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how to test lock-in amplifier

Started by kellyb September 12, 2015
Is there a simple circuit to test a lock-in amplifier?  I bought one off ebay but don't want to spend lots of time setting it up if the thing doesn't work.  Any help much appreciated.

kelly
A sound card will work fine. Use some freeware to create sine waves of varying phase, one on the left channel, one on the right..  In Adobe Premier you can run a low pass filter plugin on a pure sine wave, or you can download a sine and cosine wave here:

http://www.staffs.ac.uk/personal/engineering_and_technology/dp11/phase/phases.htm 

"Cool Edit" freeware has a has/or had  a scripting function that you can use to create various waves using sine and cosine functions. 


The low pass filter on a sound card output might add a few degrees of phase shift, but in reality things should be quite close.

Then mix in some noise to one channel and see if it stays locked at ~ 90' 

That will let you roughly test the phase measurement side.

Keep the sound card volume very low when it is driving the sensitive lock-in inputs.

That is a quick way...

Steve 






On Saturday, September 12, 2015 at 4:09:40 PM UTC-7, kellyb wrote:
> Is there a simple circuit to test a lock-in amplifier? I bought one off ebay but don't want to spend lots of time...
It's an amplifier. It uses electricity, has input and output impedance, gain, dynamic range, and a phase-sensing function that only makes sense when you have two signals to feed it. It also has switchable time constants. Testing all of that, isn't simple. Calibrating and verifying all the functions, isn't quick. A periodic test signal could be as simple as an audio tone test track on a CD, and phase shifting can be accomplished by driving a speaker and moving a microphone around it. That'll exercise a lot of the features.
On Saturday, September 12, 2015 at 7:09:40 PM UTC-4, kellyb wrote:
> Is there a simple circuit to test a lock-in amplifier? I bought one off ebay but don't want to spend lots of time setting it up if the thing doesn't work. Any help much appreciated. > > kelly
What model? To test send in a dummy signal, perhaps with some variable attenuation. George H.