SRS830 Lock-in and the 3 technique

Discussion in 'General Electronics Chat' started by jthargr12, Jun 22, 2012.

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  1. jthargr12

    Thread Starter New Member

    Jun 21, 2012
    Hello, I am a student doing research on thermocouples and thermoconductivity and have run into a bit of confusion with the 3ω technique.

    For reference, my setup is as follows:
    On the SRS 830 lock-in amplifier:

    Time constant is set to 10 seconds, with the 24dB option and the Sync<200Hz option enabled.
    The sensitivity is set to 500 mV.
    The signal input is set to A - B.
    The couple is set to AC.
    The ground is set to Ground.
    The reserve is set to Low Noise.
    The displays are set at R and θ.
    We are measuring on a range of 100 to 1000 Hz
    The amplitude is set to 1V.
    We are measuring both the 1st and 3rd harmonic.
    The Trig is set to Sine.
    Lastly, the source is set to Internal.

    We have the lock-in signal going out to a 4-point sample in a vacuum sealed chamber and we keep the temperature relatively constant. The signal of course goes back to the lock-in for measurement. We also have a reference signal set up.

    My question lies in a strange scenario (at least to me) as to how the amplitude is affecting the R, or signal magnitude, value.

    For example, with an amplitude of 1V, we get a R value of about 200 mV. If we take that to 0.5V, should we not get only 100mV for the R value?
    Instead, we are getting about 20mV, which does not support the concept of linearity.

    Unless, of course, the system is not linear with respect to amplitude and R.

    Thus, confusion :confused:

    Any input on the setup and why the system is behaving this way would be greatly appreciated!

    Also, if you require any clarification, please ask and I will try to provide as much detail as I can.

    Thanks again!
  2. bertus


    Apr 5, 2008
    jthargr12 likes this.
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