ALL ENGINEERS make measurements and take instrumental readings from time to time. Often the accuracy of these observations is of less importance than their change with time, nevertheless we must know whether the impressions gained from our instruments are reliable or not. This chapter is a guide to what to look for in an instrument and what to expect from a measurement. We shall limit our discussion to a few variables, though these are of the greatest importance to more than electrical engineers, namely, frequency, voltage, current, resistance, capacitance, inductance, magnetic field, temperature and displacement. Before we examine any instruments, however, we need to consider the meaning of certain words associated with measurements in general.
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