From: "Peter"
>
> On Mon, 5 Jun 2006, Padu wrote:
>> So my question follows: how do I translate that type of signal to useful
>> digital values? (i.e. How many degrees turned on each axis)?
>
> First you translate into degrees/second, and then integrate that to get
> degrees turned. The waveforms move up and down because the sensors use
> some form of lvdt to make the signal and the change in amplitude and
> bias is a side effect of that. You need to ignore the amplitude shift
> and detect peaks or zero crossings (precisely, better than 0.2% of the
> period resolution), on all axes simultaneously. Then you will have the
> instaneous difference in phase between axes, for each two axes, which
> can be scaled to degrees/second, as a signed number. By summing these
> degrees per second into an accumulator you have a crude integrator, and
> the accumulator should indicate degrees. It will drift like crazy. I
> would start by making only one axis, analog, and get some numbers for
> the accuracy and drift of that thing. You can 'measure' its accuracy and
> scale factor (approximately) by putting it on a turntable (use batteries
> for power and try to get the axis pointed right so only one axis gets
> input from the spin).
>
> An analog phase meter can be built easily, you can find schematics on
> the web. It might use a RS flipfop and a few gates, or an analog
> multiplier.
>
> Peter



I did a couple more tests today, and I'm more inclined to say that the 
device doesn't work by phase shift. Tell me if I'm right.
I got one axis (two wires: B and C), plugged wire B into channel 1 of my 
oscope and wire C to channel 2. Set the oscope to time base, pressed the ADD 
button and INVERT for channel 2. When I did that, the wave become a flat 
line (that's what I was expecting, since the two signals are equal when the 
device is resting). When I turned about the axis being measured, the 
horizontal flat line shifted up or down according to the direction I was 
turning the device.
Now, if there was any phase shift, then I'd see something other than a flat 
line in this case, wouldn't I?

Cheers

Padu 

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