CalipersFrom Wikipedia, the free encyclopedia

  (Redirected from Caliper)

For other uses, see Caliper (disambiguation).

Caliper with graduated bow 0–10 mm

A caliper (British spelling also calliper, or in plurale tantum sense a pair of calipers) is a device used

to measure the distance between two opposite sides of an object. A caliper can be as simple as

a compass with inward or outward-facing points. The tips of the caliper are adjusted to fit across the points to

be measured, the caliper is then removed and the distance read by measuring between the tips with a

measuring tool, such as a ruler.

It is used in many fields such as mechanical

engineering, metalworking,forestry, woodworking, science and medicine.

Contents

  [hide] 

1 Nomenclature variants

2 History

3 Types

o 3.1 Inside caliper

o 3.2 Outside caliper

o 3.3 Divider caliper

o 3.4 Oddleg caliper

o 3.5 Vernier caliper

o 3.6 Dial caliper

o 3.7 Digital caliper

o 3.8 Micrometer caliper

4 Comparison

5 Use

6 Zero error

7 See also

8 References

9 External links

Nomenclature variants[edit]

A plurale tantum sense of the word "calipers" coexists in natural usage with the regular noun sense of "caliper".

That is, sometimes a caliper is treated cognitively like a pair of glasses or a pair of scissors, resulting in a

phrase such as "hand me those calipers" or "those calipers are mine" in reference to one unit.

Also existing colloquially but not in formal usage is referring to a vernier caliper as a "vernier" or a "pair of

verniers". In imprecise colloquial usage, some speakers extend this even to dial calipers, although they involve

no vernier scale.

In machine-shop usage, the term "caliper" is often used in contradistinction to "micrometer", even though

outside micrometers are technically a form of caliper. In this usage, "caliper" implies only the form factor of the

vernier or dial caliper (or its digital counterpart).

History[edit]

The earliest caliper has been found in the Greek Giglio wreck near the Italian coast. The ship find dates to the

6th century BC. The wooden piece already featured a fixed and a movable jaw.[1][2] Although rare finds, caliper

remained in use by the Greeks and Romans.[2][3]

A bronze caliper, dating from 9 AD, was used for minute measurements during the Chinese Xin dynasty. The

caliper had an inscription stating that it was "made on a gui-you day at new moon of the first month of the first

year of the Shijian guo period." The calipers included a "slot and pin" and "graduated in inches and tenths of an

inch."[4][5]

The modern vernier caliper, reading to thousandths of an inch, was invented by American Joseph R. Brown in

1851. It was the first practical tool for exact measurements that could be sold at a price within the reach of

ordinary machinists.[6]

Types[edit]

Inside caliper[edit]

Two inside calipers

The inside calipers are used to measure the internal size of an object.

The upper caliper in the image (at the right) requires manual adjustment prior to fitting, fine setting of this

caliper type is performed by tapping the caliper legs lightly on a handy surface until they will almost pass

over the object. A light push against the resistance of the central pivot screw then spreads the legs to the

correct dimension and provides the required, consistent feel that ensures a repeatable measurement.

The lower caliper in the image has an adjusting screw that permits it to be carefully adjusted without

removal of the tool from the workpiece.

Outside caliper[edit]

Three outside calipers.

Outside calipers are used to measure the external size of an object.

The same observations and technique apply to this type of caliper, as for the above inside caliper. With some

understanding of their limitations and usage these instruments can provide a high degree of accuracy and

repeatability. They are especially useful when measuring over very large distances, consider if the calipers are

used to measure a large diameter pipe. A vernier caliper does not have the depth capacity to straddle this large

diameter while at the same time reach the outermost points of the pipe's diameter. They are made from high

carbon steel.

Divider caliper[edit]

Main article: Compass (drafting)

A pair of dividers

In the metalworking field, a divider caliper, popularly called a compass, is used in the process of marking

out locations. The points are sharpened so that they act as scribers, one leg can then be placed in the dimple

created by acenter or prick punch and the other leg pivoted so that it scribes a line on the workpiece's surface,

thus forming an arc or circle.

A divider caliper is also used to measure a distance between two points on amap. The two caliper's ends are

brought to the two points whose distance is being measured. The caliper's opening is then either measured on

a separate ruler and then converted to the actual distance, or it is measured directly on ascale drawn on the

map. On a nautical chart the distance is often measured on the latitude scale appearing on the sides of the

map: one minute of arc of latitude is approximately one nautical mile or 1852 metres.

Dividers are also used in the medical profession. An ECG (also EKG) caliper transfers distance on

an electrocardiogram; in conjunction with the appropriate scale, the heart rate can be determined. A pocket

caliper versions was invented by cardiologist Robert A. Mackin.[7]

Oddleg caliper[edit]

Oddleg calipers

Oddleg calipers, Hermaphrodite calipers, or Oddleg jennys, as pictured on the left, are generally used to

scribe a line a set distance from the edge of a workpiece. The bent leg is used to run along the workpiece edge

while the scriber makes its mark at a predetermined distance, this ensures a line parallel to the edge.

In the diagram at left, the uppermost caliper has a slight shoulder in the bent leg allowing it to sit on the edge

more securely, the lower caliper lacks this feature but has a renewable scriber that can be adjusted for wear, as

well as being replaced when excessively worn.

Vernier caliper[edit]

Main article: Vernier scale

Parts of a vernier caliper:

1. Outside jaws: used to measure external diameter or width of an object

2. Inside jaws: used to measure internal diameter of an object

3. Depth probe: used to measure depths of an object or a hole

4. Main scale: scale marked every mm

5. Main scale: scale marked in inches and fractions

6. Vernier scale gives interpolated measurements to 0.1 mm or better

7. Vernier scale gives interpolated measurements in fractions of an inch

8. Retainer: used to block movable part to allow the easy transferring of a measurement

The vernier, dial, and digital calipers give a direct reading of the distance measured with high accuracy and

precision. They are functionally identical, with different ways of reading the result. These calipers comprise a

calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance

between the jaws is then read in different ways for the three types.

The simplest method is to read the position of the pointer directly on the scale. When the pointer is between

two markings, the user can mentally interpolate to improve the precision of the reading. This would be a simple

calibrated caliper; but the addition of a vernier scaleallows more accurate interpolation, and is the universal

practice; this is the vernier caliper.

Vernier, dial, and digital calipers can measure internal dimensions (using the uppermost jaws in the picture at

right), external dimensions using the pictured lower jaws, and in many cases depth by the use of a probe that is

attached to the movable head and slides along the centre of the body. This probe is slender and can get into

deep grooves that may prove difficult for other measuring tools.

The vernier scales may include metric measurements on the lower part of the scale and inch measurements on

the upper, or vice versa, in countries that use inches. Vernier calipers commonly used in industry provide a

precision to 0.01 mm (10micrometres), or one thousandth of an inch. They are available in sizes that can

measure up to 1,829 mm (72 in).[8]

Dial caliper[edit]

Mitutoyo dial caliper

Instead of using a vernier mechanism, which requires some practice to use, thedial caliper reads the final

fraction of a millimeter or inch on a simple dial.

In this instrument, a small, precise rack and pinion drives a pointer on a circulardial, allowing direct reading

without the need to read a vernier scale. Typically, the pointer rotates once every inch, tenth of an inch, or 1

millimeter. This measurement must be added to the coarse whole inches or centimeters read from the slide.

The dial is usually arranged to be rotatable beneath the pointer, allowing for "differential" measurements (the

measuring of the difference in size between two objects, or the setting of the dial using a master object and

subsequently being able to read directly the plus-or-minus variance in size of subsequent objects relative to the

master object).

The slide of a dial caliper can usually be locked at a setting using a small lever or screw; this allows

simple go/no-go checks of part sizes.

Digital caliper[edit]

Digital caliper

A refinement now popular is the replacement of the analog dial with anelectronic digital display on which the

reading is displayed as a single value. Rather than a rack and pinion, they have a linear encoder. Some digital

calipers can be switched between centimeters or millimeters, and inches. All provide for zeroing the display at

any point along the slide, allowing the same sort of differential measurements as with the dial caliper. Digital

calipers may contain some sort of "reading hold" feature, allowing the reading of dimensions even in awkward

locations where the display cannot be seen. Ordinary 6-in/150-mm digital calipers are made of stainless steel,

have a rated accuracy of 0.001 in (0.02mm) and resolution of 0.0005 in (0.01 mm). [9] The same technology is

used to make longer 8-in and 12-in calipers; the accuracy for bigger measurements declines to 0.001 in

(0.03 mm) for 100–200 mm and 0.0015 in (0.04 mm) for 200–300 mm. [10]

Many Chinese-made digital calipers are inexpensive and perform reasonably well. One point worth noting is

battery current when they are turned off. Many calipers do not stop drawing power when the switch is in the off

position; they shut down the display but continue drawing nearly as much current. The current may be as much

as 20 microamperes,[11] which is much higher than many established brands. Sometimes calipers may not work

properly when the battery voltage has dropped relatively little; silver cells, preferably selected from a datasheet

to have a constant voltage for most of their life, may give a much longer usable life than alkaline button

cells (e.g., SR44 instead of LR44).[11][12]

Increasingly, digital calipers offer a serial data output to allow them to be interfaced with a dedicated recorder

or a personal computer. The digital interface significantly decreases the time to make and record a series of

measurements, and it also improves the reliability of the records. A suitable device to convert the serial data

output to common computer interfaces such as RS-232, Universal Serial Bus, or wireless can be built or

purchased. With such a converter, measurements can be directly entered into a spreadsheet, a statistical

process control program, or similar software.

The serial digital output varies among manufacturers. Common options are

Mitutoyo's Digimatic interface. This is the dominant name brand interface. Format is 52 bits arranged as 13

nibbles.[13][14][15][16]

Sylvac interface. This is the common protocol for inexpensive, non-name brand, calipers. Format is 24 bit

90 kHz synchronous.[17][18]

Starrett[19]

Brown & Sharpe[19]

Federal

Mahr (appears to offer Digimatic, RS232, and USB)

Tesa[19]

Aldi. Format is 7 BCD digits.[18]

Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw.

Some digital calipers contain a capacitive linear encoder. A pattern of bars is etched directly on the printed

circuit board in the slider. Under the scale of the caliper another printed circuit board also contains an etched

pattern of lines. The combination of these printed circuit boards forms two variable capacitors. The two

capacitances are out of phase. As the slider moves the capacitance changes in a linear fashion and in a

repeating pattern. The circuitry built into the slider counts the bars as the slider moves and does a linear

interpolation based on the magnitudes of the capacitors to find the precise position of the slider. Other digital

calipers contain an inductive linear encoder, which allows robust performance in the presence of contamination

such as coolants.[20] Magnetic linear encoders are used in yet other digital calipers.

Micrometer caliper[edit]

Main article: Micrometer

A caliper using a calibrated screw for measurement, rather than a slide, is called a micrometer caliper or, more

often, simply a micrometer. (Sometimes the term caliper, referring to any other type in this article, is held in

contradistinction tomicrometer.)

Comparison[edit]

Each of the above types of calipers have their relative merits and faults.

Vernier calipers are rugged and have long lasting accuracy, are coolant proof, are not affected by magnetic

fields, and are largely shock proof. They may have both centimeter and inch scales. However, vernier calipers

require good eyesight or amagnifying glass to read and can be difficult to read from a distance or from awkward

angles. It is relatively easy to misread the last digit. In production environments, reading vernier calipers all day

long is error-prone and is annoying to the workers.

Dial calipers are comparatively easy to read, especially when seeking exact center by rocking and observing

the needle movement. They can be set to 0 at any point for comparisons. They are usually fairly susceptible to

shock damage. They are also very prone to getting dirt in the gears, which can cause accuracy problems.

Digital calipers switch easily between centimeter and inch systems.They can be set to 0 easily at any point with

full count in either direction, and can take measurements even if the display is completely hidden, either by

using a "hold" key, or by zeroing the display and closing the jaws, showing the correct measurement, but

negative. They can be mechanically and electronically fragile. Most also require batteries, and do not resist

coolant well. They are also only moderately shockproof, and can be vulnerable to dirt.

Calipers may read to a resolution of 0.01 mm or 0.0005 in, but accuracy may not be better than about

±0.02 mm or 0.001 in for 150 mm (6 in) calipers, and worse for longer ones.[21]

Use[edit]

Using the vernier caliper

A caliper must be properly applied against the part in order to take the desired measurement. For example,

when measuring the thickness of a plate a vernier caliper must be held at right angles to the piece. Some

practice may be needed to measure round or irregular objects correctly.

Accuracy of measurement when using a caliper is highly dependent on the skill of the operator. Regardless of

type, a caliper's jaws must be forced into contact with the part being measured. As both part and caliper are

always to some extent elastic, the amount of force used affects the indication. A consistent, firm touch is

correct. Too much force results in an underindication as part and tool distort; too little force gives insufficient

contact and an overindication. This is a greater problem with a caliper incorporating a wheel, which

lends mechanical advantage. This is especially the case with digital calipers, calipers out of adjustment, or

calipers with a poor quality beam.

Simple calipers are uncalibrated; the measurement taken must be compared against a scale. Whether the

scale is part of the caliper or not, all analog calipers—verniers and dials—require good eyesight in order to

achieve the highest precision. Digital calipers have the advantage in this area.

Calibrated calipers may be mishandled, leading to loss of zero. When a calipers' jaws are fully closed, it should

of course indicate zero. If it does not, it must be recalibrated or repaired. It might seem that a vernier caliper

cannot get out of calibration but a drop or knock can be enough. Digital calipers have zero set buttons.

Vernier, dial and digital calipers can be used with accessories that extend their usefulness. Examples are a

base that extends their usefulness as a depth gauge and a jaw attachment that allows measuring the center

distance between holes. Since the 1970s a clever modification of the moveable jaw on the back side of any

caliper allows for step or depth measurements in addition to external caliper measurements, in similar fashion

to a universal micrometer (e.g., Starrett Mul-T-Anvil or Mitutoyo Uni-Mike).

Zero error[edit]

The method to use a vernier scale or caliper with zero error is to use the formula 'actual reading = main scale +

vernier scale − (zero error)'. Zero error may arise due to knocks that cause the calibration at the 0.00 mm when

the jaws are perfectly closed or just touching each other.

when the jaws are closed and if the reading is 0.10mm, the zero error is referred to as +0.10mm.The method to use a

vernier scale or caliper with zero error is to use the formula 'actual reading = main scale + vernier scale − (zero error)' thus

the actual reading is 19.00 + 0.54 − (0.10) = 19.44 mm

Positive zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a

positive reading away from the actual reading of 0.00mm. If the reading is 0.10mm, the zero error is referred to

as +0.10mm.

when the jaws are closed and if the reading is −0.08mm, the zero error is referred to as −0.08mm..The method to use a

vernier scale or caliper with zero error is to use the formula 'actual reading = main scale + vernier scale − (zero error)' thus

the actual reading is 19.00 + 0.36 − (−0.08) = 19.44 mm

Negative zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a

negative reading away from the actual reading of 0.00mm. If the reading is −0.08mm, the zero error is referred

to as −0.08mm.