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                                                           NMEA / Synchro


Points North Ltd,  
Rosyth Europarc, Rosyth, 
Fife, Scotland, KY11 2YB
Tel  +44(0)1383 417084
Fax +44(0)1383 414677 
Mobile  07860 885154  




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The interface receives data by NMEA 0183 signal and generates low power synchro, resolver, or sine-cosine output. The output will drive a single synchro motor or numerous electronic interfaces.



Applications are to generate synchro gyro or wind instrument synchro, when retrofitting with an instrument without a synchro output. Specialist applications are to re-generate synchro from recorded data. The interface has numerous ratios of operation, besides being able to produce sine-cosine or resolver output. Thus it can be used in military coarse-fine servo loop applications, on a gyro retrofit.

The adjustable voltage output is about 35 volts maximum, so it can be used for many applications such as driving Anschutz repeaters or even higher voltage synchros, which will be found to follow well at lower voltages. The sine-cos or resolver type of output could be used to feed an autopilot, which provide their own reference, as provision is made for an external reference input.


INPUT:          NMEA 0183. Heading or wind sentences. (Current version software)


SYNCHRO:  Nominal 10 to 35 volts maximum line to line.

Adjustable. 5VA total.

S1, S2, S3, with virtual centre at ground plane of interface.

RESOLVER: Nominal 20 volts maximum.

S1 S2, referenced to ground plane.

S1, S2 AC relative to sine and cosine of angle.

REFERENCE: Nominal 25v or 50 v from main transformer, or from an external reference input. Jumper selected. (May be 50 - 500 Hz)

ACCURACY: Within 1 degree of synchro or resolver output. Approx. to 9 bits.

NMEA            Jumper J3      (0) Heading. True has priority over Magnetic.

INPUT:           (1) Wind angle from $WIMWV true or relative sentence.

RATIO            Jumper J2      (0) = 1:1

OPTION:       (1) = Other ratio typically 360:1 as set in EPROM location 54H.

Also available, 10:1, 30:1, 36:1, 90:1, 180:1, 360:1

OUTPUT       This selects the function of the interfaces

CONFIG:       EPROM location 5CH. 0 = resolver. 1 = synchro.

POWER:       115v/230v 50/60Hz nominal at 25 VA approx.

(Transformer secondary 2 x 25v)

HOUSING:    Duck Egg Green diecast box

PRINCIPLES OF GENERATING OUTPUT: The input angle is read from the NMEA 0183 input. The microprocessor rotates the synchro output to any new position, going through all digital states towards it, not just jumping there. This is to attempt to move a synchro receiver smoothly and reduce the jerk caused by any sudden jump of the input. The rotation speed is adjustable by a screwdriver hex switch, from about 2 to 10 degrees per second. There are 360 "states" per revolution. The software slows the rotation speed as it approaches the final position.

A change of input of one degree results in a change of one state in the 1:1 mode, but it passes through 360 states in the 360:1 mode.

The circuit uses digital to analogue circuitry and three audio power op-amps.

GROUND REFERENCE: The synchro or resolver output has a ground reference at R2 and at the virtual centre of the three phases. This is not a problem when driving synchros. If certain external interfaces require an isolated output then small transformers can easily be fitted to the output, or even capacitive isolation could suffice.




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