Hi guys,

I am an engineer but have not knew the variable frequency drive before, now I want to build a constant pressure water supply system to supply our company, the system constant pressure approx 0.2MPA, I want it stop running automatically when nobody needs water, I have a variable frequency drive and a pressure transmitter, I do not know how to set it, anyone any advise?

In the constant pressure water supply system, variable frequency drive is the core part of the whole water supply system. The system consists of: motor pump is the output, the speed is controlled by variable frequency drive to achieve variable flow and constant pressure control. The VFD drive accepts PID controller signal to control the pumps speed, pressure sensor detects the water pressure of the pipe network, and send the signal to PID controller, to adjust the frequency of the variable frequency drive by PID controller to control the speed of the pump, to achieve a closed-loop control system.

Control method:
a: S1-COM terminal control start/stop
b: If the feedback signal is remote pressure gauge. take the power on +10V terminal.
c: Given signal, given by the control panel (keyboard).
d: Water supply card relay output wiring terminals: RT1A, RT1B, No. 1 frequency pump; RT2A, RT2B, 1 working frequency pump;

Hope it helps.

I suggest add an additional flow switch behind the pump for start/stop control, it's best to use PLC control system, if you just use PID control function of the variable frequency drive, the speed will slow significantly.

Detect the pump pressure by pressure sensor, and then fed back the value to the PLC, closed-loop calculation (such as PID) in the PLC, finally write the value into the variable frequency drive and control the value.