I have used an HP LCR meter at work but never paid any attention to the
frequency at which the measurement is made. I wonder what discrepancies in
measurement values of L and C could be encountered if one measured at
various RF frequencies, and why they might occur. I have seen such
discrepancies, using a popular antenna analyzer, even though I was careful
not to introduce sources of error, like lead lengths.
Thanks,
On Tue, Mar 30, 2010 at 3:58 AM, Jim Thomson <Jim.thom@telus.net> wrote:
> Date: Sat, 27 Mar 2010 16:02:13 -0800
> From: "Zeitler, Lane LT, FST-1" <zeitlel@cpr3.navy.mil>
> Subject: [Amps] L and C "meter"
>
> I am curious as to what you guys are using to measure the L and C of
> your circuits/components. I looked at the B & K 875-B and it can be had
> for $192.00 on Amazon dot com. I do not know if this is reasonable but
> the meter seems to offer quite a bit and the accuracy according to the
> specs seems pretty good.
>
>
>
> Lane
>
> Ku7i
>
> ## I bought a new B+k 875-A back in 1992. Still works superb.
> ## last year, I bought a new 875-B. Both units are an industry
> standard, and just don't crap out. The 875-B comes with a
> 3 yr warranty. They both use 1 khz square wave for the measurement
> freq.
>
> ## The newer 875-B will measure lytics up to 20,000 uf. [875-A will
> only measure up to 2000 uf] 875-A measures DC resistance. The
> 875-B measures AC resistance.. and now has a 2 ohm scale.. and measures
> down to .001 ohm. Both of em will measure down to .1uh and .1pf
>
> ## Both will measure uh up to 200 Henries ! We have used the 875's
> at work for measuring huge chokes, etc. The 875-B has a front panel
> adjustable zero set.. which is a big bonus. The older 875-A didn't...
> and I always
> had to remember to subtract .66 uh for the 2 x 12" long test leads.
> The B
> model comes with 2 x 6" test leads.
>
> ## The AS Aim 4170 is even better, but requires a PC.
>
> ## Bottom line is, I require something that will accurately [1%]
> measure typ stuff
> ,like a 2.2 uh tank coil, or measure the stray C of cab side walls [typ
> 1-2 pf] ,
> big and small chokes, and also audio chokes and xfmr's. The 875-B will
> also measure
> the ESR on HV lytics..down to .001 ohm. You can spot a bad cap asap.
> Both will also measure D on caps.
> Being able to now measure up to 20,000 uf [ instead of 2000 uf] is a big
> bonus these days.
> All my hv lytics are > 2000 uf. B4 I had to put 2 x in series.
>
> ## the real bottom line is.. with out some kind of lcr meter, or similar
> device, you are dead
> in the water, when playing with amps. A YC-156 has 35 pf C.. between
> anode and grid flange
> on the wooden test bench.. which rises to aprx 53 pf.. when bolted to
> chassis. A 3CX-3000A7
> is 24 pf.. and rises to 33 pf, when inserted into socket and grid ring. A
> YU-148 is 24.5 pf.... and
> rises to 39.6 pf when installed in socket.
>
> Think abt it. For amps,[ and ham radio in general].. all you are playing
> with is pf and uh.....
> and stray pf and stray uh. Not having a LCR meter is like not owning a
> screw driver !
> It's the number 1 tool. Want to know how long that coil of 213 is ?
> Just measure the C between
> braid and center conductor... then divide by XXX .
> I measure all the C on control cables, coax etc.. and document it. Very
> useful when it comes to
> trbl shooting. We started using lcr meters a few yrs ago on new ADSL
> equipment /turn ups
> in the local telco I worked at. Once C readings were taken on known
> good cable assy's, and esp
> pot's splitter/filter assys... finding a bad one was real easy. Get 2 x
> rings crossed.. or 2 x tips crossed
> in a factory splice, or a contractor splice..and the C readings instantly
> change.. dead give away.
>
> Later...... Jim VE7RF
>
>
> F
>
>
>
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--
Jack, W6NF
Silver Springs, NV
DM09ji
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