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PWM & EMI

Which product is right for your exact requirements

PWM & EMI

Postby Nate » Fri Oct 19, 2007 9:31 pm

I need equipment to monitor amps and temperature of DC motors.

If a Pico current clamp is across a wire that has 15 kHz of PWM will this throw the reading off? The PWM will vary from 0 to 100%, the zero and 100% I am sure is covered.

I will also need to measure motor casing temperatures; however the place I need to monitor the most is right where the magnetic energy is the strongest. What would this do to something like a "K" style thermocouple?

We are talking 5 to 1000 amps depending on motor and system. I know shunts work fairly well in this situation but are not a mobile as a Pico amp clamp would be. I am looking at the PP253.

Thanks
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Postby PeterF » Tue Oct 23, 2007 2:50 pm

Hi,
This is a situation where it is necessary to try it out first! The current clamp high frequency response will only be a few KHz at these currents but you might get a reasonable reading since it will be just averaging the PWM back to an equivalent DC value.
As for the type K thermocouple, if it feeds into our TC-08, it will have a balanced differential input with good common mode rejection. The interfering field will be a higher frequency and can be also rejected by the software itself. It is not guaranteed to work, but it has a good chance in this case. Careful positioning of the lead will also help.
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Postby Nate » Tue Oct 23, 2007 9:29 pm

PeterF, thank you for your response. If it is only off a little I can calibrate for the off-set. These instruments are primarily for a dynamometer but I like the idea of using them else where when needed. Yes I can put the thermocouple in different locations if needed, I like to explore worst case scenarios.


Is it possible to interface a Picoscope with a cell phone that uses Windows as the OS and has a USB connection? I have my phone with me anyway and a Picoscope would allow me to have an oscilloscope at my convenience anywhere!

Am I in dream land with this idea?
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Postby PeterF » Thu Oct 25, 2007 8:55 am

Hi Nate,
Yes, I am afraid you are unlucky with the cell-phone idea! It has nowhere near enough horsepower to do the job.
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