A
caliper (
British spellingAmerican and British English spelling differences are one aspect of American and British English differences.- Historical origins :In the early 18th century, English spelling was not standardized. Differences became noticeable after the publishing of influential dictionaries...
also
calliper) is a device used to
measureIn science, measurement is the process of obtaining the magnitude of a quantity, such as length or mass, relative to a unit of measurement, such as a meter or a kilogram...
the distance between two symmetrically opposing sides. A caliper can be as simple as a
compassA compass or, more properly, pair of compasses is a technical drawing instrument that can be used for inscribing circles or arcs. As dividers, they can also be used as a tool to measure distances, in particular on maps...
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
rulerA ruler, or rule, is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is essentially a straightedge used to rule lines and the calibrated instrument used for determining measurement is called...
.
They are used in many fields such as
metalworkingMetalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewellery. It therefore includes a correspondingly wide range of skills,...
,
mechanical engineeringMechanical Engineering is an engineering discipline that was developed from the application of principles from physics and materials science. Mechanical engineering involves the analysis, design, manufacturing, and maintenance of various systems...
,
gunsmithA gunsmith is a person who repairs, modifies, designs, or builds firearms.Gunsmiths may be employed in:*factories by firearms manufacturers,*armories by military or law-enforcement agencies,*sporting goods stores, or...
ing,
handloadingHandloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely-assembled, factory-loaded cartridges...
,
woodworkingWoodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was certainly one of the first materials worked by primitive human beings. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many...
,
woodturningWoodturning is a form of woodworking that is used to create wooden objects on a lathe. Woodturning differs from most other forms of woodworking in that the wood is moving while a stationary tool is used to cut and shape it. Many intricate shapes and designs can be made by turning wood.There are two...
and in
medicineMedicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
.
Nomenclature variants (colloquial only)
A
plurale tantumA plurale tantum is a noun that appears only in the plural form and does not have a singular variant, though it may still refer to one or many of the objects it names...
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. However, this usage is mostly
colloquialA colloquialism is an expression not used in formal speech, writing or paralinguistics. Colloquialisms are also sometimes referred to collectively as "colloquial language". Colloquialisms or colloquial language is considered to be characteristic of or only appropriate for casual, ordinary,...
and the regular noun sense of caliper usually dominates, especially in writing. There is no rigorous grammatical logic to defend the plurale tantum sense; it is just the way language sometimes naturally flows colloquially.
Also existing colloquially but not in formal usage is referring to a vernier caliper as a "vernier".
History
The earliest caliper has been found in the
GreekAncient Greece is the civilisation belonging to the period of Greek history lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman conquest of Greece after the Battle of Corinth. It is generally considered to be the seminal culture which provided the...
GiglioGiglio Island is an island and Italian comune situated in the Tyrrhenian Sea, off the coast of Tuscany, part of the Province of Grosseto.-Geography:...
wreck near the
ItalianItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
coast. The ship find dates to the 6th century BC. The wooden piece already featured a fixed and a movable jaw. Although rare finds, caliper remained in use by the Greeks and
RomansAncient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC. Located along the Mediterranean Sea, it became one of the largest empires in the ancient world....
.
By the
Han DynastyThe Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty and succeeded by the Three Kingdoms . It was founded by the peasant rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty of the former regent Wang Mang...
(202 BC – 220 AD), the
ChineseChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
also used the sliding caliper, which they made of bronze and manufactured each tool with an inscription of the day, month, and year it was made (according to
Chinese era nameA Chinese era name is the era name, reign period, or regnal title used when traditionally numbering years in an emperor's reign and naming certain Chinese rulers . Some emperors have several era names, one after another, where each beginning of a new era resets the numbering of the year back to...
s and
their lunar calendarThe Chinese calendar is lunisolar, incorporating elements of a lunar calendar with those of a solar calendar. It is not exclusive to China, but followed by many other Asian cultures. It is often referred to as the Chinese calendar because it was first perfected by the Chinese around 500 BCE...
).
The modern vernier caliper, reading to thousandths of an inch, was invented by American Joseph R. Brown in 1851. His Brown and Sharpe company inaugurated true precision manufacture in the United States. It was the first practical tool for exact measurements that could be sold at a price within the reach of ordinary machinists.
Inside caliper
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
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.
Divider caliper
In the metalworking field
divider calipers are used in the process of
marking outMarking out or layout is the process of transferring a design or pattern to a workpiece, as the first step in the manufacturing process...
suitable workpieces. The points are sharpened so that they act as scribers, one leg can then be placed in the dimple created by a
center or prick punchA punch is a hard metal rod with a shaped tip at one end and a blunt butt end at the other that is usually struck by a hammer. A variety of punches are used in engineering, but often the purpose is to form an impression of the tip on a workpiece.- Center :...
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 a
mapA map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
. 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 a
scaleThe scale of a map is usually defined as the ratio of a single unit of distance on the map to the corresponding distance on the ground. Although this is true for accurate large scale maps, covering a restricted area, it is not true for map projections of the curved surface of the Earth to the plane...
drawn on the map. On a
nautical chartA nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...
the distance is often measured on the
latitudeLatitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...
scale appearing on the sides of the map: one minute of arc of latitude is approximately one
nautical mileThe nautical mile is a unit of length corresponding approximately to one minute of arc of latitude along any meridian....
or 1852
metreThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
s.
Dividers are also used in the medical profession. They are used to measure electrocardiogram (ECG) lines. This instrument is called an
ECG caliper or
EKG caliper. These calipers have changed through the years, and there are even pocket calipers, invented 20 years ago by cardiologist Robert A. Mackin.
Oddleg caliper
Oddleg calipers,
Hermaphrodite calipers or
Oddleg jennys, or just plain Ol' Jennys, as pictured on the left, are generally used to scribe a line a set distance from the edge of 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
A variation to the more traditional caliper is the inclusion of a
vernier scaleA vernier scale is an additional scale which allows a distance or angle measurement to be read more precisely than directly reading a uniformly-divided straight or circular measurement scale...
; this makes it possible to directly obtain a more precise measurement.
Vernier calipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and depending on the manufacturer, depth measurements 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 both
metricThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
and
inchAn inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
measurements on the upper and lower part of the scale.
Vernier calipers commonly used in industry provide a precision to a hundredth of a millimetre (10
micrometreA micrometre or micron is one millionth of a metre,or equivalently one thousandth of a millimetre....
s), or one thousandth of an inch.
A more precise instrument used for the same purpose is the micrometer.
Dial caliper
A further refinement to the vernier caliper is the
dial caliper.
In this instrument, a small
gearA gear is a component within a transmission device that transmits rotational torque by applying a force to the teeth of another gear or device. A gear is different from a pulley in that a gear is a round wheel that has linkages that mesh with other gear teeth, allowing force to be fully...
rack drives a pointer on a circular
dialA dial is generally a flat surface, circular or rectangular, with numbers or similar markings on it, used for displaying the setting or output of a timepiece, radio, clock, watch, or measuring instrument...
. Typically, the pointer rotates once every inch, tenth of an inch, or 1 millimeter, allowing for a direct reading without the need to read a vernier scale (although one still needs to add the basic inches or tens of millimeters value read from the slide of the caliper). 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
leverIn physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object....
or screw; this allows simple
go/no-goA Go-NoGo gauge refers to an inspection tool used to check a workpiece against its allowed tolerances. Its name derives from its use: the gauge itself has two tests; the check involves the workpiece's having to pass one test and 'fail' the other .It is an integral part of the quality process...
checks of part sizes.
Digital caliper
A refinement now popular is the replacement of the analog dial with an
electronicElectronics is a branch of science and technology that deals with the controlled flow of electrons. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation,...
digital displayA display device is an output device for presentation of information for visual, tactile or auditive reception, acquired, stored, or transmitted in various forms. When the input information is supplied as an electrical signal, the display is called electronic display...
on which the reading is displayed. Some digital calipers can be switched between metric and inch units. All provide for zeroing the display at any point along the slide, allowing the same sort of differential measurements as with the dial caliper but without the need to read numbers that may be upside down. 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.
With all of these benefits, digital calipers have by no means replaced the dial caliper. Digital calipers typically do not have the beam structure of a dial or vernier caliper and therefore do not have the repeatability or accuracy to an amateur user.
Ordinary 6-in/150-mm digital calipers are made of stainless steel, have a rated accuracy of .001" (.02mm) and resolution of .0005" (.01mm).
The same technology is used to make longer 8-in and 12-in calipers; the accuracy for bigger measurements declines to .001" (.03mm) for 100-200mm and .0015" (.04mm) for 200-300mm.
Increasingly, digital calipers offer a serial data output to allow them to be interfaced with a
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator...
. This means measurements can be taken and instantly stored in a
spreadsheetA spreadsheet is a computer application that simulates a paper worksheet. It displays multiple cells that together make up a grid consisting of rows and columns, each cell containing either alphanumeric text or numeric values...
or similar piece of software, significantly decreasing the time taken to take and record a series of measurements. The output of non-name brand calipers is usually 24 bit 90 kHz synchronous. A suitable interface to convert the output to
RS-232In telecommunications, RS-232 is a standard for serial binary data signals connecting between a
DTE and a
DCE . It is commonly used in computer serial ports...
levels and format can be built or purchased.
Like dial calipers, the slide of a digital caliper can usually be locked using a lever or thumb-screw.
Digital calipers contain a linear
encoderAn encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
. A pattern of bars is etched directly on the
Printed circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring 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
CapacitorA capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force...
s. As the slider moves the capacitance changes in a linear fashion and in a repeating pattern. The two capacitances are out of phase. 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.
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.
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, resist magnetic fields and shock proof. Can have both metric and imperial scales. However they require good eyesight or a magnifiing glass to read and are hard to read from a distance or at awkward angles.
Dial calipers are 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. Cons, only moderately shockproof. Very prone to dirt in the gearing causing errors.
Digital calipers switch easily between metric and imperial systems. Can be set to 0 easily at any point with full count in either direction. Can take measurments even if the display is completely hidden by setting to 0 in place then withdrawing and closing completely which shows the measurement in negative.
Cons, mechanically fragile, electronically fragile. Most require batteries. Most do not resist coolant well. Only moderate shock resistance. vulnerable to dirt.
The accuracy of all these types is basically the same at +/- .001" for 6" calipers.
Micrometer caliper
A caliper with a micrometer built in 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 to
micrometer.)
Use
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
elasticIn physics, elasticity is the physical property of a material when it returns to its original shape after the stress under which it deforms is removed. The relative amount of deformation is called the strain.- Modelling elasticity :...
, 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 advantageIn physics and engineering, mechanical advantage is the factor by which a mechanism multiplies the force or torque put into it. Generally, the mechanical advantage is calculated as follows:or more simply:...
. 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
zeroCalibration is the set of operations that establish, under specified conditions, the relationship between the values of quantities indicated by a measuring instrument and the corresponding values realized by standards...
. 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.
Since the 1970s a clever modification of the moveable jaw on the back side of any caliper allows for "step"-measurements. For example: the distance from the side of a screw head to the edge of a surface.
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