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