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I'm performing an experiment in which I send a sine wave into a test device and try to measure its response which will be in the order of a few \$\mu\$V. This response is obtained from the buffered output of a controller box (commercial device belonging to the setup). Because of the available equipment I would like to measure this signal with a lock-in amplifier.

The problem is that due to the nature of the test device's feedback loop, the signal may get a DC offset of +/- 10 V at random moments. While there is a TTL reset available to remove this offset as quickly as possible, I fear that the 10 V will damage the input of my lock-in amplifier (sr830).

Is there an over-voltage protection circuit that I can build in between my device's output and my lock-in's input to protect the lock-in from these occasional high voltages?

DaanMusic
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  • What is the damage-free input range of your SR830? Also, what's the bandwidth of your signal of interest? – Marcus Müller Jan 27 '21 at 15:05
  • The signal of interest is purely the signal that has the exact same frequency with respect to the input sine wave (~ 10 Hz). Thanks for your answer below. I checked the specs page but could not find it there. – DaanMusic Jan 27 '21 at 15:23

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Manual, page 4-5:

Do not apply more than 50 V to either input.

Your 10V is fine. AC-couple the input and your sudden 10V movements will remain spurious events. If you want to avoid any flyback voltage accidentally exceeding 50V (I don't see that happening), adding a TVS diode between shield and signal would be an option

Marcus Müller
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