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AD2S1210 looking at COS and SIN in x-y mode on a scope

I have a AD2S1210 converter and it is working but when I put a scope probe on SIN and another probe on COS and put the scope in X-Y mode I expect to get a circle when I rotate the resolver and instead I get an ellipse.  I have the AD2S1210 in differential mode.  when I run an older AD2S80 in single ended mode I see the circle I expect.

  • HI Philip314159,

       Kindly share scope shots of what you observe. Thanks.

    Regards,

    Jonathan

  • Well I figured out that I get the circle that I expect when I go to x-y

    mode if I do not try to center the display.

    COS and SIN have a DC offset so the circle appears in the upper right

    hand corner of my display.

    I have scope photos of SIN SINLO and (SIN - SINLO)

    The attached photo shows these signals raw but if I average them the

    trace is much thinner.  So I am wondering why the trace is so wide.  I

    see the same width on the exc output as well.

    I attached a picture of SIN - COS and it should be a straight line but

    instead I get two lines which means there is some jitter that I cannot

    explain.

    thanks for your help.

    Phil

  • Also I notice that the SIN COS inputs have a high impedance.  I have the

    same circuit as the AD2S1210 eval board (attached) and I am wondering if

    this circuit is the best one for working with a servo motor that has a

    switching power supply.

    I have it operational and it is working fine but I was just wondering

    about the high impedance inputs.

    Maybe there is a better circuit for working with switching servo drives.

    Phil

  • Hi Jonathan,

    Please see my attached scope photos.

    The scope photos are for a two foot cable between the resolver and the

    AD2S1210.

    I put a 345 foot cable between the resolve and the AD2s1210 and I see a

    voltage Increase

    between SIN - SINLO of about 0.5 volts.  Do you have any idea why the

    voltage would increase ?

    thank you

    Phil

  • Hi Phil,

       Some impedance will surely contribute offset with the system. The long cable and the traces can be a source of offsets. Have you tried using a resolver with a shorter cable? Switching power supply can contribute noise in to the system.

    Regards,

    Jonathan

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