Why do voltmeters read a varying output as constant?

Hi Guys,

Just wondering why a voltmeter will read a slightly AC voltage centred upon a DC level as a constant DC level, and not show the fluctuations on the screen?

Thanks

albad said:

Hi Guys,

Just wondering why a voltmeter will read a slightly AC voltage centred upon a DC level as a constant DC level, and not show the fluctuations on the screen?

Thanks

Click to expand...

I really think that depends on the specific meter and the sample time it uses and any software filtering it might use. My Fluke model 45 has three selectable sample times, slow (with higher digit resolution, medium and fast and when in fast sampling it can show variations. One method to read AC ripple riding on a DC level is to put the meter in AC voltage function and you can then read the AC ripple voltage. Some better meters measure true RMS value and therefore integrate any AC ripple into the value displayed rather then try and track it. So again it really depends on what specific meter one is using and the features and functions it has available.

Lefty

Also depends on frequency of AC signal.

I see.
Didnt think it was to do with sample times, as then it could sample at a point on the wave, giving a varying output still.

Could it be done with hardware, such as a capacitor to smooth the varying voltage at the centre level?