Cheap auto-ranging multimeter

[Pugglt Auld Jock]

Due largely to ignorance on my part I've killed off a few multimeters as I've journeyed along the road to electronic/electrical enlightenment. I must be getting better at using them because I haven't damaged one in quite a while and my present one is now suffering from selection problems with it's main function selecting rotary switch. Makes a change to be wearing one out instead of chucking the smoking remains in the bucket!

With my incompetence always in mind, I've always bought "cheap and cheerful" offerings, This is my present one:



It's now unreliable because sometimes when you twist the selector to a particular setting it just fails to establish connection and you have to twist the switch a little to either side to get the screen to display. Probably dirty connections I'd guess? So I've been thinking of dismantling it and trying to clean it up when I came across this whilst doing the fortnightly shop in Lidl this morning:



At just under £10 I had to have one. It's auto-ranging too, a feature I've never previously had. Seems to have plenty of functions within ranges I'll find useful and an audible continuity checker too:



I don't know what the square wave signal generator would be used for though - probably something to clever for a simple mind like mine!

I see they've got a digital clamp meter next week for 12.99, don't know if I'll be able to resist!

 

[Cheest]

Broke a few but never let the smoke out of one. Square wave is above my pay grade.

I have a lot multi meters because I'd be out with a trainee or a sales dweeb trouble shooting their latest problem that became mine. I would invariably ask, "Where's yer meter?" and get "Huh?" as the usual response. So, I'd go buy one and give it to them. That ended a couple years ago when I went out and asked again for the meter I just bought a week ago and they'd left it home.

Before anyone asks me why I didn't have my meter with me, trainees and sales dweebs are supposed to have one. When I get there it usually has a dead battery, is missing its' leads, or is broken. Now, if I end up buying one in the field, it comes home with me.

The only time I had to buy one for myself in the field was when I was working in Mexico. The one I brought with didn't have a broad enough range in the function I needed for trouble shooting, so the rep in Mexico City took me to an electronics store. I thought I'd died and went to heaven. Found the meter I needed and it cost less than the one I brought with me. I gave the one I had to one of the mechanics that had been helping me.

 

[Pugglt Auld Jock]

Oh, there y'go, - The Function Generator. The 1 kHz square wave signal generated is used, among other things, for checking and repairs on headphones, amplifiers and other electronic devices and components. - Straight word for word from the manual! So never a truer word, if in doubt read the manual! Now I know what it does but still no idea how to use that function. Doubt if I'll ever explore it?

 

[PuntoHowTo]

These days I have a very Cheap Maplin "UNI-T" hand held multimeter, not very clever, just a big dial to select your range. All the usual stuff that you'll never use diode testing, transistor tester, etc. But its been very handy for about 6-7 years now if not more, I think it cost me about £10 - 15 but it doesn't have a square wave generator. I suppose its not a bad thing to have if you want to check a speaker is working, just press it on the speaker terminals and you should get a 1khz tone from the speaker?

The LIDL parkside stuff isn't bad at all, and I'd definitely be tempted to get a cheap clamp meter.

Years ago I used to work for Fluke, the people most electrical engineers would think of if you talked about multimeters. Because all the hand held stuff was made in China, we reserved only the fancy stuff that could not be trusted to china.
I used to work on their 8508A Which was a bench multimeter that had ridiculous accuracy, and a ridiculously matching price tag, something like £5k a unit. Now I let the smoke out of many of those and also fixed them again. I also used to work on the 9100 Calibrator, which was another Computer sized piece of equipment which you could use to calibrate something like a hand held multimeter.

The reason I tend to stick to the most basic meter is that worst case you select the wrong range and pop an internal fuse, where as some auto ranging kit can be damaged by putting it on too high a voltage/current before it can adapt.

Also I learned that 1000V really hurts if you're half asleep and not looking where you put your fingers, definitely a great hang over cure though

 

[Pugglt Auld Jock]

regarding "blowing up" meters my most shameful moment was years ago when I managed to ruin a really good quality analog AVO meter. It wasn't the typical "brick" like device we older chaps would probably recognize, it was a "Multi minor": http://www.richardsradios.co.uk/multiminor.html Still a very good meter and probably the highest quality one I'd ever owned - I was given it by an old chap who had been retired for some time and completely given up on things due to ill health.

Around that time I was given a really old compressor:



Which was not compressing. The fix was simple, it just had a broken return spring in one of the flap valves but I also decided to up it's output by fitting a more powerful motor and larger motor pulley so the pump would spin faster. Made brackets etc and got it all ready to go but when I switched the power on the motor just "growled" but didn't rotate. Being young, ignorant, full of self confidence and knowing absolutely nothing about AC electric motors I decided to have a go at finding out what was wrong with it so I set the meter to Ohms scale - cringe - and started continuity checking - major error! - Not knowing that it used a sodding great capacitor which was now nicely charged up because I'd been trying to run the motor, the poor thing gave a subdued "POP" and gave off that dreaded hot "fishy" smell which spells doom to all things electrical and never worked again on any of the scales. I did dismantle it thinking it might just be a fuse but there was evidence of burning inside so I gave up and bought my first digital multimeter. To this day I feel a sense of guilt that I ruined this lovely meter which the nice old chap gifted me. If he was anything like I am with my tools, He'd probably treasured it and cared for it for years and in one moment of youthful ignorance I'd wrecked it! I try to convince myself that it probably wouldn't be of much use on modern electronics - and might even damage them - doesn't stop the feelings of guilt though!

On reflection I'm very lucky not to have "wrecked" myself! - it was a pretty "meaty" capacitor!

 

[DaveMcT]

I might get one of those. My cheapy multimeter must be at least 15 years old. Still working but for how long?

Saying that the numerous cheap vernier micrometers Ive bought since then have almost always gone titsup pretty quickly.

 

[s130]

Safety Advice.

When working on anything over 50V or capable of delivering more than 10A ALWAYS wear safety glass. Ideally you should wear them because "you never know for sure" what one may encounter.

I can profess to be a retired professional electrical engineer and have designed everything from electronic circuits up to 300kV 10kW kit.

I've been zapped twice in my working life but the error I've made twice and fear the most is stupid use of a multimeter on house electrics.

This has been when for stupid reason I've had the meter on 10A+ current range and tried to measure voltage. The resultant "SPLASH" / "FLASH" / "POP" and flying molten metal can easily take out or seriously damage an eye.

What many people don't realise is that many multimeter's with a 10A+ range are NOT fused. Instead they use a calibrated series shunt through which the current to be measured is passed through and the meter actually measures the voltage drop (mV or uV) across the series shunt.

So when you get it wrong you are using your meter leads to completely short circuit the supply WITH NO CURRENT LIMIT/FUSE. In a house on a ring main then we are talking a lot of energy all dedicated to blowing away all the metal and copper at the points of contact. With meter leads then the points of contact a pointed with minimal surface area so adding to hazard.

 

[DaveMcT]

The probe points ARE the limiting factor hence all the molten metal.

 

[s130]

An interesting side channel is that in my professional career I've never had any issue. There seems to be that magical/professional/other factor that kicks in. But when you get home, relax, "yes I know what I'm doing", is when things go bad!

 

[Pugglt Auld Jock]

Probably I shouldn't comment further because it's been quite some time since I had "un incident" and I don't want to jinx it!