Getting the same return string while reading multiple times from a GPIB instrument

[Simon Gustavsson]

I'm having problems reading data from a GPIB instrument.
I'm using a sequence similiar to this:
1. Send a "MEAS:SCAL:PRES?" command to the calibrator to measure the current pressure.
2. Read the result string sent from the calibrator.
3. Send a "SYST:ERR:NEXT?" query to check if an error has occured.
4. Recieve the error string from the calibrator.

When running the program, the error string sometimes contains the same data as the pressure reading. For example, if the calibrator's pressure output string was "1.0000000e2", the error string might be "1.0000000e2" or sometimes just "20, No Errors", with the extra "2" added to the normal "0, No Errors".
The problem a
ppears to occure randomly, a rough estimate would be that it happens one time out of 50 readings.

Are there any relevant GPIB card settings I can change to fix the problem?

[Albert.Geven]

It looks to me that more data is send or data end is signalled to early by hte iocard.
Maybe you should check the gpib bus cable speed. The default is much too fast for almost all instruments. Put it on 2 microseconds (the slowest speed). And we always disable autopolling, to prevent asynchronous actions.

[Rob Cole]

Try putting a short delay (say 10ms) between reading and making the next request. This could just be a timing problem. The buffer hasn't cleared before you make your next read.

Rob