Questions about basic usage of a DMM - Page 1
Forum section: electronics / beginners

author: ksio89
author_rank: Contributor
timestamp: October 06, 2021, 08:56:10 pm
content: Hello folks, my first post here. I've been lurking the forums for a while, seeking recommendations of digital multimetres, and after a lot of research, I purchased an Aneng AN870 (aka Richmeters RM219 or ZOTEK ZT219). From what I've read, this seems to be one of the best Chinese DMMs available in its price range, and while it's no Fluke or Keysight, it's still a very capable model for a newbie hobbyst like me, maybe even overkill. I received mine today and tested a lot of functions, the first impressions were good and so far it's working fine. However, I still have some questions about basic usage of this DMM:1. I want to measure resistance, capacitance, test diode polarity bias and continuity, can I just buy these components at an electronics store and test them? Of course I do have electronic equipment such as PC motherboards, but I think it's too much hassle and I don't want go disassembling things just for that. Also, I want to be able to read the specified value on the components.2. What would be the best way to measure current (in any scale), as I need to place the probes in series with the circuit? The manual tells me to break the circuit path, is that the same as saying I need to measure in series and not parallel? Also, as an ammeter needs very low resistence in order to reduce voltage drop and not affect the current reading much, that also means I also risk damaging the meter if I expose it to large voltages, like 230V mains voltage?3. According to Lygte-dk review of the AN870 (https://lygte-info.dk/review/DMMAnengAN870%20UK.html), the 20A input is not very reliable due to heat generated by a current of 20A or higher, and also because of the large drift (5% at 19A), which is higher than the specified tolerance (delta of 0.8%+3) at 19.999A scale. In short, shall I just avoid measuring currents expected to be close to 20A then?4. Can I use rechargeable Ni-MH AA batteries instead of alkalines to power the DMM, or the lower nominal voltage (1.2V vs 1.5V) will affect the readings? Or the only difference is that the meter will complain about low battery sooner? The Ni-MH batteries are slight longer, but fits the battery holder with some persuasion.5. is there a "DMM usage for dummies" tutorial here or in another website? Something like a straight to the point guide with pratical measurements, so I can reproduce them myself and fully understand how to use all the functions of a multimetre.

author: TimFox
author_rank: Super Contributor
timestamp: October 06, 2021, 09:23:39 pm
content: 1. Yes2. Yes, you need to break the circuit (anywhere along the current path) to measure current with a DMM. Clamp meters can be used if you can surround a single wire in the path: AC units are reasonably priced, DC responding units are expensive. If you know what you are doing, you can carefully measure current in a conductor that is 230 V from ground, but the insides of the meter will be at that voltage and that is dangerous to the operator. A very expensive fast-acting fuse is included on 10 A scales to protect against applying 230 (or even 120) volts across the ammeter terminals: it may not protect the insides of the meter, but should keep the unit from exploding in your face with the extremely high current from that incorrect connection.3. Besides the safety considerations, accurately measuring high currents is best done with an external “shunt” resistor and the voltmeter. I suggest you read up on shunts for that purpose.4. That depends on the DVM: consult the manual.

author: xrunner
author_rank: Super Contributor
timestamp: October 06, 2021, 09:29:40 pm
content: Quote from: ksio89 on October 06, 2021, 08:56:10 pmBuy an electronics "grab bag" on Ebay for $10 or less. You will get an assortment of components to test. Might be more interesting then buying individual components.

author: ksio89
author_rank: Contributor
timestamp: October 07, 2021, 01:54:19 am
content: Quote from: TimFox on October 06, 2021, 09:23:39 pmThanks for the replies. So I believe I should generally only try to use the meter to measure currents in 19.999mA and 19.999uA scales?Quote from: xrunner on October 06, 2021, 09:29:40 pmThat's pretty interesting, thanks. I've seen some listings of bags that also come with other componentes such as leds, transistors, crystal oscilators, inductors etc. I'll look for a grab bag with components that are relevant to my needs, do you have any specific you could recommend me?

author: xrunner
author_rank: Super Contributor
timestamp: October 07, 2021, 01:58:44 am
content: Quote from: ksio89 on October 07, 2021, 01:54:19 amNo I really don't have a specific suggestion. It's hard to say exactly what you are going to get unless the seller specifies it. Hey for ten bucks it's not a big deal.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 07, 2021, 02:23:39 am
content: ksio, good suggestions all around.For your last question #5, check Afrotechmods tutorial about multimeters. It is very basic but gets to the point.https://afrotechmods.com/tutorials/2011/11/27/multimeter-tutorial/He has several other interesting tutorials and experiments:https://afrotechmods.com/tutorials/Quote from: xrunner on October 07, 2021, 01:58:44 amOne additional tip that might help you further is to get a smallprotoboardto connect these parts together. Stores in Brasil such as Baú da Eletrônica, Proesi or Paresteck have them (and you don't run into the risk of delays and missed packages through customs).As with anyone starting with electronics, it is interesting to find a project you like, get the parts to assemble it and learn through this process. You can check theBlog do Piccofor magazines from the 1980s that had simple but functional circuits to get started with very basic electronics (Bê-a-bá da Eletrônica, Divirta-se com a Eletrônica, Saber Eletrônica, etc). If you are interested in newer technology, then you are probably better served with one of the multiple tutorials on the internet (one ishere).P.S. I am not affiliated to any of those stores or channels.

author: magic
author_rank: Super Contributor
timestamp: October 07, 2021, 06:59:58 am
content: From the review you linked:QuoteI have one AN870 and it works with NiMH and the readings are within spec on the ranges I tried (mainly VDC and OHM).But I haven't performed thorough testing to see if it really stays stable to the last digit over full 2.2~3V supply range.It uses a 1.23V shunt reference so there is some potential for drift if the circuit around the reference is dumb enough.

author: ledtester
author_rank: Super Contributor
timestamp: October 07, 2021, 08:01:24 am
content: Quote from: ksio89 on October 07, 2021, 01:54:19 amYour AN870 has the following fuses to protect current readings:- a 20A fuse on the 20A input- a 200mA fuse on the mA/uA inputIf you blow a fuse you won't be able to use that input until you replace the fuse.So you should select the input based on how high of a current reading you expect it to be.If the current could be more than 200 mA, use the 20A input.If you know the current can't be more than 200 mA, you can use the mAuA input.Also, as a beginner I wouldn't use this meter anything that's mains powered. Stick to low voltage circuits only.

author: Shock
author_rank: Super Contributor
timestamp: October 07, 2021, 03:30:18 pm
content: Avoid using multimeters on mains powered circuits until you know how to use it and have read up on safety.Devices like microwaves, crt/plasma/lcd tv, radio/amplifiers, transformers and inverters, can supply and store high voltages, from hundreds to many thousand, always understand the circuit you are working on.Avoid taking unknown current measurements, you are limited by the multimeters protection on the selected current range and power sources can deliver very high currents (especially in fault conditions), it will just blow fuses or damage the meter.As mentioned we can solve the calculation for current in safer ways with ohms law across a known resistance. Think of the current function as a piece or wire, stick it across a voltage and bang! Something will die. Typically you will know the approx result before taking a measurement.Old broken PC power supplies have plenty of parts. Watch youtube for multimeter tutorial videos.

author: ksio89
author_rank: Contributor
timestamp: October 07, 2021, 07:50:57 pm
content: Thanks guys for the replies, those tips are very helpful for beginners like me, I really appreciate them. I will keep the meter away from mains and other sources of high voltages before I learn more about electronics. I have basic (graduate level) knowledge of eletromagnetism, but solving the textbooks examples is very different to doing measurements in real life.By the way, I found the answer to my own question #5: I took an online course provided by Fluke, (Digital Multimeter Basics Online Course), which was exactly what I was looking for. It teaches how to use all the functions of a handheld DMM, scales, resolutions, specs, etc. and also explains briefly about safety and when to use different test equipments or acessories, such as clamp ammeters to measure high currents. The lessons are a instructional videos describing real life situations, and even has interactive quizzes at the end of each lesson to test if the watcher assimilated the knowledge presented.I was impressed by how didatic the content was, and though I usually prefer text instead of videos, the content was excellent and easy to follow, and I'll definitely watch more courses on Fluke training website. If anyone else wants to take it, it's very worth the time spent to watch it:https://www.fluke.com/en-us/learn/online-courses/digital-multimeter-basics-online-course

author: wizard69
author_rank: Super Contributor
timestamp: October 10, 2021, 06:47:37 pm
content: Glad to hear you found what you are looking for. contrary to popular opinion expressed in the online world, reading the manual should be one of the first things a person does after getting a new instrument. Even if it is the 100th meter you have purchased, a new tidbit in the manual could prove to be useful. The more complex the instrument the more important the manual.At your level you certainly will want to stay away from high power circuits. There are some good youtube videos out there that highlight the use of multimeters in diagnostic work so it is worth while to look them up. Part of using a multimeter is in learning basics DC and AC concepts, so a good text that goes into these basics and the use of multimeter to explore what is covered will be very useful. If you want free here NEETS, the old Navy electronics program is worth a look.You will also most likely learn that more equipment is required to follow some of the intro programs. This might include battery power for DC, or a power supply, another multimeter might be in your future too.As for components to test, salvage is a good idea. Not so much for high quality components but rather to learn desoldering of components. Often you can find through hole components in old power supplies. Through hole components will be easier to work with on a bench. If you are going to purchase stuff I'd start out with through hole components in boxes of 50 or a 100, or reels of resistors if they are an extremely common size. The key word is "common", where having 100 on hand is easy to justify. Slowly build up your resistor inventory over time. Capacitors are a little big harder to make suggestions upon mainly because there are so many types and sizes. If you have projects in mind, order what you need for a project plus a few more, some capacitors keep better than others, I would not build up a huge inventory of electrolytics for example. At least not like you would for resistors. In the end salvage teaches you a useful skill so please don't dismiss it.

author: ksio89
author_rank: Contributor
timestamp: October 13, 2021, 06:06:03 pm
content: Quote from: wizard69 on October 10, 2021, 06:47:37 pmI read the manual, but the information was way too condensed. In that Fluke online course, the content was much more comprehensive yet streamlined, it teaches you how to use each function and how it works on real situations, absolutely brilliant didatics. Actually the whole Fluke help website is excellent, there are plenty of articles teaching to use various tools and diagnosize problems, I've already learnt a lot from reading them, whoever writes those deserve a raise because they're very easy to follow.Thank you very much for the tips, I guess that salvage computer PSUs and motherboards are good sources of components for testing. I have a cheap 40W soldering iron, don't know if it will be able to desolder the components without ruining them. I don't think I'll do projects myself anytime soon, as I only have very basic knowledge of electronics.