Which statement describes the devices used to provide speed reference signals in a closed-loop speed control system?

• A. Tachometer/generator
• B. Optical encoder
• C. Both tachometer/generator and optical encoders
• D. Voltage regulator

Answer: (C)

In a closed-loop speed control system, you need a signal that reflects how fast the shaft is actually turning so the controller can compare it to the desired speed. A tachometer or tachogenerator mounted on the shaft yields a voltage that is proportional to speed, giving continuous analog feedback to the controller. An optical encoder, on the other hand, provides speed information through pulse frequency: as the shaft spins, the detector reads pulses and the controller converts that into speed (and, with proper wiring, direction as well). Because both devices deliver a signal that represents the real speed of the motor, either can be used to feed the loop and regulate speed. A voltage regulator, by contrast, stabilizes supply voltage and does not provide speed feedback information.