Measure power mVA (Watt) with a 121gw

[chlor]

As my old multi meter is more than 20 years old and can not measure power, I gave myself a 121gw for birthday present.

One thing I will use it for is educating my kids but the instructions for measure power is not that easy to understand. Please find a suggestion attached.

[Benta]

The idea is to measure voltage and current simultaneously, which your setup also shows.
Note that you only measure apparent power (VA), not real power (W), so this only works with resistive loads.

[coppercone2]

great scott !

[coppice]

I just looked at the manual for the 121GW, and it is not very clear about connecting the meter for power measurements. I would have expected the COM terminal to be connected to the load, and the mA/uA terminal to be connected to the source. However, the connection arrangement you show is what the manual implies, without showing in a nice clear picture. Does the meter measure voltage between the V/ohms terminal and the mA/uA terminal when in VA measurement mode, or is the burden voltage of the current measurement not compensated for?

[picburner]

The connection in the figure corresponds to the power in mW(mVA)
Connecting to the 500mA (low burden) terminal the power will be in W(VA).
The connection of the DUT and the power supply in the figure are correct.

[NiHaoMike]

The idea is to measure voltage and current simultaneously, which your setup also shows.
Note that you only measure apparent power (VA), not real power (W), so this only works with resistive loads.

The Mooshimeter can measure real power since (IIRC) it has dual ADCs. Does the 121GW only have a single ADC multiplexed between current and voltage and it turns out the mux is too slow to handle real power measurement?

[Benta]

The idea is to measure voltage and current simultaneously, which your setup also shows.
Note that you only measure apparent power (VA), not real power (W), so this only works with resistive loads.

The Mooshimeter can measure real power since (IIRC) it has dual ADCs. Does the 121GW only have a single ADC multiplexed between current and voltage and it turns out the mux is too slow to handle real power measurement?

Normally DMMs use a dual-slope converter (=slow). AC is measured using a front-end, either just a rectifier or a TRMS converter. No matter which, in the end it's a DC measurement. Multiplexing between the two DC values is simple.