DMM functions - Page 1
Forum section: electronics / testgear

author: najrao
author_rank: Regular Contributor
timestamp: January 28, 2019, 10:43:37 am
content: I wonder why NO common hand-held DMM offers measurement of inductance. I can and do use a dedicated LCR meter, but that does not answer my question.As a minimum, I need 10uH to 100H, preferably autoranging. We all do: switch mode and EMI suppression inductors range micro- to milli-henries; "power" and audio transformers and chokes go on to tens of henries or even more.From ferrite beads to chip inductors to toroids to r-core transformers, inductors abound in circuitry. If I can quickly check inductance values, i can assess a transformer for shorted windings, turns ratio, volt-s of the core --- even estimate how many turns in each winding of what wire size, all without even energizing the beast. In short, predict the entire design, performance and ratings!Directly measuring the Q could be useful sometimes.too.Tracing printed circuits by continuity alone frequently leads to false positives, an inductor on the way showing up as a short and remaining undetected. I have solved many a problem by using the LCR meter instead. Interestingly, a low (milli) ohm meter I use measures by applying 1kHz sine ac mV through a multi-ratio CT, and picks up the signal on the much higher voltage (one or two) volt CT primary. Very convenient for checking printed circuits which show false shorts due to inductors.They do offer capacitance ranges don't they? Why discriminate against the poor inductor, just because it does not fail so often?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 28, 2019, 11:40:45 am
content: A good lcr use dedicated precision lcr circuit, up to 100-200khz or even moreA Dmm or bench meter with say : capacitance measurement is a basic help tool, it wont check ESR D Q R etc ... I have Flukes 189, Gossen Metrawatt, BK Precision 5490, they all heck capacitor up to 30,000 50,000 uf, BUT they wont tell the ESR and many important tests factors.A good dmm with theses added circuit may not be cost effective, if it was the case, we should have seen more of them ?A good basic lcr would be an DE-5000, sure you have thoses small cheap lcr meter / component tester starting around 20$ who can do a good starting job.If not satisfied, you could build your own meter / lcr and do a kickstarter design project ??A de-5000 with is 2 dedicated / specialized chips, could easily be integrated in modern DMM, not sure if the dmm inputs could be shared in kelvin mode with the lcr section, you could lose some CAT specs doing so ? unless adding some input shielded relays $$, more input protections ... and relays over time can go bad and have contacts problems.

author: Fungus
author_rank: Super Contributor
timestamp: January 28, 2019, 06:52:22 pm
content: My theory is that LCR meters have a very different set of controls on the front than a Multimeter does. They also work best with a dual display, which few multimeters have.Trying to combine the two into a single gadget is unlikely to produce anybody's dream device.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 29, 2019, 12:24:47 am
content: Quote from: najrao on January 28, 2019, 10:43:37 amI've played with a couple of them. The 194II is spec'ed for 10uH to 300mH. I can't think of the other brand I had looked at. Both have very poor specs and I really didn't see much point in the feature. I have a few B K RLC meters that I like. Mine are fairly old now. One developed a problem with the synthesizer that I needed to repair but no other problems. Cost is about what you would expect for a decent handheld meter.http://www.summit.co.kr/product/pro02_6.htm

author: TurboTom
author_rank: Super Contributor
timestamp: January 29, 2019, 08:21:16 am
content: Another reason for DMMs not having inductance test included is that this requires rather low-impedance circuitry inside the meter and that these are very difficult to protect from over voltage events. Connect the instrument accidentially to an AC outlet in inductance mode and it's done... A dedicated LCR meter is way less likely to be exposed to that error situation, here it's basically capacitors with a remaining charge being connected. Just my thoughts...

author: beanflying
author_rank: Super Contributor
timestamp: January 29, 2019, 09:17:08 am
content: Have a bit of a trawl of this thread for a different approach to LCR in circuit testing.https://www.eevblog.com/forum/testgear/truth-about-canadian-lcr-tweezer-manufacturers/msg2068102/#msg2068102Still coming up with some numbers and what I do or don't like about them but so far the LCR Research is the front runner

author: mqsaharan
author_rank: Regular Contributor
timestamp: January 29, 2019, 06:44:53 pm
content: Quote from: najrao on January 28, 2019, 10:43:37 amThe following forum thread might help here.https://www.eevblog.com/forum/testgear/new-der-ee-lcrdmm/The same thread contains the link to scanned user manual duplicated here as well.https://drive.google.com/file/d/0Byt2j0t-2qO3UUVYMHY3dExaaWsI don't own this meter. So I cannot say how well it works. But from the specs, it seems to come close to your requirements. Also, I cannot say how forgiving it will be for (Hi)V on LCR function.Meter itself seems to have proper input protection built in.This DMM might be based on ES166 Front End chip from Cyrustek.http://www.cyrustek.com.tw/spec/ES166_web.pdfI hope it helps.Regards,Qasim.EDIT: I didn't check all the pictures. The front end chip on DE5003/4 is ES51930.http://www.cyrustek.com.tw/spec/ES51930_web.pdf

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: January 29, 2019, 07:51:34 pm
content: Amprobe 37XR-A does inductance.I have the meter, but I did not use the feature yet. So I can't judge how it compares to a real LCR meter.

author: najrao
author_rank: Regular Contributor
timestamp: January 30, 2019, 09:23:37 am
content: Thank you all, friends. I have learnt a few things. I will keep a look out for the simpler offers available, and may be graduate to the more sophisticated if needed. I do electronics for hobby, not to earn a living.