EEVblog 1465 - Measure Inductors Using a Multimeter - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: March 31, 2022, 10:15:56 am
content: How you can use your multimeters capacitance range to measure inductors, using the reciprocal method.

author: DeepSOIC
author_rank: Newbie
timestamp: March 31, 2022, 11:07:40 am
content: this does not make any sense to me. April fools, i persume?

author: madires
author_rank: Super Contributor
timestamp: March 31, 2022, 01:39:07 pm
content: Some DMMs don't use an AC test signal at all. Their capacitance measurement is based on V_c(t) = V_in * (1 - e^(-t/RC)), i.e. the time needed to charge the capacitor to a specific voltage.

author: Anthocyanina
author_rank: Frequent Contributor
timestamp: March 31, 2022, 03:14:53 pm
content: Quote from: DeepSOIC on March 31, 2022, 11:07:40 amI think so too! the troll doll can be seen in the top right!

author: Barny
author_rank: Frequent Contributor
timestamp: March 31, 2022, 04:09:48 pm
content: Sadly my DMM isn't supporting this methode.But mine supports the comparing methode.If you measure an known in inductor and an unknown capacitor in series, the goal is to reach zero on the DMM in capacitor mode.When the DMM reaches next to zero, the used capacitance is the inductance value of the coil.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 31, 2022, 04:27:57 pm
content: Quote from: madires on March 31, 2022, 01:39:07 pmCharge with constant current for fixed time**, & measure voltage. Then use q = amps * time and q = CV to solve for CThat's why you get a triangle on the 'scope (there's a symmetric CC discharge as well).** (edit) - or until fixed voltage reached and measure the time, same calculation but explains why frequency changes with capacitance under test, but the sawtooth amplitude doesn't.

author: TimFox
author_rank: Super Contributor
timestamp: March 31, 2022, 04:42:39 pm
content: One of my favorite test instruments is an ancient, vacuum-tube enabled, admittance bridge from Wayne-Kerr, model B221, that measures capacitance (displayed in farads) in parallel with resistance (displayed as conductance in mhos) at a fixed frequency, 1592 Hz.That frequency (10,000 / 2pi) was chosen to facilitate inductance measurements from negative susceptance.Since this was before pocket calculators, the manual includes a table of reciprocals.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 31, 2022, 06:33:26 pm
content: I have an old DIY LCR meter inspired by an old (1990s) Elector article that also uses the "magic" 1592 Hz to get easy cap, resistance and Inductance reading with just shifting the decimal point.This frequency was also used for metrology grade capacitance measurements.

author: TimFox
author_rank: Super Contributor
timestamp: March 31, 2022, 06:59:25 pm
content: The Wayne-Kerr B221 is a great machine. The bridge itself uses switched ratio transformers for the most-significant digits, and the ratios of integers are invariant over lo, these many years.The capacitor standards are hermetically-sealed polystyrene (I believe) that have remained in calibration, as well.But the real beauty is the null indicator: a pair of dual magic-eye tubes, with an intermediate amplifier between them, that gives an instantaneous readout of the null voltage over a very wide dynamic range.

author: thm_w
author_rank: Super Contributor
timestamp: March 31, 2022, 08:30:34 pm
content: Quote from: DeepSOIC on March 31, 2022, 11:07:40 amIt works on almost any modern meter.Try for yourself.Quote from: Barny on March 31, 2022, 04:09:48 pmSwapping the polarity of the leads would fix it.Positive goes to the outer winding, on SMD inductors this is marked with a dot.

author: isometrik
author_rank: Regular Contributor
timestamp: March 31, 2022, 10:42:52 pm
content: I was biting for a few minutes, and then escaped the bait.

author: ludzinc
author_rank: Unknown
timestamp: March 31, 2022, 11:50:06 pm
content: I'm still mad about this:Well played Sir, well played.

author: golden_labels
author_rank: Super Contributor
timestamp: April 01, 2022, 12:12:19 am
content: My UniT UT-70A can measure inductance, but only for relatively large values. No way to measure inductance of a straight wire. I was happy to try this method, but it didn’t work. What a rubbish!

author: TheNewLab
author_rank: Frequent Contributor
timestamp: April 01, 2022, 02:40:43 am
content: Slip to the side on this video..What is the LCR precision measurement device? I mean the open source source box on the lower left. Never sen that before. IS there a build for that. and who order PCB from?Inductance. Once I bought an LCR meter and the frequency I need to measure inductance...That's all I use. Glad to learn this. Maybe out in the field .Industrial electrical jobs? That said, I am now really curious which DMMs I have that do use a sine or triangle signal.April fools? maybe a little, yet I remember a very old Delton Horn repair book that had all those formulas for determining XCand XL

author: Fungus
author_rank: Super Contributor
timestamp: April 01, 2022, 11:36:19 am
content: Quote from: DeepSOIC on March 31, 2022, 11:07:40 amThe secret to April Fools day isn't to rush around posting "It's an April fool thing, everybody!!! (And look at me!! I'm so smart I spotted it all by myself!!!!)"Nope. The secret is to post something like "I tried it on my meter and it worked!".I'm not holding my breath though.

author: EEVblog
author_rank: Unknown
timestamp: April 01, 2022, 12:02:32 pm
content: Quote from: TheNewLab on April 01, 2022, 02:40:43 amhttps://www.ak-modul-bus.de/stat/rlc_box_standard,pd730!0,,RLC-BOX1.html

author: grumpydoc
author_rank: Super Contributor
timestamp: April 01, 2022, 12:04:36 pm
content: Quote from: Fungus on April 01, 2022, 11:36:19 amGiven that everybody knows that Dave puts out an April Fool early on 1st April Australian time - and therefore usually on March 31 in the rest of the world the best April Fool might be that he puts out a legit but dodgy sounding video at the appointed hour and then watches everybody debate it.I'd try it for a laugh but don't have many inductors lying around.

author: golden_labels
author_rank: Super Contributor
timestamp: April 02, 2022, 10:28:49 am
content: Now, April 1st being globally over, we can comment normally.I applaud Dave twice! It took me a moment to realize something doesn’t up. It’s not the only “how is that even possible” thing one can do on a DMM, so no alarm bells ringed instantly. But grabbing a multimeter and presending that without preparation during today’s live was just perfect!

author: EEVblog
author_rank: Unknown
timestamp: April 03, 2022, 12:18:02 pm
content: I expect this video will be referenced for the next decade