Square Wave Current Measurement

[briansalomon]

I recently had a customer who needed the square wave current of some instrumentation to be certified as accurately as possible. I searched and found no standard available for measuring this parameter but I did have a certified Fluke A40A-10A current shunt with a data sheet showing a spec of 0.03% from DC to 20Khz. The spec is for a sine wave.

I am using an HP 3325A generating a 1hz square wave into a Datron (Wavetek) 4600 trasconductance amplifier and using a Tektronix TDS 640A oscilloscope to measure the output.

Used this way the shunt appears to respond to a square wave exactly the same as a sine wave.

Simply adding the specifications of everything I used to prove this I am getting a tolerance of +/- 1.68% @ 10A/1hz. (the TDS 640A was used to adjust the 3325A output)

Does anyone have a better method of measuring square wave current?

[RFCAL]

Try the TCP's or the A621 or A622 probes

Tektronix current probe solutions offer:

    The broadest range of AC/DC and AC-only current probes
    Measurement accuracy from uAs to 2000 A
    Best-in-class bandwidth up to 120 MHz
    Best-in-class current clamp sensitivity down to 1 mA
    The only products with 3rd Party Safety Certification (UL, CSA, ETL)
    The only products with bare wire voltage ratings
    Automatic readout and scaling when used with Tektronix oscilloscopes so you don't have to convert volts to amps or manually set the scaling

[USMC kalibrater]

TCPs are probably the best method

[briansalomon]

I searched and could not find anything but "typical" current measurement tolerances for any of the Tektronix current probes. The customer service rep couldn't find this either.

My version of GIDEP shows nothing for these either. Does anyone have a spec?

[MetVet]

http://www.tek.com/sites/tek.com/files/media/media/resources/TCPA-Amplifiers-and-TCP300-400-Probes-Datasheet-60W1645810_2016.02.01.11.29.29_13540_EN.pdf

[briansalomon]

So far, I have found no current probe available with a tolerance for a square wave current measurement. TIG welders used for nuclear production equipment and other critical applications produce a square wave current that is critical.

The Fluke A40A tolerance is specified from "DC to 20 Khz" but is specifically intended for RMS and this model is limited to 20A.

I wonder if there are any Metrologists or Metrology Engineers who could explain how one would go about assigning a tolerance for this parameter to an existing current shunt?

[CalLabSolutions]

You could use a current shunt and a 3458A in sampling mode.  That is how I would tackle the problem. 

If you are looking at the current at 1 Hz Square Wave, then you are pretty much looking at DC with the 3458A in sampling mode.   

Mike

[briansalomon]

Thanks. That's a solution I hadn't thought about. If I can get it to work it will improve the accuracy quite a lot. I'll try it when I get some spare time.