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Triggering problems between 2400 & 2182a

Posted: August 24th, 2011, 3:10 pm
by alr206
I have been having trouble when using a Keithley 2400 Sourcemeter in conjunction with a Keithley 2182a nanovoltmeter. I am trying to do a differential conductance test, where current is sourced and measured on the 2400, and voltage is measured on the 2182a. For the sourced current, I am using a modified linear staircase. This staircase is sourced repeatedly upon an external trigger (to be timed with a specific event occurring in my test). To do so, on the 2400 I have created 'n' arming layers that correspond to the number of sweeps, and 'm' trigger layers corresponding to the number of sourced currents within the staircase. On the 2182a, I set a sample count of 1, and a trigger count of 'n'*'m'. The buffer on the 2182a is also set to hold 'n'*'m' data points. However, a problem occurs with the triggering during the test, and the 2182a buffer is not filled due to at least one measurement not being made. The 2400 sources and measures all of its data points.

When I change both the 2400 & 2182 NPLC settings to 0.01, and set the 2400 so that trigger count=2, arming count=2 & the 2182 so that trigger count=4, the program works perfectly. When I slow down the NPLC settings (to 1) on either piece of equipment OR increase the # of triggers (steps in a sweep), I lose one data point from the 2182. There is a missing output trigger on both the 2400 and the 2182. The missing trigger/data point always seems to occur in the last arming layer.

FYI - the 2400 has the arm layer input on pin 1, trigger layer input on pin 2, & trigger layer output on pin 3. The 2182a is left at its default of trigger layer input on pin 2 & trigger layer output on pin 1. The 2400 pin 2 is connected to the 2182a pin 1 & the 2400 pin 3 to the 2182a pin 2. I am using LabView version 7.1.

I have done further experiments using an oscilloscope to monitor the incoming and outgoing triggers. When I separate the two pieces of equipment, and hook them up to power supplies that can quickly drop from ~3-5 V to ~0-2 V, I see every output trigger I am expecting.

Is there anyway that the input trigger line from the one piece of equipment can have a large voltage/current that effectively hides the output trigger from the other piece of equipment? Any help would be greatly appreciated. I'm kind of stuck until I can figure this trigger problem out. I've included my labview VI below.

Thanks for your help!

Re: Triggering problems between 2400 & 2182a

Posted: May 9th, 2012, 10:28 am
by jmichel
I wonder if you're having a similar problem to mine. I get a duplicate reading in the last reading of the 2182A buffer as if it wasn't triggered but just sent the previous reading to the buffer. Sometimes it doesn't happen but most of the time it does. I've monkeyed around with the NPLC and trigger delays, but nothing seems to be a fail-safe against this problem. Previously, I had a problem where the triggering would hang, but I just changed the order of when I retrieve data from the 2400 and from the 2182A. If I get data from the 2400 first then get the data from the 2182A, nothing hangs and I get all the data, except for the duplicate last data point.