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Re: Capacitance Measurement Question



Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Ray,

	The leads can affect the measurements.  I have a set of leads only 1.5
inches long for caps.  Also, be sure to make the contact real good.
Sometimes brand new stuff needs a little scuffing in to get good contact.
One of my meters does capacitance and it has two wide slots to stick the
cap leads into.  I need to plug the cap in and out a few times to get good
contact but then it seems stable.  Sometimes new meters with the big dials
on them for range need to have that dial run back and forth a few times too
to clean the contacts.  I don't think temperature should affect these
meters greatly.  Don't worry about the cheap part.  Even the cheapest
meters usually have the same elctronics in them as some of thie nice meters
(the case and labor cost are what differs) and for what you pay, any meter
will do wonderful things!

Cheers,

	Terry


At 09:37 AM 12/27/2000 -0500, you wrote:
>Hi all,
>
>Hoping everyone had a Merry Christmas :-) One of the items of
>my Christmas wish list that made it under my tree was a new
>DMM that could measure capacitance. Yes, up till now, I've done
>all of my coiling measurements without the benefit of a means for
>measuring my caps. The DMM is a Velleman made in China and 
>was pretty cheap, but it seems to work well and I'm sure it will suf-
>fice for my needs :-)
>
>Now to my question. I noticed that when measuring the capacitance
>of my various capacitors that there will often be a variability in the 
>measurement readings that I get on the same capacitor from one 
>reading to the next. It seems that it can vary by around ~ 10% or so.
>I'm figuring that the difference in ambient temperature can cause a
>drift in the capacitance. It is ~ 70* F in the house and around 30*F  
>outside (yesterday). One of the coldest Decembers on record in my
>area has made experimenting in an unclimate-controlled shop a lit-
>tle uncomfortable (I do have a small kerosene heater). I noticed on the
>manual with the DMM stated that the calibration is guaranteed for a
>year, when the ambient temp is kept in the 18*C to 28*C range. So
>maybe cold temps affect the accuracy of the DMM itself?
>
>I thought I would throw this question out to the list as there couldn't
>be a more authoritative think-tank out there regarding this matter :-)
>
>David Rieben
>