We use various types of electrical measuring instruments in electrical engineering and science fields. We primarily categorize these measuring instruments as the absolute instruments and secondary instruments.
The instruments which give the measurement directly without any previous calibration are the absolute instruments. Only the deflection of the pointer on the dial is enough to indicate the measured quantity. For example, a tangent galvanometer is such instrument. Because, it indicates the current instantaneously by deflecting the pointer on the dial.
Secondary instruments are those instruments which give their measured value after calibrating them with some standard measuring instrument. In such type of instrument, the pointer deflects due to the effect of measuring quantity. Here, the deflection becomes meaningless unless we calibrate the scale with some standard measuring instrument. In our daily life, we use mostly use secondary instruments for measuring purposes. Besides, we use the absolute instruments in laboratories to standardize secondary instruments.
We can further classify the electrical measuring instruments in three categories. Here, the types of electrical measuring instrument are indicating instrument, recording instrument and integrating instrument.
Indicating instruments are those instruments which only indicate the instantaneous value of the quantity. After viewing the position of the pointer one can obtain the instantaneous value of the quantity under measurement. Normal voltmeter and ammeter come under this type of instrument. Indicating instrument does not keep any record of the quantity being measured.
Recording instrument keeps the record of the quantity being measured for a specific period of time. So, it essentially has a graphical representation of the variable quantity being measured. It represents the measured quantities for a specific period of time on a display screen or on paper.
But this type of measuring instruments does not give any instantaneous value of the quantity. Also, it does not give any graphical representation of the variation of measured quantity over a time. But it gives a total measured quantity for a certain interval of time. Therefore, the household energy meter or kilowatt-hour meter comes under the category of integrating instrument. Here we can only view the total quantity of energy consumed from the initial installation time to the instant when we are taking the reading of the meter. Also, the ampere-hour meter used for measuring the consumption of a battery comes under this category.
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