I need to buy a multimeter. I noticed that for the resistance some
have 2000k and some have 20M, which I believe are totally different.
Which one is better to have? Or does it even matter? I'm mostly
interested in testing something that's around 2M. So I don't know if
it matters which multimeter I get.
Partly it may be matter of what you will use it for!
For household electrics the cheapest one may be fine.
It's also a matter of knowing how to use it; practically not
If you are measuring batteries, home electrcity etc.it doesn't matter
If you are tinkering or repairing with electronic circuits, it may be
desirable to have one that has a high resistance so that it affects
what one is working on the least.
For example if you put a meter of 2,000 kilohms (That's 2 megs by the
way) across a circuit that itself has resistance of say 2 megs you
will get a wrong reading (a very wrong reading). That's why high
quality bench testers can be 50 meg-ohms, so they have virtually no
effect on what they are measuring.
If testing 12 volts DC for the car, or whether an electric heater of
around 10 ohms is OK, or 115 or 230 volts AC it won't matter!
Megohm = 10^6 or one million ohms
Kilohm = 10^3 or one thousand ohms
Ohm = one ohm
All are measurments in units of resistance to the flow of electric
A low impedance meter actually works better for home electrical
testing. For electronics testing the high impedance meter works
best. The higher the impedance the less the meter itself will affect
the circuit being measured. If you are measuring outlets in your home
you would want the meter to reject currents that are induced into
adjacent wires. If measuring a resistor in-circuit on a PC board in
an electronic device you would want a high-impedance meter so that the
meter itself has little effect on the thing being measured.
An analog VOM meter would be an example of a low-impedance meter, most
DMM's are high impedance (like an old VTVM meter).
(I'm assuming you are asking about the rated impedance of different
meters and not the choices on the selector knobs since you mentioned a
20meg ohm vs 2k ohm meters).
On Sun, 29 Mar 2009 10:32:59 -0700 (PDT), svu geek
It all depends on what you want to do with it. If you are just looking
for something to work on things around the house 20k/v is plenty and
may actually be better for "power" circuits. (they do not have the
phantom voltage problem). The very high impedance meters are for
working on electronics like CMOS where circuit loading gives you bad
readings. Unfortunately they get sold to homeowners and would be
electricians who will show up here asking why they have 30-40v on a
For resistance measurements, more is better. A short circuit is ideally
zero ohms, and it goes up from there.
Practically speaking, you might never need to measure more than 2 MegOhms,
which is a high enough value for most uses.
On digital meters input impedance is pretty high already. High Z gives
more accuracy by not loading circuit under measurement but some times it
is not useful for it's high sensitivity. That is why I still have old
tank Simpson 260, Fluke, and even an old VTVM when dealing wth high
frequency circuit. On top of that o'scope if I need to see something
when numbers don't help. Some times also simple test light is enough.
The real question is: What is the use of the multimeter? If you were an
electronics pro, you wouldn't be asking this question. If you just want
to fix stuff around the house, go cheap. Maybe not $5 Big Lots cheap,
but say $15 or $20 cheap at Walmart or the big box hardware chain
stores. I'd pay more for digital, myself, just for the convenience.
On Sun, 29 Mar 2009 10:32:59 -0700 (PDT), svu geek
The resistance you plan measure, 2M ?, had nothing to do with the
resistance of the meter. All mulitmeters can measure a wide range of
voltages, probably enough for anything you'll want, unless your
intrests broaden a lot. (For example, you need a special probe to
measure the 25000 volts on a color tv picture tube, but you will never
do that. And if you need to see if there's voltage to a picture tube,
you can just put a little neon bulb in a soda straw, and hold it near
the thick wire. If it lights up, you have voltage. :) )
Just for the record, on an analog meter and iiuc on a digital meter,
it's 2K or 2meg ohms/volt, ohms per volt. I think that means that the
resistance in the meter circuit is 2K or 2M times the greatest value
at the right end of each analog scale. That is, the resistance
changes for each dial setting. Not sure what it means in digital, but
I hate to like new-fangled stuff, but I do in this case. I think you
can easily learn to ignore phantom voltages in AC current and that is
pretty much the only drawback to high impedance meters. While there
are high-impedance analog meters (Like FET-VOMs) they are quite
uncommon. Most are digital and the advantages of digital are
auto-polarity (no need to get the red and black right when measuring
voltage), auto-zeroing and auto-maximum for resistance measuring, and
for some slightly more expensive meters, auto-ranging (no need to set
a dial to the 2, 20, 200, or 2000 volt scale, etc. It figures it out)
Analog don't and can't afaik have any of these things.
OTOH, analog have the advantage that you can put the meter on
resistance and watch a capacitor charge or discharge. After a while,
I felt I could tell a good cap by the way the needle moved. You can
also watch a discharge with the meter on DC voltage, but iirc for all
but really small caps, it takes too long.
It's nice to have a continuity tester with a buzzer built-in, so you
don't have to look at the meter for this simple task. The very cheap
Harbor Freight meters don't have that, and maybe some others don't, so
if you want that, check if it has it.
So: With that overload of technical information by some very
knowledgeable posters it comes back to; "What do you want to use it
If just to test household stuff a reasonably cheap digital display
meter under $20 probably OK.
Learn how to use it, keep the internal battery (replaced) although
they last a long time. Although some/many digitals will shut
themselves off after a few minutes to conserve the battery, anyway.
Check that it has, or make good test leads. The sort that have
substantial rubber over a spring clip are good, so fingers don't have
to touch metal clips contacting possibly live wiring. An extra lead
and/or extension can sometimes be helpful and can be stored in the
same case with the meter.
Make sure electric power to a circuit IS turned off before using the
ohmmeter scale .... that's the one where the meter is most vulnerable
and is using it's own internal low voltage battery to test a 'dead'
circuit. You don't need to hook that setting of the meter,
inadvertently, to say a 115 volts wall outlet and blow the proverbial
you know what out of the meter!
However many do have a special small protective fuse (usually a few
milliamps) inside and some even provide a spare fuse! Resist the
temptation to 'fix' the fuse with Al foil (unless very temporarily and
you know exactly what you are doing) because next time one makes a
mistake (and we all do occasionally!) It's very easy perched on an
awkward ladder with cramp in the bad left leg to forget that you were
just testing for continuity with the ohmmeter setting; and then touch
it on 115 or 230 volts ...................... darn!!!!!!!!! That may
very well damage the meter!
Congratulations to the OP for asking though.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.