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[Phys-L] Re: Lab DMM Recommendations?



Just occurred to me the soln. (assuming the cheapie will do) is to give
each student one of them (you have a lab fee, no?); if one destroys
it, one buys the replacement.

bc, who, of course, meant instructive for the students.

Bernard Cleyet wrote:

"... the top current range is 200 mA, it does not auto shutoff. I like the manual range, and I don't mind the 1% accuracy, but I hate to give up the 2A range.


Back in the old days, i.e. fifty years ago. The first exercise was to
take a "basic" one mA d'Arsonval and turn it into a Volt meter and an
Ammeter. Seems to me an easy, but instructive exercise to turn your
cheapie 200 mA range into a two Amp. one

bc, still in the past when the latest was a VTVM!

p.s. at $4/ea. is it still penny wise and pound foolish for a
beginners' class?

Michael Edmiston wrote:



We had similar problems... trying to buy meters for less than $20 and
not having them hold up.

We switched to Beckman, Wavetek, Meterman about 10 years ago and have
had good luck with them. I listed three names because the very same
meters have gone through at least three name changes.

Most of the meters used in our calculus-physics labs are model 15XL. We
have about 20 of these. The oldest ones say Beckman Instruments, the


cut

There is also a new model, the 5XP, for $39.95. That's considerably
less expensive. Here is what you give up... Model 5XP is not
autoranging, its accuracy is 1% rather than 0.5%, the top current range
is 200 mA, it does not auto shutoff. I like the manual range, and I
don't mind the 1% accuracy, but I hate to give up the 2A range. Also,
the loss of auto shutoff could use enough batteries to make the 15XP
less expensive in the long run unless you have better luck getting
students to turn off meters than we have.

In our physical science labs we did not want to spend the money for the
15XL and now not the 15XP. But we had really bad luck with cheap
meters. We finally bought some Meterman DM2 meters which cost $29.95.
Even though this is substantial, I am sure we have saved money over the
throw-away $10 models. There are two problems with the DM2 which make
it less than ideal for the regular physics labs... the top current range
is 200 mA, and the input resistance on the voltage ranges is only 1
megohm whereas typical good digital meters are 10 megohm. However, for
physical science, these meters work and have really held up well. No
damage (other than fuses) in 24 units in service for 6 or 7 years.

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu