AC clamp Meter. What's it actually reading?

[seagull369]

This question is in regards to a true-RMS clamp meter set on amps ac,,, On the non-inrush setting, is the value displayed considered to be a true-RMS reading of the current waveform it's analyzing? When on the inrush current reading, is that simply just giving you the largest peak current (I-max) value it's able to capture?

 

[u2slow]

Your first question.... A true-rms meter gives you an true-rms reading. That's the whole point.

The second.... you have to find out how the manufacturer defines the feature. I suspect it will be the RMS value of whatever inrush it captures.

 

[nadogail]

Some meters will hold a peak reading, others will also read DC.

 

[Metal-Marc]

Yes.

 

[Ole Slewfoot]

I think they actually measure Mutual inductance, but I'm notphysicist.

 

[RPH]

As with anything electrical math is involved. Most use a resistor used as bourdon resistor across transformer windings. This measures a voltage drop across it. The math is required for the types of non-sinusoidal waveforms.

 

[dave*99]

As with anything electrical math is involved. Most use a resistor used as bourdon resistor across transformer windings. This measures a voltage drop across it. The math is required for the types of non-sinusoidal waveforms.

I think you mean burden resistor.
Bourdon invented the Bourdon tube for measuring gas pressure.

 

[RPH]

I think you mean burden resistor.
Bourdon invented the Bourdon tube for measuring gas pressure.

Yup, you right. Don’t know brain fart or autocorrect.

 

[dave*99]

As with anything electrical math is involved. Most use a resistor used as bourdon resistor across transformer windings. This measures a voltage drop across it. The math is required for the types of non-sinusoidal waveforms.

Thankfully the true RMS meter does the math. Often the waveform that must be measured is a combination of more than one of those neatly drawn waveforms.
The true RMS meter digitizes the signal and calculates the reading.

A simple way to think of RMS is it is the heating value of the waveform.

If you connected a resistor to a DC source and measured its temperature then switched to a complicated AC waveform and the resistor rose to the same temperature…… you would know the RMS value was the same for both.

 

[rlitman]

Is your meter an AC only clamp meter, or an AC/DC current clamp. They work fundamentally differently.
Also, most meters sample more quickly than they refresh their displays, so your inrush measurement will likely be higher than a max-hold type current reading, if your meter has both modes.