SMU 2612B Help with Timer Based Measurements

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Killilea, Niall
Posted 2 months ago by Killilea, Niall

Hi all,

I am looking for help with a measurement using a Keithley 2612B. What I want to do is

1. Apply a set voltage (typically ~4V)

2. Immediately begin recording current data to a buffer

3. After a set amount of time/counts of measurements turn off the voltage

Here is my Lua code:

  1. function run_experiment(voltageLevel, voltageApplicationTime, samplingInterval)
  2.  
  3.     chargingTimer = trigger.timer[1]
  4.     chargingTimer.count = voltageApplicationTime / samplingInterval
  5.  
  6.     chargingTimer.delay = samplingInterval
  7.  
  8.     smub.reset()
  9.  
  10.     smub.source.func = smub.OUTPUT_DCVOLTS
  11.     smub.source.rangev = voltageRange
  12.     
  13.     smub.nvbuffer1.appendmode=1
  14.     
  15.     smub.measure.rangei = 0.01             -- Set current range for measurement
  16.     smub.measure.autozero = smub.AUTOZERO_OFF
  17.     smub.measure.autorangei = smub.AUTORANGE_OFF
  18.     smub.measure.count = voltageApplicationTime / samplingInterval
  19.     smub.trigger.measure.i(smub.nvbuffer1)  -- Measure current into buffer1
  20.     smub.trigger.measure.action = 1
  21.     smub.trigger.measure.stimulus = chargingTimer.SOURCE_COMPLETE_EVENT_ID
  22.  
  23.     chargingTimer.stimulus = smub.trigger.ARMED_EVENT_ID
  24.  
  25.     smub.source.levelv = voltageLevel
  26.     smub.source.output = smub.OUTPUT_ON
  27.  
  28.     waitcomplete()
  29.  
  30.     if smub.nvbuffer1.n > 0 then
  31.         printbuffer(1, smub.nvbuffer1.n, smub.nvbuffer1.readings)
  32.     else
  33.         print("No data in nvbuffer1.")
  34.     end
  35.  
  36. end

What am I doing wrong? No data is being created in the buffer and I do not understand why. No errors are being created either. For first tests I set samplingInterval = 0.1 to make things simple but always there is nothing in the buffer!

Additionally, voltageApplicationTime is set to 5.0 so values generally are sensible.

Any help is greatly appreciated thanks!!!

Killilea, Niall
Posted 2 months ago by Killilea, Niall
OK so I have a hideous solution to this problem - to use the integration time as the sampling interval. Any update on how to use the timer is welcome, or otherwise if there are any issues with how I chose to do this, thanks to anyone reading! 
  1.     smub.measure.nplc = samplingInterval * 50  --effective timing interval
  2.  
  3.    --setup smu:
  4.     smub.source.func = smub.OUTPUT_DCVOLTS
  5.     smub.source.rangev = 20.0
  6.     smub.nvbuffer1.appendmode = 1
  7.     smub.measure.rangei = 0.01
  8.     smub.measure.autozero = smub.AUTOZERO_OFF
  9.     smub.measure.autorangei = smub.AUTORANGE_OFF
  10.  
  11.   --setup the measurement:
  12.     smub.measure.count = math.floor(voltageApplicationTime / samplingInterval)
  13.     smub.trigger.measure.i(smub.nvbuffer1)
  14.     smub.trigger.measure.action = smub.ENABLE
  15.  
  16.   --initiate measurement:
  17.     smub.source.levelv = voltageLevel
  18.     smub.source.output = smub.OUTPUT_ON
  19.     smub.trigger.initiate()

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