Re: Another question...
- From: Michael Black <et472@xxxxxx>
- Date: Tue, 1 Apr 2008 09:51:54 -0400
On Tue, 1 Apr 2008, Dave wrote:
The following link shows an LCD meter carried by my local parts depot. ItWho knows what he means. If it's a digital meter, then of courese
says "panel meter" and the sales associate tells me it is actually a voltage
meter that comes with some resistors used for setting it to the proper range
for whatever the user wants. And it only has two pins for input (I haven't
actually seen it yet, so I am quoting what he told me.) *He* says it
doesn't contain an A/D converter, it's just a meter (?) My question: is it
likely that this does its job through the use of comparators, or some such,
and maybe it really doesn't contain an A/D converter chip? Or can I likely
buy this, break into and modify it, and then use it as the readout for my
transistor tester, showing the gain of the device under test?
http://www.ace4parts.com/Products/PMLCD--LCD-PANEL-METER__PMLCD.aspx
there's some sort of analog to digital conversion. The specifics of
how it's done (which may confuse people like the salesman) doesn't matter
to the end user.
A panel meter is just that, a meter intended for mounting on a panel.
They had them in the days of analog meters, they have them in the
days of digital meters. All it means is a fixed range meter.
Any DMM has that sort of thing deep inside it, the difference being the DMM is multi-range and multi-function so it adds switching ahead of the "panel meter"/fixed range meter to divide input voltage to a range that the meter can handle, and adds things like a current source for measuring resistors and semiconductor junctions, and adds some sort of AC to DC conversion circuitry to allow for measuring AC voltages, and adds a shunt resistor so you can measure the voltage drop across that shunt resistor to measure current through a circuit.
As long as the voltage range of the panel meter is sensitive enough for
your needs, then it should be fine. If you need really find sensitivity,
you may need to look further. If you need to measure larger voltages,
then that's taken care of with a couple of resistors acting as a voltage
divider.
Of course, for hobby use the only real advantage of buying a digital
panel meter is size. SInce you can get DMMs for as low as ten dollars,
that may be the cheapest way to get a digital meter, placing it behind
your project panel and treating it as a fixed range panel meter. But the
actual panel meter is bound to be smaller.
Michael
.
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