On Wed, 8 Aug 2012 18:07:43 -0400, "Jim Wilkins"
wrote:


"Winston" wrote in message
...
On Wed, 08 Aug 2012 11:44:59 -0700, PrecisionmachinisT wrote:

"Winston" wrote in message
...
On Wed, 08 Aug 2012 12:37:40 -0400, Jim Wilkins wrote:

(...)

If you want to measure winding resistance accurately, force about
an
Amp through it and measure the voltage drop. At 1A, 1 mV is one
milliOhm.

Yes. A Kelvin connection. It is very useful.
http://en.wikipedia.org/wiki/Four-terminal_sensing

My old Triplet 630 seems to work just fine for this and since the
"B"
cell only needs replacement about once every 30 years......

That's peachy for getting a 'ballpark' idea and probably quite
sufficient
for most motor servicing without the need of a Kelvin connection.

When you *do* need much better precision and accuracy, a Kelvin
connection with a good digital meter is hard to beat. In a previous
lifetime, I was able to estimate current flow in a very low
impedance
application by using a measured PCB trace as my current shunt.
'Worked a
treat.

--Winston

I have a nice calibrated lab milliOhm sitting in front of me. I doubt
a Triplett can show it's actually 0.6 microOhms over.

Braggart.

Well, I have coolth in the shop once again. I found a zero
capacitance in the cap (and infinite resistance), so I called around.
The local shops wanted $35 and $42 for the damned thing, so I called
my buddy. When I got there, he could only find 25uf cap, so I was out
of luck. He then told me where the local Grainger was in Medford, so
I went there. It had gone out of business over a year ago. When I got
to the chiropractor's office, there was an HVAC guy there. When he
asked the chiro if there was anything else he could supply, I gave it
a shot. Ayup, he had a 30/5uf cap for $15, so I bought it on the
spot.

I had a scare at first. I installed the cap, buttoned up the cabinet,
and came in the house to turn on the thermostat. Hmm, no relay click
and no condenser fan noise! What could it be? It was then that I
remembered that I hadn't plugged in the fuse block for the disconnect.
It worked fine after that, for some reason. Whew!

--
Another belief of mine: that everyone else my age is an adult,
whereas I am merely in disguise.
-- Margaret Atwood