ID set to ‘HE’. If date and time information is available from a GPS source. in the order stated.4 Course Recorder Output The Meridian Gyrocompass transmits the following NMEA 0183 sentences. If the DIP switch settings determine a 10Hz update rate for either Channel 1 or Channel 2. to local time to obtain UTC. If the checksum is present in the original received sentence. then the heading output defaults to the NMEA 0183 HDT format.2. If a valid sentence is not available from a GPS source. 4.0C DPN 060070 . it is recalculated and inserted in the output sentence. at 4800 baud with a 1Hz update rate: ❐ Heading – Transmitted as either the NMEA 0183 HDT or the VHW output sentence format as determined by the setting of a DIP switch. with the sign of local zone hours. the Meridian Gyrocompass transmits the NMEA 0183 HEZDA sentence with empty fields. Page 14 of 16 © SG Brown Issue 2. Local time is generally negative for East longitudes with local exceptions near the International Date Line.Meridian Gyrocompass Figure 4–17: NMEA 0183 ZDA sentence structure Note: Local time zone is the magnitude of hours plus the magnitude of minutes added. Refer to Figures 4–10 and 4–11 respectively for a description of the NMEA 0183 HDT and VHW output formats. 0C © SG Brown Page 15 of 16 . 4.2. DPN 060070 Issue 2. 4. Figure 4–18: NMEA 0183 sentence with optional checksum The checksum consists of an asterisk followed by the checksum calculated by exclusive ORing the eight data bits of each valid character preceding the asterisk. it appears as an extra field inserted before the carriage return character as shown by example in Figure 4– 18. The output is at 11.5 NMEA 0183 sentence with Checksum If the optional checksum is to be sent with any of the above NMEA 0183 sentences.4 – Technical Data 4.2. The resolver reference voltage is a nominal 36V 400Hz supply generated internally.6 Other Output Formats 4. The output is at 8V maximum voltage per phase signal from a 1:1 resolver driven directly by the gyrocompass azimuth gimbal. The resolver sine and cosine outputs must be electrically isolated from each other.2 Resolver Output The resolver heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2–4 for connection details. Electrical loading specification: ❐ Not less than 5k between any two S lines.6.6. in the sentence. ❐ Not less than 1k between the two R lines.2. ❐ Not less than 1k between the two R lines.8V maximum line-to-line voltage derived electrically from a 1:1 resolver driven directly by the gyrocompass azimuth gimbal. but excluding the ‘$’ symbol.1 Synchro Output The synchro heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2–4 for connector details. The synchro reference voltage is a nominal 26V 400Hz supply generated internally.2. Electrical loading specification: ❐ Not less than 5k between any two S lines. Contact the SG Brown Service Department for technical advice if necessary. The Meridian Gyrocompass transmits the absolute value of the checksum in ASCII characters representing the value in HEX. 6. 4.6.2.0C DPN 060070 . Positive rates of turn are to starboard. Page 16 of 16 © SG Brown Issue 2.2.Meridian Gyrocompass 4. The ROT output is a bipolar analogue voltage in the range ±10V to represent rates of turn from –20° to +20° per second. The stepper output is a TTL compatible S-encoded signal with a 10mA sink capacity.4 Rate of Turn The ROT output is calculated by the internal processor and made available continuously at TB3 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2–4 for connection details.3 Stepper S-Code The stepper S-code output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2–4 for connection details. Always power-off the system before you remove the cover for maintenance work.2 Test Connector Page 4 There is a 60-way test connector that allows you to measure critical voltages and signals. The following sub-sections explain some very basic procedures that you may attempt if you suspect the system has developed a fault. Observe all local safety regulations as you work on the equipment. Inappropriate tampering with the internal controls and components of the gyrocompass can lead to damage or serious performance degradation. and only when necessary. Any deviation from normal operation appears as an error message.0C © SG Brown Page 1 of 8 . CAUTION Perform these simple maintenance instructions only if you have the skills and experience required. with the cause declared as a sequence of decimal points on the four-character display panel. Do not remove the gyrocompass cover unless you have the necessary skills and experience to perform maintenance work on a system of this nature. 5. Perform the tests described in this section of the manual and have the results available when you contact SG Brown for technical assistance. NEVER open the gyrocompass cover or make any adjustments inside the gyrocompass unless you are entirely confident in your actions. contact SG Brown for advice and technical assistance before you begin any maintenance work on the system. If you are in any doubt. 5. This sub-section explains some very basic tests and adjustments that you may perform on the system. Reconnect the safety grounding straps and refit all safety covers to the equipment before you poweron the system.1 Built-in Test Equipment Page 2 The Meridian Gyrocompass performs a self-test routine during the initialisation sequence and monitors its status continually during normal operation.5 – Maintenance 5 MAINTENANCE WARNING There is a danger of serious injury from voltages inside the Meridian Gyrocompass. There is very little need for user maintenance on the Meridian Gyrocompass and you should never need to remove the covers. DPN 060070 Issue 2. 2V DC (0V DC ±0.5V DC +5V DC ±0.Y.2V/–0.R.2V DC –15V DC ±0.2kHz 10V AC ±1V @ 480Hz (18V AC ±1.O. use the following table to investigate the cause.2V DC at start (1-min)) +5V DC ±0.2V DC at start (2-min)) 0V DC ±1V DC Control Board digital Control Board digital Control Board analogue 0110 Failure of synchro-todigital converter 58 to 43 53 (+ve) to 51 54 (+ve) to 51 12V AC ±0.1V DC +15V DC ±0.7V DC) Ship’s mains/PSU DC/DC PSU DC/DC PSU DC/DC PSU Control Board analogue Control Board analogue Control Board analogue 0010 Failure of AC power supply 19 to 43 20 to 43 21 to 43 58 to 43 57 (+ve) to 18 2.0C DPN 060070 . In these fault conditions.1 BUILT-IN TEST EQUIPMENT Figure 3–2 is a list of nine failure codes delivered by the built-in test equipment if it detects a fault in the gyrocompass.2V DC at start (1-min)) +5V DC ±0.5V at start (1-min)) 12V AC ±0.2V DC (0V DC ±0.1.2V DC at start (2-min)) 0V DC ±1V DC Control Board digital Control Board digital Control Board analogue 0101 High azimuth pick-off signal 10 (+ve) to 18 16 (+ve) to 18 38 (+ve) to 51 +5V DC ±0. You can measure the voltages and signals on the pins of the 60-way test connector (refer to Table 5–2 for details of the test connector).5V at start (1-min)) 10V AC ±1V @ 480Hz (18V AC ±1.2V @ 400Hz (5.2V @ 400Hz +5V DC ±0. with the illuminated decimal points at positions 1 to 4 identifying the detected failure. Table 5–1: Test measurements Failure Code Measure Expected value Signal source 0001 Failure of DC power supply DC supply 42 (+ve) to 43 44 (+ve) to 43 17 (+ve) to 18 50 (+ve) to 51 52 (+ve) to 51 45 (+ve) to 18 18V DC to 36V DC +24V DC ±0.1 1000 Page 2 of 8 Check connections between: Distribution PCB TB1/21 and RCU S+ Distribution PCB TB1/22 and RCU S– © SG Brown Issue 2. the four-character display will show G.L. If the built in test equipment detects a fault.5V DC) × cos heading Control Board analogue Control Board analogue Control Board analogue 0111 High pendulum signal 26 (+ve) to 51 28 (+ve) to 51 (–10V DC ±0. + F.5mV DC) × speed(kts) × sin hdg × tan local lat North = +ve latitude.5V DC –24V DC ±0.2V DC Control Board analogue Control Board analogue Control Board analogue Control Board analogue Control Board analogue 0100 High tilt pick-off signal 10 (+ve) to 18 16 (+ve) to 18 37 (+ve) to 51 +5V DC ±0.4V DC ±0.2V DC +5V DC (+0. South = –ve latitude Control Board analogue Control Board analogue Perform the azimuth drift test – see sub-section 5.2V DC (0V DC ±0.2V DC) × sin local latitude (–8.5V DC) × sin heading (5.2V DC (0V DC ±0.I.5mV DC ±0.Meridian Gyrocompass 5.5V AC ±0.125V AC @ 19.A.4V DC ±0. 1 and 3.3. Measure and.3. 2. Refer to sub-sections 3.1. Use a digital meter set to measure DC volts and monitor the Tilt Bias between pins 30 and 51 of the 60-way test connector (with the positive test lead on pin 30).5 – Maintenance 5. 1. 5.2 Azimuth Bias Adjustment You may use the following procedure to eliminate small angles of heading error from the Meridian Gyrocompass. 4. Wait for one hour and then note the heading (H2) shown on the RCU display. Calculate the azimuth drift rate (H2 – H1) degrees per hour.1. Adjust the Azimuth Bias potentiometer RV9 to cause a change in the azimuth bias voltage that will produce the necessary change in compass heading. Turn the Azimuth Bias potentiometer anticlockwise to cause the heading to change towards a lower reading. You must turn the potentiometer anticlockwise to compensate for azimuth drift towards higher readings. 5. 3. Figure 2–4 shows the location of the Tilt Bias potentiometer.0C © SG Brown Page 3 of 8 . 6. adjust for azimuth drift as described in sub-section 5.2°/hr. Use a digital meter set to measure DC volts and monitor the Azimuth Bias between pins 29 and 51 of the 60-way test connector (with the positive test lead on pin 29). Adjust the Tilt Bias potentiometer RV7 by 400mV × drift rate (°/hr). Take care when you adjust azimuth bias – make only small adjustments each time and then allow the gyrocompass to settle for three hours before you make any further adjustments.1 above before you adjust the azimuth bias. Note the initial heading (H1) shown on the RCU display. 3. A 60mV DC change in Azimuth Bias will produce a 1-degree change in heading DPN 060070 Issue 2. Use the DIP switches to set DG mode – refer to Table 2–5. if necessary.2 to set the latitude and speed. 7.1 Azimuth Drift Adjustment You may use the following procedure to measure and. 2. Repeat steps 1 and 2 above to ensure that the calculated drift rate is less than 0. Ensure that the gyrocompass is static and is operating in DG mode with the Speed input set manually to zero and the Latitude set to local latitude. Note the original position of the azimuth bias control before you start so that you can restore the starting condition if necessary. Figure 2–4 shows the location of the Azimuth Bias potentiometer. if necessary.1. adjust the azimuth drift: 1. 8V RMS 400Hz synchro S3 phase 4 26V_SYNCHRO_R1 26V RMS 400Hz synchro R1 reference 5 0V_SYNCHRO_RES 26V RMS 400Hz synchro R1 reference 6 GA_MODE Directional gyro mode control (+5V logic) 7 GC_MODE Gyrocompass mode control (+5V logic) 8 AA_MODE Auto alignment mode control (+5V logic) 9 LAT_NS Latitude north selection control (+5V logic) 10 SERVO_EN Tilt and azimuth servo enable control (+5V logic) 11 WHEEL_BOOST Gyro wheel supply boost control (+5V logic) 12 LOG_OK Speed log OK flag (+5V logic) 13 GPS_OK GPS OK flag (+5V logic) 14 SYS_FAIL System fail flag (+5V logic) 15 GYRO_RDY Gyrocompass ready flag (+5V logic) 16 PREPARE Prepare mode (servo nulling) (+5V logic) 17 VCC 5V DC supply 18 GND 5V DC supply return 19 PICK_OFF_SUPPLY_1 Gyro pick off supply 2.Meridian Gyrocompass 5.8V RMS 400Hz synchro S2 phase 3 S3_SYNCHRO_RES 11.3e–3 × speed(kts) × cos[heading]) 28 SPEED_E_TORQ Speed E torque i/p signal (–8.2 TEST CONNECTOR There is a sixty-way test connector accessible behind the removable panel on the top of the gyrocompass cover.8V RMS 400Hz synchro S1 phase 2 S2_SYNCHRO_RES 11.5V RMS 19. A test box (SG Brown part number 929195) is available to facilitate connection to the 60-way test connector. Table 5–2: Sixty-way test connector Pin Name Function 1 S1_SYNCHRO 11.5e–3 × speed(kts) × sin[heading] × tan[latitude]V DC Page 4 of 8 © SG Brown Issue 2.0C DPN 060070 .2kHz sine wave 20 WHEEL_SUPPLY_1 Gyro wheel supply 0 phase 10V (18V) RMS 480Hz square wave 21 WHEEL_SUPPLY_2 Gyro wheel supply 90 phase 10V (18V) RMS 480Hz square wave 22 PWMO Compass card illumination PWM control 5V 85Hz square wave 23 B Gravity control signal ±150mV DC/min T=60s 24 10V 10V DC positive voltage reference 25 _10V 10V DC negative voltage reference 26 LAT_TORQ Latitude torquing input signal (–10 sin[latitude])V DC 27 SPEED_N_TORQ Speed N torque i/p signal (7. Release and remove the securing screws and lift off the panel to see the two DIP switches and the test connector. 1V DC/deg heading) 55 RS232_RX_TEST RS232 receive port reserved for product testing 56 RS232_TX_TEST RS232 transmit port reserved for product testing 57 AC_OK AC supply (19kHz.2V DC (400mV/deg/hour heading) 31 TILT_TEMP Bias adj. ACW –ve 50 15V 15V DC positive supply 51 0Va Supply return for ±15V DC 52 –15V 15V DC negative supply 53 SIN_DC Analogue voltage proportional to sin(heading) (±0.2V DC (60mV/deg heading) 30 TILT_BIAS Bias adj. 480Hz and 400Hz) OK flag (+5V DC logic) 58 400_REF_HI Reference supply 12V RMS 400Hz 59 AZ_MOTOR_HI Drive to azimuth follow-up DC servo motor 60 TILT_MOTOR_HI Drive to tilt follow-up DC servo motor DPN 060070 Issue 2.1V DC/deg heading) 54 COS_DC Analogue voltage proportional to cos(heading) (±0.013V DC/mA (torquer scale factor 10°/hr/mA) 36 AZ_TORQUER_LO Azimuth torquer signal 0.j to azimuth torquer ±2.5V DC/deg/s (10V DC max) CW +ve.0C © SG Brown Page 5 of 8 .006V DC/mA (torquer scale factor 10°/hr/mA) 37 TILT_PICK_OFF_DC Demodulated gyroscope tilt pick-off signal 38 AZ_PICK_OFF_DC Demodulated gyroscope azimuth pick-off signal 39 NOT USED 40 NOT USED 41 NOT USED 42 24V 24V DC positive supply 43 0V Supply return for ±24V DC 44 –24V 24V DC negative supply 45 PSU_LO PSU (+5V DC and ±15V DC) under voltage flag (+5V DC logic) 46 NOT USED 47 NOT USED 48 NOT USED 49 ROT Analogue rate of turn output (0.5 – Maintenance Table 5–2: Sixty-way test connector (Continued) Pin Name Function 29 AZ_BIAS Bias ad. to tilt torquer ±2. to azimuth torquer proportional to temperature (60mV/deg/hr heading) 33 T Temperature ref (non-inverted) from gimbal thermistor (DC V proportional to temp) 34 T_ Temperature ref (inverted) from gimbal thermistor (DC V proportional to temp) 35 TILT_TORQUER_LO Tilt torquer signal 0. to tilt torquer proportional to temperature (400mV/deg/hr heading) 32 AZ_TEMP Bias adj. Meridian Gyrocompass Figure 5–1: Simplified functional block diagram Page 6 of 8 © SG Brown Issue 2.0C DPN 060070 . 0C © SG Brown Page 7 of 8 .15A 250V 929164 Gland Plate assembly 929190 RCU Mounting Kit 929194 Transit case 929195 Test box DPN 060070 Issue 2.5 – Maintenance Table 5–3: Spares list for Meridian Gyrocompass 929060 SG Brown P/N Description 929033 Gimbal assembly 929066 Control Board Analogue 929083 Control Board Digital 929049 Control Board Remote 929045 Display Board 929074 DC/DC Power Supply 856000 Filter #1 929160 Filter #2 346808 Fuse link 3. 0C DPN 060070 .Meridian Gyrocompass Page 8 of 8 © SG Brown Issue 2. In a practical gyrocompass. when it is spinning. However. To an observer on the surface of the earth. DPN 060070 Issue 2. Figure A–1: Free-spinning gyroscope With the gyro rotor stationary.0C © SG Brown Page 1 of 8 . it is easy to turn the gimbal suspension about either axis and allow it to remain there in a balanced condition. the gyro rotor is the specially designed spindle of a motor that rotates at a constant speed. This apparent deviation occurs because. The suspension allows unrestricted movement about the vertical and horizontal axes so that the gyro rotor can adopt any orientation. the earth rotates relative to it. ❐ The rotation of the earth about its own axis. the gyrocompass depends upon the following: ❐ The inertial properties of a freely spinning gyroscope. ❐ Gravity.A – Operating Theory A OPERATING THEORY A gyrocompass is a navigational instrument that provides a true north indication without reference to the earth’s magnetic field. the free spinning gyroscope would appear to ‘tumble’ in its gimbal suspension once in every 24-hour period. This property causes the spin axis of the rotor to remain pointing in the same arbitrary direction in space and to resist any influence that tries to redirect that axis. although the spin axis actually remains fixed in space. For its operation. the gyro rotor exhibits a property called gyroscopic inertia. Figure A–1 shows a free-spinning gyroscope mounted in a balanced gimbal suspension. For simplicity. this explanation assumes the gyro rotor continues to spin perpetually at a constant speed. the gyroscope would appear to turn clockwise (at the north pole) or anticlockwise (at the south pole) about its vertical axis once in 24 hours. the revolutions that such a gyroscope performs every 24 hours would make it difficult to use as an instrument of navigation. the spin axis would appear to tumble about its horizontal axis with the eastern end of the spin axis rising. the gyroscope would complete a single revolution in its gimbal suspension so that the spin axis would again point in the original direction relative to the observer. the gyroscope would appear to tumble about its horizontal and its vertical axes to complete one single revolution in 24 hours. To make the gyroscope north seeking. the gyrocompass uses gravity control and an effect called precession. Page 2 of 8 © SG Brown Issue 2. To an observer at some intermediate latitude with the gyroscope oriented in some arbitrary initial direction: ❐ The gyroscope would tumble about the north-south direction at – Ω cos λ and about the east-west direction at Ω sin λ . The ideal situation is for the gyroscope to align perfectly with the spin axis of the earth so that it maintains a north-south orientation with no apparent tumbling during each 24-hour period.1 NORTH-SEEKING GYROSCOPE Given a constant spin rate and frictionless gimbals. To an observer at the equator: ❐ With an initial spin axis alignment level and parallel to a meridian (so that it points in a true north-south direction). there would be no observable effect on the gyroscope during the 24-hour period. A. ❐ With an initial spin axis alignment level and perpendicular to a meridian (so that it points in the east-west direction). To an observer on the surface of the earth. the gyroscope described above will always maintain its initial alignment relative to free space. ❐ With the initial spin axis level. there would be no observable effect on the gyroscope during the 24-hour period.Meridian Gyrocompass The apparent movement seen by the observer would depend on the location of the gyroscope and the initial direction of the spin axis. where Ω is the earth rotation rate (15° per hour) and λ is the latitude of the gyroscope. ❐ With an initial spin axis alignment somewhere between these two extremes. After 24 hours. To an observer at one of the geographic poles: ❐ With an initial spin axis alignment vertical (so that it aligns with the axis of earth rotation).0C DPN 060070 . the gyroscope spin direction will be the same as the direction of applied torque. it follows that the rotor will rotate about an axis that lies at right angles to the axis of applied torque.A – Operating Theory Consider the example shown below where the gyroscope rotates about its spin axis in the direction shown. This is the axis of precession. ❐ It will continue to move in the direction OB as the rotor spins. Precession When an externally applied torque acts on the gyroscope suspension in the direction shown. The net result of these two movements actually starts to move the point on the circumference of the rotor in the direction OC. Summary: If a free spinning gyroscope comes under the influence of a torque whose axis is perpendicular to the spin of the gyro rotor. should alignment occur. a point on the circumference of the rotor at 'O' will attempt to move in two directions simultaneously: ❐ It will accelerate in the direction OA under the influence of the applied torque. Eventually. precession will act in the direction shown. the spin axis of the gyroscope will turn sufficiently so that its spin axis coincides with the axis of applied torque. The direction of this precession is such that. a precession results that tends to align the spin axis with the axis of applied torque.0C © SG Brown Page 3 of 8 . Since every point on the circumference of the rotor experiences the same effect as it passes through point O. DPN 060070 Issue 2. at which point there will no further tendency for the gyroscope to rotate about the precession axis. In this example. which is the resultant of the two perpendicular influences. Two conditions are therefore possible: 1. In this off-balanced condition. Therefore. In the balanced condition shown. In this off-balanced condition. This is because the earth rotates while the gyroscope maintains a fixed orientation in space. Figure A–2: Gravity control of a gyroscope It is more common for the initial alignment of the gyroscope to be at some angle away from true north. precession arising from the anticlockwise torque would move the north end of the rotor eastwards. With the gyroscope spinning in the direction shown. in doing so. the weight would try to return to its central location and.Meridian Gyrocompass Consider the example shown in Figure A–2(a). 2. shown in A–2(c). Gyroscope initially level and aligned to the west of north. because this condition arises from a westerly misalignment between the gyroscope and the meridian. the effect of the bottom weight is to drive the gyro rotor towards closer alignment with the meridian. With the spin axis of the gyroscope initially level but with the north end pointing to the west of true north. over time the north end of the spin axis would begin to tilt upwards with rotation of the earth. Page 4 of 8 © SG Brown Issue 2. With the spin axis of the gyroscope initially level but with the north end pointing to the east of true north. shown in Figure A–2(b). over time the north end of the spin axis would begin to tilt downwards. However. the weight would apply a clockwise torque to the gyro suspension. In this example.0C DPN 060070 . which shows a free spinning gyroscope aligned so that its spin axis is level with the horizon. However. the spin axis of the gyroscope aligns with the local meridian so that its north end points north. Gyroscope initially level and aligned to the east of north. the arrangement would briefly be balanced as shown in Figure A–2(a). the arrangement would briefly be balanced as shown in Figure A–2(a). would apply an anticlockwise torque to the gyro suspension. the weight suspended from the gyroscope bearings has no effect on operation and the gyroscope will maintain its alignment with the meridian. to cancel the drift caused by the earth’s rotation. as the operating latitude increases towards either of the poles. to produce a workable gyrocompass. For a given gyroscope. A. the gyrocompass must apply a controlling correction torque. In the gravity controlled gyroscope. This would cause the vertical axis of the error ellipse to reduce progressively towards zero. modern gyrocompasses. Tilt is detected by an electronic pendulum or accelerometer and the resultant electrical signals are used to produce torques that have the same effect as a suspended weight. perpendicular to the spin axis. By reducing the amplitude of ellipsoidal excursion in one plane. exercise gravity control by an indirect method. Therefore.0C © SG Brown Page 5 of 8 . there is a greater tendency for the gyroscope to experience azimuth drift with time. The sense of this torque would be to cause a precession that would drive the spin axis towards the horizontal. a tilt of the rotor spin axis produced a torque about the horizontal axis to drive the spin axis towards alignment with the meridian. it follows that the amplitude of excursion in the other plane reduces proportionately to settle the gyro horizontally and in the meridian. The application of latitude correction causes this elliptical path to be symmetrical about a point projected from the north end of the gyro rotor when horizontal and aligned with the meridian. In practice. However. However.2. This process results in the north end of the gyro DPN 060070 Issue 2.2 Gyro Damping Whenever the gyroscope does not align perfectly with the meridian. When operating at the equator. The size of the ellipse depends on the initial displacement of the gyro axis away from the meridian and the horizontal plane.2 GYROCOMPASS CORRECTIONS A. precession caused by gravity control and the horizontal component of the earth’s rotation will cause the north end of the gyro rotor to trace out an anticlockwise elliptical path. A. To generate this correction torque the gyrocompass needs to know the operating latitude. One practical method for doing this is to include electrical feedback so that a tilt in the rotor spin axis also produces a torque about the vertical axis.1 explains how the addition of gravity control to the gyroscope gives it the north-seeking characteristic necessary for use in a gyrocompass. such as the Meridian Gyrocompass.2. there must be some form of damping.1 Latitude Correction Sub-section A. The rate of change of azimuth due to the earth’s rotation is constant for a given latitude. reducing the horizontal axis simultaneously. the ratio between the major and minor axes of this error ellipse is constant.A – Operating Theory Precession arising from the clockwise torque would move the north end of the rotor further west and therefore into closer alignment with the meridian. such a simple gravity control would be sufficient to maintain alignment with the meridian with no further need for corrections. 2. and inversely proportional to the cosine latitude. Page 6 of 8 © SG Brown Issue 2. three times as large at latitude 70°. speed information must come from an external source such as a speed log or a GPS receiver. A.Meridian Gyrocompass rotor tracing a decreasing spiral path. and nearly six times as large at latitude 80°. the gyro would settle slightly to the west of true north. If left uncorrected therefore. The north-south component of speed is the product of actual speed and the cosine of the course made good. Speed related errors are therefore greatest when travelling in a northerly or a southerly direction. or be applied manually. this effect would interfere with the north-seeking properties of the gyrocompass because the compass would be unable to determine whether the tilt came from a misalignment or from the northward motion. eventually settling with the gyroscope horizontal and aligned with the meridian. Eventually.3 Speed Error Figure A–3 shows that the north end of a meridian-aligned free spinning gyro will appear to rise as it moves northwards from the equator. Figure A–3: Gyrocompass speed error Speed-related error is directly proportional to the north-south component of speed. the compass must know the direction and speed of travel.0C DPN 060070 . This upward tilt is independent of the earth’s rotation. To correct for these effects. While it uses its own self-generated heading information to determine the direction of travel. This means that any error when the compass is on the equator would become twice as large at latitude 60°. If left uncorrected. the northward travel would cause an upward tilt that would cause the gyroscope to precess towards the west and then to go into a settling spiral. given a constant speed of northward movement. At latitudes above 80° the gyrocompass becomes virtually unusable as a north seeking instrument. or be applied manually. ❐ To maintain correct true north alignment. and the speed of travel. the gyrocompass must receive additional information concerning its operating latitude.3. A directional gyro does not north seek. Speed information must arrive from an external source.3 to set the DG operating mode. ❐ Also to maintain accuracy the gyrocompass needs to know its direction of travel.3 SUMMARY ❐ A gyrocompass will indicate the true north direction after an appropriate settling period. DPN 060070 Issue 2.0C © SG Brown Page 7 of 8 .A – Operating Theory A. the gyrocompass acts as a directional gyro. Follow the instructions in sub-section 3. In this mode. which it generates itself. Note that the Meridian Gyrocompass can be used successfully in high latitudes with the DG mode selected. but can maintain a reference heading for a short period. ❐ A gyrocompass becomes progressively less effective as a north seeking instrument at higher latitudes. 0C DPN 060070 .Meridian Gyrocompass Page 8 of 8 © SG Brown Issue 2. See Corrections Loss of GPS 3–5 Loss of speed signal 3–6 M Maintenance Error modes 3–5 Test connector 5–4 Manual speed input 3–5 N NMEA data formats 4–4 North-seeking gyroscope A–2 O Operation Continuous operation 3–8 Lay-up 3–8 Power failure 3–8 Power-off 3–8 Power-on 3–3 Operation during lay-up 3–8 P Power failure 3–8 Power-off 3–8 Power-on 3–3 Precession A–2 R Rate of turn analogue output 4–16 RCU Controls and indicators 3–2 Issue 2. A–5 D Data formats 4–3 Analogue rate of turn output 4–16 Resolver output 4–15 Serial NMEA 4–4 Stepper S-code 4–16 Synchro output 4–15 DIP switches 2–10 Distribution Board connections 2–7 E Error modes 3–5 GPS 3–5 Gyro failure 3–6 Speed log 3–6 F Fault identification 5–2 G GPS 1–5 GPS failure 3–5 Gravity control A–2 Gyro damping A–5 DPN 060070 Gyro failure 3–6 Gyrocompass configuration 2–10 Gyroscopic inertia A–1 I Installation Alignment 2–4. A–5 Latitude correction.Contents A Adjustments Azimuth bias 5–3 Azimuth drift 5–3 Test connector 5–4 Alignment 2–4.0C © SG Brown Page 1 of 2 . 2–12 Cable types 2–4 Choosing a location 2–3 Connections to Distribution Board 2–7 L Latitude correction 1–5. See RCU Controls 3–2 Correction Speed A–6 Corrections 3–4 Latitude 3–4. 2–12 Analogue rate of turn output 4–16 Auxiliary inputs 1–5 Azimuth bias adjustment 5–3 Azimuth drift A–5 Azimuth drift adjustment 5–3 C Cable types 2–4 Connections 2–7 Continuous operation 3–8 Control unit. A–6 Speed correction. See Corrections Speed log failure 3–6 Stepper S-code output 4–16 Synchro output format 4–15 T Test connector 5–4 Toppling 2–3 Page 2 of 2 © SG Brown Issue 2. See RCU Resolver output format 4–15 S Speed correction 1–5.Meridian Gyrocompass External location 2–9 Remote Control Unit.0C DPN 060070 .