DMM Minimum Capacitance Measurements ?

[Jim F.-3]

.
Subject: DMM Minimum Capacitance Measurements ?
To: Elecraft List

Please,
 
What is the lowest capacitance value you can measure with the popular  DMMs ?
 
(in picoFarads ?)  DMM specs do not spell out what the minimum capacitance  is..
 
Jim - W1FMR
 
.


Best Regards,

Jim
   
 AMERICA;    WE ARE STILL BLESSED !













Best Regards,

Jim
   
 AMERICA;    WE ARE STILL BLESSED !










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[L. D. Ingram]

Jim,

I imagine different DMMs have different lower ranges, but what ever the
lower range is, you can measure even smaller capacitors by paralleling them
with one that does fall into the lower range of your particular DMM. First
measure the value of the capacitor that falls within your DMM's range then
connect the smaller one in parallel - the difference in the new value
measured is the capacitance of the smaller one. Of course with small values
you have to use the shortest possible test leads and make sure they stay
about the same distance apart for both measurements.

Larry Ingram   AG4NN   K2 sn 2529

<snip.
>What is the lowest capacitance value you can measure with the popular  DMMs ?
>
>(in picoFarads ?)  DMM specs do not spell out what the minimum
>capacitance  is..
>
>Jim - W1FMR
>
>.
<snip>

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[Ron D'Eau Claire-2]

Jim, W1FMR asked:
What is the lowest capacitance value you can measure with the popular  DMMs
?
 
(in picoFarads ?)  DMM specs do not spell out what the minimum capacitance
is..

---------------------------

My Radio Shack DMM will accurately measure capacitance as low as 2 or 3 pf.

It has a parasitic capacitance of about 111 pf, but that's not a serious
problem when working with small capacitors. I simply subtract the parasitic
capacitance from the reading (113 pf - 111 = 2 pf). The meter has sockets
for capacitor leads to avoid variable parasitic capacitance from the test
leads. I've checked it for accuracy with values at low as 2.2 pf.

It will work with the test leads attached too as long as I'm careful to lay
the leads out so they don't move around. I've measured the value of caps I
can't plug into it easily (e.g. a large variable cap) by arranging the leads
so they are close to but not touching the cap and noting the parasitic
capacitance. Then I touch the leads to the cap and note the change.

I can't guarantee how other DMMs will react, but since a relatively small
number of special-purpose I.C.s are used in virtually all DMMs, I'd expect
other DMM's in its price class ($70) to behave much the same.

Ron AC7AC



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[Fraser Robertson]

Jim, from memory typical DMM's do not have low capacitance ranges.  I have a
LCR type portable DMM that has more useful ranges, but is not so good for
voltage and current measurements.  It's lowest capacitance range is 200pF
full scale so it's possible to measure C's in the pF region.  Over here such
meters cost about £80, a lot more than typical cheap DMM's.  I found it very
handy for checking C's and L's when building the K2.

73 Fraser G4BJM

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[Brian Mury-3]

On Tue, 2005-11-01 at 13:23 -0800, Jim F. wrote:
> What is the lowest capacitance value you can measure with the popular  DMMs ?
>  
> (in picoFarads ?)  DMM specs do not spell out what the minimum capacitance  is..

My Meterman 34XR has 4 scales - 4000, 400, 40 and 4 uF max scale,
resolution is 1 nF. Not terribly useful for things like building K2's -
which annoys me, because I bought it to build my K2, and intentionally
bought a meter that can measure capacitance. That's what I get for not
paying attention to the range that it could measure... :-( Oh well, it's
still a very nice meter.

I'll probably end up buying this: http://www.aade.com/lcmeter.htm when I
can afford it and want to spoil myself. The specs say it can measure
".010 pf to 1 uF (most units measure to 1.5 uF)". Also inductance: ".001
uHy (1 nHy) to 100 mHy (most units measure to 150 mHy)".

--
73, Brian
VE7NGR

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[n6wg]

Brian
You won't regret buying the LC IIB meter when you can.
It is pretty much the defacto standard among QRP builders.
Good luck and 73
Bob N6WG
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