Comparator

comparator

Instrument for comparing something with a similar thing or with a standard measure, in particular to measure small displacements in mechanical devices. In astronomy, the blink comparator is used to examine photographic plates for signs of moving bodies. Machinists use comparators or visual gauges to centre or align work in machine tools.

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comparator

A device that compares two quantities and determines their equality.

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comparator [kəm′par·əd·ər]

(analytical chemistry)

An instrument used to determine the concentration of a solution by comparing the intensity of color with a series of standard colors.

(computer science)

A device that compares two transcriptions of the same information to verify the accuracy of transcription, storage, arithmetical operation, or some other process in a computer, and delivers an output signal of some form to indicate whether or not the two sources are equal or in agreement.

(control systems)

A device which detects the value of the quantity to be controlled by a feedback control system and compares it continuously with the desired value of that quantity.

(engineering)

A device used to inspect a gaged part for deviation from a specified dimension, by mechanical, electrical, pneumatic, or optical means.

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Comparator 

in astronomy, a measuring device whose operation is based on the principle of comparing two astrophoto-graphs, spectrograms, and the like, one of which is taken as the standard. There are several types of comparators, which are distinguished by their purpose and method of comparison. Some comparators compare the second pulses of clocks with the time of contact of micrometers (tape recorded) of transit instruments. In measuring the tape in such comparators, the distance between the second impulses of clocks is the standard. In spectrocomparators, spectrograms of stars are compared and the displacement of one or another group of spectral lines belonging to one star from the same group of lines belonging to another star (or laboratory light source) is measured. In this way, the radial velocity of a specific star can be established if the radial velocity of the reference star (comparison star) is known.

Comparators also include certain instruments that help detect changes that have occurred in celestial bodies; this is done by comparing two astrophotographs or spectrograms obtained at different times. Such comparators are blink comparators, in which the comparison is accomplished by alternately looking at two photographs (blinking). In stereocomparators the change in position of a celestial object relative to other objects is revealed by simultaneously looking at two astrophotographs by means of a stereoscopic image of the shift.

E. A. IUROV

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Comparator 

a measuring instrument used to compare linear quantities with a measure or scale. A comparator measures the difference between two quantities whose nominal magnitudes are close; this provides high precision of measurement. A comparator may be used to compare a dimension of the object being measured with the distance between lines on a standard scale (line comparator) or with the end block (end comparator). Instruments of a different type, which also use a comparative method, are sometimes also called comparators (for example, an interference comparator).

Measuring devices used in comparators include microscopes with vernier, scale, or optical eyepiece micrometers; photoelectric microscopes with digital readout; and interferometers.

Lengths measured with comparators range from fractions of a millimeter to dozens of meters. Comparators are used in metrology for comparing length standards 0.1 to 4 m long, in machine building for checking part dimensions up to 1 m, and in geodesy.