PWM or “Pulse Width Modulation” (also known as “Pulse Duration Modulation” or PDM), is a modulating control signal, comparable to an analogue 0-10 VDC or 0-20 mA signal. It can be used to send the requested rotational speed to an EC motor or AC fan speed controller. Another application example is to transmit the requested position to an actuator powered damper.
Typically, the EC fan speed will increase in proportion to the value of the analogue 0-10 VDC or 0-20 mA signal. For a PWM signal – a continuous train of electronic pulses consisting of a HIGH and LOW part - this works as follows:
- The frequency of the PWM signal determines the duration of one complete HIGH / LOW cycle. For example, a frequency of 1.000 Hz means: every second, the PWM signal counts 1.000 HIGH / LOW cycles.
- The comparison of the duration of the HIGH part, compared to the FULL signal (expressed in percent and also called “duty cycle”) determines the speed at which the motor or fan should run or in case of an actuator powered damper, the requested position.
A power supply is required to generate a PWM control signal. Most Sentera devices with analogue output feature an integrated power supply (3,3 VDC or 12 VDC), but in case the EC motor requires a PWM signal with a specific amplitude, an external power source should be applied.
So when using a Sentera device to control a fan (or actuator powered damper) via PWM, make sure that both the frequency (in Hz) and the amplitude (in VDC) of the modulating output of the Sentera device correspond to the frequency and amplitude requested by the external device.
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