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4132 fast trigger measurements in sequence source mode

Hi,

 

I am using a SMU 4132 to power a DUT in sequence source mode.

The sequence could be as simple as 0V - 3V - 0V. A FPGA executes a test sequence which starts and ends by a trigger on a PXI trigger line to power up and power down the SMU.

I also use a 2nd PXI trigger line to make current measurement.

All works very well.

 

A complete test sequence last 100ms and I would now make several current measurements with a time interval around 500 µs. The time interval is not deterministic but it is generated by the FPGA test sequence.

It seems it is not possible to have small time interval.

 

Could you tell me if it is possible and how I should configure the 4132 ?

I can post my VI if necessary.

 

Thanks and best regards,

Benoît Chantepie

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Benoît,

 

The measurement time on the PXI-4132 is determined by a combination of the Aperture Time and Samples to Average properties. Please refer to the NI PXI-4132 Measurement Configuration and Timing help topic for more information, as well as the Aperture Time and Samples to Average help topics.

 

Because you are triggering and using Sequence Source Mode, I assume you are using niDCPower_FetchMultiple to take measurements. If you are not, I would recommend doing so.

 

When you say that you are trying to make current measurements, are you attempting to source current, and then measure current, or are you still sourcing voltage but measuring current? If you use FetchMultiple, it returns simultaneous voltage and current measurements. If you are trying to switch from sourcing voltage to sourcing current, you will need to abort, configure a new Sequence, and re-initiate.

 

To achieve the best timing accuracy, you should also trigger the current measurements.

 

Due to a quirk of the integrating ADC used on the PXI-4132, changing the Aperture Time does incur a fairly substantial delay (if memory serves, somewhere around 120-160 ms).

 

Please let us know if you have any further questions.

 

Thank you,

 

Tobias
Principal Software Engineer
Driver Software
National Instruments
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Tobias,

 

Thanks for your detailed answer.

 

I always source voltage and I want measure current.

I set the aperture time to 0 in order to be coerced to the minimum value and I use only 1 sample per measure. Autozero is set to False.

 

Yes, I use the FetchMultiple VI and yes I trigger the current measurements.

 

Is there a settling time between 2 measurements in my this kind of application ?

Is it possible to acquire 2 measure of the current with less than 1 ms between them if I use an aperture time of 320µs ?

 

I also monitor the current activity of my DUT on a scope with a differential probe accross a series resistor and my first current measurements done by the 4132 is always the correct value but never the second and others.

It is why I think there is a important delay between 2 measurements.

 

Best regards,

Benoît

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Benoit, You should definitely be able to obtain measurements via triggers well under 1 ms apart. That said, your Aperture Time may be too short of a time for your output to settle, based on what your DUT is doing. If you increase the Aperture Time, do your measurements improve? How far off from the expected value are you? When you receive the trigger, does the current appear to be stable on the scope? As a minor aside, the minimum aperture time is 260 us at 60 Hz Powerline Frequency and 312 us at 50 Hz, not 360 us. Either way, the smaller the aperture time, the less accurate your measurements will be. Please let us know what you find.
Tobias
Principal Software Engineer
Driver Software
National Instruments
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