Measuring Instruments and Their Properties
Measuring instruments are the technical objects that are specially developed for the purpose of measuring specific quantities. A general property of measuring instruments is that their accuracy is known. Measuring instruments are divided into material measures, measuring transducers, indicating instruments, recording instruments, and measuring systems.
A material measure is a measuring instrument that reproduces one or more known values of a given quantity. Examples of measures are balance weights, measuring resistors, measuring capacitors, and reference materials. Single-valued measures, multiple-valued measures, and collections of measures are distinguished. Examples of multiple-valued measures are graduated rulers, measuring tapes, resistance boxes, and so on. Multiple-valued measures are further divided into those that reproduce discrete values of the corresponding quantities, such as resistance boxes, and those that continuously reproduce quantities in some range, for example, a measuring capacitor with variable capacitance. Continuous measures are usually less accurate than discrete measures.
When measures are used to perform measurements, the measurands are compared with the known quantities reproduced by the measures. The comparison is made by different methods, but so-called comparators are a specific means that are used to compare quantities. A comparator is a measuring device that makes it possible to compare similar quantities and has a known sensitivity. The simplest comparator is the standard equal-armed pan balance.
KeywordsAdditional Error Primary Standard Metrological Characteristic Accuracy Class Secondary Standard
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