145 Measuring Instruments

Instruments serve two functions in maintenance— checking equipment condition and on-line monitoring. It is often impossible to know whether some equipment is functioning properly without measuring a temperature, pressure, or other parameter associated with the operation of the equipment. For example, the only indication that a steam trap is not working properly may be the absence of a regular clicking as the trap opens and closes, and this noise may be detectable only with a stethoscope. A similar use of instruments is checking on the effectiveness of repairs. Another function of instrumentation is to observe major system operating parameters so that equipment can be operated with the minimum effective use of energy. Instrumentation for this purpose is generally mounted permanently, with gauges readable either at the equipment or at some central location.

Measuring instruments used in maintenance can be classified by type or by function—by type according to what they measure, by function according to what system they serve. A classification of instruments into these categories is shown in Table 14.18, followed by descriptions of each instrument in the table.

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