More beginner questions (digital multimeter)

[Lucretia MacEvil]

I know to start manually on the highest scale and work your way down
when using it on unknown voltage etc (or use AUTO scale), but I was
wondering about if you wanted to measure the voltage from say, an
unknown/unlabeled wall wart. If you don't know if the end voltage is
AC or DC how do you proceed?

Can you damage the DMM if you try to measure AC on the DC settings or
vice versa?

Does your DMM get damaged when you put the red lead on the (-) and the black
lead on the (+) of a battery?

Next question, please...

 

[Phil Allison]

"AB"

I know to start manually on the highest scale and work your way down
when using it on unknown voltage etc (or use AUTO scale), but I was
wondering about if you wanted to measure the voltage from say, an
unknown/unlabeled wall wart. If you don't know if the end voltage is
AC or DC how do you proceed?

** Set the meter to read DC, if there is no reading the wart is AC or dead.

Set the meter to AC - see which it is.

Can you damage the DMM if you try to measure AC on the DC settings or
vice versa?

** No.


........ Phil

 

[Homer J Simpson]

I know to start manually on the highest scale and work your way down
when using it on unknown voltage etc (or use AUTO scale), but I was
wondering about if you wanted to measure the voltage from say, an
unknown/unlabeled wall wart. If you don't know if the end voltage is
AC or DC how do you proceed?

Can you damage the DMM if you try to measure AC on the DC settings or
vice versa?

You CAN measure DC on the AC range. However try a high DC range low enough
to get some indication. If the polarity changes when you reverse the probes
it's a DC supply.

 

[Phil Allison]

"Homer J Simpson"

You CAN measure DC on the AC range.

** Only with some DMMs - most have a blocking cap.

However try a high DC range low enough to get some indication. If the
polarity changes when you reverse the probes it's a DC supply.

** Bollocks.

If you get a reading on the DC range - the wart is DC.

DMMs reject AC signals on their DC volts ranges.




....... Phil

 

[AB]

I know to start manually on the highest scale and work your way down
when using it on unknown voltage etc (or use AUTO scale), but I was
wondering about if you wanted to measure the voltage from say, an
unknown/unlabeled wall wart. If you don't know if the end voltage is
AC or DC how do you proceed?

Can you damage the DMM if you try to measure AC on the DC settings or
vice versa?

 

[Chris]

I know to start manually on the highest scale and work your way down
when using it on unknown voltage etc (or use AUTO scale), but I was
wondering about if you wanted to measure the voltage from say, an
unknown/unlabeled wall wart. If you don't know if the end voltage is
AC or DC how do you proceed?

Can you damage the DMM if you try to measure AC on the DC settings or
vice versa?

Start with the DMM on high AC volts and get a measurement. If it's
reading zero, switch to high DC volts and dance down.

A good DMM won't self-destruct trying to read AC volts on a DC range.
Some cheaper DMMs will, though, especially if you put them on DC and
try to measure line voltage AC (although the display will be all over
the place). For a low voltage wall wart, though, it shouldn't be
lethal even for the cheapies.

Good luck
Chris