The correct answer is D. electrical resonance frequency meter.
A Weston frequency meter is a type of frequency meter that uses a Weston cell to measure the frequency of an alternating current. A reed vibrator frequency meter is a type of frequency meter that uses a reed switch to measure the frequency of an alternating current. A heterodoxy frequency meter is a type of frequency meter that uses a heterodyne circuit to measure the frequency of an alternating current. An electrical resonance frequency meter is a type of frequency meter that uses the principle of electrical resonance to measure the frequency of an alternating current.
Electrical resonance occurs when the frequency of an alternating current is equal to the natural frequency of an electrical circuit. When this happens, the current in the circuit is amplified. This principle can be used to measure the frequency of an alternating current by using a circuit that has a known natural frequency. The current in the circuit is then measured and the frequency of the alternating current is determined from the natural frequency of the circuit.
Electrical resonance frequency meters are the most accurate type of frequency meter. They are also the most expensive type of frequency meter. They are typically used in laboratory settings where high accuracy is required.
Weston frequency meters are less accurate than electrical resonance frequency meters, but they are less expensive. They are typically used in industrial settings where accuracy is not as important as cost.
Reed vibrator frequency meters are the least accurate type of frequency meter. They are also the least expensive type of frequency meter. They are typically used in consumer products where accuracy is not important.
Heterodoxy frequency meters are not commonly used. They are more complex than the other types of frequency meters and they are not as accurate.