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Q. Many electrical devices used on motor vehicles are operated by electric motors or solenoid valves where the motor speed or the solenoid position needs to be altered (Figure 5). The control signal for many of the motors and solenoids is a digital control signal provided by an electronic control unit or power control module. A process known as ‘Pulse Width Modulation’ (PWM) is
often used to alter the control signal, which in turn alters the speed of the motor or the position of the solenoid.
Which of the statements best describes how Pulse Width Modulation works?
a) Pulse Width Modulation is a process that increases or decreases the width (or time) of the ON pulses and OFF pulses of the control signal so that when the ON pulses are longer, the OFF pulses are shorter. These changes to the pulses then increase or decrease the average
voltage and current provided to the electrical device (e.g. an electric motor).
b) Pulse Width Modulation is a process that increases or decreases the frequency of the pulses of the control signal so that the width (or time) of both the ON and OFF pulses increase and decrease together. These changes to the pulses then increase or decrease the average voltage and current provided to the electrical device (e.g. an electric motor).
c) Pulse Width Modulation is a process that increases or decreases the peak voltage of the ON pulses of the control signal, which then increases or decreases the average voltage and current provided to the electrical device (e.g. an electric motor).
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