Analog voltmeter does not go back to zero

[remzo]

Hi all,

I wanted to use the output of a DAC pin of the ESP 32 to control a voltmeter and use it as a display.

This almost seemed to work but suddenly the volt meter has chosen a new 'zero' at .5 volt.

The ESP32 sends out different voltages and the meter responds. But not so accurate since .5 is the new zero.

Can I somehow reset this meter?

 

[crutschow]

Does the meter not go back to zero when the DAC signal is physically removed?

 

[remzo]

Yes. (I just found out a video is not allowed... )

 

[Les Jones]

As crutschow's question is "Does the meter NOT go back to zero" when the meter is disconnected from the DAC do you mean that it does NOT go back to zero ?

Les.

 

[remzo]

It does not go back to zero indeed. In the photo the volt meter is disconnected.

If I switch + and - the DAC signal makes the meter go to zero (and it tries to go even lower).

 

[JimB]

The mechanical "zero adjustment" mechanism has been disturbed, I guess by your fingers when you picked up the meter.

Try moving the the part indicated by the red arrow.
When that part is vertical, the meter pointer should be at zero.

JimB

 

[Nigel Goodwin]

It does not go back to zero indeed. In the photo the volt meter is disconnected.

If I switch + and - the DAC signal makes the meter go to zero (and it tries to go even lower).

The mechanical zero adjustment on the meter needs setting properly, as JimB has just posted as I was typing

 

[Nigel Goodwin]

A further point, why has the meter been removed from it's casing?, there will be an adjusting screw on the casing.

 

[Diver300]

I was just about to say what JimB said, and Nigel was about to say.

I think some engineers of a certain age have experience of analogue meters.

 

[remzo]

Thanks JimB, Nigel and Diver300, it was exactly that unnamed thingy. The adjusting screw corrects a little bit but not so much.

I've another voltmeter with the same problem and will take a look at that one too.

 

[Les Jones]

I think that some dirt has got in between the coil and the magnet. Just moving the zero adjustment by accedent should give readings that were consistently out by the zero offset error.

Les.

 

[Tony Stewart]

I wonder if a large negative voltage or an impact stretched the spring.

 

[Nigel Goodwin]

I wonder if a large negative voltage stretched the spring.

More likely it's just been physically moved, as it's uncased and not protected, and the OP appears to have no idea how it works (too young).