signal noise messing up my panel volt meter?

[monster]

hi

has anyone encountered noise problems when using a panel volt meter? my motor voltage reading is ossilating all over the place!

 

[rkosiorek]

i'l bet that you are using one of those cheap LED or LCD panel meters. it would not be an issue with old moving coil meters.

could be one of two problems. most likely is that most of these meters need to be powered by an isolated supply. if you power them with the same voltage that you are trying to measure it will cause ground loops and erratic readings. easiest way to check would be to power the meter using a couple of batteries.

the instructions (destructions?) that came with the meter might also state if it needs an isolated supply.

rick

 

[Tiberius]

Are you trying to measure the motor voltage?
That is a complicated 3 phase waveform.

Nick

 

[monster]

thanks for your replys. im trying to measure the voltage across a small dc motor (2wires). i have tried it will a 9v battery as supply but it still ossilated a lot.

but multimeters work fine???

 

[Tiberius]

Matthew, that will be easier than a bike motor, but it will still be a noisy waveform.

A multimeter will have some smoothing/filtering for doing AC measurements and probably leaves that in circuit when doing DC ones. A naked panel meter may not. If its a digital panel meter then it only takes a small jitter to make the display look crazy. As Rick says, an old style mechanical analogue one would do its own smoothing.

You could try a simple RC smoothing circuit, values won't be critical.

Nick

 

[monster]

can you suggest where i might find one? i already tried a capacitor over the motor wires -no joy