How to test the CM3?

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LinuxUser13
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How to test the CM3?

Post by LinuxUser13 » Sun Jul 21, 2019 1:37 pm

Our new CM3 we got in 07/2019 said it had been calibrated 11/2017 which was surpisingly long ago for a new purchase. Before doing production measurements I'd like to test the device. What kind of end user test would you propose (we do not have a calibrated 3 phase current supply).

As a start I have attached the 3 delivered standard clamps on my desktop and started a recording clamps closed but no wire inserted. I did expect recordings on 0mA. Instead I did see different recording per clamp, some over 0.5A. After 12 minutes clamps 1 and 3 were about 0A /<10mA. However clamp 2 settled at 360-355mA with a slight noise. Clamp 2 started at about 900mA.
Moving the clamps about on the table did not alter the signal.

My questions are
- do I have a problem with the device calibration or clamps?
- is that a sensible test? If not what is a better setup. I'm looking for a kind of "zero" confirmation
- Why is there is such a long settling time? I have been sampleling inductance coil data from microcontrollers in ms rates so I wonder about the technical limitation. Even the Settings dialog allows a sample rate of 100ms. I would have guessed that there is severe low pass filtering at work to get rid of the noise maybe paired with some very slow ADC mode to get high accuracy. Just in case that assumption is correct, wouldn't an alternate mode in the firmware to configure the ADC to lower precision and reduce low pass filtering allow for high-noise but hi-speed transient recording? At purchase time I was not aware that the device was "not suitable for measuring current transients" (§20, FAQ pdf document). Having time sampled recordings of network spikes are a very useful usecase IMHO. I am thinking 0.5s or lower, not 5min. A network mode to trigger UDP firing(sending) to a given IP with a timeout and multiple sample per packet could optimized network throughput.
- The Data sheet said 3 channels. In another post on this forum I found a statement that for 3 phase recording the data is sampled serially. Does that mean 3channels = 1 ADC with 3xMUX ?

Thanks for any feedback and sorry for the large post

Martyn
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Re: How to test the CM3?

Post by Martyn » Mon Jul 22, 2019 7:52 am

I am surprised on the CM3 date, can you contact support@picotech.com and let them know where and when you purchased the unit.

The unit has a 3 channel multiplexer before a single high resolution ADC, and for a single channel the conversion time is 720msecs. The device is not intended for looking at fast changing and low level signals, so it may be that it is not the correct device for you.

Please follow up on these issues with the support team.
Martyn
Technical Support Manager

LinuxUser13
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Re: How to test the CM3?

Post by LinuxUser13 » Tue Jul 23, 2019 9:53 am

Thanks for the yery quick reply. The very fast and competent replies on this site are really outstanding. Thank you. I will contact support via email as suggested

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