The valve electric device control box is mainly composed of a power module, a control module, a drive module, a display module and a protection module. The power module is responsible for converting the external input power into the voltage required by the various components of the control box. The control module, as the "brain", receives and processes various control instructions and feedback signals; the drive module provides driving current for the electric actuator according to the instructions of the control module to realize the opening, closing and adjustment of the valve; the display module displays the valve status, operating parameters and other information in real time; the protection module ensures the safe operation of the system through overload protection, short circuit protection and other mechanisms. These modules work together to form a complete control system.
Manual control is the basic function of the valve electric device control box, which is particularly important in emergency situations or system debugging. The operator directly sends instructions to the drive module through the buttons on the control box panel (such as open valve, close valve, stop button). For example, when the valve opening button is pressed, the control circuit is turned on, and the drive module transmits current to the motor of the electric actuator. The motor drives the deceleration mechanism, which in turn drives the valve stem of the valve to rotate or move linearly to open the valve. During this process, the limit switch in the control box monitors the valve position in real time. When the valve reaches the fully open or fully closed position, the limit switch is triggered to cut off the power supply to the motor to prevent damage caused by excessive movement of the valve.
In automatic control mode, the control box needs to work in conjunction with an external control system (such as PLC, DCS system). The external control system sends control instructions to the control box according to process requirements (such as pipeline pressure and flow setting value). The instructions are usually transmitted in the form of 4-20mA current signals or digital signals of communication protocols such as Modbus and Profibus. After receiving the instructions, the control module of the control box compares them with the feedback signal of the current position of the valve, and calculates the operating parameters of the drive motor through the PID (proportional-integral-differential) adjustment algorithm. The drive module controls the motor speed and direction accordingly, so that the valve opening reaches the target value, and the process parameters are accurately adjusted.
Analog signal transmission is widely used in valve control, and the most common one is 4-20mA current signal. The 4-20mA signal output by the external control system represents different control instructions, such as 4mA for fully closed valves and 20mA for fully open valves. After receiving the signal, the control box converts the current signal into a voltage signal through the signal conditioning circuit, and then converts the analog quantity into a digital quantity through the A/D converter for processing by the control module. At the same time, the control box feeds back the status information such as the valve position to the external control system in the form of a 4-20mA signal to form a closed-loop control. This signal transmission method has strong anti-interference ability and is suitable for medium and short-distance signal transmission.
With the development of industrial automation, digital signal transmission is becoming more and more common. The control box supports communication protocols such as Modbus and Profibus, and exchanges data with external devices through interfaces such as RS485 and Ethernet. Taking the Modbus protocol as an example, the master device (such as PLC) sends a message containing address, function code, and data to the control box (slave device). After parsing the message, the control box performs the corresponding operation and transmits the feedback data back in the protocol format. Digital signal transmission has the advantages of long transmission distance, large data volume, strong anti-interference ability, and is easy to realize the networking and centralized monitoring of multiple control boxes.
Due to the existence of interference sources such as electromagnetic interference and power supply fluctuations in industrial environments, the control box adopts a variety of anti-interference measures to ensure the accuracy of signal transmission. At the hardware level, the signal is transmitted through shielded cables to reduce electromagnetic interference; filter circuits are set to suppress power supply noise; photoelectric isolation technology is used to cut off the conduction path of interference signals. At the software level, digital filtering algorithms are used to process the collected signals to remove noise interference; the accuracy of data transmission is verified through the check code mechanism (such as CRC check) to ensure reliable interaction between control instructions and feedback information.
The valve electric device control box works closely with the electric actuator to achieve precise control of the valve. The control box outputs a drive signal to the electric actuator according to the control instruction, and the electric actuator converts electrical energy into mechanical energy to drive the valve to move. At the same time, the position sensor (such as potentiometer, encoder) in the electric actuator detects the valve position in real time and feeds the signal back to the control box. The control box adjusts the drive signal according to the feedback signal to form a closed-loop control to ensure that the valve opening is consistent with the control command. In addition, the torque sensor in the electric actuator can detect the torque change during valve operation. When the torque exceeds the set value, an alarm signal is sent to the control box, and the control box stops the motor operation in time to prevent damage to the valve or actuator.
