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In article ,
says...
On 23 May 2004 22:33:59 GMT, something compelled
(C1gmlm), to say:

My electronic module went bad on my Cold Machine and the shop suggested that I
check the resistance of the compressor. When I check the resistance between 2
of the points my meter shows .8 ohms. When I touch the 2 leads of the tester
together I get a .4 reading. Do I subtract .4 from the original reading to get
the true resistance in the compressor? I have 3 different points to to check.
Thanks

Zero the ohm meeter before each test. There should be a knob or
something.

If your meter does not have a zeroing capability, then yes, subtract the
"shorted" reading.

Another approach for such low resistance tests is to use a large power
resistor to pass a current of 1 to 10 amps thru the circuit to be tested,
using a separate 12V battery. If the current is known, most digital
multimeters will read small voltages much more accurately than small
resistances. Do ohm's law: R=E/I so if the current is 10 amps and the
voltage across the device under test is .05 volts, the resistance is .005
ohms. Practically, about 1 amp is fine for most motor winding tests
unless it's a large starter motor etc. You need to know the actual
current you are 'forcing', usually by having a known series "current
limiting" resistor (perhaps 10 ohms rated at 25 watts or more) and
measuring the voltage across IT to calculate the current.

Make sense, or do you need more??

I do this often to measure relay contact resistances, motor windings,
circuit breaker internal resistance, cabling resistance etc.

--
Regards, Terry King ...In The Woods In Vermont

Capturing Live Music in Sound and Images
http://www.terryking.us