TDS 2024 GPIB measured value different to that on screen.

[ChristinaJ]

I have a TDS 2024.

When I try to read channel 2 via GPIB I get a ceiling value (E+ 37) and not the value on the scope screen.

Channels 1 & 3 can be read with no problem.

Does anyone know why this may be?

Many thanks for any help you can give,
Christina

[cball]

Which measurement command are you using to query the result?

[ChristinaJ]

Which measurement command are you using to query the result?

MEASURE:MEAS2:VALUE?

I'm reading each channel seperately.

[cball]

The MEAS:MEAS<X> commands refer to the on screen measurements. The <x> here indicates which measurement you are working with however, not which channel to make the measurement on. So, if I wanted to setup the on screen measurements for CH2 amplitude, as the only on screen measurement, then I would do the following:

MEASU:MEAS1:TYPE AMP
MEASU:MEAS1:SOU CH2
MEASU:MEAS1:STATE ON

-trigger the scope here and make sure you have a good acquisition

MEASU:MEAS1:VALUE?


One trap that you can fall into is that the MEASU:MEAS commands are updated periodically by the scope. If you trigger the scope, then immediately query the MEASU:MEAS1:VALUE?, it might still have and return the measured value from the last acquisition. If you use the MEASU:IMM commands instead, it will calculate the value on the fly for you, and return the results so that you know it is from the current acquisition. There is only 1 MEAS;IMM slot though, so if you need to do several measurements, you will have to change the MEAS:IMM:TYPE between each query.

[ChristinaJ]

Many thanks for your help.

I managed to fix the problem by shifting my external trigger pulse in time. I think it was a synchronisation problem and I was somehow trying to read the value too soon after the trigger.