Keithley 2000 DMM AC Read Overflow

Question

I’ve been having problems controlling a Keithley 2000 DMM during AC volts measurement using IVI. When reading AC Volts the DMM will intermittently sense an ‘overflow’ and return the value NaN. I’m using IVI and TestStand 3.0 but get the same problem with IVI and LabWindows 7.0.
The set-up is as follows:
Device: Keithley 2000 DMM, GPIB device number 6
Device interface: GPIB, DMM set-up in MAX as GIPB0::6::INSTR
IVI Driver version: 3.02, downloaded from the NI web site
IVI Compliance Package version: 2.1
NI-488.2 version: 1.70
NI-DAQ version: 7.1.0f1
MAX version: 3.0.2.3005
For test purposes I’ve connected the DMM front panel input high and low and set the inputs mode on the Keithley to front, this should mean that I get a very low Voltage reading. I’ve then run the LabWindows/CVI IVI control sample code provided with the IVI driver. At the initialisation panel I’ve entered the logical name. At the configuration panel I’ve selected Volt AC measurement but left everything else as default. The second configuration panel I’ve left as default. At the Read panel I’ve left all setting as default. Pressing the read button up to about 20 times with about a second gap in between each press will eventually lead to an ‘overflow’ reading.
Any help/explantion will be appreciated
Steve

Answer 1

Here are the results of my investigation into this problem, it’s two fold:
1. Keithley have informed me that their engineers in the US have just seen the problem I’ve been seeing and are working on a firmware update. Currently here is no date for the release of the updated firmware but I’ll be informed when this it’s ready.
Note: I’ve found that the read AC Volts overflow problem only occurs when the read trigger delay is set to zero seconds.
2. The TestStand DMM IVI configuration step always sends a trigger delay of zero seconds regardless of the trigger delay set.
In my TestStand sequence the DMM IVI configuration sets the read trigger delay to 3 seconds but as noted above this is sent a zero seconds thus invoking the Keithley DMM AC Volts read overflow problem.
See attached VISA call log captured by NI Spy. The first 22 call are made when the DMM IVI configuration step is called form TestStand the next 22 calls are made by the IVI DMM sample code configuration provided by National Instruments when DMM configuration is run thorough LabWindows. Note call 12 (IVI DMM TestStand) has the trigger delay set to zero seconds (should be 3 seconds) and call 34 (IVI DMM LabWindows) has a delay of three seconds.
I’ve found a workaround as follows:
After each call to the TestStand DMM IVI configuration step an additional step that calls the TestStand IVI Tools step can be added. The IVI Tools step can be set-up to specifically configure the DMM Trigger Delay to 3 seconds. I’ve proven that this individual call does in fact send the correct trigger delay command to the DMM thus alleviating the AC Volts read overflow problem.
Can NI confirm that this problem does exist with the DMM IVI step and when they plan to fix it. I’ve attached the TestStand sequence file that I’ve been using to investigate the problem.
Thanks
Steve
Attachments:
DMM Overflow.zip ‏9 KB