Understanding current measurement on an irregular waveform

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SUMMARY

The discussion centers on using a Keithley 2400 source meter to generate a ~120Hz AC signal for resistance measurement of bulk semiconductor materials. The user measures AC amperage through a 1.01 ohm resistor with a Keithley 2000-20 multimeter, observing a discrepancy where the meter reads .94A AC during a sweep compared to 1.01A DC. The user seeks to understand the impact of non-sine waveforms on measurement accuracy and the potential sources of error, particularly during polarity switching.

PREREQUISITES
  • Understanding of AC measurement techniques
  • Familiarity with Keithley 2400 source meter functionality
  • Knowledge of resistance measurement principles in semiconductor materials
  • Basic concepts of waveform generation and analysis
NEXT STEPS
  • Research how to configure the Keithley 2400 for square wave output
  • Learn about the effects of waveform shape on AC measurement accuracy
  • Investigate timing issues in source meters and their impact on measurements
  • Explore advanced AC measurement techniques for semiconductor applications
USEFUL FOR

Electrical engineers, semiconductor researchers, and technicians involved in precision measurement and waveform generation will benefit from this discussion.

tempneff
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I hoped to use a Keithley 2400 source meter to generate a ~120Hz AC signal by outputting a 2-point sweep from 1A to -1A on an infinite trigger. The waveform image is attached below.

The end goal is a resistance measurement for bulk semiconductor materials, we prefer AC measurement to avoid thermoelectric drifts. To validate my input current I am measuring AC amperage through a verified 1.01 ohm resistor with a Keithley 2000-20 multimeter.

The meter measures .94A AC during the sweep. If I send 1A without sweeping and read DC current, it measures 1.01A; as expected.

I'd like to better understand the difference in magnitude. How is the measurement impacted by an "AC" current. Is there something problematic math-wise by not sending a sine wave.

current_waveform.PNG
 

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Why are there dwells at 0A when switching polarity? Is that maybe where the 7% error is coming from?
 
Could be. I think it is inherent to the timing of the source meter. I have the delay set to zero, but we know that isn't possible.
 
Is there a way to set the source to be 2App square wave with a -1A offset, instead of it being the two point sweep? I'm not familiar with that generator...
 

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