Very basic multimeter questions.

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Simon Bartlett - 29 Dec 2003 23:38 GMT

Hi group.

I've always used a multimeter on a trial and error basis, till I get a
reading that looks like what I should get. I think it's time now that I
try and understand what's going on though. As such, I've composed a
list of simple questions, the answers to which would be a great help to
me.

1. The fused connector is rated to 500v max, 200mA max. Does that mean
500v at 200mA? If I want to check a circuit running 12v 1A, can I
safely use the fused connector or do I have to use the un-fused
connector?

2. I was trying to measure a current on a circuit of 12v 1A. To be
safe, I used the unfused (10A) connector. I couldn't get a reading of
volts at all (perhaps I should have tried amps). Should the 10A
connector give identical readings to the fused connector where the
current is within the fused connector's range?

3. The Volts DC selector scale has points at 200m, 2000m, 20, 200, 500.
Does the m refer to milli as in 200 millivolts, 2000milivolts? Of not,
what?

4. The Amps DC selector scale has points at 200(funny u symbol), 20m,
200m, 10. What is the funny u symbol? And again, does the m stand for
milli?

5. The transistor tester has NPN and PNP markings. By looking at a
transistor, how do I know if it's a NPN or PNP?

6. The transistor tester has letters around the circle, e E B c E e c
b. What's the story there? How do you know which to use?

If anyone has a good reference that will answer similar questions, that
would be much appreciated. I had a look at some sites offering
multimeter basics, but weren't quite basic enough :-)

Reply to this Message

Peter Bennett - 30 Dec 2003 00:40 GMT

>Hi group.
>
[quoted text clipped - 8 lines]
>safely use the fused connector or do I have to use the un-fused
>connector?

I don't know your meter, so can't answer this one (perhaps you should
post these questions again, mentioning the make and model of your
meter.)

>2. I was trying to measure a current on a circuit of 12v 1A. To be
>safe, I used the unfused (10A) connector. I couldn't get a reading of
>volts at all (perhaps I should have tried amps). Should the 10A
>connector give identical readings to the fused connector where the
>current is within the fused connector's range?

To measure current, you must break the circuit, and insert the meter
in the break, so the current flows through the meter - AND set the
meter to read current.

With the meters I've used, you have to move the read meter lead from
the "Volts" socket to a socket labelled "Amps" or "mA". My meter has
one socket labelled "10A", and another labelled "mA". The "mA" socket
is used when measuring currents up to 200 mA, and the 10A socket is
used for larger currents.

To measure voltage, you put the red meter lead in the socket marked
"Volts/Ohms" (or something like that), and connect the two leads to
the two points in the circuit you want to measure between. You do not
break into the circuit when measuring voltage.

>3. The Volts DC selector scale has points at 200m, 2000m, 20, 200, 500.
>Does the m refer to milli as in 200 millivolts, 2000milivolts? Of not,
>what?

Yes - "m" is "milli", or .001

>4. The Amps DC selector scale has points at 200(funny u symbol), 20m,
>200m, 10. What is the funny u symbol? And again, does the m stand for
>milli?

The funny "u" is a greek letter "mu", which is used to indicate
"micro", or .000001

>5. The transistor tester has NPN and PNP markings. By looking at a
>transistor, how do I know if it's a NPN or PNP?

With North American transistors (part numbers starting with "2N"),
there is no way, other than looking them up in a book (or on the web).
I think European transistors may indicate the sex and application in
the letter prefix.

>6. The transistor tester has letters around the circle, e E B c E e c
>b. What's the story there? How do you know which to use?

E, B, and C are the emitter, base and collector leads of a transitory.
The manual for the meter should give you some indication of how to
connect a transistor.

>If anyone has a good reference that will answer similar questions, that
>would be much appreciated. I had a look at some sites offering
>multimeter basics, but weren't quite basic enough :-)

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Reply to this Message

Costas Vlachos - 30 Dec 2003 01:06 GMT

> Hi group.
>
[quoted text clipped - 8 lines]
> safely use the fused connector or do I have to use the un-fused
> connector?

You will have to use the unfused connector. This is because your circuit is
drawing 1A and the fused connector is rated at 200mA max. This rating is
independent of the circuit voltage (as long as it is below 500V).

> 2. I was trying to measure a current on a circuit of 12v 1A. To be
> safe, I used the unfused (10A) connector. I couldn't get a reading of
> volts at all (perhaps I should have tried amps). Should the 10A
> connector give identical readings to the fused connector where the
> current is within the fused connector's range?

Usually the unfused connectors in a multimeter are used only for current
measurement. If you want to measure voltage you should use the connector
marked with "V" on the multimeter (usually the fused one). If measuring
current, the 10A connector should be used for high currents, and the fused
one for low currents. The 10A connector may in fact only work when the
multimeter is set to the 10A range. For all other ranges use the fused
connector.

> 3. The Volts DC selector scale has points at 200m, 2000m, 20, 200, 500.
> Does the m refer to milli as in 200 millivolts, 2000milivolts? Of not,
> what?

Yes, it means milli.

> 4. The Amps DC selector scale has points at 200(funny u symbol), 20m,
> 200m, 10. What is the funny u symbol? And again, does the m stand for
> milli?

The "u" symbol means micro (i.e., 200 microamperes). The "m" is as above.

> 5. The transistor tester has NPN and PNP markings. By looking at a
> transistor, how do I know if it's a NPN or PNP?

Have a look at the transistor's data sheet. It will tell you the type and
the pin layout.

> 6. The transistor tester has letters around the circle, e E B c E e c
> b. What's the story there? How do you know which to use?

B: base, C: collector, E: emmiter. Check the transistor's data sheet and
connect each pin to the corresponding point on the multimeter.

> If anyone has a good reference that will answer similar questions, that
> would be much appreciated. I had a look at some sites offering
> multimeter basics, but weren't quite basic enough :-)

You probably already know this, but just in case. To measure voltage you set
the multimeter to a suitable V range and V connectors, and connect the probe
*in parallel* to the circuit under test. To measure current you select a
suitable A range and A connectors, and connect the probe *in series" with
the circuit (i.e., you break the circuit and then insert the probes).

Hope this helps.

Regards,
Costas
_________________________________________________
Costas Vlachos Email: c-X-vlachos@hot-X-mail.com
SPAM-TRAPPED: Please remove "-X-" before replying

Reply to this Message

Costas Vlachos - 30 Dec 2003 01:28 GMT

> > 1. The fused connector is rated to 500v max, 200mA max. Does that mean
> > 500v at 200mA? If I want to check a circuit running 12v 1A, can I
[quoted text clipped - 4 lines]
> is drawing 1A and the fused connector is rated at 200mA max. This rating
> is independent of the circuit voltage (as long as it is below 500V).

Hmmm, my reply above is a bit misleading...

Just to clarify, the above is true only if you want to measure the circuit's
current. For voltage measurement you should use the fused connector (that's
probably the only connector you can use for voltage measurements anyway).

So it all depends on whether you are measuring V or I. For V you use the
fused connector, no matter how much current the circuit draws. For I you use
the fused one for small currents (up to 200mA) or the un-fused one for high
currents (up to 10A).

Apologies for any confusion caused!

Costas

Reply to this Message

Simon Bartlett - 30 Dec 2003 02:35 GMT

Thanks Peter and Costas.

That made a lot of sense. I was trying to read volts with the circuit
broken, instead of parallel. I now see that one connector is volts up
to 500v, or Amps up to 200mA, depending on what I'm measuring at the
time. The other connector is only for Amps (and I was trying to use it
for volts).

Again, thanks for all the help.

Simon

> Hi group.
>
[quoted text clipped - 32 lines]
> would be much appreciated. I had a look at some sites offering
> multimeter basics, but weren't quite basic enough :-)

Reply to this Message

Electronics Forum / Basics / December 2003

Very basic multimeter questions.