ADA2200 EVALZ Help

Hello,

I have been working on replacing a test setup at my company that utilizes a Lock In Amplifier, and I am running into some issues due to a lack of understanding on my part.

To preface this, I will say that the test equipment is most likely from the 1970's (8-CFA by Vibro-Meter) and unfortunately after it was acquired by us, it no longer functions. The application is measuring a bridge voltage that has been excited by an AC signal. I gather that the system I am trying to replicate is working on a wheatstone bridge that has been excited by an 8 KHz signal. I am assuming that the bridge voltage is being used as the input for the lock in amplifier. The output was then read on an oscilloscope. The bridge voltage that I am trying to detect will most likely be on the level of 1 µV.

I am hoping to use the board as a replacement for the broken equipment. If I am understanding this correctly, if I ensure that my bridge supply voltage is a 6.25 KHz signal, that is in sync, I should get a DC voltage at the output of the board that could then be measured using a DMM or an oscilloscope? 

Is there anything that I am missing?

Thanks in advance for the help.

-Dakotah Barnes

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  • 0
    •  Analog Employees 
    on May 15, 2020 1:39 PM 9 months ago

    Hi Dakotah.  

    Your understanding is correct.  The excitation voltage frequency of the bridge needs to be synchronous to the sampling frequency of the ADA2200.  You always want to sample the bridge at the same point in the excitation period.  Have you looked at CN-371?  This shows an example of using the RCLK signal to drive an LVDT (which would be the bridge in your case).  This is a good way of assuring the excitation and ADA2200 sampling are perfectly phase aligned.

    Brian

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  • 0
    •  Analog Employees 
    on May 15, 2020 1:39 PM 9 months ago

    Hi Dakotah.  

    Your understanding is correct.  The excitation voltage frequency of the bridge needs to be synchronous to the sampling frequency of the ADA2200.  You always want to sample the bridge at the same point in the excitation period.  Have you looked at CN-371?  This shows an example of using the RCLK signal to drive an LVDT (which would be the bridge in your case).  This is a good way of assuring the excitation and ADA2200 sampling are perfectly phase aligned.

    Brian

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