Stepper compass output 2

[Mycroft]

Engineers

I have four conductors carrying the A,B,C and common from a repeater gyro board. The board is inaccessible and the outputs are required to be connected accordingly

how can I be sure using only a meter to locate the common cable? I have measured across the pairs but do not find a common reading between one cable to the other three. I believe that not all the steps output the DC voltage at the same time but am not entirely sure how to read the required voltages to be sure of the connection to make good?
If the common is connected to the port of an intended voltage output will I damage the internal rectifier board?

Please help me with this for which I am truely grateful

thank you in advance

Mycroft

 

[itsmoked]

What resistance readings do you get?
And do yo get them with the test leads to the meter reversed?

 

[Mycroft]

I didn't measure for resistance as I am unsure of the expected resistance output of the four cable inputs?

Please advise if you can

Thank you

 

[itsmoked]

If you think one of the lines is a common then you will get a different resistance measurement from that common to AB&C lines as compared to the readings between the AB&C lines themselves.

 

[fsmyth]

'smoked, all the "gyro"-related stuff I have ever seen
are 3-phase Y-connected synchro's. Usually with a
separate single-phase feed to the remote.

Mycroft, if you have access to a 'scope, it is easy.
Rotate/reverse the scope leads until you find a
clean single-cycle waveform.
For a Y-connected encoder:
Any two of the signal leads will have a complex
waveform; any one of the signal leads to common
should be a single sine or square wave (depending
on the encoder type).
For a delta-connected encoder:
Any two of the signal leads will have a single
waveform consistant with the signal on any other
pair of signal leads. There may or may not be a
decent signal to the "common". It may be only a
shield lead.
I have never been in a situation such as this
armed only with a meter, but it might be possible
to make a determination using the AC jack on a
Simpson 260 or similar analog meter, and going by
levels. If all you can find is a digital meter
(seems to be the norm mostly nowadays, sadly),
then make an adaptor; 0.1 uf or so in series with
the signal, with a 1 to 5k resistor as an input
load across the meter leads. Might have to add
the same thing across the input leads if the drive
is high-impedance. Voltages will not be accurate,
but they should be consistant.

Now, all that being said, it may very well be a
binary-encoded signal. In that case, ALL the
measured voltages will be different. Gonna be
real hard to determine which is which with only
a voltage level. In this case, the "common" is
the reference (may or may not be circuit "ground").
With no drive from the remote (powered off), there
should be some combination of connections which will
yield a reasonably similar resistance to the "common".
It may be a very high resistance if the encoder uses
FET drive, and may be confusing to measure remotely.

<als>

 

[VEBill]

The subject title says: 'stepping compass'

The stepping compasses that I've read about are literally a normal compass where the needle can be pulled down with an electromagnet to form a potentiometer wiper against the usual resistance track.

In other words, you let the compas needle float free, and then when it is time to measure the compass, you apply power to the solenoid which slams the needle down and then you read the resistance to determine where the needle was pointed.

These are commonly used in marine bouys.

If the device has an internal circuit card with diodes and so on, then you're probably going to have problems figuring it out with a meter no matter what it actually is...

 

[fsmyth]

Ah. Never met a "stepping compass".
In which case you are completely right. It's gonna be
hard to determine what's what, unless it is directly
connected to the potentiometer, and you have some
control over when/where the pointer stops.
<als>

 

[itsmoked]

Sounds simply barbaric... I guess that's why the buoy directions vary so wildly.

Both interesting replies.. Thanks guys.

 

[Mycroft]

Thanks goes out to every reply received.

I solved the problem to locate the common with the resistance test and then simulated a change in course to log the step updates to ascertain the A,B and C connections

Once again thank you to all

Mycroft

 

[itsmoked]

Happy sailing!
May you never broach upon a Lee Shore.