Re: Pythagorean Idea for Inductance Meter?

["Tesla list" <tesla-at-pupman-dot-com>]

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

Hi,

I have not been following close but maybe the RC4200 8-pin Analog 
multiplier would do most of the work here for just about $2.50:

http://www.fairchildsemi-dot-com/ds/RC/RC4200.pdf

Multiplies, divides, square root, square, RMS...

The RC4200 is a little old so their may be far better chips out there like 
MPY634 :

http://www-s.ti-dot-com/sc/psheets/sbfs017/sbfs017.pdf

A little pricey at $18 but maybe it will save a bunch of effort.

Cheers,

         Terry



At 09:01 PM 11/10/2002 -0800, you wrote:
>Couldn't get a huge number of opamps, lay out a suitable PC board, choose
>appropriate discrete components, and get it suitably linear (or nonlinear,
>as the case may be), and have it work over time and temperature...  Each
>component costs money, in layout, soldering, etc.  And, while junky opamps
>in the surplus bin might be cheap, good ones aren't, nor are good quality
>sockets, nor are precision resistors, etc. It all adds up.
>
>I'll take a modern microcontroller based LCR meter against any 40 year old
>design analog bridge.. especially if you need to make measurements at more
>than one frequency so that you can get the frequency dependent variations
>and figure out the parasitic C around the L.
>
>Not that it can't be done entirely analog, and that analog designs have
>their definite place (say, 1-5% accuracy, real low power, limited
>measurement range needed...).  If you're going to read the result on an
>analog meter with a pointer (5% at best), then, yes, a microcontroller might
>be overkill.
>
>I don't know that laziness has anything to do with it. Sure, I could make
>microwave measurements with a slotted line and a diode detector, but, gosh,
>the 8510 does a much better job, and is a lot more accurate to boot. If I
>had to do all the cal measurements and back out the various factors by hand
>it would take weeks to reduce just one set of measurements.  I don't know
>that one could even, with infinite amounts of hand calculation, get the same
>quality results from hand measurements that you could from an automated
>analyzer.. stability over time between making the cal measurements and the
>unknown is probably a limiting factor.
>
>I'd rather spend my time working with the inductor than making a measurement
>tool to measure it.
>
>That said, there is a satisfaction in making precision measurements or
>measurement tools the old fashioned way, but it's for some visceral
>satisfaction, or as a hobby, not for productivity or quality.  Heck, very
>few people build tesla coils because they're useful.. We build them because
>the building and operating of them is fun.  You could probably count the
>number of people int he world who actually earn a living making tesla coils
>on one hand.
>
>
>--