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low frequency signal amplification

Discussion in 'General Electronics Discussion' started by Omid Zandieh, Jul 15, 2015.

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  1. Omid Zandieh

    Omid Zandieh

    Jul 15, 2015
    Hello People,
    I have a small question regarding a project I'm working on. I don't have an electrical background so I'm quite stuck in a part and don't have a clue on what should I do.
    To keep it brief, what I'm trying to do is read the signal of an RTD which has a DC current going through it (generated by a commercial DC current source). because of the size of the RTD and other considerations, the current going through it is rather small and so the voltage signal I see from RTD is also small (order of 5 mV). What I want to do is to amplify this signal and look at a certain frequency (5~10 Hz) using a lock in amplifier.
    What I'm trying to do and seem to be unsuccessful at, is using an AD524 to amplify the signal (I have attached the datasheet if anyone is wondering). I set up a board according to the datasheet (easy since it has internal resistors for gain set), but when I measure the output terminal and reference voltage difference and compare it with input voltage, the value is far from accurate. Instead of a gain of 100, I'm getting a gain 120... I've tried gains of 10 and 1000, but it's still off around the same amount (getting gains of 12 and 1200). I tried changing the chip thinking it might be a defect, but I got the same result. I feel like the problem is with grounding and the reference I'm using but I can't seem to quite figure it out.
    Anyhow, I understand that diagnosing a circuit like this is rather challenging, so I would appreciate it if any of you has any other, easier to implement solutions for me. I simply want to amplify a mV level voltage accurately

    Attached Files:

  2. davenn

    davenn Moderator

    Sep 5, 2009
    RTD = Resistive Temperature Detector from what I can find, please give a part number and datasheet link
    please state if it means something else to you

    If I am correct on your sensor. Why would you think you are getting a varying freq from it ?
    you should be getting a low voltage DC that varies with temperature

  3. LvW


    Apr 12, 2014
    Let´s take as an example a gain of 10. Did you use the resistors as mentionmed on page 17 of the data sheet?
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