Points North Ltd.

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

SYNCHRO RETRANSMISSION UNIT - 903 SX

INTRODUCTION.

The 903-SX interfaces to a gyro or electronic compass. It outputs medium power synchro transmission with ratios 1:1 to 360:1. Applications include refitting a ship with a new gyro, whilst retaining the existing repeaters.

The majority of commercial synchro systems are 360:1 or 1 revolution per degree, and these are catered for by the 903-SP high power model. This SX model is the answer for gyro repeater systems with 90X and 36X etc.

HEADING INPUT is only from an NMEA 0183 source, which most modern gyros give as standard if this is not the case use an AMI-GFV Marine interface convertor.

SYNCHRO OUTPUT.

The 903-SX output is generated by digital to analogue conversion with three power amplifiers. The synchro output rotates through 360 states per revolution, except for 180:1 and 360:1 where it has 100 states, with software control of the rotation speed. You need to specify the ratio with your order, as it is pre-set in the EPROM.

The 903-SX generates an adjustable synchro voltage of maximum 54 volts, so it will drive Anschutz repeaters (20/24v) and several others of nominal 50 volts.

The 903-SX provides a smooth rotation, and it interpolates the rotation to 2 decimal places of degrees. Gyros, which output heading to more than one decimal place, will cause the synchro to rotate very smoothly. If the gyro or interface can only provide heading to 0.1 or 1/6^th of a degree the rotation is bound to move in steps of 0.1 or 1/6^th of a degree. The SX software controls the rotation speed to reduce any oscillation on the synchro receiver.

SAFETY FEATURES

Unlike the 903-SP the 903-SX can not itself detect a fault on the output such as a short circuit or faulty amplifier. Fit an external alarm such as the 991 Compass Comparator to monitor the system input and output.

CHECK OF EXISTING REPEATERS

When replacing a defective gyro it has sometimes been found too late that there are also old and worn out repeaters.  Just one stalled repeater can ruin the whole system. You should advise the owner that all repeaters and the Autopilot should be mechanically checked, including the synchro brushes.

The 903 setting to work instructions offer advice, but the warranty we give does not allow for faulty repeaters.

SPECIFICATION

INPUT:         

 NMEA 0183 heading, magnetic or gyro or Cetrek data.

OUTPUT:  

Reference output nominal 55v or 110v 50/60 Hz at 1 Amp. Switch selectable.

For 400/500 Hz connect an external reference supply.

Synchro output adjustable 0 to 40 volts max at 20VA per phase. (60VA max.)

Use additional transformer adapter for other voltages.

Synchro output protected against overload.

Synchro frequency is normally 50/60Hz, or 400/500 with external reference.

Synchro precision 360 values per revolution at most ratios.

That is 1 degree resolution at 1:1. 1/36^th degree resolution at 36:1 etc.

Precision 0.05 degree at 180:1.  0.01 degree at 360:1 

ALARM RELAY: Held open when ok. Closes on power failure or alarm is disabled.

                               Pulses when the 903 detects gyro fault. Fit an external alarm.

CONTROLS:       Alarm cancel/on/off switch. Main on/off switch.

                               Rotation rate and test select rotary switch.

POWER:       Nominal 110/220v 50/60Hz at 600VA. Fused, switched and filtered. Earth is essential.

DC OUTPUT: 18 volts at 200 mA for external interface 909 or 950.

HOUSING:    Duck Egg Green electrical cabinet with door for indoor bulkhead mounting. Size 400 wide x 500 high x 150 mm. Supplied with undrilled gland plate.