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Peak-to-Peak undermeasurement ADC200/50

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Peak-to-Peak undermeasurement ADC200/50

Postby Jonathan_Jones » Wed Jun 06, 2007 8:04 am

Hi - I'm (re)-evaluating our stock of ADC200 units for outcurrent range of systems, and have a question...I'm probably jsut doing something wrong... :-)

When measuring a RF wave form (our typical range is 800Khz - 2MHz) I cannot seem to get accurate Peak-To-Peak measurements - either using the cursors or via the add-in measurement.

I have a 200V setpoint on the RF, and am measureing through a 100x probe (set correctly in Picoscope) yet my PtP measurement always seems to come in about 20% less than actual. I have confirmed the test device is giving 200V PtP on a benchtop scope, yet two different ADC200s both give identical results. Frequency measurements are spot on - yet PtP always seems low - even on a DC pulse (~4uS timescale, interval 34uS). I have also tried 2 other RF sources, and different apmplitudes but no success.

I am wondering if the ADC200/50 is underpowered for this type of measurement (maybe bandwith/sampling rate is too low?) or if I've just set something up incorrectly !

I have attached a picture to illustrate.

Thanks in advance

Jon
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Postby ziko » Wed Jun 06, 2007 11:17 am

Hi and thank you for your post. I have spoken to one of the engineers regarding this.

"Any of the ADC200 range should be adequate for looking at a 2MHz signal.
The most likely explanation of your problem is that the scope probe is not trimmed correctly for the ADC200. You need to re-trim probes when moving them between scopes (or even between channels on the same scope) to compensate for the different input characteristics of each channel. If you are moving the probe between a benchtop scope and the ADC200 he'll need to re-trim it each time."

Hope this helps.
Ziko

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Postby Jonathan_Jones » Thu Jun 07, 2007 2:58 pm

Hi

Thanks for the info - that sorted it :-)
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