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Triggering problems between 2400 & 2182a

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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alr206
Posts: 4
Joined: July 14th, 2011, 10:06 am
Country: United States

Triggering problems between 2400 & 2182a

Post by alr206 » August 19th, 2011, 1:06 pm

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. I believe the 2400 may not be triggering properly. When I have run the test with external triggers from independent power sources for the trigger pins on the 2182a & 2400, the test runs fine and all data points are measured. FYI - my NPLC settings for the 2400 & 2182a are set equal to 1; the number of steps/sweeps does not seem to matter. 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

Could the triggers possibly be occurring too closely to each other, thus missing a trigger? Or does the 2400 not perform its final trigger before idling? I've included my labview VI below. Thanks for you help!
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Keithley 2400 2182a Differential Conductance.vi
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alr206
Posts: 4
Joined: July 14th, 2011, 10:06 am
Country: United States

Re: Triggering problems between 2400 & 2182a

Post by alr206 » August 24th, 2011, 2:59 pm

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.

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.

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.

Thanks!

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