121GW multimeter - resistance auto range expectations - Page 1
Forum section: electronics / testgear

author: cardre
author_rank: Contributor
timestamp: January 21, 2022, 06:05:28 am
content: New owner of a 121GW that I just purchased new and received a couple of days ago. Bit of an upgrade from my old Sparkfun meter!Anyway, just wondering what I should be expecting when in resistance measuring mode. When its auto ranging and I'm trying to zero out the test leads by crossing them with the little indents near the tip to get a good contact, I hit the 'REL' to zero it out, but its still jumping around, sometimes even up to over an ohm. I'm trying my best to keep the pressure evenly on them, but its constantly jumping around. I tried this also with and without holding my fingers onto the actual tips. I can see the little bar meter along the bottom just 'twitching' occasionallyIs this to be expected with auto ranging? I've noticed it, but not so much, when I put it in specific (low resistance) ranges, its also jumping around when trying to zero out the leads resistance. With the auto ranging it also can sometimes be taking quite some time (> 1 second) to settle down even though I'm making a firm contact.At first I didn't push the leads in all the wayand seat them down properly, just went as far as it felt firm, but obviously wasn't all the way in. As its new, I didn't want to use too much force, but they're now definitely pushed in properly (pretty much sits flat against the face of the meter) and I'm still having this issue.Its probably more of a pain when just testing random resistors of unknown values (0 ohm to 1M), otherwise I can put it into the expected range(s) and it seems then to do a much better job at quickly showing the right value.So is this expected behaviour, or do I have a problem with either the test leads or the meter?Hope I'm not asking a dumb question!Thanks.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 21, 2022, 10:22:55 am
content: Are you doing this in close proximity to a mains powered LED light, or some other item with a switched-mode power supply? The EMI from these can cause problems sometimes.

author: cardre
author_rank: Contributor
timestamp: January 21, 2022, 10:49:56 am
content: I was trying it out in front of my dual monitor computer (while reading the manual on the screen), so I'll try moving away from there and try again and see if its any better.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 21, 2022, 11:59:39 am
content: In the scenarios I saw this happen (low ohms jumping around), the problem was not on the tip of the leads but on either the plugs, the wire or the jacks.To test the plugs and jacks, turn them around to see if the measurement settles. In cheap multimeters (or ones with faulty components) there is a point where the contact is very solid and the measurement will settle.To test the wires, try to move limited parts of them (especially around the joint points on the probes or the plugs) while keeping everything else still. I have spotted many failures due to wear and tear. You can also simply change the leads to see if the measurement settles.At last, you can suspect the meter itself: a part inside that is loose, or the range switch that is not making good contact. For the range switch you can try to apply some pressure and see if the measurement changes (it should never do that, BTW). If that is the root of the issue, this becomes a case for a deeper repair or complete replacement.I personally never saw a weak electric or magnetic field influence low ohms measurements - only when you are measuring hundreds of kΩ or MΩ.Good luck!

author: Caliaxy
author_rank: Frequent Contributor
timestamp: January 22, 2022, 12:22:35 am
content: Quote from: cardre on January 21, 2022, 06:05:28 amExpect it to be very slow in resistance mode. Mine is too.Quote from: cardre on January 21, 2022, 06:05:28 amAn ohm sounds too much. Try waiting a bit longer before hitting 'REL'. Mine goes down to its lowest value in quite a long time (3-4 s, or longer). The test leads that came with the meter go as low as 0.03 ohms, and the value seems to vary with the pressure applied to the tips. With other high quality leads (gold plated Brymen and Hioki) it shows 0.001 ohms (or even 0.000), but it takes a while to reach that low value.Quote from: cardre on January 21, 2022, 06:05:28 amThe auto ranging is very slow on this meter. It seems to start always from its highest range (Mohms), then it goes down towards the lowest range, passing through all of them, sequentially. Again, mine takes at least 3 or 4 s to show anything close to 0 ohms if you start with the leads in the air. When you open the circuit, the meter starts ranging up sequentially and it also takes a few good seconds to decide it's "OL". When measuring a resistor, it doesn't show intermediary values, but you see how it moves the decimal point digit by digit then it jumps to the next range and so on until it finally decides to display a number. When you short the probes, it might actually show successive values around zero. It's one of my slowest ohm meters.Other than that, it seems quite precise and it's a great meter.

author: cardre
author_rank: Contributor
timestamp: January 22, 2022, 05:10:28 am
content: Quote from: Caliaxy on January 22, 2022, 12:22:35 amAh ok, I see.Quote from: Caliaxy on January 22, 2022, 12:22:35 amYeah I've seen the videos where Dave is quickly tapping the two leads and how fast the continuity beep was. Realised after though that's with the leads that no longer come with the meter. Still it's not too bad for that setting and nice to see can switch between 30 and 300 ohm.Quote from: Caliaxy on January 22, 2022, 12:22:35 amOk, this seems to be the same sort of behaviour that I'm seeing so I guess its expected.As per the other suggestion above, I've also tried moving away from other devices and it did improve some, but not a great amount. So I guess just need to get used to way this works.I wonder if a firmware update might improve the situation? Is this one of the 'hackable' abilities of the meter, or is this auto ranging capability baked into the hardware of one of its chips?