1.the advantages of constant temperature and constant pressure water supply.

Constant temperature and pressure water supply system is very important for life, for example, in the process of housing water supply, if the tap water supply pressure is insufficient or short-term water cut-off, it may affect the lives of residents. If the water supply pressure is insufficient or there is no water supply, the fire can not be extinguished quickly, which may cause heavy losses and casualties. Constant temperature water supply ensures that the user's water is kept within the set temperature range. Therefore, it is of great economic and social significance to adopt the dual constant pressure water supply system of life/fire fighting in living quarters.

Based on the above situation, our company developed a water supply system for a hotel, using Siemens 224 CPU plus our own UniMAT digital quantity module and temperature module as the main control unit, using Siemens inverter, according to the system state can quickly adjust the working pressure of the water supply system to achieve the purpose of constant pressure water supply.

2. the basic control strategy of water supply control system.

The control system is composed of motor speed regulating device and programmable logic controller (PLC), which optimizes the speed regulating operation of the pump group and automatically adjusts the number of pumping units. The closed-loop control of the water supply pressure is completed. The purpose of stabilizing the water supply pressure and saving electric energy is achieved when the flow of the pipe network changes. The control target of the system is the outlet pressure of the main pipe of the pumping station. The value of the feed water pressure set by the system is compared with the actual value of the feedback pressure of the main pipe. After the difference is input into the CPU operation, the control command is issued to control the number of pump motors running and the speed of variable pump motors running, so that the pressure of the main pipe of the pumping station is stable. On the set of pressure values. Constant pressure water supply is a closed loop control of industrial process realized by PID or PI function of frequency converter. The pressure signal (4-20mA) measured by the pressure control point is directly input into the frequency converter, which is compared with the pressure value set by the user. The result is converted into the frequency regulation signal to adjust the power frequency of the pump motor by the built-in PID operation of the frequency converter.

The communication between frequency converter and PLC calls only USS library program, and programming is simple and clear. UniMAT Temperature Module (231.7PD22) temperature measurement error control within 1 C, can effectively ensure the detection of water temperature, the digital input channels to detect low water level signals, the output channel according to the set procedures to control the operation of the switches and water valves, to ensure the correct operation of the system.

3.the basic composition of the water supply system

Frequency conversion constant pressure water supply system uses a Siemens inverter to drive four 0.5KW power motors, which can operate in both frequency conversion and power frequency mode. The user sets the water pressure through the man-machine interface, and monitors the electrode speed, frequency, running state and water pressure through the touch screen.

Starting mode: In order to avoid the impulse current when starting, the motor uses frequency conversion starting mode, from the inverter output terminal to gradually increase the frequency and voltage. Before starting, the inverter must be reset.

Frequency conversion speed regulation: according to the water supply pipe network flow, pressure change automatic control inverter output frequency, so as to adjust the motor and pump speed, to achieve constant pressure water supply. If the output voltage and frequency of the equipment can not meet the requirements of water supply when the output voltage and frequency rise to the power frequency, the PLC issued instructions No. 1 pump automatically switched to the power frequency power operation, until No. 1 pump completely quit the frequency conversion operation, after resetting the inverter, No. 2 pump into frequency conversion operation.

Multi-pump switching: according to the need of constant voltage, adopt the principle of no primary and secondary switching, that is, "start first stop" access and exit. In the PLC program, by setting the working number of the frequency conversion pump and the number of power frequency pumps, the pump increase or decrease can be judged by whether the given frequency reaches the upper or lower limit frequency. When the water consumption is small, the auxiliary pump is used.

The water supply system is divided into three parts, one is cold water, the other is heated hot water. The two parts of water are collected to the third part by water valve control. The part is equipped with water temperature detector, which feeds back the temperature signal to UniMAT temperature control module, and then controls the switch of the first two parts of the water valve by PLC to control the third part of water. The temperature is kept within a set range.

In order to prevent a pump from working for a long time, any pump can not run continuously for more than 3 hours. When the number of power frequency pumps is zero and one pump is running in the state of frequency conversion, start the timer, when it reaches 3 hours, the pump number of frequency conversion pump changes, that is, switch to another pump. When a pump runs in the power frequency state or the auxiliary pump starts, the timer stops counting and zeroing.

Fault handling: it can alarm the lower limit of water level, frequency converter, PLC fault and so on. PLC failure, the system automatically transferred to manual mode.

Monitor program: System main form of four button controls, respectively, parameter settings, real-time monitoring, start and close the system, users can modify the actual situation of pressure, temperature settings.

The main control functions include:

(1) pressure setting value range: 0.30-0.60Mpa; water temperature setting range: 5 C -60 C.

(2) correction factor: mainly for correction of pressure display, so that pressure display is consistent with the pressure gauge.

(3) reset button: press down in operation, which will restart the system and return the parameters to the initial settings.

(4) Setting button: Press this button after the text box input pressure settings and correction coefficients, pressure settings and correction coefficients can be sent to the lower computer through the serial port.