Help on buying a multimeter

[mhennessy]

Interesting - that's obviously not a feature of the cloned ICL7106 that is usually found in these. None of the adverts I've looked at recently list auto power-off as a feature, but I have just found a listing on Alibaba.com that does. That one differentiates itself from the others by having a sliding power switch, as opposed to the usual "off" position on the rotary function switch. Is that the same for your recent samples?

[HamishBoxer]

My advice, buy the one you first spotted and it will serve your requirements well.

Despite not being short of a meter or few I am very tempted myself at the price and I just love test gear!

[paulsherwin]

Mark, no, externally they are bog standard with the usual rotating switch. Maybe they aren't truly auto off but switch to an ultra low power mode after a while. I can't remember if the display blanks.

Just about any meter mentioned in this thread will satisfy the OP's initial requirements. It's really not worth anguishing over. If you buy a cheap meter now and subsequently feel you need a higher quality instrument, then buy a better one then. It's always useful to have spare meters around.

[The Philpott]

Tempted by the toolzone one David has featured, especially at that price.

The only exception (that I can think of) to the argument for (exclusively) auto-ranging DMM's is if your hobby extends to the aforementioned shadowy world of acquiring test equipment. I have known a meter on its resistance range to start at the low end before stepping up to the higher ranges; if at the time you are using it to interrogate an analogue test meter this can pulse a damaging amount of current through the movement of the latter before it settles down.

[David G4EBT]

Originally Posted by mhennessy

None of the adverts I've looked at recently list auto power-off as a feature.

The Toolzone large digit meter I mentioned in post #22 has auto shut off, as I stated in the post.

The 200mA range is also on a separate fused socket from the Amps range.

I can't actually think of any features or benefits that it doesn't have which would be of benefit to anyone restoring vintage radios, beginner or otherwise.

As with most meters, if you poke 240V into it while on the Ohms range, you'd be looking for another meter, but anyone who does that is coming close to being a contender for the Darwin Awards and needs to consider their own safety.

As I stated, the Toolzone Large Digit meter can presently be bought for £11.00 post free on Amazon.

https://www.amazon.co.uk/Toolzone-Di.../dp/B002NH2SDU

A hard act to follow.

(I don't have shares in the company!).

[TonyDuell]

Originally Posted by 60 oldjohn

If it has not been mentioned already, I would put "Auto Off" high on the list of features. So easy to miss switching off when leaving the shack.

Odd... I have a cheap Uni-T multimeter, and the first thing I did to it was work out how the auto-off operated and solder a link between emitter and collector of the appropriate transistor on the PCB.

The reason is that the mode I use most is the continuity beeper. If I am tracing a connection, say to the pins of an IC and get no beep as I stroke the probe along the pins, I do not want to have to worry if it's because the connection genuinely doesn't go there or because the darn meter has turned itself off again. Having to replace the PP3 battery because I left it on is cheaper then me going (in)sane from the above. In any case I have left it on overnight occasionally and the battery did not go flat.

Related to that, I find a fast-responding continuity beeper to be essential. Cheaper meters tend to be better than expensive ones for this. In general the contiuity beeper is also the diode test mode. The meter passes a constant current through the probes and displays the voltage between them. Cheap meters use an analogue comparator to trigger the beeper if the voltage is low enough (meaning a low enough resistance betwen the probles), which is fast, albeit not too accurate as to what resistance actually causes the beep. More expensive ones use a digital comparison on the output of the ADC and are noticeably slower. I've rejected at least one Fluke for this.

For the sort of work I do (and I suspect most repairs discussed here) you do not need a very accurate meter. If you measure an HT line as 245V and the service manuals says it should be 250V (or even 260V) it's likely that's not the problem. If you measure it as 10V then it is. Any DMM will be accurate enough for that sort of work.

And as for safety. I would happily use a cheap DMM to measure the CRT electrode voltages (a few hundred volts) in, say, a monitor I was repairing. Even if the insulation breaks down there will not be enough current flowing to do serious damage to me. The meter would not explode. But I would not poke about inside my consumer unit with a cheap meter.

[mhennessy]

Originally Posted by David G4EBT

The Toolzone large digit meter I mentioned in post #22 has auto shut off, as I stated in the post.

That sub-conversation was specifically about the ubiquitous DT-830 meters, not your Toolzone

But come to think of it, I should mention the Uni-T UT61E, which is a ~£30 meter that is often recommended because it comes with a simple PC interface that can be used for data logging. I've done a full review on my site. That is a meter that does not have auto power-off. That's quite deliberate, because of the logging function, but it's worth highlighting as an exception to the rule.

I was surprised that there's apparently no way of manually over-riding this, as the opposite is usually true for meters that do auto power-off (usually by holding down a button while powering up).

Power consumption of that meter is only 1.3-2.5mA, so it's hardly a big issue.

[mhennessy]

Originally Posted by David G4EBT

As with most meters, if you poke 240V into it while on the Ohms range, you'd be looking for another meter, but anyone who does that is coming close to being a contender for the Darwin Awards and needs to consider their own safety.

Actually, you might be surprised. Most meters made today will survive 240V when in all modes other than current - and by "survive", I mean that they don't just not blow up in your face, but that they will continue to work perfectly as if nothing happened. Accidents happen to the best of us.

[The Philpott]

The only thing that I own that has auto-power off currently, is the casio calculator. I fall back on the APO facility on this as in my experience many of the little sliding switches wear out before anything else does- this particular switch has been in the 'on' position since 1985 for this reason- an identical calculator purchased at the same time by my mother which has religiously been switched on and off manually at every use, has the iffy switch disease!

[Boulevardier]

"The reason is that the mode I use most is the continuity beeper."

I'd echo that, but why is it that most of the DMMs I've come across have barely audible beeps for continuity test? This is a real pain!

Mike

[Refugee]

If diode and continuity are both on the same setting they make you jump when you get an unexpected short circuit one.

[Radio Wrangler]

No multimeter does everything.
You can't even buy one with any confidence that it will do almost all of what you'll need because you can't predict all you're going to do.

Pick something mainstream, fairly well made, with the usual ranges and features and you'll be OK. Just so long as you dodge the tat and dodge any weird specialist things, you'll be so close to OK it makes no difference.

Learn what not to attempt with it, learn when to be cautious, and you'll be safe.

This is a bottomless question which can be agonised over ad infinitum. Sometimes a good answer really is to flip a coin.

Stockton's first law: The cost of making a decision is inversely proportional to the benefit of making the right decision.

David

[Phil G4SPZ]

Originally Posted by Boulevardier

"The reason is that the mode I use most is the continuity beeper."

I'd echo that, but why is it that most of the DMMs I've come across have barely audible beeps for continuity test? This is a real pain!

Mike

Isn't using a DMM as a simple continuity beeper rather akin to using a sledgehammer to crack a nut? I have a couple of analogue meters which incorporate proper electromechanical buzzers that are audible in the next room! A 1970s Japanese TMK Model 500, and a 1940s era Taylor Model 88A.

[Oldcodger]

I always remember the words of my old GPO TO mentor as an apprentice, telling me that any good engineer would check the range on his meter before testing. The problem with auto ranging meters is that you tend to forget this mantra.
I'm most probably in the professional ( or ex professional ) user bracket. But I've been using meters for over 50 years. Once upon a time, the only reliable way to test a semiconductor was using something like an Avo on the ohms range, testing between the junctions. I remember a discussion we had at MSDS on junction testing, which went- polarity one way - open circuit. Leads other way , half scale, on ohms, and junction is ok. At that time, Digital meters gave odd results, but these days the diode range is usefull.
For transistor circuits ,and voltages up to about 50v, then most meter leads are adequate. BUT for work on valve stuff, then decent leads are needed. It's not really a problem on equipment where an isolated supply is used, but for any voltages where the voltages are WRT mains earth, then even if working with one lead tied to ground, any failure of the insulation on the lead connected to the high volts side could lead at least to a nasty tingle. Fortunately, one test on valve equipment ( where the chassis has been proved isolated from mains), is to check the cathode voltage ,against that recorded on the circuit diagram.
Fortunately, these days, most DIGITAL meters( evn the cheap ones) have an input resistance ( quoted in older analogue meters as KOHM/VOLT, with 20 KOhm/volt being a god example) in excess of 1Mohm/volt.
Meter leads- if you have probes proven safe above any voltage you wish to test, then one old trick I've used is to make leads from mains cable ,rated of course higher than any current you may wish to measure.

[Boulevardier]

"Isn't using a DMM as a simple continuity beeper rather akin to using a sledgehammer to crack a nut?"

Not really, if I have a DMM on the bench and already fitted with leads/probes, then I should be able to use it to test continuity, rather than fish out yet another test instrument to add to the clutter. Also, if you've got probes delicately balanced using both hands to test continuity of a thin pcb track, then you don't want to be looking elsewhere on the bench to see a continuity indication, you want to hear it. If they're going to include a sounding device then why not make it easily audible?

[IanBland]

My two pennorth-

I've got three. The most expensive came from Farnell, it's a Tenma (I think they're Uni-Ts rebadged or summat) 72-7732A. It's auto-ranging and Class IV which means you can use it standing in a puddle outdoors or whatnot. Next down is a bog-standard Draper job I bought in Ryness donkeys years ago. It's Class II I think which means you should only use it on 12V while standing on a rubber mat with another person nearby to poke you with a bit of wood, but I used it for a huge amount of maintenance work during my time doing that and while the probes aren't the best shrouded in the world, it worked a treat.

Third on the menu is my elderly analogue Maplin Precision Gold (with J-Fet inputs!) which about a year ago I got round to repairing, having blown the lowest ohms range back in the 80s.

I've tested the Draper against the Tenma and its voltage range so long as you're on something like RMS was giving surprisingly close readings. I must admit I use it most of the time particularly for continuity as it has an instant beep (the Tenma sits and thinks about it for a frustrating fraction of a second too long). You need that when you might only get a moment's beep (e.g. if you're trying to invoke a short in something you think might be intermittently shorting). And during my time engineering I used it routinely on 415V (sorry, 400 now isn't it?) without mishap.

(My other main bit of test gear was a volt stick. Gawd knows how we managed before volt sticks were invented.)

So, the Tenma has some useful extra ranges compared to the Draper- I find the frequency range surprisingly useful just to see if there's a signal there or not) and it's true RMS, and it looks the biz. But the Draper (according to the internet much the same is selling in the low 20s of GBPs currently) does most of what one needs from a multimeter most of the time.

The Maplin is nice when I want to watch a needle twitch./.>

[Craig Sawyers]

Originally Posted by Boulevardier

"The reason is that the mode I use most is the continuity beeper."

I'd echo that, but why is it that most of the DMMs I've come across have barely audible beeps for continuity test? This is a real pain!

Mike

I bought one of the chunky green continuity testers that RS used to sell maybe ten years ago - 424-002. Great purchase. Nice and loud. By listening to the frequency and loudness of the beep you can get an idea of the resistance between the terminals.

Dead simple - a 9V battery and a speaker which must have an oscillator inside it.

Blimey - the last one that sold on the auction site went for over fifty quid!

Craig

[Station X]

Originally Posted by Oldcodger

I always remember the words of my old GPO TO (Technical Officer) mentor as an apprentice, telling me that any good engineer would check the range on his meter before testing. The problem with auto ranging meters is that you tend to forget this mantra.

Why would you need to check the range of an auto ranging meter? Surely only the function ie Volts, Amps or Ohms matters?

[The Philpott]

I set about a basic calibration on my cheapie hand-held DMM's, and was not entirely surprised to see that it was possible to trim the 20vDC range- but this threw the 2vDC range out by an unacceptable amount. This leaves you with the choice of which range you are going to use the most..or trim both so they are 'out' by a similar amount! This, i assume, is down to the main chip.

Having spoken about the DT3266L previously, i had an incident yesterday where the selector managed to sit in a no man's land between 600vdc and 2kohm ranges, which then produced nonsense readings on checking resistance.

[mhennessy]

No, it won't be the main chip - it'll be the divider resistors.

The better meters from the likes of Fluke et al use precision thick-film divider networks that have been laser-trimmed to give the required ratios, while being tolerant to overloads and very stable with time. These resistor networks are expensive, but are one of the real benefits you get with a name-brand multimeter.

Meanwhile, the current crop of cheap multimeters that I recommend obviously don't use those - but instead they use software calibration. Having built the multimeter, the errors caused by the divider resistors (usually surface-mount MELF resistors) in each range can be trimmed out. That's why the meters I've measured are much more accurate than their basic specification suggests - they generally agree with my Flukes to within a couple of counts. It'll be interesting to see how they hold their calibration long-term.

Of course, modern Flukes have software calibration in addition to the expensive networks. This means that again, the specifications are quite conservative because they are much more accurate in practice than the spec suggests.

There is a downside - naturally - with software calibration: it's often harder (sometimes impossible) to perform a DIY calibration; it just depends if the required information is available (the cheap meters using the DTM0660 chipsets can be done). However, such meters tend to hold their calibration for much longer than the types with pre-set resistors (which can be knocked, and might not be as stable as convention resistors).

There's a bit more information about these networks here: https://www.eevblog.com/forum/blog/e...stor-networks/