What is PWM?

The full name of PWM is Pulse Width Modulation. PWM is a way to control analog devices with a digital output. Another way to put it is that you can output a modulating signal from a digital device such as an microcontroller(MCU) to drive an analog device. It’s one of the primary means by which MCUs drive analog devices like variable-speed motors, dimmable lights, actuators, and speakers. PWM is not true analog output, however. PWM “fakes” an analog-like result by applying power in pulses, or short bursts of regulated voltage.

Why does circulator pump need PWM?

PWM make it possible to control the pump in a remote distance through a digital cable transmitting digital signal. Pumps with PWM control are widely used in the gas boilers systems and heat pump systems.

How does PWM work on circulator pump?

Control principles

When PWM signal is connected, the operation of circulating pump is controlled by PWM signal. If there is no PWM signal, the operation of circulating pump is controlled by internal control logic.

PWM input signal

At high PWM signal percentages (duty cycles), a hysteresis prevents the circulating pump from starting and stopping if the input signal fluctuates around the shifting point. At low PWM signal percentages, the circulating pump speed is high for safety reasons. In case of a cable breakage in a gas boiler system, the circulating pump will continue to run at maximum speed to transfer heat from the primary heat exchanger. This is also suitable for heat pumps to ensure that the circulating pump can transfer heat in case of a cable breakage. When PWM input signal is 0% or 100%, the pump will switch to non-PWM mode (normal mode), and the default system will have no PWM signal input.

PWM Feedback Signal

PWM feedback signal reflects operation status of the pump.

If the pump power voltage goes below the voltage signal value, then its output signal would be set as 75%. If pump rotor being blocked, the output signal would be set as 90%, then the warning would be given.

PWM signal application

PWM signal can be used to measure power consumption of the pump. Also it can be used to detect the actual operating status of the system rather than by measuring the system itself. The signal is also applicable to comparing velocity setting value and feedback.

Take PWM circulator pump HE25-6 for example:

A boiler system sends a PWM signal setting of HE25-6 to 41%, see Figure A.

When the control system detects the 41% PWM signal, the circulator pump flow rate will be set to about 1.2m³/h and corresponding head of delivery is 2.7m, see Figure B.