Moving disc meter.

[dr pepper]

I have a oil pressure guage from a seaking helicopter, I'd like to make this work as a voltmeter for now.

It has 3 discs attached to the shaft for the pointer, one just has a magnet around it so I guess this is just for damping.
The other 2 discs have electromagnet coils around them with copper shunts.
I'm assuming that this guage works similar to a frequency meter, where the ac currents in the coils pull the pointer one way or the other depending which is greater.
So I was thinking of putting 400hz (standard aircraft power freq) ac through a resistor, maybe 10ma to one coil, and the same ac supply to the other coil through a pot, and see if varying the pot moves the pointer.
Anyone have any knowledge of this kind of guage, I've never seen inside one like this before.
A 555/4017 and some small trannys as a h bridge would make a little control circuit, or maybe a power op amp.

 

[dr pepper]

Update I put my sig gen through a lm380 audio amp ic then into one of the coils at 16v/400hz, I get full scale.
So I guess bringing the other coil up to the same power with another lm380 the pointer will come back down to zero.
So I need a 0-10v gain control for the lm380 to get a 0-10v voltmeter.

Edit: sussed it, one coil is energised with 24vac 400hz continuous, and the other when 0v the meter reads zero, and when slowly brought up to 24vac 400hz the meter reads fsd, so its a balance of the 2 24vac 400hz signals that control the meter.
I noticed too that if I put the lm380 into saturation it still works well, so I can do this with square waves from a pic, pwm will probably work.

 

[Rave0035]

Got a photo of this thing?
Mike

 

[dr pepper]

Yup.