Milliohm meter

Hello Steve,

Welcome to the element14 Community, we hope you are enjoying it! I will move this to the Test & Measurement area as it is a better fit.

Thank you,

Jamie

My choice would probably be Cambridge/IET 510A with 1uOhm resolution and 0.02% basic accuracy

There are some deals on ebay from time to time, but it is pretty rare... I believe that new one cost around 2k USD.

However, for more reasonable budget I would use my DER EE (IET) DE 5000 LCR meter, with 20000 counts on 20 ohm range (parallel/series mode) it has 1 m Ohm resolution, or DC resistance resolution of 10 m Ohms. Nice thing is that it is not expensive and it supports 4 wire measurement.

A DC check (meter) is unlikely to show a shorted turn.

If you check around they often use a 'growler' which is basically the primary winding of a transformer.

If the armature under test is introduced the shorted turn represents a significant load (being a short) and it starts buzzing and vibrating as the magnetic field is loaded.

couple of links

http://www.vintage-radio.net/forum/showthread.php?t=14317

http://www.google.co.nz/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CBsQFjAA&url=http%3A%2F%2Ftoshont.c…

sorry got to run but try this in google, there are quite a few others.

checking shorted turns

Mark

Another way to measure milliohms reliably is to use a normal lab power supply and a decent multimeter with millivolt range.

If you are allowed to pump 1A  DC through a winding, measuring the voltage over the winding will give you the resistance (R=V/I -> with I = 1 -> R=V). Of course, increasing the current will increase resolution. If needed, you can buy / build a precision power resistor to check your current source once in a while.

For measurements of this type, of course you'll need to use Kelvin Connections -> Kelvin Connected - ElectroWiki

I've used a setup of this type to characterize contact resistance of several types of connectors. Do be aware that heating copper will increase its resistance.

Even you are using standard milliohm meters... Dont forget to calibrate it at every measurement to eliminate probe resistance

All very useful ... but

If I read correctly the intention was to check windings for a shorted turn.??

I turn shorted in 100, 200 or even 50 may not show any reading change, unless the motor had a previous reading stored.

I found the reference to the device

http://en.wikipedia.org/wiki/Growler_%28electrical_device%29

http://cr4.globalspec.com/thread/78322/shorted-turns-tester

Mark

I fully agree that testing for shorted windings with a miliohm meter is not the best thing to do.

I believe that there are some testers around for that purpose, probably based on the "ringer" type used to check flyback transformers back in the TV repair days, I would probably try to measure impedance with an LCR meter and try to make some educated guess... However, I have never tried this, I don't work with poly phase AC systems, so take this with a grain of salt

Hi Steve,

My Hameg 'scope has a "component tester" function for testing Semiconductors etc.

It may be worth trying a component tester on the winding with a shorted turn...Comparing it to a winding that you know works.

This would be more likely to work with windings with a higher DC resistance.

philb

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