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Old 09-18-2015, 04:35 PM   #2050 (permalink)
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Originally Posted by e*clipse View Post
I'd like to thank you for providing that example and reminder of why shielded analog inputs are important. Sometimes it's a bit too easy to think "aww, that's not that important - it's just a matter of a few mV...."
No problem ... I have a bad habit of using what is at hand instead of what I should be using.

On another note, I was reading a paper about taking measurements of motor parameters to make the control programs work better:

They mentioned an RLC tester to measure the motor inductance and very low resistances. Damn! You can measure that?? That tool must cost a lot...
Here's a nice used one - for only $37,950!
Agilent 4294A 40 Hz to 110 MHz Precision Impedance Analyzer w Fresh Calibration | eBay

But seriously, you can buy fairly nice hand-held ones from BK Precision:
Model 878B, 40,000 Count Dual Display Handheld LCR Meters - B&K Precision
We use a megger on motors to see if there are ground faults, resistance line to line to see if the phases are balanced - if the phases are shorted part-way through the resistance won't match ... that's about it. Once or twice we've checked insulation with a hi-pot. Sorry for the jargon - I can look up the *REAL* names of the instruments if you like

To measure small resistance on large motors we use a ducter. It is an ohm-meter that uses higher current to measure small resistance. 1 amps or 10 amps. The probes are sharp and there are two for + and two for -, so you get a reading on 'corrosion' as well.

The vendor that we use to rewind our motors uses this RLC type of equipment as well as partial-discharge .. a method of measuring insulation breakdown.

As I mentioned - our industrial controllers do their own tuning. It's a 5 minute process when we change a motor to tune to the new motor and away it goes. It just means I have to drive to site some evenings and weekends when motors fail in production ...

Have you used anything like this at work? If so, any suggestions for what to look for in a good, affordable one?
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e*clipse (09-18-2015)