Measuring PWM "effective Voltage"

[desertstalker]

Originally Posted by Fishface

While there are a number of digital voltmeters that read RMS voltage the cheaper ones read the peak voltage as they simply rectify and filter the voltage.
They usually specify RMS voltage measurement in the specs.

Never met such a meter, all the ones I have seen will give AC values in RMS (includes the cheapies).

[Fishface]

Originally Posted by desertstalker

Never met such a meter, all the ones I have seen will give AC values in RMS (includes the cheapies).

I'll clarify that:
They read the correct RMS voltage for sine wave input. They do this by rectifying and filtering the signal then dividing it by 0.7071 to get the RMS value.
On a PWM square wave it is likely they will read a similar value for different pulse widths.
More sophisticated meters have a chip that can sample the input signal and calculate the true RMS value. These will give a valid reading of a PWM output.

True RMS is a feature that you will find on all the current Fluke range but you won't get it on a cheap budget meter from Jaycar.

It was less common a few years ago so many older meters will not feature it.

[gcflora]

ok, multimeter has arrived!

I can read the voltage of batteries.

The instructions are horrible. I don't know which sockets to plug the probes into :/

I am using "COM" and the 600V / 400mA (400mA/250V~) ones.

The other option is "COM" and 10A/500~ Max.

Dunno which is right (the instructions are useless)

What is "COM"?

Edit: Digitech QM1327 meter

[Mjollnir]

com = common = reference ground

[gcflora]

Originally Posted by Mjollnir

com = common = reference ground

Ahh, ok thanks. I guessed that but I really wasn't sure at all.

[shift]

Originally Posted by gcflora

I am using "COM" and the 600V / 400mA (400mA/250V~) ones.

The other option is "COM" and 10A/500~ Max.

From a picture of it, the plug on the left is only for measuring current; which you are not doing.

So use COM and the right hand one for everything.

[gcflora]

Ok, just plugged the probes into the wall: 238.8V. This is obviously why my framerate is sometimes too low

[dakiller]

Originally Posted by gcflora

Ok, just plugged the probes into the wall: 238.8V. This is obviously why my framerate is sometimes too low

No it isn't, and don't do that again. Mains power will kill if you don't know what you're doing.

(maybe you are being sarcastic, but I'm not sure)

[gcflora]

Originally Posted by dakiller

No it isn't, and don't do that again. Mains power will kill if you don't know what you're doing.

(maybe you are being sarcastic, but I'm not sure)

Yes I was being sarcastic. And yes, that would be a dumb thing to do if not knowing what one was doing.

Edit: My apologies for making a joke (trying to) about something as serious as that.

[gcflora]

Anyway, moving on from my stupid (VERY stupid) attempt at a joke...

The multimeter I bought (taking into account dakillers advice) measures the "effective" voltage (0-12V DC, PWM), perfectly! Very pleased. Thanks to dakiller and everyone else in this thread.

It is already revealing secrets: https://sourceforge.net/p/phoebetria...read/26a11933/

I hope to play some more tomorrow. I've ordered another Recon and will try and hook that up via an "external" usb port (mentioned in another thread).