Bench Multimeter

[Bushbaby]

Hi all and apologies for my long absence !
I have been thinking about buying a bench multimeter as when I do get a chance for work (rare at the moment) its always at a work bench. I'm wondering if i can do better than my old Maplin Precision Gold N56 in terms of functionality. 

Any thoughts?

Best Regards

Rob

[peter scott]

Hi Rob,

You should definitely read through Mark's thread:
http://golbornevintageradio.co.uk/forum/...p?tid=5501

Peter

[Nick]

Mark's thread is indeed excellent, however you stated "Bench Multimeter" which implies a bit more accuracy than a hand-held DMM.

What sort of accuracy/features are you after? And how much are you prepared to pay

[ppppenguin]

For ordinary radio and TV mending any DMM will be more than accurate enough. It's down to features and robustness. Sometimes an analogue meter will be better. The 2 examples I can think of are when the swing of the needle gives you useful information in a way that digits can't. Many DMMs have a bargraph scale that can replicate this capability to some extent. The other is in electrically mucky environments, such as around the line timebase of a TV, where a DMM can give horribly false readings. Better DMMs will be more immune to this problem, experienced users will be more aware that it's happening.

[Terry]

For ordinary radio and TV mending any DMM will be more than accurate enough.

Too accurate sometimes!

Something which never seems to be explained to beginners is such things as tolerances and limitations to measurement accuracy.

For example, equipped with even the most rudimentary DMM, when taking voltage measurements on a old radio where the voltages shown on the service sheet were taken with an AVO Mk 7, many, possibly the majority, of the voltages on a set in perfect working order will be much higher than shown.

To a lesser extent there will still be errors in the voltages originally taken on an AVO Mk 8.

We might read something like "I changed R15 because its value had dropped from 1k to 908 ohms."  Whilst an analogue meter cannot provide a reading of such high precision, it will give a reasonably accurate reading in this case but the novice is overlooking the note at the bottom of the component listing that says "All resistor values ±20% unless otherwise stated", so it could have been any value from 800 to 1200 ohms from the day it was fitted.

Perhaps not directly relevant to this thread but should we have somewhere for useful information like this? I'm sure I posted a diagram I created showing tolerance limits for different ranges of resistor, E6 (20%),E12 (10%), & E24 (5%) but it must be buried in the middle of another thread and I haven't a clue where to find it! (I do still have the original, though.)

[Mark Hennessy]

Another reason for wanting a bench multimeter is the convenience of mains operation and the thing always being where you left it! Plus, some have nice, bright LED or VFD displays, rather than LCDs, which can be a bit murky and have viewing angle restrictions.

There are plenty of bench multimeters with hand-held specs. The Fluke 45 is one I'd recommend - these can be quite cheap (mine was about £80), and have a nice crisp VFD display. These displays are prone to fading with age, so inspect the pictures carefully before buying. In terms of specification, it's similar to the top of the range hand-held Flukes, which is arguably rather more than is needed for most service work, but it doesn't hurt to have extra precision if you know how to interpret the results.

It's also worth saying that most bench multimeters allow you to change the displayed resolution. The Fluke 45 has 3 modes - fast, medium and slow - and the more digits you need, the longer it takes to make the measurement. Even on slow, it's still as fast as a normal multimeter.

Another meter worth investigating s/h is the Fluke 8050A. Make sure you get one with a good LCD, as they are prone to failure at this age. This is a tiny little meter, but still has plenty of useful features. It is manual ranging though. Some have internal NiCad batteries (which need to be present and in good condition for the unit to work correctly); others are mains only.

New, the UNI-T UT804 might be worth investigating. It costs around £200, and appears to have a lot of functionality for the price. I've never seen it in the flesh, but will say that the quality of UNI-T stuff appears to have improved in recent times. The UT803 is even cheaper, but comparing them, I'd say that it's probably worth going for the 804 if I had to pick between them.

In short, I'm sure you can improve on the old Maplin meter. You might not need to go for a bench multimeter specifically to get what you're after - although you might still fancy one for various reasons - perhaps let us know a bit more about what you have in mind...

[ppppenguin]

While Mark's points are all valid I don't feel any need for a bench DMM. My old Fluke 87 and various cheaper DMMs do everything I need of them. I admit I'm doing much more desing work than repair but I don't see that it would make much difference except that my requirements for accuracy are often greater.

The tool I really wouldn't be without is a 'scope. For my design work it is utterly essential and I need capabilities well beyond low cost instruments. It is incredibly useful for service work, even if old timers sometimes pooh pooh the idea. "Real (service)men don't need scopes" For repair and restoration a simple 20MHz dual trace instrument is more than adequate. Secondhand Hamegs etc are available at very modest prices.

[Refugee]

I have found that bench meters tend to have some capacitive coupling to there earthed chassis so you have to make sure the connections are good or else they can float close to the expected reading causing the odd mistake.
I have got a Fluke 8800A and its terminal resistance is 100M so the leads pick up everything if they are not connected securely but then it is very useful for high impedance work.

[BusyBee]

For me it isn't anything too specific, but a variation for the job I need to do. I use an old Avo 8 for current measurement. A cheap digital meter for general use, or my Fluke 77 if I want to be more certain, and my Oscilloscope all the time. For 98% of things the cheap digital meter is good enough.

Tracy

[Diabolical Artificer]

I like my Fluke 8600A for the odd time I want to measure something more accurately and it can measure up top 20meg rather than 10m on my usual DMM as well as 1200v. At £25 inc postage it was a snip.

Andy.