Pico Technical Support and Discussion Forum

jom · Super User Joined: 08 Apr 2007 Posts: 32

Has anyone noticed that the time domain Vrms and the Frequency measurements are wrong. I've got a time signal at 40 kHz 2Vpp that the measuremens say are 230 mVRMS and 28 kHz.

Also, the SINAD measurement on a frequency domain needs to be "edited" then hit "OK" for it to reset or some such. Otherwise the value is wrong.

Any ideas?

jom

PS: The scope windows (both time and freq) say the waveform is 2Vpp (OdBV) and 40 kHz.

jom · Super User Joined: 08 Apr 2007 Posts: 32

Nobody has seen this problem?

jom

picojohn · Site Admin Joined: 11 Jun 2007 Posts: 391

Hello Jom,

We are trying to understand the behaviour described in your posting:

Comment 1.
'Has anyone noticed that the time domain Vrms and the Frequency

measurements are wrong. I've got a time signal at 40 kHz 2Vpp that the

measuremens say are 230 mVRMS and 28 kHz'.

Response:
Is this always the case? We have not been able to recreate that.

Comment 2.
'Also, the SINAD measurement on a frequency domain needs to be "edited"

then hit "OK" for it to reset or some such. Otherwise the value is

wrong'.

Response:
It is unclear exactly what you mean here. Also, how did you

independantly test the SINAD value of the signal?

Would you please send the .psdata file for this behaviour to

support@picotech.com so that we can take a look at it.

Regards
John

jom · Super User Joined: 08 Apr 2007 Posts: 32

Comment #1: It is not always the case. But it did happen again yesterday with the Vrms value. I did notice yesterday that the Vrms value was ready "not enough data". This was odd since there was a LOT of data given my timebase was pretty high so as to get a good spectrum view. I'll try to get that psdata to you later today.

Comment #2: As to the SINAD. I understand your question. At some point I'll get a reading of, say, 30 dB. Then after a time, maybe I change something in the set up of the scope, the reading is entirely different, say, 1 dB. So when I say "wrong" I really mean the value had changed considerably even though the input was the same. Whether it was correct to begin with is reasonable given what was being measured and the spectrum view it gave. I then will click the mouse on the measurement and hit "edit measurement". Then I click "OK" and then the reading returns to it's original value....sometimes.

I also have tried that same "fix" with the Vrms to no avail.

Thanks for looking into this.

jom

ziko · Posted: Wed Aug 22, 2007 8:52 am Post subject:

Hi Jom as John had discussed with you on email, he has managed to recreate the problem and characterised its behaviour. Just to keep you informed the problem is due to using measurement settings when huge amounts of data is being collected. The problem will be resolved in a future release of the software, however in the meantime you can reduce the number of samples that are measured by choosing to measure only between two rulers or by changing the maximum number of samples. Use auto set up to ensure that you have an optimal number of cycles on the screen.

Kind regards

jom · Super User Joined: 08 Apr 2007 Posts: 32

I've notice another anomaly with some of the measurements. This time it is the "DC Average" on the scope. For some reason this is off a bit. I have the scope hooked to a DAC output along with a DVM. The scope and DMV do not give the same result. I would think they would since the DVM doesn't do any more than a DC average. On the surface this may not say much but I tried a completely different DVM (not the same make or model) and it gave the same answer as the first DVM. Am I wrong in assuming the scope measurement should give the same value?

Any ideas?

Thanks

jom

ziko · Posted: Mon Jan 14, 2008 1:15 pm Post subject:

Hi Jom could you send me your .pssettings file or your .psdata file if it it is not too big. Also could you tell me what measurements are you getting and what you are expecting. If your .psdata is too big could you send the settings file and do a print screen on the waveform.

Kind regards

jom · Super User Joined: 08 Apr 2007 Posts: 32

How/where do I send a file to you?

Thanks

jom

ziko · Posted: Fri Jan 25, 2008 4:27 pm Post subject:

Hi could you send it to support@picotech.com

Kind regards

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