Electronics > Beginners

How to see effect of True RMS

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mwb1100:
I've got a meter that doesn't do True RMS and a meter that does.  I've read a bunch of stuff about how important TRMS is and seen some youtubes about it.  but I'd like to experiment a little myself.

Is there some item that I'm likely to already have at home (or can buy cheaply) that will show me the effect that TRMS has on meters?  It would be especially nice if the thing had a knob where I could change the magnitude of the effect. 

Some of the information I've come across mentioned light dimmers - my house doesn't have any at the moment, but I suppose I could get one and put it in a box.

BrianHG:
If you have one of those cheap DC12v to 120v inverters with modified sine wave output, the difference between the True RMS readout and Non-True RMS readout should be big.  If you have a pure-true-sine wave inverter, both meters should read the same.

spec:
Hi mwb1100

This is just a bit of thinking out loud- but you did say you wanted to experiment. :)

Get a resistor and somehow attach a temperature to voltage sensor chip to the resistor. Connect your multimeter, set to volts to the output of the temperature sensor.

If you then apply a DC voltage across the resistor, you will get a reference temperature  for true RMS. Then you can put any voltage signal across the resistor and get a temperature reading for comparison.

For example if you put a 1V RMS sine wave across the resistor you would get the same temperature as for 1V DC.

By the way, at one time, this is how true RMS was measured.

Karlo_Moharic:
Get signal generator and try measuring voltage at different freq (within specified range of both multimeters).

mvs:

--- Quote from: mwb1100 on November 22, 2018, 05:14:56 pm ---Is there some item that I'm likely to already have at home (or can buy cheaply) that will show me the effect that TRMS has on meters?

--- End quote ---
Any device with bad power factor (some small switching power supplies, led an CFL lamps) will do that for AC current measurement.

But out of safety reasons, i would suggest you to get old style 60Hz transformer with low voltage secondary coil and use diode in series with some dummy load (resistor, light bulb, etc.) to get non-sinusoidal current consumption.

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