Products > Test Equipment
New MicSig/EEVblog DP10007 HV Differential Probe
Martin72:
Found one.
https://blog.teledynelecroy.com/2021/04/how-to-test-cmrr-of-differential-probes.html
EEVblog:
--- Quote from: Martin72 on September 06, 2022, 08:33:08 pm ---Now I got one, how can I test it to see if it´s still a problem ?
--- End quote ---
Function gen into a 50 ohm load into a scope, largest voltage you can generate.
Connect both diff probes to the positive side of the 50ohm load, make sure they are twisted.
Measure the diff probe output amplitude in ratio to the input with 20*log(Vout/Vin)
10MHz spec is -40dB IIRC.
PartialDischarge:
--- Quote from: EEVblog on December 22, 2022, 08:37:57 am ---
Measure the diff probe output amplitude in ratio to the input with 20*log(Vout/Vin)
--- End quote ---
One trick here is that the attenuation ratio of the diff probe has to be taken into account, ie if the input is 1Vrms and the output at 1:1 scope setting is 1mV, then the CMRR is not 60dB but 60dB-probe att.
I never know if manufacturers are playing with this, and for example in the Lecroy image the CMRR for the x50 and x500 look suspiciously similar, for x500 the CMRR should be at least 20 dB worst, although this can depend on the actual behaviour of the probe... best to test
EEVblog:
--- Quote from: PartialDischarge on December 22, 2022, 09:05:40 am ---
--- Quote from: EEVblog on December 22, 2022, 08:37:57 am ---
Measure the diff probe output amplitude in ratio to the input with 20*log(Vout/Vin)
--- End quote ---
One trick here is that the attenuation ratio of the diff probe has to be taken into account, ie if the input is 1Vrms and the output at 1:1 scope setting is 1mV, then the CMRR is not 60dB but 60dB-probe att.
I never know if manufacturers are playing with this, and for example in the Lecroy image the CMRR for the x50 and x500 look suspiciously similar, for x500 the CMRR should be at least 20 dB worst, although this can depend on the actual behaviour of the probe... best to test
--- End quote ---
Ah, yes, of course. You set that as the probe ratio on the scope.
The manufacturer could very well diddle this. It should be specifically mentioned in the datasheet if it's output referred, but it never is.
Martin72:
@Dave:
:-+
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