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While I understand that the sensitivity in Lock In amplifiers should be as close as possible to the range within which the signal to be measured lies, I could not find a more technical description of how exactly is this implemented. (Take, for example, the Signal Recovery 7265 (data sheet here) Lock In).

Nick Alexeev
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student1
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1 Answers1

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Sensitivity in this case is related to gain.

The sensitivity is the signal level required to drive the amplifier to full scale. If your sensitivity is set too high (too low full scale voltage or current) then you get overloading. If you set it too low (too high full scale voltage or current) then the noise performance may be sub-optimal.

Spehro Pefhany
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  • OK let's say I am measuring the output of a Wheatstone bridge, which is a fluctuating signal near zero. In most cases my signal is in the order of a few micro volts, so I set my SEN to, say, 10 uV. Are you saying it would be better to set it to, say, 50 uV (for the same gain, say 60 dB) ? – student1 Aug 12 '15 at 13:43
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    I think it depends on the maximum noise level etc. [Here](http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/AboutLIAs.pdf) is a decent reference. I found the manual for the SRS 830 pretty useful. – Spehro Pefhany Aug 12 '15 at 14:34
  • I use the Signal Recovery 7265 and is good, but their manual is more about operation than about technical details. – student1 Aug 13 '15 at 16:30
  • Here is the definition from the STS 830 manual: "The sensitivity of the lock-in is the rms amplitude of an input sine (at the reference frequency) which results in a full scale DC output. Traditionally, full scale means 10 VDC at the X, Y or R BNC output. The overall gain (input to output) of the amplifier is then 10 V/sensitivity. This gain is distributed between AC gain before the PSD and DC gain following the PSD. Changing the dynamic reserve at a given sensitivity changes the gain distribution while keeping the overall gain constant." – student1 Aug 13 '15 at 16:32
  • The go to source is Meade's book. https://archive.org/details/Lock-inAmplifiersPrinciplesAndApplications/Lock-inAmplifiersMlMeade/ – D Duck Oct 11 '22 at 19:15