Posted Fri, 07 Jul 2023 08:52:22 GMT by Ermazze, F
Hello all,

I am new to this forum. I hope to be in the good section

I need to produce an AC current at different frequencies with a Keithley 6221 current source.
Then, I need to measure the induced voltage drop across a resistance (RTD) at all the frequencies produced, by using an Ametek 7230 lock-in amplifiers, phase locked with the current source.

I managed already to lock the lock-in amplifier to the source by using a phase marker output from the trigger link cable (as explaned here https://forum.tek.com/viewtopic.php?t=45)

However, I have problems at low frequencies. The lock in is not quite well phase locked to the source. 
I believe this comes from the fact that the phase marker is not a TTL signal as requried by the lock-in amplifier (I also checked this with an oscilloscope).

Is there a way to output a TTL signal from the Keithley trigger link cable, so to properly lock the Lock in amplifier?
If so, how can I setup that?

Thank you very much
Best wishes
Federico


Ps:
Here is what I tried without success:
I tried to pilot the Keithley source by the lock-in (so the inverse). However, I only managed to trigger the source at the frequency of lock inm but I could not really lock the two. For example, the Keithley starts to send a wave at each trigger signal from the lock-in but the form and frequency of the wave that it generates is not dependent on the lock-in (for instance, I can send many portion of a 100 Hz sine wave at a 2kHz frequency set by the lock-in. I could manually set the two frequencies to be the same, but I think this may cause errors in the measures since the waves will never be properly synchronised) 

Thank you very much for any help you can give!
Posted Fri, 21 Jul 2023 10:53:34 GMT by C, Andrea
Surprised to hear the phase marker signal is not TTL for you.
What was input R of the scope when observing it?  Were you also temporarily disconnected from the lock-in trigger when evaluating?
Can you try different line within the TLINK for phase marker?

is the lock-in using falling edge trigger from 6221?

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