Andrea C

Glad to hear you solved it.

FYI for others, if you turn off auto range for current measure, and set a fixed range, the allowed values of current compliance limit must be within that selected measure range.  This is why too small for sense range error is raised.

If auto range is on, then it is possible to have a much higher value for current compliance than the presently in use measure range by the auto range algorithm.

Since your *IDN? query is working well, I'd say your communication is proved.

You are getting a timeout on the other query because it is not a valid command for the 2611B.
Therefore, that command will not cause any response message and your gpib read times out.

I suggest you consider updating the firmware level.  You are at 3.0.3.  Version 3.4.2 is available for your unit.
You need a login to the tek.com site, but otherwise is a free download.

Also while there, download the reference manual which details the commands that the 2611B does understand.
The user manual offers a subset of that info and some typical use case scenarios.

If you want to know the line frequency you can write a command:  print(localnode.linefreq).
Then read the response that is "printed" to the output queue.

Downloads for the 2611B

 

For your incorrect current measurement, try some manual operation and progressively add cable and probes.
So how low are measurements of current for just instrument?
If nice and small, restore zero check and modify connection to just one cable or connector.
Then measure again.

Some BNC cables can give quite a lot of “popcorn” spurious current noise.  Make sure you don’t have that before measuring the sample.

Is your piezo material in a shielded enclosure?  If not, then I image you will get a lot of measurable change just due to environment.  Wave your hands or walk by while measuring.  You can probably detect the motion as charged dust from air impacts the sample surface.

Hi Michael.  Great feedback!  I’ll make sure the factory/firmware engineers are aware of your report.

So, you will generate V and I data as function of some changing amount of mechanical stress?

For voltage, how high is high?  I suspect the sample also has high source impedance.  Therefore your volt meter needs input R spec larger than the source R to avoid loading errors.  Suggest the electrometer 6514 or 6517B.
Alternatively, a SourceMeter with low current ranges can be put into force 0 amps and limit voltage to some value higher than what you expect to measure.  Something like 2636B or 2635B has 1nA source range and offers quite good input R when behaving like volt meter good up to 200V.  Use 2657A if you need higher voltages.

By definition, a good v-meter has zero current flowing into or out of the meter.  So makes it not feasible to also measure the current on those same connection points with same instrument.  Unless the instrument is a SourceMeter, then it can change its configuration and force 0 V with current limit higher than you need to measure.
But understand I am describing two sequential measurements:  measuring V when force 0 Amps, then measuring I when forcing 0 V.  Can this work for you?

If envisioning two meters, how will you connect them?  Seems the amp meter will compete with the V meter for what the charge stored on your sample should do.

 

Not sure about pyMeasure and what actual SCPI commands it is sending to the 2400.
Looks like a loss of synchronization between the code and the instrument state since the error handler is itself throwing an error!

But since it is working mostly, I am wondering if baud rate of the RS-232 is playing a role.
On our old forum, there are some posts about dodgy RS-232 behavior at the fastest baud rate.  
Try slowing down to 19K baud rate.

If trouble persists, can you reduce the code into smaller bit that shows the issue?
Alternately, try using pySerial or pyVISA and directly send the SCPI commands understood by the 2400.

There is a Verification procedure and a separate Adjustment procedure.
When I used "tweak" I was thinking to carry out the Adjustment procedure.

For just the DC Amps, you've indicated the zero is out of tolerance.
Is it only 10uA range, or is the 100uA range also affected?
What about the full scale 10uA level?  Is that in spec?  Have you adjusted it whether it seems to need it or not?

And I was just guessing that perhaps the adjusted DCV zero might have some impact on the DC Amps A/D converter readings too.

If it continues to be out of tolerance, it seems an RMA for service to understand root cause is needed.

 

Hi Sergey,

The tspnet.write is not limited to just a few characters.  Not sure what the upper limit is, but is not 5.
Here is some sample code where the feature is used to interact with a Watlow temperature controller and many of the commands used there with tspnet.write are longer than 5 characters.

https://github.com/tektronix/keithley/tree/main/Instrument_Examples/DAQ6510/Use_the_DAQ6510_to_Control_a_Temperature_Chamber

Sometimes we have to deal with string is really a null terminated array of characters.
Google up ASCII (decimal) code for certain character.  the Zero is 48.  Null is 0.
Line feed is 10;  Carriage Return is 13.


 

Double checking:  when you access the zero, are you open circuit/not connected to your current source standard?

Prior to the DC Amps adjustment, did you first do the DC Volts?
The DC volts procedure has both a zero and full scale procedure step, whereas DC Amps has only full scale.
Perhaps tweaking up the DCVolts offset will impact the DC Amps offset.

Internally, the amps function is measuring the volts across a resistive shunt, so DC Volts could be related.

If you have done both DCV and the Amps is still out of tolerance, I suggest you contact your local sales office/service center.

As for the manual section I referenced, I see it is gone from what is presently posted on tek.com for the 6485.
I have some older revisions on my computer.

I'll upload the relevant pages for the topic of how the source R and C of the DUT interacts with the picoamp meter (or electrometer) current measure functionality.