What speed does a frequency meter directly indicate?

A frequency meter is designed to measure the frequency of alternating current (AC) voltage. The frequency of the AC is related to the rotational speed of machinery that produces that AC, such as generators. Thus, when measuring the frequency output of a generator, which typically operates at a specific RPM to produce a standardized frequency (like 60 Hz in the U.S.), the frequency meter directly indicates the speed of the generator.

The relationship between frequency (in hertz) and rotational speed (in RPM) is given by the equation:

[ \text{Frequency (Hz)} = \frac{\text{RPM} \times \text{Poles}}{120}. ]

This equation illustrates how any change in the generator's RPM will affect its output frequency. Since the question specifically asks which speed the frequency meter indicates directly, the correct answer focuses on the generator RPM, as it is the primary application of a frequency meter in this context.

In contrast, other options such as motor, pump, or fan RPMs could also be indirectly measured if the equipment is designed to produce a specific frequency upon their rotation; however, a frequency meter is most commonly and directly associated with the output of generators.