Xref: utzoo sci.electronics:9159 sci.physics:10837 rec.ham-radio:16255 Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!aplcen!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!usc!rutgers!texbell!swbatl!adams From: adams@swbatl.UUCP (4237) Newsgroups: sci.electronics,sci.physics,rec.ham-radio Subject: Capacitance Meter Stuff (Long) Message-ID: <1077@swbatl.UUCP> Date: 27 Dec 89 20:42:20 GMT Organization: Southwestern Bell Tele. Co. - Advanced Technology Lab - St. Louis Lines: 135 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. -- uunet!swbatl!adams or adams@swbatl.swbt.com | Tom Adams: 314-235-7459 BOOKS WANTED: pre-1930 radio, electrical & scientific topics.