Thread: $40 micrometer accurate to 0.00005" = credible ?

http://www.amazon.com/iGaging-Digita...ription-iframe

Is there too many decimal places here ?

No it is showing 5 ,unless it was stated as being 1,2,3 or 4 it looks right.

Originally Posted by steamingbill

www.amazon.com/iGaging-Digital-Electronic-Micrometer-Display/dp/B0087TMUQ8/ref=zg_bs_2983255011_1#product-description-iframe

Is there too many decimal places here ?

Hi Bill,

Probably + or - the last digit. Common with a lot of digital readouts.


Just done a search on UK Amazon since the USA website vendor doesn't ship outside the USA.
Same micrometer is £50,00p plus postage. There are three on the first page.

It can display to that level, but whether it is that accurate is questionable. At that level thermal effects and measuring technique have large influences, so while the micrometer may be able to discriminate to that level in reality the value displayed is probably better regarded as a random number distributed somewhere around the true value.

Michael

Hi Bill this is worth a watch about the accuracy.
It seems Mitutoyo has put out a micrometer that measures accurately down to 0.1 micron repeatedly.
Pretty rare thing.

phil
http://youtu.be/P5hMWKl7F18

Originally Posted by Steamwhisperer

Hi Bill this is worth a watch about the accuracy.
It seems Mitutoyo has put out a micrometer that measures accurately down to 0.1 micron repeatedly.
Pretty rare thing.

phil
http://youtu.be/P5hMWKl7F18

I think that mike costs about $20000.. I have a Mitutoyo mike with .00005" resolution but it is only accurate to +-.0003" at 20C. I think that the cheap mike would probably less accurate than the Mitutoyo one.

Where does it say that it's accurate to 0.00005"?

Originally Posted by Steamwhisperer

Hi Bill this is worth a watch about the accuracy.
It seems Mitutoyo has put out a micrometer that measures accurately down to 0.1 micron repeatedly.
Pretty rare thing.

phil
http://youtu.be/P5hMWKl7F18

Hi Phil,

I'm guessing that this sort of equipment typically gets kept in temperature controlled clean rooms. To Michael G's comment about thermal effects and techniques, I'd add that cleanliness counts as well. I could easily see that you might have to wipe the item, to be measured, down with lint free ethanol impregnated wipes, for example. You might also be limited in terms of touching the item because the heat input from your hands would change it's dimensions. The cost of developing policies and procedures might be significant.

Nice bit of kit though.

Cheers

The Beryl Bloke

Originally Posted by Pete F

Where does it say that it's accurate to 0.00005"?

My apologies,

See text below
Accuracy claimed 0.00016"
Resolution claimed 0.00005"

My fault, looked at the number stamped on the instrument in the picture then getting accuracy and resolution confused - I need to smarten my act up and get a better understanding of both terms. I know theres been numerous posts about it in the past but I still haven't got it sorted out inside my head. Will go and do some learning. Now.

See text below


Professional Tool, SUPER Precision
Crisp, clear, easy-to-read LCD display, accurate to 0.00016". Hardened and ground spindle with carbide anvil ensure durability and accuracy. Comes in a case with adjustment wrench, instructions booklet, ball attachment and extra battery.
Features:

• BONUS: Ball attachment
• 2 measuring modes Metric/Inch Standard
• Large LCD Display
• Absolute & Incremental Modes
• Automatic Switch Off
• Accuracy +/- 0.00016"
• Range 1-2"/25-50mm
• Resolution 0.00005"/0.001mm
• Carbide Measuring Surfaces
• Direct USB SPC Output available
• Meet or Exceeds Federal Accuracy Standards

Originally Posted by steamingbill

My fault, looked at the number stamped on the instrument in the picture then getting accuracy and resolution confused - I need to smarten my act up and get a better understanding of both terms.

If you think that's confusing, wait until you get to accuracy v precision

Looks to be the same one

http://www.aliexpress.com/item/Good-...444_6,201409_3

Originally Posted by Pete F

If you think that's confusing, wait until you get to accuracy v precision

Precision and resolution are effectively the same as the reproducibility of a measurement.

All they mean is that if many repeated identical measurements (same object and instrument) are made then a nominal % (typically 95%) of the values should be within the precision.

On one of the You tube reviews of this instrument you can see the effect of resolution when he goes to zero the instrument. He performs the zeroing repeatedly until he gets a zero - that's probably a combo of some dust and the resolution of the instrument.

Accuracy refers to the absolute uncertainty of a measurement.

In terms of temperature effects.
The coefficient of steel @ 25ºC is approx 0.00001 m/ºC.
Hence a 10ºC change on a 1" (25.4mm) dimension in steel will change the dimension by
10 x 0.00001*0.025.4 = 0.00254 (~0.002 mm), 100º will be ~20 microns.

This is consistent with the claimed accuracy of 0.00016" or 0.0041mm
Or to look at things the other way around, the claimed accuracy will handle a temperature change of no more than ~ 16º

As BB says, cleanliness, and also surface smoothness are for most cases (especially DIY) more significant than temperature.

Originally Posted by steamingbill

I need to smarten my act up and get a better understanding of both terms. I know theres been numerous posts about it in the past but I still haven't got it sorted out inside my head.

G'day Bill,
Has your lack of understanding had a negative impact on the quality of your work? If not, what's the problem?
Chris

Originally Posted by BobL

Precision and resolution are effectively the same as the reproducibility of a measurement.

Ah, no, they're not I'm afraid. Precision, resolution, and accuracy have very specific meanings in metrology, and they're often confused. Something can have high resolution but not be accurate or precise. Something can be precise but not be accurate, nor have high resolution. So it goes on. They are all independent. Ideally of course, we'd all like to have something that's accurate, precise, and of high resolution. That's not always possible.

My favourite diagram to describe the differences is the target image.



If you want to include resolution in this the analogy would be to take a telescope and zoom in on where the darts land. The higher the resolution, the greater the magnification of the telescope.

With things like micrometers, I would encourage people to stay away from cheap Chinese rubbish. Your measuring tools are the foundations upon which you build all your work. If you can't trust them, then the game is over before it even begins. Good tools are expensive, however they often come up used in good condition for no more than the Chinese rubbish.

I have a very repeatable chinese micrometer, it is consistently off by 0.01mm at various points of travel... In some places it might be +0.01mm, other places -0.01mm..

It is very repeatable though