Best practices for not damaging DMM? - Page 1
Forum section: electronics / testgear

author: bird333
author_rank: Newbie
timestamp: January 08, 2023, 02:25:17 am
content: I'm new to using a DMM. Are there steps I should take between switching to different modes to prevent damage to the meter or to the equipment? Thanks for any suggestions.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: January 08, 2023, 02:35:10 am
content: I've got two related suggestions:When you turn the meter off after make a current measurement, move the leads back to the "volt measuring" position. Don't just set the meter down and go about your business.Before you probe a voltage, make sure you didn't forget to do the above. I've blown two or three too many current fuses in my multimeters just from laziness/carelessness. Develop good habits from the start so you don't have to work to develop them later after making embarrassing mistakes.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 08, 2023, 04:08:41 am
content: Quote from: bird333 on January 08, 2023, 02:25:17 amNever send one to me. I have a history of damaging poorly designed meters beyond repair.Quote from: Excavatoree on January 08, 2023, 02:35:10 amAgree. Best solution is put that gray matter to use. If you can't be bothered to understand what you are trying to measure and how to measure it, it's a foregone conclusion.Of course, some meters can handle far more abuse than others. Higher cost doesn't suggest the meter will be more robust. The last meter I looked at was a very high end Keysight. Testing suggests that meter's switch with just normal use would fail prematurely when compared with other higher class meters. If you want a meter that will last, start with buying a good meter.Enjoy your new meter.

author: J-R
author_rank: Super Contributor
timestamp: January 08, 2023, 08:14:15 am
content: I think a good habit to form is disconnecting the leads from what you are measuring before changing modes. With typical DMM test probes, this can be as simple as letting go so they break contact with whatever you were measuring.But most DMMs have input protection for all functions, so the worst that should happen to the DMM on a typical electronics bench is you could blow a fuse (a typical DMM will have a high-current fuse around 10A and a low-current fuse around 500mA).However, there are some DMMs that do not have a fuse for the 10A range, so that might be worth discovering now on purpose rather than later by accident. This could damage the DMM, probes or your other equipment.A common misunderstanding among new users is how to measure current with a DMM, which is a series circuit, not parallel.What DMM(s) do you have?

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 08, 2023, 09:08:01 am
content: One way to damage the DMM is to have the battery leaked in it.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 08, 2023, 09:29:11 am
content: Don't try to measure how many amps "has" a 12V battery, or even worst, how many amp "are at" the mains socket outlet.

author: Nominal Animal
author_rank: Super Contributor
timestamp: January 08, 2023, 09:41:48 am
content: Quote from: RoGeorge on January 08, 2023, 09:29:11 amAh yes, don't be me. I had a couple of extension cords pulled through a 1" plastic pipe (impact shielding in a garage-type situation) for work lights, and needed to check which one was which. So, I connected one, and measured the AC voltage at the other end. Because I was thinking "I must measure AC voltage, and not AC current; remember: NOT AC current!", I switched my DMM to ~A, of course, and stuck the probes in.ZAP.Oopsie. Only blew the DMM fuse, though.

author: Ian.M
author_rank: Super Contributor
timestamp: January 08, 2023, 09:43:35 am
content: J-R's comment about disconnecting before changing modes needs extending for cheaper/older meters with manual ranging. Every time you switch ranges while measuring current in an inductive circuit, the contacts are likely to arc and burn away a little bit at their edge. Do that too often and it will become unusable, so develop the habit of disconnecting before moving that big knob! Most handheld DMMs have the range switch contacts integrated on the PCB, so if you damage them the only option is a new meter.For old higher value Analog multimeters, always switch to the Off position after use and definitely before transporting them. Its extremely common for the off position to directly short the meter's movement to apply heavy damping to the pointer to better withstand mechanical shocks.

author: NickKUK
author_rank: Contributor
timestamp: January 08, 2023, 10:30:50 am
content: DMM AC measurement typically uses a capacitor. That doesn't magically discharge instantaneously. So moving the probe around can lead to small shocks being applied to more lower voltage or more sensitive components.For low "HV" a set of croc clips is useful but really you want proper HV probe to cope with any accidental transients. With HV you don't want you/your fingers near the kit in operation. With a properly designed HV supply it should bleed down after shut off (after testing the grounding, the controlled start and bleed down test is my second test of the build) so you typically won't be moving the probe around until it's all bled and that bleeds the DMM down with it.Think about this measuring 25 or 75Vdc then to 1.8/3.3Vdc skipping across a PCB.I think everyone has has blown a DMM fuse measuring current at some point - it's a right of passagefollowed by

author: AVGresponding
author_rank: Super Contributor
timestamp: January 08, 2023, 10:32:03 am
content: After measuring an AC voltage, short the leads together before touching them or measuring anything else, to make sure the coupling cap in the meter is discharged.99 times out of 100 this isn't necessary, but you don't want to try for that 1 in a hundred...

author: orb
author_rank: Regular Contributor
timestamp: January 08, 2023, 11:03:18 am
content: Do a triple check before you even think about to measure something.

author: bastl_r
author_rank: Regular Contributor
timestamp: January 08, 2023, 01:10:59 pm
content: If you want to measure the voltage on a larger transformer, turn it on first and then contact the test probes.Many years ago I destroyed a HP3457a....The input hybrid, all the protection transistors and the 8052 on the measurement side....I had incorrectly connected a large toroidal transformer on the primary side, and after the fuse tripped, made three more power-up attempts....

author: Brumby
author_rank: Unknown
timestamp: January 08, 2023, 01:14:18 pm
content: Quote from: Nominal Animal on January 08, 2023, 09:41:48 amQuite some many moons ago, I had a guitarist friend ask me what was a good multimeter to buy. I pointed him to Fluke and he threw $700 at buying one. I was stunned - but I was soon glad when he told me he tried measuring his "household current".Cue: your trick.I got a call to say it made a loud noise and wasn't working properly - the casualty also being a fuse. I'm forever thankful I pointed him to a meter that could handle that.

author: Brumby
author_rank: Unknown
timestamp: January 08, 2023, 01:15:56 pm
content: +1 on the Current measurement caveat.Never leave a meter in current measurement configuration.

author: tooki
author_rank: Super Contributor
timestamp: January 08, 2023, 02:29:33 pm
content: Here’s one: never use a multimeter to try to measure anything inside itself. Every once in a while there’s a thread here about someone killing their multimeter because they tried measuring its own battery voltage, for example.

author: Fungus
author_rank: Super Contributor
timestamp: January 08, 2023, 03:06:54 pm
content: Quote from: Brumby on January 08, 2023, 01:15:56 pmYep. Andalwaysmeasure current on the 10A range first. Never start on the mA range.Second: Don't turn the dial with the probes connected to anything.You don't say what DMM you own or what you're doing with it but I think you'll have a hard time doing any damage if you follow those three rules.

author: nightfire
author_rank: Frequent Contributor
timestamp: January 08, 2023, 03:28:24 pm
content: To sum up:Best practice independent of an digital or analog multimeter include turning your brains on and think about what you want to measure exactly and what the expected value would be.Then:- begin with Volts measurement first to check IF voltage is present and if it is present at the estimated points- begin with highest range first (or make sure autorange is engaged)- disconnect the wires after usage OR at least put them in the Volts input to prevent accidents like having wires in the Amps socket and probing for voltage- will go boom- usually the device under test (DUT) should be powered up first, then go measure- to prevent nasty inrush spikes frying the multimeter- do not use cords longer than necessary- they tangle and push stuff from the desk- only do Ohms/diode tests etc. if confirmed that there is no voltage present- replace blown fuses with correct (and expensive) types that can withstand the short circuit power, do not cheap out on this

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2023, 04:18:15 pm
content: Buy a hard case to store it and its accessories in when not in use. I use Nanuk but there are lots of options.

author: BillyO
author_rank: Super Contributor
timestamp: January 08, 2023, 04:21:45 pm
content: I always turn my meter off and remove the leads after each use.All my leads(DMM, scope probes, alligator leads, etc..) are always removed from my equipment and hung up.If I have to measure both voltage/ohms and current in a given situation, I use two meters. I know this is not going to be an option for everyone but at a very minimum if you are moving between measurements turn off the meter and remove the positive lead.

author: Fungus
author_rank: Super Contributor
timestamp: January 08, 2023, 06:53:36 pm
content: Quote from: BillyO on January 08, 2023, 04:21:45 pmHuh? Everybody here has at least 20 multimeters...(or is getting there)

author: coromonadalix
author_rank: Super Contributor
timestamp: January 08, 2023, 06:53:52 pm
content: For current measurementsI use an 0.1ohms 50watt shunt, enough for the most current home equipment or a clamp meter AC-DC 6 amp / 60 amp ranges, who has an good zeroing functionYou dont over heat the meter, you dont blow some expesives fuses Ie: 10$ in my meters busted a few 400 ma fuses recently over some 500ma peak surrent loll, lessons learnedloll i have 8 meters loll

author: bastl_r
author_rank: Regular Contributor
timestamp: January 08, 2023, 07:54:45 pm
content: Quote from: bastl_r on January 08, 2023, 01:10:59 pmI forgot to mention: The HP was set to voltage measurement and the test leads were plugged in correctly. Only the transformer was connected incorrectly so that there was a massive overvoltage which first destroyed the protective circuits of the multimeter and then the hybrid circuit.

author: BillyO
author_rank: Super Contributor
timestamp: January 08, 2023, 08:11:36 pm
content: Quote from: Fungus on January 08, 2023, 06:53:36 pmI've only got 17 .. I suck

author: NickKUK
author_rank: Contributor
timestamp: January 08, 2023, 09:14:48 pm
content: Quote from: bastl_r on January 08, 2023, 01:10:59 pmAnd don't leave the probes on when powering off..