[simpits-tech] Wiring of POT and EPL

[Jim S]

At 28-2-03 23:23, you wrote:
> > Ok, the synchro isn't using the DC, the circuit board is.  The sine/cosine
> > signal *must* be AC for the synchro to resolve.  The only time you'll use
> > DC for sine/cosine is in an air-core motor.  A synchro is a six wire
> > device, an air-core motor is a 4 wire device.  I don't know what tricks
> > Malwin is doing, but I've never seen a _real_ synchro function on DC.
>
>Well yes.... but I'm sure you can tell me where on that circuit they make 
>up the 400Hz
>:-) Believe me Gene... it's like this with all the other Synchros I have 
>in instruments
>too... no 400Hz.... Like I said I don't know how they do it, but they _DO_ 
>it somehow....
>
>Martin

A quick observation here might clarify matters. I looked at the picture and 
the key
is in some of the circuitry that can be seen in the lower right part. The 
integrated
circuit (blak thing with lots of legs for those who don't know) with the 
number 324
on it is actually a quad operational amplifier. First, remember that the 
instrument
is only the display device to the pilot. The sensors for what is being 
displayed on
most of the instruments are elsewhere, and it is the signal from these sensors
that is transmitted to the instrument. The most reliable way to send an 
accurate
positional type signal in an aircraft is by the use of the symchro-resolver 
technique.
There are two possibilitirs in the instrument shown.

1- in an instrument that only needs to drive a pointer or something of 
similar low
    mass, the RX type synchro/resolver will receive a three phase AC signal 
PLUS
    a reference signal (also AC at the same frequency) from the TX 
synchro/resolver
    in the sensor device.

2- in an instrument that has a reasonable mass to move, a DC servo/gearing 
system
     is used to drive the heavy components and the synchr/resolver is 
driven as part of
     the servo feedback loop (similar to the pot in a R/C servo, but 
continuous rotation).
     The operational amplifier seen in the picture is probably being used 
to boost the
     weak RX synchro/resolver signal so that it can be used to accurately 
determine
     the null-point for the main DC driving servo.

Now with any luck, I have completely lost most of you, but believe me, the 
400Hz AC
signal IS being used. If anyone really wants to know how these things work, 
I can point
them to some URLs that give a full treatise on the subject.

Sorry for the lengthy input, but I could see a couple of you coming to 
blows over this.

BTW, in the simulator systems that these instruments come from, the AC 
signals are
generated by the expensive chips mentioned earlier. You just dont get given 
that part
of the system when you buy the instrument.

Jim.