Mains Voltage

[bernardgreen]

A well cared for and good quality analogue meter like an Avo 7 or 8 can be as accurate as a good digital meter. The mirror behind the needle enables reading with the eye directly above the needle.

Most analogues respond quicker to changes in voltage, the Avo needle will tremble if the voltage is not stable whereas a digital meter with a long sample time will not display any jittering.

The Avo is a bench test meter, it needs gentle handling and does not like being thrown into a tool bag.

 

[JohnW2]

Another interesting topic. Are analogue meters (like Avo meters) more accurate than modern digital meters?

Comparing 'accuracies' is not all that straightforward, but my guess would be that, in practical terms, they are probably similar, at least if one considers physically fairly large analogue meters (i.e. long,ideally 'mirrored', scales). Don't forget that digital meters usually display results with a higher precision (number of significant figures) than is really justifiable in terms of their accuracy, and therefore give a misleading impression of their true 'accuracy'.

There are at least two potential values of analogue meters. First, per the way this discussion arose, basic analogue meters (not 'electronic' ones {like the 'valve volmeters' of olden days} which happen to use an analogue meter movement to display the measurement) have a much lower input resistance/impedance than modern digital meters, thereby avoiding the 'detection' of voltages due to stray pick-up etc which have a very high source impedance (some digital meters have the option to include a 'shunt' across the probes to reduce input impedance to addressthis issue). Secondly, if one is measuring a voltage or current which is rapidly varying, a digital meter may never 'settle down', and an analogue one gives one at least a reasonable indication of what is going on.

Kind Regards, John

 

[plugwash]

A well cared for and good quality analogue meter like an Avo 7 or 8 can be as accurate as a good digital meter.............The Avo is a bench test meter, it needs gentle handling and does not like being thrown into a tool bag.

And theres the rub, under ideal conditions it might compare reasonably to a modern handheld DMM but it won't compare well to the modern handheld DMM if both of them are "thrown into a toolbag" every day and it also won't compare well to a modern high end bench DMM.

 

[JohnW2]

And theres the rub, under ideal conditions it might compare reasonably to a modern handheld DMM but it won't compare well to the modern handheld DMM if both of them are "thrown into a toolbag" every day...

True, but there used to be 'ruggedised' moving-coil analogue meters for use 'in the field' which, amongst other things, had a means of locking the meter movement during transport, to minimise damage.

Particularly for some 'monitoring' purposes, analogue displays (which obviously does not necessarily mean analogue innards) have their advantages - as witness some of the things you'll still find on the screens on the flight decks of the most modern aircraft. However, that's a whole different issue.

Kind Regards, John

 

[JBR]

Well, I'd like to thank you all for some very interesting responses to my question. Although I have a (not particularly expensive) digital multimeter, there's something about those Avo meters I find attractive!

The last response about analogue v. digital is very true. I can look at an analogue watch and recognise the time without thinking about it (and without the need for the numbers), but doing the same with a digital watch I have to think for a second or two what those numbers mean! Perhaps I'm just not used to them!

 

[JohnW2]

The last response about analogue v. digital is very true. I can look at an analogue watch and recognise the time without thinking about it (and without the need for the numbers), but doing the same with a digital watch I have to think for a second or two what those numbers mean! Perhaps I'm just not used to them!

No, I don't think it's just you. The perceptual psychologists and ergonomics folk have looked at this a lot over the years. If one needs a precise numerical answer, then a digital display is obviously what one needs. However, if one wants to know whether 'the engine temperature is about right', or 'the time is about ten past 2', then one can 'take in' that information, subconsciously, more rapidly from an analogue display. Having a whole panel of analogue displays (e.g. engine parameters) arranged so that 'straight up is normal' for all of them enables abnormalities to be perceived far more rapidly than if one has to read a whole pile of digital numbers.

Analogue displays also usually avoid the most of the pitfalls associated with misreading (sometimes with catastrophic results) a digital display (classically misidentifying the position of a decimal point).

Kind Regards, John

 

[westie101]

Having a whole panel of analogue displays (e.g. engine parameters) arranged so that 'straight up is normal' for all of them enables abnormalities to be perceived far more rapidly than if one has to read a whole pile of digital numbers.

You can just see a set of "electronic" analogue displays in the top right of this photo on a larger screen, they could well be engine related displays. This is on an Airbus A380



Slightly smaller A Hawker 750

 

[JohnW2]

You can just see a set of "electronic" analogue displays in the top right of this photo on a larger screen, they could well be engine related displays. This is on an Airbus A380

Indeed - and if they are engine parameters, and the engine was healthy, it looks at if it's a case of "1 o'clock is normal", rather than the 12 o'clock I suggested!

Kind Regards, John

 

[westie101]

Notice they have an inset (or alongside) digital display for the exact reading.

Here is an older set of instruments, full analogue but with inset digital

DHC-8-300

 

[JohnW2]

Notice they have an inset (or alongside) digital display for the exact reading.

Indeed - and that's obviously 'the best of both worlds'.

Kind Regards, John

 

[westie101]

Indeed - and if they are engine parameters, and the engine was healthy, it looks at if it's a case of "1 o'clock is normal", rather than the 12 o'clock I suggested!

Looking at the photos and those of another Hawker (Beech Super King Air), there doesn't seem to be a standard. On that type the maximum seems to be at the 9 o'clock position!

Though as crew have to be "type rated" on these types I doubt it is a problem

 

[bernardgreen]

I recall a production line where essential information was displayed on a screen using 8 virtual analogue meters. Operators hated it. It was replaced with 12 vertical bar graphs ( adding 4 more values ) which were all the same height when things were running properly. Much more use to the operators working on the line. If they were level at the top the machine was running fast, level near the bottom is was slow but in both cases OK.

 

[JohnW2]

I recall a production line where essential information was displayed on a screen using 8 virtual analogue meters. Operators hated it. It was replaced with 12 vertical bar graphs ( adding 4 more values ) which were all the same height when things were running properly. Much more use to the operators working on the line. If they were level at the top the machine was running fast, level near the bottom is was slow but in both cases OK.

That's obviously essentially the same concept, and different people will have different preferences (maybe based on what they are used to - e.g. pilots may be used to looking at lots of 'dials'). However, the point obviously is that any sort of analogue displays (of which the 'bar graph' is just another example) arranged so that they all look the same (same 'height', same 'needle' position etc.) when things are normal facilitates very much easier and more rapid detection of abnormalities than if the person had to read 8 or 12 digital displays and then work out (probably with different normal references for each) what, if anything, was abnormal.

If multiple digital displays are 'unavoidable' in that sort of situation, at least one can have them changing colour when they are display figures in/out of 'normal' ranges.

Kind Rewgards

 

[ban-all-sheds]

I really ought to add an Avo (or two) to my collection.

He says, having forgotten he owned one of these:

Avo M2042


And also one of these:

which even though it is badged the BBC M2030, and is made by Goerz, has a lot of similarities to the larger M2042.

Both, I feel, come from the Megger stable.

 

[ricicle]

Looks like someone's already got his initials on one of my old analogue meters

Untitled

• ricicle
• 7 Oct 2013
• 1