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SR830 Lock In Amplifier Not Reading Reference Signal

  1. Feb 6, 2014 #1
    So here is my dilemma:

    We have our SR830 in a MOKE set-up. The modulation of the laser is with a chopper at approximataly 336 Hz. The reference signal is not being picked up by the SR830, but using the same cable the reference frequency is coming up on our oscilloscope. ie, plug the cable into the oscilloscope or DMM and we get the appropriate frequency. Plug it into the SR830, and the "Unlock" light is on with a frequency of exactly 1 kHz, which my adviser says it means it's not getting a signal. The rest of the SR830 seems to be in good working order. Both CH1 and CH2 are picking up signals from our photo detector. Any thoughts or suggestions?

    Sorry if the post is skim on details, I'm new to all this.

    Thanks for your time,
    Danny
     
  2. jcsd
  3. Feb 7, 2014 #2

    meBigGuy

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    Gold Member

    "The SR810 and SR830 Lock-In Amplifiers have differential inputs with 6 nV/√Hz input noise. The input impedance is 10 MΩ, and minimum full-scale input voltage sensitivity is 2 nV. "

    WOW that's some instrument.

    The reference input needs to be 400mV pp minimum. You didn't mention what the voltage is.

    Has the setup ever worked?

    Does the instrument work in other setups with an external reference?

    Can you drive the external reference with a signal generator to test its acquisition range?

    Just guessing.
     
  4. Feb 7, 2014 #3
    Thanks meBigGuy. We measured the voltage on the reference signal and it was only around 140 mV so we switched our detector and got the reference frequency where it should be. Thanks a bunch for the quick response!


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  5. May 4, 2015 #4
    I am measuring voltage output from the pick-up coils of a vibrating sample magnetometer using the SR830 lock-in amplifier. The problem is that the channel 1 output voltage cannot be stabilized at all. I read the manual but that is not helpful either. What can I do to stabilize the reading ?
     
  6. May 5, 2015 #5

    f95toli

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    Gold Member

    *Reduce the amount of noise in your measurement setup. Lock-ins can "cut through" quite a lot of noise, but there are always limits and this should always be the first step
    *Increase the amplitude of the input signal
    *Make sure you have the SR830 is on the optimal sensitivity range
    *Increase the time constant
    *Turn on the filters on the input.

    Generally speaking, there will always be some trade-off between measurement speed and sensitivity; if your noise is mainly white you can detect some very small signals with a lock-in if you increase the time constant.
     
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