Digital Calipers

[Peter G. ShawParticipant @peterg-shaw75338]

Neil,

It doesn't matter what the internal resolution may be, well ok it does, but when the specification for the device states specifically plus or minus one digit, then taking the stated display resolution gives a tolerance of plus or minus 0.01mm regardless of what the display shows. Giving 10.00 mm was just an example, stating say 1.00mm plus or minus 1 digit makes the possible display error even worse.

I do think that all this guff about digital being the be all and end all is massively overblown. Yes digital has some advantages over analogue, but it needs one to be circumspect about and to just consider what is actually happening. In our case, digital makes for easier reading, to say nothing of units conversion and zero setting, but one does have to keep in mind the specification.

Horses for courses springs to mind.

Peter G. Shaw

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Peter G. Shaw on 04/08/2018 18:20:39:

… when the specification for the device states specifically plus or minus one digit, then taking the stated display resolution gives a tolerance of plus or minus 0.01mm regardless …

.

Very fair comment, Peter … which remains true for any digital display.

It's maybe worth looking at Mitutoyo's own assessment of 'Horses for courses'

I have chosen the 'scales' as an example, from roughly 2/3 down this page: **LINK**

http://www.mitutoyo.co.uk/en_gb/downloads/product-information/

MichaelG.

.

Digital Scale & DRO Systems

Mitutoyo Digital Scales are available as standalone units with built-in Digimatic display, convenient for retrofitting to equipment where moderate measuring accuracy is sufficient, or in the highly accurate Linear Scale form designed for machine tool and measuring machine applications.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Peter G. Shaw on 04/08/2018 13:51:24:

I haven't bothered with the digitals because for one thing any reading is subject to plus or minus one digit. Which means that, eg, 10.00mm could be measured as 9.99 or 10.01mm. Hardly accurate in my view!

…

As you guess, I'm not a fan of digital measuring devices!

Peter G. Shaw

 

One good thing about the ± 1 digit issue is the reminder that the instrument has limitations.

Most digital calipers are only accurate to ±0.02mm – worse than the precision of the display. No point in worrying about the display being out by ±0.01mm when the caliper itself isn't that good.

An ordinary analogue caliper isn't mechanically any more accurate than it's digital cousin and it may be much worse. But the most serious weakness of analogue instruments is that they are easily misread. They depend entirely on good eye-sight and correct interpretation of the display. Parallax, misreading dial markings, and misplacing vernier scale alignments are all common mistakes. The best of digital displays is that they are much harder to misread.

For many applications a digital display is better than an analogue, but not all. Numeric displays aren't good at indicating rate of change. On a lathe, the rpm counter should be digital because you want to set a steady value. On a tyre pressure gauge, I prefer an analogue dial because needle movements are informative about leaks. As you say, horses for courses.

Dave

 

 

 

 

Edited By SillyOldDuffer on 04/08/2018 21:04:19

[Peter G. ShawParticipant @peterg-shaw75338]

SOD,

Most digital calipers are only accurate to ±0.02mm – worse than the precision of the display. No point in worrying about the display being out by ±0.01mm when the caliper itself isn't that good.

The trouble then, is that the errors can be cumulative, so the total inaccuracy is now plus or minus 0.03mm.

Otherwise, I agree with what you say, but would point out that when analogue ruled supreme, people were aware of the problems and took appropriate precautions even though mistakes did still occur.

Cheers,

Peter G. Shaw

[Author]

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