2.Clean the ends of the anvil and spindle before making a measurement
– Any dirt on either of surfaces could affect the reading
3.Check for zero error by closing the micrometer when there is nothing between the anvil and spindle
Metre rule：1 mm Tape ：1 mm
Vernier calipers：0.1mm， Micrometer screw gauge
0.05mm，0.02mm
0.01mm
27
2-1 Measurements
Measuring lengths with meter rule
Precision : 1 millimeter
Measuring lengths with tape
Precision : 1 millimeter
1
2-1 Measurements
Measuring lengths with metre rule
• Main scale on the sleeve • Circular scale on the thimble
• There are 50 divisions on the thimble • One complete turn of the thimble moves the
spindle by 0.50 mm • 0.50mm/50= 0.01 mm
2-1 Measurements
How to read a vernier caliper?
• Check zero error. Close the calipers so that the jaws touch lightly but firmly with each other.
• Close the calipers so that the jaws touch lightly but firmly on the sides of the object being measured.
8
10
1 mm + 33*0.02 mm=1.66 mm
0.1cm+ 0.01*6.6 cm=0.1cm+0.066 cm=0.166cm
11
21 mm + 3 *0.1 mm = 21.3 mm = 2.13 cm
2.1cm + 0.01*3 cm = 2.13 cm
20 mm + 3*0.05 mm =20.15 mm 2.0cm + 0.01*1.5 cm = 2.0+0.015cm= 2.015 cm
2-1 Measurements
How to read a micrometer screw gauge?
• Check zero error • Turn the barrel until the jaws just tighten on the
object. Using the friction clutch ensures just the right pressure. • Read the main scale to the nearest 0.5mm • Read the additional fraction of a millimeter from the fractional scale
• Correct way to read the scale on a ruler • Position eye perpendicularly at the mark on the
scale to avoids parallax errors(视差) • Another reason for error: object not align
1 mm + 0.02*33 mm=1.66 mm 0.1 cm + 0.01*6.6cm = 0.166 cm
Main scale Vernier scale
Precision
9 mm 10 divisions 1/10mm=0.1mm
19 mm 20 divisions 1/20mm=0.05mm
2-1 Measurements
no object
Notice
Zero error
It is negative . Zero Error =-0.1 mm*（-3）=−0.3 mm
measure an object ： 0 mm + 0.1mm*6=0.6 mm
Correct Reading:
0.6mm−(−0.3mm)=0.9mm
2
2-1 Measurements
Measuring lengths
Vernier calipers
Micrometer screw gauge
3
2-1 Measurements
Vernier calipers
The structure
The mechanism: how it works ?
o 2 students a group, 10 minutes in total
o Everyone should use the Micrometer Screw Gauge o The experimental report is part of homework
Notice: make several measurements from different angles.
Activity
2-1 Measurements
Micrometer screw gauge
How to deal with zero error?
2-1 Measurements
Precautions when using a micrometer 1.Never tighten thimble too much
• Look at the zero on the vernier scale.Read the main scale ,just to the left of the zero.This tells you the length in millimetres.
• Then look at the vernier scale.Find the point where one of its markings is exactly aligned with one of the markings on the main scale.Read the value on the vernier scale.This tells you the fractional of a millimetre that you must add to the main scale reading.
–The reading should be zero, but it is common to find a small zero error –Correct zero error by adjusting the final measurement
25
2-1 Measurements
Activity Experiment: Micrometer Screw Gauge
2-1 Measurements
1. Read the scale on the sleeve. The example clearly shows12 mm divisions. 2. Still reading the scale on the sleeve, a further ½ mm (0.5) measurement can be seen on the bottom half of the scale. The measurement now reads 12.5mm. 3. Finally, the thimble scale shows 16 full divisions (these are hundredths of a mm).
Zero error（零位误 差） ：+0.3 mm
measure an object ： 10mm + 0.1mm*6=10.6 mm 1.0 cm + 0.01*6 = 1.06 cm
Correct Reading:
10.6mm−(+0.3mm)=10.3 mm 1.06 cm-0.03 cm= 1.03 cm
The method: how to use it ?
2-1 Measurements
The structure of the Vernier caliper
5
0
6
How it works 2-1 Measurements
21 mm + 0.1 mm *3 = 21.3 mm 2.1cm + 0.01*3 cm = 2.13 cm
2-1ImMperaosvuinregmpreenctision in measurements
Micrometer screw gauge
The structure
The mechanism: how it works ?
The method: how to use it ?
2-1 Measurements
Micrometer screw gauge
The structure
2-1 Measurements
Micrometer Screw Gauge • To measure diameter of fine wires, thickness of