Essential Measuring Instruments for the Newcomer. / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Essential Measuring Instruments for the Newcomer.

1 2 3 4 next

Move Thread

LAN_403

Proud Mary

Sun Oct 04 2009, 10:38AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi folks!

I've noticed over and over again that folk fairly new to electronics ask us for advice about some circuit that doesn't work, but seem to have no means at all of measuring the voltages at key nodes, which would often make diagnosis a simple matter for the more experienced members.

Some of who have expensive-looking multimeters sometimes seem not to know how to use them to anything like their full potential as diagnostic tools,
which is not surprising for folk who are self-taught and haven't had the advantage of any formal training.

The point of this thread is to look at economical instruments the mystified (

! ) can either buy or make themselves.

Nowadays, the primary diagnostic tool is the multi-meter, so that's where we'll start. By way of experiment, I bought a good-looking, very robust, hand-sized multimeter with a nice large display and a rubber shock jacket on ebay for Â£10 (US$ 16 / 11 Euros / 93 NOK) - it doesn't even have a brand name, but is clearly a Chinese design inspired by Fluke. (I say 'inspired' because it is not a copy, or a counterfeit Fluke, but looks rather like like one)

I then tested it against my recently calibrated Fluke 887AB AC/DC Differential Voltmeter - accurate to 6 figures - and was amazed at the accuracy of the Â£10 device, which came within a few percent of the Fluke figure, on all ranges except the 200M (a rare feature for a cheap multimeter) where the error rose to about 5%. On the 20A range (another feature often missing from cheap meters) the error rose with current, finally showing 19.8A against my 0.1% current standard of 20A - more than satisfactory for all but the most specialized work. It can also measure hfe, and basic diode tests, but no capaciance, inductance, or frequency, as you get with the all-singing all-dancing species of multimeter.

So this should dispel the myth that you have to spend a lot on a multimeter to get good results. The things to avoid are the very small meters. Something with an 1 1/4" LCD display like this one is easy to read from a distance, so the instrument can be hung up at the back of the bench (it has a hook point in the rubber jacket) and came with perfectly reasonable and safe test leads.

Now that's enough from me, folks, and I hope to see some stuff here covering everything from how to choose a decent meter for your particular purpose, to how to use the meter in all sorts of tests and fault-finding operations, but, hey, let's not make it a brand-fest, fellas - it's no good saying "I wouldn't choose anything but Fluke or Keithley $$$$) when most here have limited budgets and want to use them as best as they can.

So: what is a good multimeter? How can we tell the good from the bad? What facilities do we really need on a meter? How can we best use the meter we've got to learn about what is going on in a circuit.

For years I went out in all weathers to service the transmitters on automatic light ships, where I sometimes had to work in appalling conditions of sea-sickness for days on end (the lightships are in all the worst possible places, of course!) with only one measuring instrument, the legendary, the one and only truly great, Avometer Model 8, and no matter what the fault was, that was all I had to find it with. (There were no plug in cards to make life easy, so everything had to be done by me alone with a soldering iron on the restless, pitching, stinking, rusty ships) but a sense of smell was often as good as the meter once you had got the salt water out of your nose!

)

Once we're done with multimeters, we'll see what our common opinion is about the next most important piece of test gear is, and so on)

So that's enough blab from me folks. Over to you:

Frosty90

Sun Oct 04 2009, 01:23PM

Registered Member #1617 Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139

I'd agree 100% you dont need to spend big money for a decent meter! I purchased a 'generic' (chinese) brand meter from a local electronics place for about $90 and it is great, accurate, (although it doesnt do true RMS voltage, but I only ever use the AC scale for mains/50hz sine waves anyway.). It also does R, L (although limited range) and C, which is handy,diode test, frequency (upto about 15kHZ I think) temperature (but I usually use an infrared 'non-contact' thermometer), 10 A AC/DC (I would like more, but some sort of current shunt suffices, plus I have a big 50A analouge meter anyway, and a 400A 'Kyoritsu' clamp meter, which i got second hand for about $15). The only thing it doesnt have is a tansistor beta tester, but for that I have an el cheapo $10 multimeter!
The only thing I dont like about it is the fuse for the 10A range is a very expensive, high fault current thing, and its hard to find anywhere that sells it, as I foundout when I tried to measure voltage using the A scale

Features I'd say are a must on any meter: AC/DC voltage upto say 500v, AC/DC current (alot of cheaper meters only go to 10A, and this is usually sufficient), Resistance upto a couple of megohm, L and C is nice, but usually add to cost, continuity 'buzzer' (beeps when a low resistance) is a nice convenience, and hfe tester is nice. And a back-light with a large display is really good to have.

Cheers,
Jesse

rp181

Sun Oct 04 2009, 01:38PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I like having as many things in one instrument as possible, I have this:

It is expensive, but I did not pay for it

It has all the standard functions, plus a infrared thermometer, two thermocouple (type K) inputs, capacitance, inductance, continuity buzzer. This is much larger than most meters, but That really does no bother me.
Also important to look for:
A stand
uses standard batteries. My older cheap meter used small 12v batteries that were expensive.
Removable fuse, the old meter mentioned had a fuse, but it was soldered on.
frequency counter is useful too.

Mads Barnkob

Sun Oct 04 2009, 02:26PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I think that you have left out a few important things that makes multimeters expensive.

Any cheap multimeter will likely not be able to withstand the same surges, voltage spikes etc as a good Fluke can, the cheap ones are more likely to blow up than contain these faults.

The catagories where the meter can be used, I would never use a cheap meter on anything higher than catagory II measurements, simply because its dangerous!

There are numerous testing videos on youtube regarding these issues.

Proud Mary

Sun Oct 04 2009, 02:51PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Here, for the benefit of those not persuaded they should pay ten times more for a Fluke instrument as their first multimeter, is the Toolzone Digital Multimeter which I reviewed favourably above.

I reported incorrectly that it does not have a capicitance range - it does in fact have five ranges from 2n to 20uF, but I'd forgotten about them because I never have cause to use them. (I have a Peak Atlas ESR+ Capitance Analyser for that, which shows both C and ESR)

I have used my humble Toolzone meter extensively over the past 12 months, without disaster or mishap of any kind, and find it very reliable, and the large digits invaluable. For most practical purposes, it is as good as my Thandar bench multimeter, and it has features such as a fairly accurate 200 megohm resistance range and a 20A DC current range which are unusual in budget meters. I use this cheap meter precisely where it might be destroyed by rogue spikes, so as not to risk more costly instruments, but it has carried on, undaunted!

teravolt

Sun Oct 04 2009, 03:35PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

a decent DMM is essential for doing good tesla work. There must be some easily built circuits that can interface with a dmm that might be able to be used to tell things like resonance, field strength, and peak voltages to help the builder. I have found that the oscope is the moast usefull and desired equipment for doing the type of work we do but is unabtailable for some, is there any circuits that can be built with lesser equipment

Bjørn

Sun Oct 04 2009, 05:18PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

When my digital multimeter had a high voltage accident I bought a cheap one at the grocery store as a temporary replacement, it was about half the cost of the one Harry got. It was just as accurate as the old one so no need to replace it. I made a stand for it and a BNC adapter so I could use proper oscilloscope probes on it.

We have some information about multimeters in the wiki

Mads Barnkob

Sun Oct 04 2009, 07:17PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I bought the cheapest LCR meter I could find on ebay from China, its just as precise as capacitance measurements as my Fluke and Elfa meters.

My point about expensive meters is that they are just safer, not necessarily that much better in money/performance ratio.

Steve Conner

Sun Oct 04 2009, 07:46PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I'd say that for general hobby electronics work, all you need is a cheap DMM of the kind Harry describes, and a 20MHz dual trace scope, the kind they use in college labs.

As you get more specialized, there's virtually no limit to the amount of test equipment you can collect. The fun really starts when you're working in the industry and spending someone else's money.

If I could only take one piece of test equipment to a desert island, it would probably be an Avo Model 8.

Proud Mary

Sun Oct 04 2009, 07:57PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steve McConner wrote ...

If I could only take one piece of test equipment to a desert island, it would probably be an Avo Model 8.

Thanks for the heads up on the Avometer Model 8, Steve. It's built like a brick bathroom, is built to Rolls Royce standards, is simple to operate, and the Mk III goes all the way up to 2.5kV ... a ruddy marvellous piece of kit which you can easily pick up on ebay Â£30 or Â£40 in its original leather case in lovely condition if you shop around. I'd wouldn't give mine away for love or money! And if you should be attacked by fierce cannibals, like Robinson Crusoe on his desert island, you can always bash them over the head with it without fear of it being broken before the skulls of the savages!

As for the scope, all I have is a "20MHz for 20 quid" ex-Army Gould double trace, as Steve suggests, and it hasn't yet failed to meet my very simple needs. Even 20MHz - 20 Megacycles - seems frighteningly fast to the Harrysaurus!

I've nowt to do with measuring anything above a couple of MHz, so 20MHz is all the bandwidth I could possibly need.

1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob