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    VFD for Constant Pressure Water Supply System

    The variable frequency constant pressure water supply system takes the water pressure of the pipe network (or the user's water flow) as the setting parameter, and uses the pressure sensor to measure the water pressure in the water supply system, and then the pressure sensor will detect the signal 0-10V or 4~20ma signal. It is transmitted to the PID loop of the VFD, and after the VFD PID processing, the running speed of the water pump is adjusted according to the output frequency signal of the variable frequency drive, so as to realize the closed-loop automatic adjustment of the water pressure of the pipe network, so that the water pressure of the pipe network of the water supply system can be adjusted according to the setting. The fixed pressure value remains the same. When the user's water consumption increases, the frequency increases, the pump speed increases, and the water supply volume increases accordingly; when the water consumption decreases, the frequency decreases, the pump speed slows down, and the water supply volume decreases accordingly. It ensures the water supply efficiency and the user's requirements for water pressure and water volume, and in a real sense, it has the effect of how much water is used, how much water is supplied.

    Basic Wiring Diagram

    VFD basic wiring diagram

    Set parameters

    Parameters that must be set when in constant pressure water supply mode.

    P7:00 1 Must select 1 in constant pressure water supply mode.
    P7:01 0 Close loop given channel selection from P7.05.
    P7:02 6 Set according to the type of on-site pressure sensor.
    P7:05 0.48 Set according to site target pressure.
    P7:19 0.22 Generally lower than P7.05 value.
    P7:20 0.52 Greater than or equal to P7.05 value.
    P7:21 2 Sleep level continuous time.
    P7:22 20 Sleep frequency can be set 20 or 30Hz.
    P7:26 1 One for one water supply mode.
    P7:27 0.6896 Set according to the range of the pressure gauge.

    The following parameters are set according to the specific requirements of the work conditions.

    P3:46 15 The second row of digital tubes shows feedback pressure, there are 2 rows of digital tubes that need to be set.
    P7:08 0.01 P7.05 allowed minimum set pressure value.
    P7:09 0.8 P7.05 allowed maximum set pressure value.
    P7:11 5 Adjust system response speed.
    P7:16 10 PID feedback disconnected detection threshold (rang: 0.0-20.0%).
    P7:17 0 PID feedback disconnection selection stop model.
    P7:18 0.1 PID feedback disconnected operation delay time.
    P7:23 2 Sleep frequency continuous time.

    Function overview

    In the constant pressure water supply mode, after setting the above parameters according to the working conditions, when b-15 (feedback pressure) is equal to or greater than the set pressure of P7.05, the frequency of the VFD will slow down according to the deceleration time of P0.18 until it drops to the sleep frequency set by P7.22. After continuous sleep frequency of P7.23, the frequency drops to 0Hz. When the pipeline pressure drops to the awakening pressure value set by P7.19, the frequency of the VFD will accelerate according to the acceleration time set by P0.17 until the pressure value set by P7.05 is reached. Then, the VFD frequency starts to circulate according to the above mode to achieve the constant pressure and pressure holding function of the water supply system.


    • In the site application, sometimes accidentally hit the potentiometer will change the given pressure of P7.05, at this time by setting P3.01 = 01 can avoid this problem.
    • After the parameters are set, the frequency starts running to 20Hz or 0Hz and then the frequency does not go up. Generally, it is necessary to check whether the actual pressure of the b-15 online monitoring is greater than the set value of P7.05. If yes, please check whether the sensor wiring is correct or not.
    • The parameter is set and start running, the frequency stays at 50Hz. When this problem occurs, it is necessary to check whether b-14 is equal to the setting value of P7.05. Second, check whether b-15 has feedback pressure, and then Check if the parameters are set correctly.
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