Old or New multimeter?

[ms660]

When I was in the R&TV servicing trade there was no digital meter that I ever saw, I serviced thousands of units including radios, TV's, record players, tape recorders, Tuner/amplifier systems etc. etc. using either an AVO 8 or Multi-Minor or equivalent.

Since I joined this forum I've noticed that a DMM seems to baffle a lot of newbies/beginners simply because they can't see where zero Ohms is....

Some folks can have all the top kit but be next to useless when it comes to fast analysis and servicing.

At the end of the day it's the nouse that counts.

My advice to those with almost no experience is to learn with an analogue meter, you'll soon be reading and understanding the circuit no problem then get a DMM if you think you're ready for it.

Lawrence.

[Bazz4CQJ]

Originally Posted by G6Tanuki

Don't chase your tail when 'odd readings' could be caused either by the actual problem or by inadequacies in your 50-year-old test-gear!

That is very true, but it does not exclude the use of analogue meters where they can offer some advantage. I must admit that that I have pensioned off a number of older analogue meters, and that my Avo8 usually sits in the cupboard.

I have a useful Sanwa analogue multimeter which is getting on, though probably younger than my Avo8. Also in frequent use is the cheap but useful analogue meter (20kohm/V, so just as specified on many old service sheets) sold by Maplin just before they folded, which was bought by many on here. That warrants a place on the bench if only for its battery test ranges (loaded), and for the price, was a good buy.

I don't know whether good quality analogue multimeters can still be found? (Edit Post Script; a quick look on eBay suggests that quality analogue multimeters may be history)

B

[David G4EBT]

Originally Posted by ms660

So far as the loading presented to the circuit by the AVO 7 is concerned it can be regarded as 500 Ohms per Volt not 1,000 Ohms per Volt for the range selected, this means that in this instance it will be 5k not 10k that's presented to the circuit when the 10 Volt range is selected as you will see in the schematic on the web page linked to below:

http://www.richardsradios.co.uk/avo7.html

Lawrence.

Thanks for reading my post Lawrence, and for your comments.

Even worse then.

So in the example I gave of a potential divider of two 100k resistors across 12V, with the meter's 5k in parallel with R2 (100K) the resistance across R2 would drop to 4.76K. Hence 12V x 4.76k/104.76k, V2 on an AVO 7 on the 10V range would display 0.54V - not 6V.

If anyone doubts this, it's easy enough to put it to the test. Connect two 100k resistors in series and apply 12V across them, then connect an AVO 7 (or in the first example, and AVO 8), and check the voltage with the meter on the 10V range, with the prods across R2.

Ohm's Law had been around since 1827 so it's well proven.

[DrStrangelove]

One of the first year lab experiments where I worked latterly was a potential divider of two 470k resistors driven from a 10V supply.

Then the Esteemed Customer was required to measure the voltage between ground and the junction of the resistors with a) the DVM in the Metex 9150 and b) an AVO 8.

It sorted the interested out from the uninterested quite successfully.

[cmjones01]

Reading this thread has made me realise that the meter I think of as my "new, modern" multimeter is at least 24 years old. It's an HP 34401A 6.5 digit bench multimeter and it actually says "Hewlett Packard" on the front rather than "Agilent". The brand changed in 1999! All the other meters I use daily are older than that.

I design electronics for a living and, like David said above, I reach for the (analogue) scope first to give me a quick snapshot of what's going on in a circuit. Absolute accuracy doesn't really matter, but the sheer amount of information the scope will show me in a few seconds is really valuable.

Multimeters are still handy though. Most frequently used is my Fluke 12 which dates from the late 1980s. It's really an electrician's meter, I think, but it's great for fault-finding, with a good continuity buzzer/diode test and a really handy "V Chek" feature in which the continuity test will automatically switch to displaying a voltage if it detects one. I use this meter a lot for seeing whether the incredibly tiny surface mount rework I've just done has any short circuits in it or not.

Second most used is the aforementioned HP 34401A. This is a pretty high-spec device, but its most useful feature is that, as a benchtop multimeter, I can always see where it is. That's not the case for portable instruments! It does have a lot of features which are just the ticket for certain jobs. The very high resolution helped me find a leaky cell in a very large battery - seeing the microvolts ticking down showed which cell was at fault. The high sensitivity is useful for precisely measuring voltage drops across bits of high-current electronics, and even seeing where the current is flowing in PCB tracks. It has useful dB modes too, and the display is easy to read (or it would be if it wasn't quite so high-mileage).

I always keep an Avo 8 around as well. It can be useful for seeing trends or peaking slow-moving signals for which the scope isn't ideal, or is perhaps busy with other things. It's also just nice to use from time to time - I use it for testing batteries in the childrens' toys, and they can relate to the moving pointer better than to flickering digits.

None of these meters have ever been near any kind of formal calibration in my ownership, at least. I have no requirement for that sort of traceability so the cost isn't justified. The meters all agree with each other within their specified accuracy and they never change (though the Fluke 12 does over-read when the low battery warning comes on, but that's easy to spot) so I don't worry about it.

In conclusion, it doesn't matter how old or new the meter is. Different ones have strengths and weaknesses for different jobs, and though I've got various ones built between 1965 and 1999 they're all relevant.

Chris

[ms660]

Originally Posted by David G4EBT

Thanks for reading my post Lawrence, and for your comments.

No problem, I've pointed out the error you've made to you before about the loading resistance of the AVO 7, but you keep making the same mistake.

Just sayin'

Lawrence.

[David G4EBT]

Originally Posted by ms660

Thanks for reading my post Lawrence, and for your comments.

No problem, I've pointed out the error you've made to you before about the loading resistance of the AVO 7, but you keep making the same mistake.

Just sayin'

Lawrence.[/QUOTE]

No worries Lawrence.

I guess I'm a recidivist.

Were it not for you putting me back on the straight and narrow, I might develop delusions of adequacy.

As it is, I fear that I'm living proof of the 'Peter Principle' and have reached my 'level of respective incompetence':

https://en.wikipedia.org/wiki/Peter_principle

I'll try harder.

[pmmunro]

David,

You may not be perfect, but then few of us are which you do well to remind us with your pleasant manner. Your informative and useful contributions to the forum are still much appreciated.

PMM

[Superscope]

Originally Posted by pmmunro

David,

You may not be perfect, but then few of us are which you do well to remind us with your pleasant manner. Your informative and useful contributions to the forum are still much appreciated.

PMM

Seconded!
We all make mistakes, like the Dalek said crawling off the Dustbin!
I make enough of them!

In order to keep this post on Topic, I also agree with the general consensus of opinion
to the original question.
Both Analogue and Digital Multimeters have their own important uses.

I use DMM's everyday, and use Classic Avo's less so, but even the Avo's get a regular airing.

I find Avo's very useful for monitoring Charge Current and Voltage of Batteries and Battery Banks.
Not having to worry about the Meters Batteries going Flat and not having the right spare handy,
especially when the monitoring is continuous and over many Hours.

An important point was made earlier though, that high quality Analogue Meters are no longer
easily available new or even made.

So now is probably good time to pick up a quality secondhand one, whilst they are
still easily and cheaply available.



Ian

[DrStrangelove]

Aye, AVO 8s haven't been the same since they took the 2.5kV or 3kV measurement facility away.

I stacked 3 in series to measure the output of an ionised air generator thingie* in the absence of a 25kV probe meter (which was at home).

*One of those thingies touted as reducing allergies & such like by making pollen & dust stick to the walls or whatever rather than inflicting themselves on me.

[ms660]

Regarding the AVO 7's loading effect, reading the voltage measurement section on page 11 of the instruction manual, you can see that the phrase "corresponding to 1,000 ohms per volt" is mentioned, that could be one reason why some say it's a 1,000 OPV meter and do the loading resistance calculations according to that.

The explanation as to what the divide by two button in the circuit does when it's pressed is on page 11 of the manual along with the circuit arrangements in Fig's 1 & 2 on that page.

http://www.richardsradios.co.uk/AVO/...structions.pdf

Lawrence.

[pmmunro]

Originally Posted by Superscope

There are some creditable analogue multimeters still available such as these:

https://www.gmc-instruments.de/en/pr...g-multimeters/

https://catalog.chauvin-arnoux.co.uk...5001-3569.html

Chauvin Aenaux even make a hybrid analogue/digital multimeter

https://catalog.chauvin-arnoux.co.uk...5011-3572.html

Both RS and Farnell,and very possibly several others, list a wide choice. Prices range from a bit more than £100 to over £500.

"AVO 8s haven't been the same since they took the 2.5kV or 3kV measurement facility away".

An AVO staff member told me that one of the reasons that the 3 kV ranges were deleted on the Model8 Mk 6 and 7 was the cost of precision multiplier resistors for these voltages and also the difficulty in meeting safety standards. It was also easier for the redesign of the of the internal circuitry, the change from flexible to rigid printed circuits without these high voltage ranges.

Latterly, there was also the problem in obtaining the sprung jewel screws.

As the price asked for the last of these Avometers was around £900, they had certainly become a premium priced instrument possibly bought only to meet military and similar test specifications.

The hazards of the high voltage Avometer ranges would possibly have been acceptable for well-trained Services personal, but these point are a whole new argument!

The "1000-ohm per volt" claim for the Model 7 was a prominent marketing feature when it was first introduced and could be justified by the fact it was correct, at least in part.

Making a robust, dependable precision analogue meter movement is expensive, especially compared to an expendable digital meter with a claimed accuracy of better than 1%, but it's worth reflecting on why these cost less than the price of a single fuse for a professional grade meter.

PMM

[emeritus]

A couple of decades ago there was an article in, I think, the old IEE journal "Electronics & Power" with a title something like "Precise, But Wrong" where the author recounted some of his troubleshooting experiences. One was a complaint from a customer who had bought a dozen or so precision voltmeters and complained that, when checked against their voltage reference standard, they were all out of spec. When he went in person to investigate, he found that, to save time, all the instruments had been connected to the standard in parallel, thereby lowering the resistance presented to the standard. When connected one at a time, all the instruments were in spec.

[Bazz4CQJ]

Originally Posted by pmmunro

Both RS and Farnell,and very possibly several others, list a wide choice. Prices range from a bit more than £100 to over £500.
PMM

Yes, I think we are talking at least £200 for anything worthwhile and that is a very fine reason why I will now show some extra respect to the analogue meters I already have .

B

[Roger Ramjet]

I have very fond memories of my old TMK multimeter from work in the mid 70's. I had to purchase it from the alarm company I worked for .... it was about £15.00 which was deducted from my wages at £1 per week. If it broke, the company would arrange for repair FOC.

Best range was the 10 DC Amps which was useful for load testing the old carbon zinc batteries, especially the 1.5V flag cells.... anything reading below 3 amps would not last until the next quarterly inspection so was replaced.

It also had a rage for testing AC Ripple which was useful for testing PSU's.


Rog

[G6Tanuki]

The one place I am happy to still use an analog meter is when doing RF alignment; it's much easier to diddle a trimmer/core for a peak or a dip as appropriate when watching a needle moving across a scale than trying to do the same while watching the last digit on a numeric display.

My current analog meter is a 1970s "Taylor" brand taut-band multimeter [30KOhms/volt] bought new, which must have seen at least 500 Pye Westminsters/Vanguards/Motafones etc get aligned over the years.

[pmmunro]

Originally Posted by emeritus

A couple of decades ago there was an article in, I think, the old IEE journal "Electronics & Power" with a title something like "Precise, But Wrong" where the author recounted some of his troubleshooting experiences. One was a complaint from a customer who had bought a dozen or so precision voltmeters and complained that, when checked against their voltage reference standard, they were all out of spec. When he went in person to investigate, he found that, to save time, all the instruments had been connected to the standard in parallel, thereby lowering the resistance presented to the standard. When connected one at a time, all the instruments were in spec.

This is another good example of why it is important to know what you're measuring and to understand the technique used.

The basic principle that it is impossible to measure something without disturbing the measured quantity is a good guide. It follows that it's important to know if the disturbance is significant.

PMM

[ms660]

Here's classic old school training film showing analogue displays in both time and current, start at 12:36 in to get the jist:

https://www.youtube.com/watch?v=u__omOnnwis

Lawrence.

[lesmw0sec]

Originally Posted by emeritus

A couple of decades ago there was an article in, I think, the old IEE journal "Electronics & Power" with a title something like "Precise, But Wrong" where the author recounted some of his troubleshooting experiences. One was a complaint from a customer who had bought a dozen or so precision voltmeters and complained that, when checked against their voltage reference standard, they were all out of spec. When he went in person to investigate, he found that, to save time, all the instruments had been connected to the standard in parallel, thereby lowering the resistance presented to the standard. When connected one at a time, all the instruments were in spec.

That reminds me of a time when we were experiencing periods of low mains voltage. The chap arrived from the electricity board and poo-poohed the reading on my AVO 8 - leaving to fetch his expensive dynamometer instrument. Connecting the same, there was absoultely no difference in the reading between the two, and as we watched, the mains sagged to 190V. He went off muttering about hot bus-bars...

[Bazz4CQJ]

I see that the inexpensive analogue meter sold by Maplin is still around (eBay) described as the Proskit MT2017 (spec attached) and priced at £33, which is not bad (20kOhm/V on DC ranges) and a transistor tester included for good measure and better than the Avo7. Of course, the OP has not been back to clarify his question.

B