Red Seal Instrumentation and Control Technician Practice Exam

How does pulse-width modulation (PWM) control power delivery to a device?

1. By varying the frequency of the signal

2. By changing the amplitude of the voltage

3. By varying the width of the pulse in a fixed period

4. By alternating the signal between high and low states

The correct answer is: By varying the width of the pulse in a fixed period

Pulse-width modulation (PWM) controls power delivery to a device by varying the width of the pulses in a fixed time period. This technique involves turning a signal on and off at a high frequency within that period, allowing for the adjustment of power delivered to a load without changing the frequency of the signal itself. The concept of PWM is based on the duty cycle, which is the ratio of the "on" time to the total period of the cycle. By increasing the width of the pulse (the "on" time) while keeping the frequency constant, more power is delivered to the device. Conversely, by decreasing the pulse width, the amount of power delivered is reduced. This makes PWM especially effective in applications such as motor speed control, light dimming, and heating elements, as it allows for precise control over the power output and efficiency. In contrast, other methods such as varying the frequency of the signal could lead to instability or undesirable performance in certain applications, changing the amplitude of the voltage may require more complex circuitry and does not provide the same level of efficiency, and simply alternating the signal between high and low states does not give the same nuanced control over power delivery that pulse-width modulation offers. Therefore, varying the width of the pulse in a fixed