Digital Multimeters (DMMs) and Precision DC Sources

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PLC configuration time - PXI 4132


  I am using a SMU PXI 4132 to measure current and voltage. The DUT I am using is a diode. I am doing  voltage measurement  followed by leakage current measurement. Voltage measurement is done at an aperture time of 0.01 PLC and the current measurement is done at 1 PLC.But When I  switch the PLC back and forth (from 0.01 to 1)  then the measurement/configuration time is really high. So is there some way of switching the nplc back and forth but still keep the configuration time low. I may need to set the plc for current measurement as 1 depending on the leakage current to be measured. But the voltage test can be done at 0.01 plc .So is there a way to avoid this long configuration time for the SMU ?

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Hi phx_tech,


I know we've been interacting via email lately, but I wanted to reply to this post so the answer to this question is made publicly available.


The best option for you is to leave the aperture time for both measurements at 1 PLC. You won't lose anything by having the voltage measurement set at 1 PLC. This measurement would just have a higher accuracy than you necessarily need. By keeping the aperture time the same for both measurements the hardware does not have to spend the large amount of time required for aperture configuration.


The reason the hardware takes so long for the configuration is because the ADC cannot configure itself during a measurement. To ensure that an attempt to do so is not made, the device waits the maximum possible measurement time (8 PLC, which is 160 ms for the 4132) before reconfiguring the aperture. So if the user has selected an aperture time of 8 PLC, the device ensures that it will not attempt to change the configuration during this measurement by waiting at least 160 ms for that measurement to complete. This configuration time is eliminated if you leave the aperture time at 1 PLC (equivalent to 16.6 ms for the 4132, which is also the default).


Hopefully this clarifies the reason for this behavior.


Chris G

Applications Engineer
National Instruments
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