121GW Power (VA) measurement shows "overflow" - Page 1
Forum section: electronics / testgear

author: tnt
author_rank: Regular Contributor
timestamp: July 13, 2022, 08:08:16 pm
content: 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 neutralA jack going to the "neutral" input of the DUTV jack going to live and also the "live" input of the DUT.What am I missing here ?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2022, 01:22:51 am
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2022, 01:31:19 am
content: 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.

author: J-R
author_rank: Super Contributor
timestamp: July 14, 2022, 05:16:39 am
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2022, 12:29:45 pm
content: Quote from: J-R on July 14, 2022, 05:16:39 amWhy? They have the decimal point. Hardware could certainly scale it. Was it for safety reasons?

author: tnt
author_rank: Regular Contributor
timestamp: July 14, 2022, 04:14:18 pm
content: 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.

author: J-R
author_rank: Super Contributor
timestamp: July 14, 2022, 05:34:34 pm
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 15, 2022, 01:28:10 am
content: 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.

author: J-R
author_rank: Super Contributor
timestamp: July 15, 2022, 09:18:32 pm
content: 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.