Posted by
Ron D'Eau Claire-2 on
Mar 05, 2005; 8:18pm
URL: http://elecraft.85.s1.nabble.com/Prep-time-tp375364p375369.html
Mike wrote:
I need to upgrade some of my gadgets, though, and one
is the DMM - my current one doesn't measure capacitance. Does anyone
have any recommendations? Would the cheap one at
http://multimeterwarehouse.com/DT9205f.htmbe good enough? It's the age old challenge of trying to not spend too
much but trying to not buy trash, too.
------------------------
Wow! Such a price! I have found consistently that one gets about what one
pays for. CE makes pretty good stuff. So what makes it cheap?
It seems to me that there are two major differences between DMMs at high and
low prices: Speed and Ruggedness.
Almost every DMM uses one of a very small number of "application-specific
integrated circuits" (ASICs)that are made in huge quantities for this
market. The price of the ASIC is largely based on its speed. A cheap DMM can
take 2 or 3 seconds to produce a reading, where an expensive one is almost
instantaneous.
Slowness is a nuisance in most readings, but it's a disaster if you're
trying to "peak" a reading in real time! You are talking about upgrading. If
your old DMM will do this, you're already fixed up. (I even keep a
d'Arsonval meter "VOM" around for 'peaking' work). But If you want something
to take over all the chores of meter readings, you need to consider that.
"Fast" meters tend to the in the +$100 range.
A full four-digit display is often very handy too, especially in a meter in
which you are trying to do "peaking" adjustments. This one looks to be a 3
or 3-1/2 digit display. That's typical of cheaper meters too.
There are some differences in other functions too, but they are usually
minor.
A lot of folks expect the accuracy of cheaper meters to be less too, but in
my experience that is not the case. Again, the resistance dividers are made
with modern precision manufacturing technology. It just isn't cost effective
for someone trying to build a cheap meter to try to find a cheap divider. So
the accuracy tends to be very similar, regardless of cost.
The other big issue that I've noticed is that the high-priced meters tend to
be more rugged. Of course, you only need a rugged meter if you treat it that
way. It's sort of a "given" that my Flukes were going to take a nose-dive
onto a steel deck plate working on ships all the time. So they had the
rubber boots attached. But around the workbench? Hasn't happened yet!
I was suddenly shy my Fluke one time when I needed a part for it. In the
middle of some work, I cruised to Radio Shack and picked up one of their
meters that sold for about $80. It's slow, but does an excellent job on
capacitance (it has a parasitic capacitance of about 111 pF, but it will
accurately measure a 5 pF cap - displaying it as 116 pF. And it goes up into
the many-microfarad. Ranges. It's a four-digit meter, and the voltages are
within a fraction of a percent of my Fluke or my Bel-Merit (an expensive
pen-type meter).
I got a freebie CE meter once from Mouser or Digi-Key when I placed an
order. Within the limits of its 3-digit display, it's as accurate as any of
my others.
Ron AC7AC
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