My cursed multimeters? (spoiler, it's my brain) - Page 1
Forum section: electronics / testgear

author: SpectrHz
author_rank: Contributor
timestamp: August 02, 2018, 02:18:43 am
content: long time no post, forum.So,I have two multimeters, an Extech 430 true RMS I bought new, and an Ideal 61-312 that I found in the trash with bad fuses. Now, Idk if I'm just stupid or having an actual issue, but I cannot use the capacitance range on either of these multimeters, I have tried to measure every kind of cap; tantalums, ceramics, electrolytics, foil, paper, all of varying values and I have only gotten a hit maybe 3 times. Every other time they both just say OL seemingly regardless of the value on both of these and regardless of how long I sit there waiting for them to autorange. As far as I can tell they both work perfectly, I have never had any issues with them apart from shit battery life on the Extech (9-volt with a backlight!)So, am I insane? stupid? is this a real problem or did the solution fly over my head? I couldn't find anything online that had to do with my issue no matter how I worded it, mostly just a bunch of guides on how to measure motor start caps with your multimeter. I have a multifunction tester that pretty reliably tells me capacitance and accurately, so it's not that i need a different meter, I just wonder why I have this curse.

author: Muxr
author_rank: Super Contributor
timestamp: August 02, 2018, 03:28:57 am
content: Not familiar with the particular DMMs you have. I can just offer a piece of advice. Before measuring capacitors make sure you drain the capacitors of any charge. As any charge could interfere with the measurement or even potentially could harm the DMM.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 02, 2018, 03:43:46 am
content: What does a 10uF or 50uF electrolytic capacitor read on the EX430?

author: SpectrHz
author_rank: Contributor
timestamp: August 02, 2018, 03:50:27 am
content: Quote from: retiredcaps on August 02, 2018, 03:43:46 am!!?? Well, a brand new 10uf measured 10.9... and 50 measured 49... wha.. I don... Ok, maybe its higher range electrolytics that work, Ill admit i don't measure electrolytics as often as ceramics and tantalums, mostly when I'm tracing circuits.

author: IanB
author_rank: Super Contributor
timestamp: August 02, 2018, 03:53:33 am
content: Quote from: SpectrHz on August 02, 2018, 03:50:27 amBe careful. You probably cannot measure a capacitor while it is in circuit. Are you making sure to unsolder one of the leads before measuring it?

author: SpectrHz
author_rank: Contributor
timestamp: August 02, 2018, 04:01:59 am
content: QuoteI know, usually I do, unless its with surface mount. The inciting incident that started this thread was actually me trying to measure the value of a decoupling capacitor on a chips unused voltage reference. I know measuring in circuit is bad, but I was under the impression that most of the time, it just causes inaccurate readings, not a complete failure to read. Am I under the wrong impression?

author: IanB
author_rank: Super Contributor
timestamp: August 02, 2018, 04:05:07 am
content: The meter measures capacitance by seeing how long it takes to charge the capacitor under test when supplying a constant current. If there are any current paths in the circuit that bypass the capacitor then the reading may be thrown completely off.

author: SpectrHz
author_rank: Contributor
timestamp: August 02, 2018, 04:08:01 am
content: ok, in this case i don't think there is but that still doesn't answer why almost everytime i test caps out of circuit i have a similar issue.

author: SpectrHz
author_rank: Contributor
timestamp: August 02, 2018, 04:11:32 am
content: Quote from: SpectrHz on August 02, 2018, 04:08:01 amEdit- I must be an idiot.I just measured some new ceramic multi-layer caps and disc caps and they measured fine... I... I don't understand, and I think I'm mostly just embarrassing myself at this pointwould esr possibly play a role? perhaps i am misremembering, but I'm almost positive it usually just sits there charging forever until saying OL..

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: August 02, 2018, 12:48:43 pm
content: Have you tried using a fresh battery? Often a DMM will not indicate your battery is low but since the meter is charging up a cap if the current is not sufficient to do this job it just sits. The most power hungry function must be the cap measurment on DMMs. I know this because sometimes the battery low indicator will come on when checking capacitors. Not in any other mode.

author: SpectrHz
author_rank: Contributor
timestamp: August 03, 2018, 12:38:54 am
content: Quote from: joseph nicholas on August 02, 2018, 12:48:43 pmon the ideal, yes, but not the extech, it sucks down batteries far too fast. It uses a 9 volt and has a backlight. Honestly I don't know what they were thinking.