34401A different readings using GPIB

[Penguin36]

Hi,
I get different readings measuring a LM399AH based voltage reference when using GPIB on my 34401A.

Using the 34401A after Reset and switching to 6 digits, the display shows stable 5.02233V (thats my reference voltage) for hours.
As I understand thats '6 digits fast' with 10 PLC, right?

When using GPIB with raspberry pi, I get higher values for the same voltage reference.

GPIB settings are:

Code: [Select]

CONFigure:VOLTage:DC 10,MAXimum
SENSe:VOLTage:DC:RANGe 10
SENSe:VOLTage:DC:NPLCycles 10

and than READ? and write to a logfile.

Logfile shows 8 digits after comma and values are higher than using 34401A without GPIB.
Values are 5.02242***  (*** different numbers because of noise I think)

Resetting the 34401A as before, don't use GPIB, I get the lower voltage again (5.02233).

Why do I get different readings?

[HighVoltage]

Because you have a "MAXimum" in your read statement
CONFigure:VOLTage:DC 10,MAXimum
If you would set the instrument manually to MAX you most likely will also get the higher number on the display.

[Penguin36]

The MAXimum statement in CONFigure:VOLTage:DC 10,MAXimum means the resulotion, so why should this influence the measurement and show higher values?

[HighVoltage]

Oh, sorry, I was wrong!

I never used the MAX command there, I always put the number in that I want the resolution to be.
What happens, if you use:
CONF:VOLT:DC 10,0.00001

[Andy Watson]

What happens if you insert a delay between issuing the read command and then recovering the value?

[Penguin36]

I‘m on work now. I will try your settings later and post results.

[Penguin36]

With CONF:VOLT:DC 10,0.00001 the readings are correct now. I don‘t know whats wrong with the previous settings. Anyway ...

[HighVoltage]

Great to hear, that you got it to work.