Instruments for measuring
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Measuring instruments [‘---]
In physical [‘---] sciences, quality assurance, and engineering, measurement is the action of
obtaining and comparing physical quantities of real-world objects and procedures.
Established standard objects and procedures are used as units. Measuring instruments, and
formal test methods which define the instrument's use, are the means by which these
numbers are obtained. All measuring devices are subject to varying degrees of instrument
error and measurement imprecision.
Scientists and engineers use a vast range of gauges (rhymes with ‘ages’) to perform their
measurements. These instruments may range from uncomplicated objects such as rulers and
stopwatches to electron microscopes and particle accelerators.
Measuring distances [‘---]
There are different types of instruments for measuring distances. At school you use a ruler or
the scale of a geometric triangle [--‘—‘---] to get the exact length of a line. At home you
have a folding rule; with its help you can measure, for example, the length, width or height
of a cupboard.
At work, precision is one of the most important features. Therefore you need special
instruments like gauges, vernier callipers, or micrometers.
Gauges are instruments used in mechanics to test, for example, the size, angle or shape of
an item being worked on or ‘workpiece’. If you find out that a workpiece has not got the
requested qualities, it is rejected. With vernier callipers you can measure, for example, the
length or diameter of a workpiece. Micrometers are used to measure very small distances.
Calliper [‘- - ]
A vernier calliper [‘- - ]
A caliper (British also spelling calliper) is a device used to measure the distance between
two opposite sides of an object. Looking at the picture you can see the outside jaw of a
vernier calliper and part of a round workpiece. What you want to measure now is the external
dimension of the workpiece. To get an exact result, you must firmly hold the workpiece
against the fixed jaw and push the movable jaw carefully against it.
If you want to measure the inside dimension of a workpiece you use the inside jaws for
getting the internal dimension. Therefore you press the fixed jaw against the workpiece. Then
move the other jaw to the opposite side.
A calliper can be as simple as a compass with inward- or outward-facing points. The tips of
the calliper are adjusted to fit across the points to be measured, the calliper is then removed
and the distance read by measuring between the tips with a measuring tool, such as a ruler.
Callipers are used in many fields such as metalworking, mechanical engineering,
gunsmithing, woodwork and medicine.
A micrometer sometimes known as a micrometer screw gauge, is a device incorporating a
calibrated screw used widely for the precise
measurement of small distances. It is used in
mechanical engineering and machining as well as
most mechanical trades, along with other metrological
instruments such as dial, vernier, and digital callipers.
Micrometers are often, but not always, in the form of
callipers.
A micrometer
An opisometer [--‘---], also called a meilograph or map measurer, is an instrument for
measuring the lengths of arbitrary curved lines.
A simple opisometer consists of a toothed wheel of known circumference [-‘---] on a handle.
The wheel is placed in contact with the curved line to be measured and run along its length.
By counting the number of teeth passing a mark on the handle, the length of the line can be
determined:
line length = wheel circumference × teeth counted/teeth on wheel.
In more sophisticated models, the wheel is connected via
gearing to a rotary dial from which the line length can be
directly read.
The instrument is most commonly used to measure the
lengths of roads, rivers and other line features on maps.
Opisometers designed for this purpose provide scales
reading the measured distance in kilometres or miles.
An opisometer
A ruler, sometimes called a rule or line gauge, is an instrument used in geometry, technical
drawing, printing and engineering/building to measure distances and/or to rule straight lines.
Strictly speaking, the ruler is essentially a straight edge used to rule lines, but typically the
ruler also contains calibrated lines to measure distances.
Different rulers
An architect's
scale is a
specialized
ruler. It is used
in making or
measuring
from reduced
scale
drawings,
such as blueprints and floor plans. It is marked with a range of calibrated scales.
For accuracy and durability the material used should be resilient and stable in its size and
shape. Scales were traditionally made of wood, but today they are usually made of rigid
plastic or aluminium (aluminum U.S.). Architect's scales may be flat, with 4 scales, or have a
symmetrical 3-lobed cross-section, with 12 scales.
An architect's scale