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Old 09-18-2015, 04:35 PM   #2050 (permalink)
thingstodo
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Quote:
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.

Quote:
On another note, I was reading a paper about taking measurements of motor parameters to make the control programs work better:
http://cache.freescale.com/files/mic...ote/AN4680.pdf

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 ...

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