A quick question Re a multi meter.

Thread Starter

Hextejas

Joined Sep 29, 2017
187
From my other thread, I was trying to see if a transistor was faulty, ( thank you Dick Cappels ).
Based upon another members post, I was looking for .6 -.7 volts. ( thank you GopherT ).
So, when I began trying to take the various BCE readings, I kept getting strange results.
Then I noticed that the meter had a diode setting.
Voila.
My question:
Is that typical, in that a meter with a built in diode feature will mess up the voltage readings for a diode ?
 

dl324

Joined Mar 30, 2015
8,848
Is that typical, in that a meter with a built in diode feature will mess up the voltage readings for a diode ?
What do you mean by "mess up"?

The meter applies a low current and shows the voltage. On my meter, it reports open circuit for LEDs that have a forward voltage of more than 2V (IIRC).
 

MaxHeadRoom

Joined Jul 18, 2013
18,995
Yes, the diode range passes a current through the diode and reads the voltage drop across it, the resistance range is usually too high to forward bias the diode, hence the diode range.
It is not intended for taking voltage readings in a live circuit.
Max.
 

Thread Starter

Hextejas

Joined Sep 29, 2017
187
What do you mean by "mess up"?

The meter applies a low current and shows the voltage. On my meter, it reports open circuit for LEDs that have a forward voltage of more than 2V (IIRC).
When I used the DC volts range, the meter acted like it was searching for something/
 

BobTPH

Joined Jun 5, 2013
2,016
There is no voltage across the junctions unless a current is running through them. Measuring on the diode range does that. Measuring on the voltage range does not, there is no voltage to read there, it is like reading an open circuit.

Bob
 

WBahn

Joined Mar 31, 2012
24,671
When I used the DC volts range, the meter acted like it was searching for something/
Remember that any meter affects the circuit it is interacting with. Under most circumstances this is not a problem. But in circuits where the interaction affects the results, you are usually in a sufficiently sensitive regime in which exactly how it affects the results depends on the range setting of the meter. So with some circuits the value with the meter in the circuit in it, when on Range 1, should be read on Range 2. But with the meter on Range 2, should be read on Range 1. Hence the meter will bounce back and forth between the ranges. Most autoranging DMMs have some means of locking the range setting manually, but sometimes it isn't very obvious how to do it.
 
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