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3706a corrupt data on 2nd scan only (out of 100s of successive scans)

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3706a corrupt data on 2nd scan only (out of 100s of successive scans)

Post by alexwaguespack » October 24th, 2017, 6:18 am

Hello, I'm running a C++ application that sends TSP commands over a raw TCP socket to the Keithley 3706a (with a 3724 dual 30ch mux installed) to read a bunch of K thermocouples. My program first sends a handful of commands to setup the device parameters then starts a periodic timer that sends a few commands to execute the scanlist at specific intervals (in the range of .25 - 1.0 seconds). I'm experiencing some odd behavior where the returned values from my 2nd scan gets corrupted. The 1st scan and the hundreds that follow work great, but the 2nd one is consistently garbage.

Since I'm displaying the readings on a temperature vs. time graph, the result is a weird spike near the beginning of every run. I've considered simply throwing away the first couple of scans, but I'd much rather address the root of the problem if possible. Any suggestions would be appreciated. the TSP commands I'm using are listed below. Thanks! -AW

Commands sent once at the beginning to set up parameters.
dmm.func = dmm.TEMPERATURE
dmm.autodelay = dmm.OFF

Commands sent every 500ms

Dave W
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Re: 3706a corrupt data on 2nd scan only (out of 100s of successive scans)

Post by Dave W » January 5th, 2018, 12:18 pm

I suspect it may be due to the dmm.autodelay setting being turned off. Having this turned off can cause the first reading to be "unsettled" as the measurement circuitry may not yet be settled. You get faster performance with it turned off, but you can run into measurement issues with it off.

Try turning it back on and see if your measurements look OK after.

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