Which two devices are used to monitor the speed of the motor for feedback in a DC drive?

• A. Tachometer and Encoder
• B. Tachometer and Voltmeter
• C. Encoder and Ammeter
• D. Voltmeter and Ammeter

Answer: (A)

Speed feedback in a DC drive relies on sensors that translate shaft speed into signals the controller can use to regulate the motor. A tachometer provides a voltage proportional to motor speed, giving a continuous analog measure of rpm. An encoder sits on the shaft and emits pulses as it turns; by counting those pulses (and possibly determining direction with a quadrature arrangement), the drive can determine speed with good precision. Using both sensors gives reliable, versatile speed feedback for closed-loop control. In contrast, a voltmeter and an ammeter only measure electrical values and don’t directly indicate how fast the shaft is turning, so they aren’t suitable for speed feedback.