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Buying a Multimeter

Theo

By Theo
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Theo Veteran

TheoDonate to Canal World

Posted
Posted

I am certain that someone with much more practical experience than me will be able to point out the important features that I need to consider.

 

I have already found from a previous thread that I need a 0.1V resolution if it is to be useful in determining the charge state of my batteries.

 

TIA

 

Nick

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Gibbo Veteran II

Gibbo

Posted
Posted
I am certain that someone with much more practical experience than me will be able to point out the important features that I need to consider.

 

I have already found from a previous thread that I need a 0.1V resolution if it is to be useful in determining the charge state of my batteries.

 

TIA

 

Nick

 

A considered opinion......

 

Buy a Fluke. Everything else is junk. Nothing comes even close for reliability.

 

Ebay has lots of older models for reasonable money.

 

Gibbo

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Theo Veteran

TheoDonate to Canal World

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A considered opinion......

 

Buy a Fluke. Everything else is junk. Nothing comes even close for reliability.

 

Ebay has lots of older models for reasonable money.

 

Gibbo

 

 

I had a look at Fluke since you have eulogised them in another thread. I was a bit horrified at the price, though. What price do you think I will have to pay for a Fluke?

 

Nick

 

 

One further thing. The specs don't ususally mention the resolution which is a nuisance.

 

Nick

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chris w Veteran II

chris w

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B & Q have a limited range of multimeters, I recentley bought one for myself £20. I find that accuracy is not an issue on the voltage ranges even the cheapest is more than adequate in that respect.

 

 

John, you are totally incorrect in that accuracy is not an issue. It's very important on boats with regard to the battery state.

 

Yesterday, for example, I met up with Mike on "Blackrose" and he asked me that very question in regard to his digital multimeter which looked the business. However, on checking the manual, the accuracy on the DC ranges was quoted as +/-2%. This is OK for a general measurement but is totally useless for checking battery terminal voltage in order to ascertain the state of charge. One needs a meter for this purpose with an accuracy of at least +/-0.5% because a 0.1v difference in terminal voltage equates to approximately a 10% charge difference.

 

So, if you measured for example a battery voltage of 12.4v with a +/-2% meter, the actual reading could be anywhere from 12.65v (100% charge) to 12.15v (50% charge). ie: useless information.

 

You don't have to pay the earth though for a good enough meter. Maplin sells a range (the Uni T range) which have +/-0.5% accuracy and even includes things like temperature measurement, frequency measurement and capacitor measurement plus all the usual stuff for around £25.

 

If you just want to know whether 12v is getting to a particular point, a 12v "screwdriver" tester for £5 or less is much more convenient to use.

 

Chris

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bottle Veteran II

bottle

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I have this one Hilka multi meter on the box it claims an accuracy of + or - 0.5% on the 20 volt range.

 

Testing some rechargeables on the 2v range it gives a reading to one hundreth of a volt the accuracy is the same claimed + or - 0.5%.

 

Now obviously this is only a claim and I cannot varify that it is true.

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anhar Rising Star

anhar

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Posted (edited)

I got one from Clarke for about £7 new a couple years ago. The DC voltage resolution for the 20v range is 10 mv, which is 0.01v, therefore suitable for 12v battery measurement according to the experts here.

 

The claimed accuracy for that range is ±0.5% at a temperature of between 18-28°C.

 

regards

Steve

Edited by anhar
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chris w Veteran II

chris w

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I got one from Clarke for about £7 new a couple years ago. The DC voltage resolution for the 20v range is 10 mv, which is 0.01v, therefore suitable for 12v battery measurement according to the experts here.

 

The claimed accuracy for that range is ±0.5% at a temperature of between 18-28°.

 

regards

Steve

 

For the avoidance of doubt, resolution and accuracy are not the same thing. Resolution tells you the smallest quantity between which the meter can differentiate. Accuracy tells you how "correct" that reading is.

 

Your meter however, looks great in both these respects.

 

Chris

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DHutch Veteran II

DHutchDonate to Canal World

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We have fluke on the boat, and its certainly a good unit, solid and well built, does the job. Doesnt mesure current however.

- However, just for messing about with, i have a bod standard £35 skytronic multimeter, which is good enough for what i use it for, and also has a 10A current mesuring facilty, which is very usefull for what i use it for.

 

 

Daniel

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chris w Veteran II

chris w

Posted
Posted (edited)
I have been adding some replys for a day or two as I am a new member.

 

Which ever meter you buy if you can run to the eacher cost pick a ture RMS type of meter with a good resolution.

 

 

Note that if you are measuring inverters with either a square wave output or a modifed sine wave output that you won't get the correct AC voltage reading on normal RMS AC meters (the vast majority of meters) because of the mathematics involved in the waveform shape. With a true RMS meter you should get a correct reading.

 

Chris

Edited by chris w
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andywatson Rising Star

andywatson

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I got a digital one from ALDI for about £6. I can't say how accurate it is but it seems to work OK , has all the usual functions and it's handy to have as a spare on the boat. Being ALDI they don't have them in all the time but for that sort of money it's a snip.

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chris w Veteran II

chris w

Posted
Posted (edited)
I got a digital one from ALDI for about £6. I can't say how accurate it is but it seems to work OK , has all the usual functions and it's handy to have as a spare on the boat. Being ALDI they don't have them in all the time but for that sort of money it's a snip.

 

If you missed it, please do read my post a few back regarding the importance of meter accuracy with regard to boats. Basically without +/-0.5v accuracy or better on the 20v DC range it's pretty useless other than for a go/no-go test on voltage.

 

Chris

Edited by chris w
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Guest

Guest

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Posted (edited)

I use one of these at work bought from Rapid. +/- 0.3V at 30V DC setting. Very good think it was £20, and has a sort of shockproof case. Certainly gets abused in my hands.

 

Edit: stupid me it is 0.3% 10mV

http://www.rapidonline.com/productinfo.asp...;moduleno=31052

 

DC Voltage

Range Resolution Accuracy* Impedance Overload Protection

326mV 0.1mV 0.5% + 2 10MΩ

3.26V 1mV 0.3% + 2 10MΩ

32.6V 10mV 0.3% + 2 10MΩ 1000V DC/750V AC rms

326V 0.1V 0.3% + 2 >100MΩ

1000V 1V 0.5% + 2 10MΩ

Edited by Guest
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Gibbo Veteran II

Gibbo

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On the issue of accuracy most modern digital multimeters can be calibrated to be within 0.5% but they rarely come from the factory like that. It's not a big job to get it done.

 

Where the "Fluke" brand name scores is very simple. I've been doing this job professionally for almost 25 years. I've owned just about every make and model of multimeter that has ever existed. The 10 or so that I still use are all Fluke and barring one recent purchase are all 10 years old or more. One is over 25 years old. No other meter I have ever owned has survived that long. Most last about 18 months if they're really lucky.

 

You do one little thing wrong with a cheap multimeter and it blows it to hell and back. A fluke just pops a fuse. Get a cheap multimeter, put it on the 10 amp range or an Ohms range and stick it across the mains. You'll see what I mean. It's no good saying "but you're not supposed to do that", it *will* happen one day.

 

The other problem with cheapo meters is they tend to read higher and higher as the battery goes flat. Now that *is* nasty. And it's a typical symptom of just about every sub £30 meter I've ever looked closely at.

 

Even other names that once had respectable reputations such as Beckman now produce crap (under a different name).

 

As someone else said Fluke 70 series meters go for between £40 and £70 on ebay. They are an old design but still one of the best around. The workhorse of most engineers.

 

I remake my statement. Fluke. Everything else is junk.

 

Gibbo

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pearley Veteran

pearley

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Couldn't agree more.As an Autoelectrician I have 3 meters in my van. A Wilkson 0 - 100 amp ammeter for checking charging current, a digital multimeter from RS costing around £70 and a calibrated Fluke that I keep for 'best'. The Fluke is the only one that will accurately measure resistances under 1 ohm.

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Keeping Up Veteran II

Keeping UpDonate to Canal World

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I agree about Flukes (not even taking into account that if one of my designs gives the correct output voltage, it's probably just a fluke). Mine is at least 15 years old, yet it still showed within calibration when I checked it last year even though it's been hot, and cold, and overloaded, and dropped, and generally mistreated in every way except it's never been dropped in the cut - yet.

 

I keep a cheap meter on the boat (two for £5 at Maplins last year, including the 9v battery) and I check it against the Fluke about twice a year. I've just thrown one away because it failed that test, and replaced it with another. I looked at the spec for it, on the box it says "basic accuracy 0.5%" which sounded pretty good. Then I read the leaflet that came with it, where it quotes accuracy as plus or minus "0.5% of range maximum, plus 1.25% of displayed reading, plus 10 displayed digits". So if you're on the 20v scale and it's reading 12.00, the accuracy is within +/- 100mV plus 150mV plus 100mV, which gives +/-350mV, a total spread (ie the possible difference in readings between two identical meters) of 700mV in 12V, nearly 6 percent. On the same battery at the same time, one would say it was 90% charged and one would say it was 20% charged.

 

Allan

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Gibbo Veteran II

Gibbo

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Posted (edited)

This is *the* workhorse of multimeters.....

 

http://cgi.ebay.co.uk/FLUKE-75-MULTIMETER-...1QQcmdZViewItem

 

Very old design but stood the test of time. I've got 4 of them. There are actually several different meters available in the same housing. They are all brilliant and tough as old boots.

 

Beware that some of the early ones (just the model 73 I *think*) are only 3 1/2 digit which means on a 24 volt system they will only display to 0.1 volts

 

That particular one has a few days left and is currently at £10 but is worth about £50 of anyone's money.

 

£40 to £50 spent on that would be money well spent compared to some brand new junk from another manufacturer for the same price.

 

Gibbo

 

Oops. Edited to read 2 1/2 digit

Oops again. Editid to put it right finally.

Edited by Gibbo
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