Pulse Width Modulation

Objectives


  • Define and calculate duty cycle and frequency
  • Define the major parameters of PWM.
  • List some applications and advantages of PWM.
  • Use measurements and graphs to determine PWM parameters.

What is PWM?

Pulse width modulation (PWM) is an electrical control and measurement technique.

It allows us to use a digital signal for measurement or control in a way that gives us the fine precision of an analog signal.

It's based on the idea that a digital signal switching on and off (high voltage to low voltage) at a high enough frequency will be treated as an equivalent to a steady analog signal.

Why Use PWM?

To vary a signal in an analog system what we are actually doing is varying the load resistance against a continuous current flow.

In a circuit controlled by an anolog voltage, there is considerable power used because of the continuous current flow in the load. This creates a great deal of wasted power being lost as heat.

On the other hand digital systems only generate heat when the voltage is at a high level. In PWM control applications, this can be a very small amount of time.

The effect is a large savings in the power used in the circuit.

Caterpillar Articulation Sensor

Pulse width modulation is used for a wide variety of control applications on mobile and plant equipment.

  • PWM is used to precisely control electrical actuators and solenoids, such as DC motor speed controls or hydraulic valve proportional solenoids.
  • PWM signals from position sensors and feedback circuits (hydraulic cylinder displacement sensor, boom or throttle position sensor).

PWM signal has a slower response time than an analog signal, but it is more stable against circuit resistance and supply voltage change.

A critical application controller or ECM may detect a wiring failure by monitoring the frequency of a PWM signal from a sensor.

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