guys i think something wrong with my multimeter

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
i dont know why but my multimeter shows higher value when measuring after a diode why is that ? here is video about it

Joined Mar 10, 2018
4,057
If you are measuring after a reverse biased diode thats a very hi z impedance
point subject to AC line pickup.

Regards, Dana.

crutschow

Joined Mar 14, 2008
24,725
What voltages do you expect to measure?
Which side of the diode is the anode?

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
What voltages do you expect to measure?
Which side of the diode is the anode?
im expecting lower voltage after diode because as far as i know diode drops supply voltage from 0.5 to 1 volt am i wrong? also the side of the diode that connected to the power cable is anode

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
If you are measuring after a reverse biased diode thats a very hi z impedance
point subject to AC line pickup.

Regards, Dana.
what does that mean is it normal ? but why my old meter didnt do that ? its first time i see this

crutschow

Joined Mar 14, 2008
24,725
the side of the diode that connected to the power cable is anode
Connect a small resistor (say 1kΩ) from the diode cathode to common, then redo the measurement.
(I assume the power cable polarity is plus?)

Joined Mar 10, 2018
4,057
im expecting lower voltage after diode because as far as i know diode drops supply voltage from 0.5 to 1 volt am i wrong?
If diode is conducting that is its forward drop. But if your meter presents very high Z
load then diode has no current thru it.

Regards, Dana.​

AlbertHall

Joined Jun 4, 2014
9,647
What is the cable connected to?

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
Connect a small resistor (say 1kΩ) from the diode cathode to common, then redo the measurement.
(I assume the power cable polarity is plus?)
i have no idea what is going on. i removed the battery and put it back on bow its showing lower voltage. evwrything is normal now ?

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11

If diode is conducting that is its forward drop. But if your meter presents very high Z
load then diode has no current thru it.

Regards, Dana.​
still didnt understand
What is the cable connected to?
its connected to 5 v phone charger

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
guys by the way my meter have relative measure button what is that for ?

Dodgydave

Joined Jun 22, 2012
9,083
" Relative" cancels out any stray pick up voltage on the leads, so your meter reads just the voltage difference on the leads.

AlbertHall

Joined Jun 4, 2014
9,647
" Relative" cancels out any stray pick up voltage on the leads, so your meter reads just the voltage difference on the leads.
Don't think so.
Say you connect the meter to a battery then press the relative button. I would expect the meter to show zero. Then connect a load to the battery and as the battery voltage falls the meter would indicate a negative voltage being the amount the voltage is now less than the original measurement. So the meter indicates the voltage relative to the reading when the button was pressed.

Joined Mar 10, 2018
4,057
still didn't understand
its connected to 5 v phone charger
If the current thru the diode is 0 on the graph what is its V ?

The upper right hand quadrant of graph is when the diode is
forward conducting, the 3'rd quadrant is when the diode is in
breakdown, usually destructive if current not limited.

Regards, Dana.

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
If the current thru the diode is 0 on the graph what is its V ?

The upper right hand quadrant of graph is when the diode is
forward conducting, the 3'rd quadrant is when the diode is in
breakdown, usually destructive if current not limited.

Regards, Dana.
so its normal if its showing more voltage then power supply when not connected to a load ? if so why is it normal now its showing lower voltage now after remove battery and connect it back

Dodgydave

Joined Jun 22, 2012
9,083
Don't think so.
Say you connect the meter to a battery then press the relative button. I would expect the meter to show zero. Then connect a load to the battery and as the battery voltage falls the meter would indicate a negative voltage being the amount the voltage is now less than the original measurement. So the meter indicates the voltage relative to the reading when the button was pressed.
That's what my meter does, it cancels out any stray pickup on the leads.

Joined Mar 10, 2018
4,057
so its normal if its showing more voltage then power supply when not connected to a load ? if so why is it normal now its showing lower voltage now after remove battery and connect it back
If leads not connected to anything, the meter will autorange to
more sensitive scale, and pick up induced V from mains wiring
in building. Fluorescent lighting a big contributor to induced V.

Not sure on second question.

Regards, Dana.

Last edited:

Muhammed Fatih Saruhan

Joined Jun 22, 2019
11
If leads not connected to anything, the meter will autorange to
more sensitive scale, and pick up induced V from mains wiring
in building. Fluorescent lighting a big contributor to induced V.

Not sure on second question.

Regards, Dana.
but after i take battery and put it back on now its showing less voltage when diode is not connected anything

Joined Mar 10, 2018
4,057

If you place leads on bench, without touching them, what does it read ?
The two leads not touching each other.

Regards, Dana.

Last edited: