Why does the integration time setting of Keithley 2000 (number of PLC) changes to medium (1PLC) from fast (10 PLC) and slow (0.1 PLC) settings, when I tried to read from Keithley?

[ICL07]

Dear All,

I am trying to change the NPLC (the integration time) of Keithley 2000 and take voltage readings. Whenever I change the settings to fast or slow and then run the VI, the NPLC changes to medium. Could you kindly tell me what is causing this? Thank you and I look forward to receiving your replies.

Regards

[Marc_A]

I haven't used the Keithley 2000, but with the 2700 the defualt is 5 cycles which is the slow rate. If you run a VI that resets the Keithley, this will be reset to slow. Maybe for the 2000, the default is medium and it's being reset.

What VI are you running? If it's an example VI, it is most likely resetting the Keithley each time you run it and this is the problem. If you wrote the VI, you can change the aperature timing to whatever you want. The VI for the 27xx drivers is Configure Aperature Timing.vi, I don't know if the 2000 drivers are the same.

[ICL07]

Dear Marc A

Thank you very much for the reply. I am using an example VI called 'configure voltage DC.vi' which allows you to change the NPLC, ragne and digital filtering settings. There are two parts to my programme as follows:

1. in the first part I run 'configure voltage DC.vi' to set the number of power line cycles and the range
2. in the second part I have written the VISA commands to read from the instrument

The default setting for the NPLC (aperture time and/or integration time) is 1 so whenever it reads from the instrument it changes the NPLC settings to the default value of 1.

Regards

[tbob]

For the NPLC setting, the higher the number, the longer it takes to get a reading.  So 10 PLC is much slower than 0.1 PLC. 

See if you can set the NPLC setting from the front panel.  Then try changing the vi to set NPLC only, then read it back to see if it matches your setting.  Sometimes changing ranges will automatically set the NPLC depending on the range chosen.  So you have to send the range command before sending the NPLC command.  This may be what is happening.