Points North Ltd.

Marine Gyro Compass / Navigational & Communication Systems   Marine Electrical & Electronic Systems

MAGNETIC COMPASS PICK OFF COIL SYSTEM  - 940 B

• Pick off coil fixes to standard compass
• Interface and junction box
• Display and processor interface, the 991-MC or 950E
• NMEA 0183 heading output
• Auto calibration facility.
• Off-course alarm or compass comparator alarm.
• Compatible with Cetrek autopilots, replacing their previous pick off coil unit.

INTRODUCTION

This is the simple Transmitting Magnetic Compass System giving a digital display and NMEA 0183 heading for navigation systems. It is a well-proven system used on many ships which do not have a gyro compass to feed the radar or autopilot. It can drive existing or new repeaters using AMI stepper or synchro transmission systems.

The grey-box contains the pick of coil interface, and all the input and output connector blocks. It acts as a central junction box, and is located within the vessel, convenient to the compass.

SPECIFICATION

INPUT:              Pick off coil with 4 metres of miniature screened cable.

                        The coil is glued centrally to the top or bottom of a standard magnetic compass.

                        Spacers are provided to give the optimum distance.

DISPLAY UNIT: 991 heading repeater interface recommended. (Trunnion or panel mount.)

                        Using the 991 gives advanced functions such as automatic variation correction

The 991 has a tape display and large digital displays available as either Single source “off-course alarm” or with a 2nd Heading, a “comparator alarm.”

These are both commonly called “off course alarm”.

OUTPUT:          NMEA 0183. Choice of HEHDT, HEHCC, HCHDM via 991 control.

                        Rate 10 per second or 1 second plus when heading changes.

                        NMEA 0183 5 volt level, 5 mA, via 47 ohms. RS422 and RS232 compatible.

ACCURACY:     The accuracy as with any similar system depends on the accuracy and adjustment of the compass itself. When well installed accuracy is generally within 2 degrees.

The system has an auto-calibration facility, accomplished in 2 ½ turns of the ship.

A deviation table may be compiled and used, as with the magnetic compass itself.

The 991 system may include internal correction tables in the future.

NMEA 0183 INPUT: May connect to a GPS to receive deviation and variation corrections.

                        Correction is applied automatically if a GPS correction is input.

CONTROL:        Internal jumper for starting auto calibration facility or on-screen control with the 991.

CETREK:           6 way terminal block compatible with 618/619 autopilot.

ALARM OUTPUT: Low current DIL relay. Contacts held open when all is correct.

                           Contacts close with loss of power and pulse if alarm condition detected.

                           An independently powered external audible alarm should be fitted.

                           A low power 5 volt alarm may be fitted to order on the 991 for OCA purpose.

CONNECTIONS: Lift off terminal blocks in the interface.

                         A 12 way miniature screened multicore cable is used between the interface and 991.

POWER:           12 to 30 volts at 30 VA or less.

HOUSING:         Interface 260 x 160 x 90 mm near “Light Admiralty Grey” or “Duck Egg Green” diecast box.

NOTES:             991 is supplied as a trunnion mounting. A flush-mount panel is available as an extra.

                         The 991 is a standard unit fitted with the Magnetic compass EPROM.

STAND-ALONE OPERATION: The pick off coil interface may be used on its own (without the 991) as a replacement for previous Cetrek pick off coil systems. Generally the interface will be purpose built for use with Cetrek autopilots, leaving off the connections not otherwise required.

Currently the NMEA output from a stand-alone interface is in one degree steps.

It is in 0.1 degree steps with the full system. A proprietary Cetrek output may be used to give 1/3 rd degree steps into Cetrek autopilots.

STEPPER RETRANSMISSION: To obtain stepper drive, utilise the AMI NMEA to stepper retransmission units available with 5 to 70 volts steps.

SYNCHRO RETRANSMISSION: The 903 series synchro retransmission units turn NMEA 0183 data to synchro of ratios from 360:1 to 1:1.

M-TYPE TRANSMISSION: The 903-M provides this system.

NMEA 0183 DATA DISTRIBUTION INTERFACE:  2 channels input, 10 outputs, 3 of which are isolated.

The Navtalk interface acts as a junction box allowing a neatly terminated installation.