121GW LowZ mode not showing AC or DC indication on Display - Page 1
Forum section: electronics / testgear

author: 66seb
author_rank: Newbie
timestamp: November 22, 2023, 09:23:50 pm
content: Hi All.Have a 121GW for many years (got it when it was on kickstarter in Dec'17 = early supporter) but something's always annoyed me:When using LowZ the voltage reading doesn't show either "AC" nor "DC" indication on the LCD, I think it's an oversight and should be patched in a firmware update (I've now updated to v2.05, still the same).I understand, from the manual that the meter's exclusively performing an AC measurement of the voltage in this mode, so why not show "AC" on the display?Kind Regards.

author: thm_w
author_rank: Super Contributor
timestamp: November 22, 2023, 10:31:08 pm
content: There is a "LowZ" indicator on the LCD, but, Fluke will show both the LoZ and AC indicators as you suggested.edit: the LowZ mode will detect if its AC or DC then display the corresponding indicator. Its not explained in the manual.I guess it could initially say "AC+DC" but I don't think its really an issue.

author: 66seb
author_rank: Newbie
timestamp: November 23, 2023, 08:23:17 pm
content: Dear tthm_w,Thank you for your reply, you're right, it detects both and indicates "AC" or "DC"................................ eventually.So I can use it to monitor and speed up the discharge to a safe level of DC circuits so I don't get a shock when rushing fault-finding, so I am relieved 'cos I expected this feature when I bought it, DC Low Z's super useful.The time the meter takes to read is excruciating, 2 seconds at least, and won't work much under 12V, when a 12v Car or SLA battery is a bit flat it sees nothing, LowZ's no good for automotive and leisure/camper use (I didn't expect it to be really, LowZ's primarily for 50+ volts applications I think, please correct me). 2 years ago whilst faultfinding van electric windows for a mate, when pressing the window buttons it wouldn't read anything in this mode, now I know why, either not enough volts or too short a press.Ultimately I wanna know the limitations of each feature/mode so I do not make bad measurements and waste time chasing red herrings. The 12V limitation is explained in the manual, OK, but only mentions it does AC so I though LowZ on this meter was limited to AC exclusively. But 2 or 3 secondsWhilst the firmware is fine then, the manual is where an overdue revision is required.6 years after the meter came out, the feature set/ manual is still not clear, I confess that I have come to not trust this instrument.Fluke's the way.

author: J-R
author_rank: Super Contributor
timestamp: November 24, 2023, 04:47:00 am
content: Personally I would not use the 121GW Low Z mode so much. First, if there is a potential for dangerous voltages, then relying on it before touching things seems unsafe. What if you drain the circuit with the Low Z mode, but then it charges back up over a few seconds after removing the DMM?Next, Low Z is 1K Ohms + 1.2K Ohms PTC. Fluke's SV225 Stray Voltage Eliminator is similar, around 3K Ohms total. That could be a lot of load to be placing on random circuits in my opinion. So I use the regular AC, DC or AC+DC modes primarily. Then switch to Low Z mode in the specific use cases that require it.The 121GW is regarded as being on the slow side, but in all fairness quite a few DMMs that I have are also slow in "Auto" modes since they need to switch back and forth between AC and DC before deciding which is more prominent.

author: thm_w
author_rank: Super Contributor
timestamp: November 24, 2023, 11:30:20 pm
content: Quote from: J-R on November 24, 2023, 04:47:00 amThis is the case with anything that has LowZ and isn't really a valid concern IMO. You'd use it to discharge a cap on a board thats not plugged in.Or to eliminate ghost voltages from wiring, the voltage may rise again but the current would be very low.QuoteYes you only use it when needed not as the default measurement method.121GW is very slow, I'd rather use a $10 cheapy for frequent everyday tasks (continuity, basic voltage testing, etc.). Most high res/multifunction meters are slow though.