another programing question

[adavies78]

Let's try this again--

This time, my question is about GPIB-VISA communication.

I'm talking to an old-ish Keithley sourcemeter (2601, firmware 1.3.3.) to do IV sweeps in a multi-channel application.  This system's been running for about 2 years without a hitch, but now all of a sudden i need to speed it up significantly to accomodate higher test volumes.  Previously I was running a double for-loop with the inner loop performing the {set source level-measure-read data} operation on a point-by-point basis to generate the IV curve, and the outer loop cycling through the channels.  In this configuration, the measurement took about 1.5s/device.

Now i'm taking advantage of the buffer capability of the SMU--queue up the entire sweep, trigger it, and then read the result out of a buffer.  The sweep itself is now down to a couple of ms, which is good, but the overall operation is now slower because of the visa-read command.  This was my diagnosis, anyway:

You can see that the VISA-Read command *does* work, but Tick 4 indicates that it takes 2.1s !

it doesn't seem to matter much how many points are in the sweep--with anywhere from 4 to 88 it still takes 2 seconds...

It also doesn't seem to matter what i put in for byte count--the 648 is the minimum i can use to get the 50 datapoints of this sweep out, but the timing is the same with a bytecount of 50 to 1024...

If i put the read outside the for loop, then it will timeout...

Anyone have any thoughts/tips on this?

THANKS!

[DennisKnutson]

Really the wrong place to be asking this type of question. Post to the Instrument Control Board<http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/bd-p/140> and at least post a snippet or better, the entire VI.

Dennis Knutson

Senior Developer- National Analytics

dknutson@nationalanalytics.com<mailto:dknutson@nationalanalytics.com>

(303)-960-8370 - Phone

(303)-362-7117 - Fax

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[MattWhitlock]

Agree with Dennis that you'll likely get the answer you need if you post to the instrument control board.  But also check the timeout setting on your VISA Configure Serial Port VI to see if it's the culprit. I doubt it, but it's worth a check.

I also checked for IVI drivers and there's this one for that model of device here:

Keithley 2601

You should try it out and see.

More generically when looking to control an instrument, I always look at the NI Instrument Driver Network (IDNet)