121GW Power (VA) measurement shows "overflow"

[tnt]

Hi,

I'm trying to measure power in AC mode with the 121GW for a mains connected device.
But the 121GW just display "overflow" ... but it's only 240V AC, and ~ 100 mA, it should handle both of those with no issues right ?

The way it's wired ATM I have :

COM going to neutral
A jack going to the "neutral" input of the DUT
V jack going to live and also the "live" input of the DUT.

What am I missing here ?

[joeqsmith]

The last manual I downloaded wasn't very good at explaining the VA mode.    I don't remember it being designed to measure AC line devices like you are attempting to do.   I thought the AC voltage was limited to 50-60 or so was all.   There was also a problem with how they suggested the meter be connected.    This owner walks you through the problem. 



Then again, it has been a few years since I looked at this meter.  There may be all new firmware and manuals that improve it.   

[joeqsmith]

Trying it with 2.02 firmware on what ever flavor of the hardware (not current) that I purchased to review.  Shorting the current input to common and injecting a 60Hz sinewave, it over ranges at about 53V.   So I don't think it's going to do what you want. 

[J-R]

This issue stems from the fact that the secondary display will only count up to 54.999 in VA modes, so specifically you are limited to a maximum of 54.999V (AC & DC).

You could use multiple 121GW units and the math mode in the app.

Also, at 240VAC, I would think you could calculate power well enough by just measuring current.

[joeqsmith]

... the secondary display will only count up to 54.999 in VA modes....

Why?  They have the decimal point.  Hardware could certainly scale it.  Was it for safety reasons? 

[tnt]

Mmm ... ok.

TBH, I was disappointed it was VA and not Watts, I was hoping it'd be able to sample enough to get at least a rough estimate of power.
But if it's in addition limited to 60V, then yeah, it's basically useless for this application.

[J-R]

It appears to be a disclosed design limitation per the manual, on page 22, note 11: "500 VA, with 50 V and 10 A."  50V is the stated limit, although it's really 54.999V.

[joeqsmith]

The manuals I have from Jan 2018 and earlier do not have this note.  The earliest was Sep 2018.   I wonder if the original intent was to support mains and it was removed for safety or if there was some other limitation. 

[J-R]

Doesn't feel safety-related as there is this note: "This channel has overload protection for up to 600V."  Perhaps a performance issue so the feature was scaled back.