L01R Micrometers

8/8/2019 L01R Micrometers

1/14

Lecture 01R: Measurements

Agenda

y Take rolly Lecture on Measurements, Precision, Accuracy

Introduction

y Pro|Engineer labdrawings can be made to high degree of accuracy+/- 0.001y To produce parts of equivalent accuracy we must be able to measure accuratelyy Methods of measurement (length)

o Rulerdivisions to 1/32 inch or 1 mm. What is the best accuracy you can achieve? When reporting data taken using a ruler, how do you represent the datapoints?

yo Caliper

Digitalreadout shows measurements to 0.1 mm Vernierreadout shows measurements to 0.05 mmis it more accurate? Dialgenerally read to 0.1 mm

o Micrometermechanical Reading micrometersinch versus metric

o Micrometer lasero Surface plateso Gauge blocks

y What causes inaccuracy in measurement?o The instrumentsources (quality, temperature, age or abuse)o The object being measured (irregular shape, dirt, temperature)o The operator (parallax, poor technique, bad eyesight, fudging)o Random versus systematic erroro Accuracy versus precision

Overcoming measurement error

o Multiple measurements, averagingwhy?o Under what circumstances will multiple measurements improve accuracy?o Under what circumstances will multiple measurements not improve accuracy?o Can making more measurements improve precision?

y Calculation of the meany Calculation of the variance


2/14

Measurement Errors and Tolerance Stackup

Ruler graduated in

mm on one side,32nds of an inch on

the other.

Measuring bar code.Head is toward the

left to align the zero

mark with the

beginning of the bar

codekind of.


3/14

Measuring bar code. Head is toward right to read length of code as 3.1 cm = 31 mm.

Note that left end of ruler now looks misaligneddue to parallax error caused by the

thickness of the ruler.


4/14

Digital caliper

measuring a Lego gear.

Note that measurement

will depend on the

rotation of the gear,

whether it is flat in

the caliper jaws, and

how tightly the caliper

squeezes the gear.

Vernier caliper

measuring the same

Lego gear. Note the

difference inmeasurement between

this caliper and the

digital one.


5/14

Caliper used to measure inside diameter of small object. Reading is 3/8 inch since the 0 line on the

sliding jaw aligns exactly with the 3/8 inch line on the body of the caliper.


6/14

Same pen barrel, measured in millimeters. The zero on the slider is between 9mm and 10mm. Look

along the slider at the vernier scale and see that the 6.5 mark seems to line up with a mark on the body.

The reading is therefore 9.65 mm.


7/14

Battery measured in inches. The 0 line on the sliding jaw is between 1-3/4 and 1-13/16 inches. The4/128 looks like it lines up with the 2.0 line on the body. The reading is therefore 1-3/4 + 4/128 = 1-

3/4 + 1/32 = 1-25/32. Perhaps easier in decimals, it would be 1.75 + 0.03125 = 1.781. How would

you round this number?

The vernier caliper can also be used as a

depth gauge. Note the tang on the end

of the slider that can be inserted into

blind holes like the pen cap.


8/14

The depth appears to be

exactly 1-13/16. Not very

interesting.

This is at a

little bit of

an angle,

but clearly

the 0 line

of the

slider isbetween

46mm and

47mm. Its

hard to see

with these

fat lines,

but the

vernier

lines for

3.0, 3.5

and 4.0 all

seem to

line up

pretty

well, so

choose the middle one3.5. Therefore the reading is 46.35 mm


9/14

Traditional micrometers. Top = outside micrometer, center = inside micrometer, bottom = depth


10/14

Micrometer showing a measurement of 0.276 inch. This type micrometer is accurate to about 0.0005.

Note that the space between 0 and 0.1 is broken into 4 increments and the vernier (the turning part)

has 25 divisions. So each of the small lines between 0,1,2, etc. is 0.025, and each line on the vernier is

0.001. Here we have 0.2 + 3x0.025 + 0.001 = 0.276.

Metric micrometer showing a measurement of 5.78 mm. The lines above center are millimeters. Below

the centerline are 0.5mm divisions, and the vernier has 50 lines, making each line 0.01mm. So we have 5

mm + 0.5mm + 0.28mm = 5.78 mm. This micrometer is accurate to about 0.005 mm, since you could

eyeball to about of a vernier line.


11/14

Inch micrometer showing a reading of 0.154. The 0.05 line is just visible to the left of the vernierplusyou can see that the vernier is just about at 4, which is a low number. This tells you that you are slightly

over the 0.05 line, not slightly under it. The knurled lever can be used to lock the micrometer in

position.


12/14

Inch micrometer showing 0.169. The 0.15 line is visible, but not the 0.175 line. So we have 0.150 +

the 0.019 showing on the vernier.


13/14

Inch micrometer showing 0.286. The 0.275 line is visible to the left of the vernier, plus 0.011 on the

vernier itself = 0.286


14/14

Optical micrometer uses

CCD camera to measure

object size to within

2 x 10-6

m = 0.002 mm

Can take 2400

samples/second

Documents

L01R Micrometers