Which of the following describes types of tachometers?

Tachometers are crucial instruments used to measure the rotational speed of an engine's components, usually expressed in revolutions per minute (RPM). The correct answer encompasses the broad range of tachometer types effectively.

The categories identified in this answer include both electrical (DC and AC) and non-electrical (mechanical) types, which highlights the diversity in tachometer designs. DC tachometers are commonly used in applications where precise speed control is necessary, while AC tachometers are utilized in various industrial settings where alternating current power sources are prevalent. Mechanical tachometers use physical movement to measure speed, reflecting a more traditional, yet still relevant, method of speed measurement.

Additionally, mentioning analog and digital tachometers illustrates the technological evolution of these instruments. Analog tachometers provide a continuous, real-time output through dial indicators, while digital tachometers offer numerical readouts, often with enhanced accuracy and additional features.

This comprehensive classification allows for a better understanding of tachometers' functionality across different applications, ensuring one can choose the correct type for specific engine diagnostics or performance monitoring tasks.