🚀 go-pugleaf

I posted an article requesting info about capacitance meters a while
back.  I got no response with the exception of a helpful message from Bob
Parnass and a request to send info on home-made capacitance meters.
So I went out and collected a lot of info on Capacitance and Inductance
Meters and Bridges.

I summarize that info at the end of this article in the hopes it will
help someone, or someone will find a better deal, or suggest
alternative manufacturers.  I'm still undecided which meter I'd buy,
but building one is starting to look better and better, given 
commercial cost and the apparent ease of doing so.

I have an article (Cap Checker by W.S Gardiner (VE6BGL) in Mar/87 73
Magazine ) with instructions for an extremely easy looking ( 1 pf to
50uF) analog capacitance meter.  This meter uses a crystal oscillator,
divided down to various values by 7490's and then measures the
capactive resistance at an appropriate frequency.

          C (unknown)
    [~]----)|---+ 	    Where [~] is the 7490's and stuff providing
                |	    assorted frequencies {f: 1hz, 10hz, 100hz ... 1Mhz}
 +--+------>|---+-->|-+     and  )| is a cap, >| a diode, [M] a meter, etc.
_|_ |                 |     
/// |     .1          |
    +------)|---------+     I assume the appropriate eqn is
    |                 |     Xc = -1/(2 pi f C)
    |    1mA          |
    +-----[M]---------+

What I don't understand is the role of the diodes and the .1mF capacitor.
I also don't see how the 1mA full scale deflection was chosen. (i.e.
what happened to pi? )

I do see how easy it should be to measure inductance with a Q-meter;
and how easy such a meter is to build, given a known frequency and a
capacitance meter.

       L       R
   +--()()()--/\/\/\-------+      Where Variable Cap C is tuned to Maximimum
   |                  |    |      Voltage on Meter M, and Unknown Inductance
  [~]                 |   [M]      L  = 1/[ (2 pi f )  C ] 
   |      C  /        |    |
   +-------)/|--------+    |
   |       /               |
   +-----------------------+


Seems that with a 555, some judicious values of f and careful choice of
value and range of C that an inductance meter is almost trivial if one
can reasonably accurately measure C. 

It also would seem I could build an inductance meter into a "Cap Checker"
fairly easy, perhaps first measuring the the unknown resonant capacitance 
at one of the available frequencies, then using that in the resonance equation,
or somehow producing a calibrated deflection.

Am I missing some large gotcha?  How would one figure out values for the
meter part of a Q meter? Why are commercial units so expensive?

Damned if I understood much of this a week ago and my "Principles of
Electronic Instumentation" suggests a voltage divider to measure
capacitance, switching a volt meter between voltage across the source
and known cap values and using:

V             /   V         = C         / ( C        + C)
 known cap         source      unknown       known      unknown

Which doesn't seem to be what the Cap Checker is based upon.

It then goes on to say this won't work for inductance, because of
unknown "mutual inductance" between the known and unknown inductors and
recommends the Q meter approach.  Say What?

I realize this is probally *old* hat to you guys, but it's getting
to be fun for this bored old systems grunt to learn these basics.
Apologize for thinking out loud here,  hope someone else is interested.

Here is the list I worked up for prices and ranges.
With the Xmas holidays I couldn't get any info on Fluke, or full lines
from Beckman and some others.  I also left off resolution and voltage, current
and resistance ranges, though most units had similar values ( ~ 200-20M Ohms
200mV-1000V, .200uA - 100ma, or 10A).   If someone sees something much better,
please let me know.  Check out the B+K 2906, and 388-HD.
--------------------------------------------------------------------------------

Capacitance Meters < $300 US

Elenco CM-1500		  (D) 		 .1pF - 20,000uF		59-C&S
Beckman Circuitmate CM20A (3.5D) 	 200pF - 20,000uF 		140-VnS
Beckman Circuitmate DM25L (D)	 	 2000pF - 20uF 	  		100-Jen
American Reliance 360-D	  (D)	 	 200pF - 20,000uF  		140-AMR
American Reliance 460-D	  (D-I,R)	 200pF - 20,000uF,200uH - 2H	170-AMR
Mercer 9670		  (3.5D)	 .1pF - 20,000uF	 	105-VnS
B+K 820			  (4D)	  	 .1pF - 1F	 		226-B+K
B+K 830			  (4D-Ar)	 .1pF - .2F			275-B+K
B+K 2832		  (3.5D-Bn,V,I,R) 2nF - 20uF			175-B+K
B+K 388-HD		  (3.5D-V,R,F)	 .1nF-20u, 20Hz -200kHz		139-B+K
B+K 2907		  (3.5D-L,V,I,R) ? - 20u			90-B+K
B+K 2906		  (3.5D-V,I,R,T) ?-20uF, -40-1832 Deg F		95-B+K
B+K 2904		  (3.5D-L,R)	 ??? - 20uF			75-B+K
Heathkit IT-2240	  (3D-B,L,K)	 200pF - 2000uF,200uH - 2000H	200-HTK
Heathkit IB-5281	  (A-B,L,R,K)	 10pF - 10uF,10uH - 10H 	90-HTK
Heathkit SM-2255	  (3.5D) 	 200pF - 2000uF,200uH - 200H	90-HTK
Heathkit IM2320		  (3.5D-V,I,R,K) 2nF - 20uF	 		68-HTK
Heathkit SM2320 	Same as IM2320 Above,assembled			78-HTK
Elenco LC-1800		  (3.5D-L,C,R)	 .1pF - 200uF,1uH -200H		125-C&S
IET  LCR-620		  (3.5D-L,C,R)	 .1pF - 200uF,1uH - 200H	269-IET
IET  CM-500		  (3.5D-Ar,D)	 1pF - 200,000uF		299-IET
--------------------------------------------------------------------------------
C&S	C&S sales Deerfield, IL 800-292-7711 (pp34 Jan90 Radio Electronics).
VnS	Van Sickle Electrical 314-621-5000 St. Louis, MO
Jen	Jenson Tools 602-968-6231 Phoenix, AZ
B+K	B+K Precision 312-889-1448, Chicago, IL
MCR	Mercer (Division of Simpson) 312-697-2265 Elgin, IL 
HTK	Heathkit 800-253-0570 (616-982-3200)  Benton Harbor, MI
IET	IET Labs, Inc. 516-334-5959 Westbury, NY
AM	American Reliance, 800-654-9838 Rosemead CA
FLK	John Fluke, 206-356-5400 Everett, WA
ELN	Elenco Precision Electronics, 800-533-2441

X-Z[,Z]: Where X is N[.n]D and N[.n] is number of Digits in display, or A for
Analog and Z is Ar for Autoranging, B  for Bridge, D for digital output 
available, R for Resistance Measurement, V for Voltage Measurement ,
L for Inductance Measurement, T for Temperature Measurement, F for
Frequency Measurement, K for Kit, Bn for Bench Model

Prices provided  by above sources rounded to nearest dollar.  I gots no
connections with anybody here and have made little effort to
verify/shop around on prices.


-- 
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BOOKS WANTED: pre-1930 radio, electrical & scientific topics.