Name: Agung Din Eka Hidayat

Class: Physics ICP-A

NIM : 1312441006

Micrometer Screw Gauge

A micrometer screw gauge is used to measure lengths of small objects such as the diameter of human hair with a precision better than that of the vernier calipers. Figure below shows an actual micrometer screw gauge.

The smallest length that the micrometer can measure is 0.01 mm. This is the precision of the micrometer. The spindle will move 0.01 mm horizontally away from the anvil when the thimble moves vertically downwards by one small division.

History of the device and its name :

The word micrometer is a neoclassical coinage from Greek micros,

meaning "small", and metron, meaning "measure". The Merriam-Webster

Collegiate Dictionary says that English got it from French and that its first

known appearance in English writing was in 1670. Neither the metre nor

the micrometer nor the micrometer (device) as we know them today existed at

that time. However, the people of that time did have much need for, and

interest in, the ability to measure small things and small differences. The word

was no doubt coined in reference to this endeavor, even if it did not refer

specifically to its present-day senses.

The first ever micrometric screw was invented by William

Gascoigne in the 17th century, as an enhancement of the vernier; it was used

in a telescope to measure angular distances between stars and the relative

sizes of celestial objects.

Henry Maudslay built a bench micrometer in the early 19th century

that was jocularly nicknamed "the Lord Chancellor" among his staff because it

was the final judge on measurementaccuracy and precision in the firm's work

A micrometer is composed of:

FrameThe C-shaped body that holds the anvil and barrel in constant relation to each other. It is thick because it needs to minimize flexion, expansion, and contraction, which would distort the measurement.The frame is heavy and consequently has a high thermal mass, to prevent substantial heating up by the holding hand/fingers. It is often covered by insulating plastic plates which further reduce heat transference.Anvil

The shiny part that the spindle moves toward, and that the sample rests against

Sleeve / barrel / stock

The stationary round part with the linear scale on it. Sometimes vernier markings.

Lock nut / lock-ring / thimble lock

The knurled part (or lever) that one can tighten to hold the spindle stationary, such as when momentarily holding a measurement.

Screw

(not seen) The heart of the micrometer, as explained under "Operating principles". It is inside the barrel. (No wonder that the usual name for the device in German is Messschraube, literally "measuring screw".)

Spindle

The shiny cylindrical part that the thimble causes to move toward the anvil.

Thimble

The part that one's thumb turns. Graduated markings.

Ratchet stop

(not shown in illustration) Device on end of handle that limits applied pressure by slipping at a calibrated torque.

When the anvil and spindle are closed, the zero mark on the circular scale coincides with the horizontal line on the main scale. If it doesn’t, the discrepancy is known as zero-error (look At the figure) and has to be subtracted from the value obtained by measurement.

Zero error is an example of a systematic error that will cause the measured value to be either too large or too small when compared to the true value.

Correct measurement = Actual measurement – zero error

Treatment of zero-error is shown below.

Reading for X1 Reading for X2 Reading for X3

To find the average diameter of a uniform rod, we take readings at several positions (at least 3).

Average Diameter = (X1 + X2 + X3 ) / 3

Techniques in measuring small quantities without using special instruments.

1) Thickness of 1 piece of paper

- Use a metre rule to measure the thickness of 100 sheets of paper.

- Thickness of 1 sheet of paper = Total Thickness / 100.

2) Diameter of a piece of wire

- Wind the wire around a thin rod or a pencil to form a tight coil, say 18 turns (Figure 13). Use a metre rule to measure the length of the coil, d cm.

- Diameter of the wire = d / 18

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