How do you use an analog multimeter to measure inductance? - Page 1
Forum section: electronics / testgear

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: January 04, 2019, 03:37:08 pm
content: I have a MF-47 meter that just about lives up to its name as a multimeter. It does ohms, volts (ac,dc), capacitance, amps (just dc) it tests batteries, it beeps on continuity of 50 ohms or less, it has an led on continuity mode, it measures up to 2.5kv and gives an hFe reading for small transistors.It also measure inductance in volts and amps.Can someone point me to a link that explains how to use this to test inductors in circuit using this function. I've checked how this measurement is done on the net but it shows the use of a sweep function generator and a scope. I get this but, everything else checks out on this meter except how do you perform this measurement as a troubleshooting or educational exercise? I've read all the manuals but they don't say much or what they say is confusing.Any help would be appreciated. Thanks

author: jpb
author_rank: Super Contributor
timestamp: January 04, 2019, 07:54:38 pm
content: When I saw your title my first thought was Wheatstone bridge where the meter would just be used for null balancing - but it is obviously not that.Perhaps it is able to apply an ac signal (an internal oscillator) and then measures the reactive ac voltage or current, but that is just a wild guess on my part.

author: calexanian
author_rank: Super Contributor
timestamp: January 04, 2019, 08:06:21 pm
content: You have to calculate the inductance therefore requiring an AC signal source and calculating inductance from your X of L calculation. Starting with a known frequency at a known voltage you can measure your series current of your coil and that would be your reactance or X. Then its a simple equation to determine your inductance. There are many factors which must be taken into account before that point though such as the dynamics of the inductor itself. I really just recommend a cheap LCR meter off of ali express or something like that.

author: cdev
author_rank: Super Contributor
timestamp: January 04, 2019, 08:29:01 pm
content: The ultra cheap ($15 will get you one)AVR Transistor testerdevices do a surprisingly good job of measuring inductance - *considering what they are*, their cost, and their limitations. They wont give you more than a very few digits of accuracy (its amazing they can do what they do!) but they will tell you within a reasonable margin what your dealing with surprisingly well, considering, until you get down to fairly small inductances. (they are an incredibly useful thing to have, to tell the truth)Unfortunately if you're interested in RF, the AVR Transistor Tester likely won't be adequate. But its a LOT better than nothing.The other suggestions will be more useful but you'll need more than just a multimeter. You'll need to build an oscillator, or measure a circuits behavior when excited by one, most likely. Being able to measure capacitance is helpful there.So, you're almost there but not quite.You should get a germanium small signal diode (1n34 would work) so you can use it to find the peak or dip in a tuned circuit with a known capacitance.Do you have any kind of frequency counter capability?

author: GeoffreyF
author_rank: Regular Contributor
timestamp: January 04, 2019, 11:22:58 pm
content: I looked up that device. It does not measure inductance in the version I found.https://www.banggood.com/MF-47-Analog-Multimeter-Voltmeter-Ammeter-Ohmmeter-Battery-Tester-p-927021.html?akmClientCountry=America&cur_warehouse=CNAnother problem is that this is a VOM. It has a low internal impedance and, it's a moving coil meter which is itself, an inductance.If you have some sort of oscillator, you can see the roll off as the frequency increases. However, even if you were able to characterize that roll off somehow, this really isn't going to tell you too much about your Inductor, for the reasons I just explained.You have the wrong tool.I suggest that you do some reading about impedance reactance, capacitance, inductance and resonance. AC circuits in general.

author: cdev
author_rank: Super Contributor
timestamp: January 05, 2019, 03:35:22 am
content: Quote from: GeoffreyF on January 04, 2019, 11:22:58 pmAhh, okay..I dont know anything about the specific meter..I was trying to figure out how he or she could measure inductance creatively without spending an arm and a leg.https://www.mikrocontroller.net/articles/AVR_Transistortester-The long thread there on the super cheap AVR device tells a pretty amazing story. Its not a single device, its a several year old, incredibly successful and useful open sourceprojectto make a multifunctional testing tool out of an AVR MCU that analyzes virtually any electronic device that has three terminals (or two two terminal devices at the same time). It does a very great job of doing a great many many things. I have an older version, that doesn't have a graphical display. There are lots and lots of different variations. But they all have a core functionality and two of the core things they do is measure capacitance and inductance. They also measure transistors of almost all types, ESR, this very cheap device successfully identifies dozens of different kinds of devices in most cases also printing out the relevant discoverable parameters.So I was more trying to address what I thought was his need to measure inductance. Until now I knew nothing about his specific meter.Quote from: GeoffreyF on January 04, 2019, 11:22:58 pmCan't blame anybody for asking, I didn't think it was a dumb question but then again as you pointed out I was mistakenly assuming that he had a more full featured meter of a different kind.BTW, I recently bought a DE-5000 and its great, also it agrees with my AVR-Transistor Tester so the AVRTT was within the "ultra cheap" context, accurate when it could come up with a measurement - it did surprisingly well for its cost. ($15) Thats unheard of for something like inductance elsewhere. (Both) also measure capacitance down to 1 pf.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 05, 2019, 05:08:23 am
content: My guess is that it uses an LR network as a differentiating network------ the "L" of course, being the DUT.One of my copies of the ARRL Handbook had both a capacitor measuring adaptor, & one for inductors.I have built a capacitor tester adaptor from an old "Electronics Australia" magazine which works similarly, & is very useful.The adaptor produces a square wave, the differentiating network then produces the familiar output waveform with positive & negative spikes, the duration of which depends upon the time constant of the differentiating network.This is (from memory) passed through a rectifier, then charges up a capacitor.The level of charge of the cap is dependent upon the spike duration, & hence, the (in my case), value of the C under test.I've only seen these made for DMMs, but I can't see why they can't be designed for the lower input Z of VOMs.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 05, 2019, 06:11:00 am
content: Sorry to barge inWhy dont you buy an Deer de-5000 its an good lcr meter ?? At the end you will need more instruments, overthinking etc .. ?Sure you will learn a few things as Calexanian previously wrote

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: January 05, 2019, 10:55:45 am
content: I guess maybe my question was not pointed enough or its just I am wrong about something. The MF-47 and the Sanwa analog multimeter have a scale that shows something as LI (I assume the L represents inductance) the u (mew) then (amps) and (volts). Its just under the part that measures hFe for its transistor checker. My question is: if its not for inductance measurement, then what's it for? The meter is a clone of the Simpson, I believe. It would make sense that this is for inductance, since the meter does a good job of checking everything under the sun that you learned about in school. It test db, ohms, volts, capacitance, amps, transistors, batteries and more so logically the capital L means inductance on that scale. Its also a different scale from the hFe scale for transistors. It is distinct for everything else.Just asking if its for inductance, which I´m convinced it is, how do you use it, if not for that purpose?Thanks for all your replies.

author: HKJ
author_rank: Super Contributor
timestamp: January 05, 2019, 11:33:51 am
content: Quote from: joseph nicholas on January 05, 2019, 10:55:45 amIf you check the manual you will see it is Load Voltage (LV) and Load Current (LI) scales.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: January 05, 2019, 12:33:51 pm
content: Yes, that correct. The scale is not measuring inductance. The manual says its not to test inductance per se, just to check circuits and the L does mean something other than inductance.Thanks.

author: Kean
author_rank: Unknown
timestamp: January 05, 2019, 01:02:19 pm
content: Quote from: joseph nicholas on January 05, 2019, 10:55:45 amI believe the LV/LI scales are for showing theterminal to terminal voltage(LV) orterminal to terminal current(LI) when in ohms range.This meter cannot measure inductance, at least not without extra external circuitry.

author: Kean
author_rank: Unknown
timestamp: January 05, 2019, 01:03:54 pm
content: Here is an article about using a similar Sanwa meterhttp://cellphonerepairtutorials.blogspot.com/2010/05/how-to-use-and-read-multimeter.html

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: January 05, 2019, 10:22:32 pm
content: Thanks for contributing, Kean. I found additional information in the Simpson meter manual. It states something like "when reading the voltage drop for diodes use the LV scale which is read from right to left to determine the voltage drop of diodes and led´s." It works just as expected as I get a drop of less than .5 for germanium diodes, and more than 1 volt for leds. It can also measure the reverse breakdown voltage of a germanium on the 100K ohms range. If you measure on the 100K ohms range it will also light most led's dimly.