Briefly analyze the control of PLC products on the various parameters of the glass melting furnace
1. System overview
The stable operation of each parameter of the glass melting furnace is very important, and it directly affects the output and quality of the glass. In the glass production process, there are strict requirements for the stability of the kiln pressure and temperature. At the same time, the writing of the kiln pressure and temperature involves other links and parameters, such as the pressure and temperature of the fuel, the pressure of the atomizing medium, and the reversing process. and many more. To achieve the stability of these parameters, and to achieve better coordination, there are different ways to achieve. With the development of microelectronics technology, PLC products are greatly enriched and improved in their functions and performance indicators. Therefore, we apply some special function modules of PLC and some ordinary I/O modules to the various parameters of the glass melting furnace. Carry out automatic control, including the various parameters mentioned above, the commutation control of the furnace, and the control of the output frequency of the inverter through the communication between the PLC and the inverter. The system has been operating in good condition since it was put into use.
2, system configuration
The upper computer part of this system selects a host computer with FIX software package, and the PLC part selects a well-known brand PLC, which has the characteristics of low cost, reliable operation and strong functions. Actuating agencies mainly include frequency converters, solenoid valves, membrane control valves, three-phase asynchronous motors, etc.
3, PLC functions
This system can be roughly divided into three parts; 1. PID adjustment part, 2. commutation system of the melting furnace, 3. communication part of PLC and inverter. The PID adjustment part includes the control of oil pressure, oil temperature, oil flow (No. 1-6), atomizing medium, kiln pressure and other parameters.
3.1PlD adjustment part
PID control is mainly through PID control unit, this unit mainly has the following characteristics: 1, l00ms high-speed sampling cycle, high-speed PID control is realized. 2. The digital filter attenuates input noise and controls unexpected input interference, making PID control an effective fast response system. 3. A variety of output specifications are available. 4. Eight groups of data settings, eight values (such as set point (SP) and alarm setting value) can be preset in eight data groups. 5. You can use the data setter to input and display the current value. 6. Advance PID control, use the characteristics of advance PID controller and automatic tuning to obtain stable PID control. 7. PLC program can be used to input and retrieve data. At the same time, we realize dual PID control through PLC program, thus realizing stable operation of kiln pressure and oil flow.
PID control can be divided into two modes: local control and remote control. Remote control is the control realized by PLC, and there are automatic and manual modes. Automatic control is fully automatic control by PLC without manual intervention. Manual control means that a valve position output value is given on the upper computer, and the valve position is controlled by PLC. Under normal circumstances, it is carried out in the automatic state under the remote control mode, and the SV value, PV value and OUT value of each PID control loop can be displayed on the host computer with a bar graph, which is very intuitive.
At the same time, the PID parameters of each control loop such as oil temperature, oil pressure, oil flow, atomizing medium, kiln pressure, etc. can be easily modified on the host computer, such as set value (SV), "P" value, "I" value , "D" value, and the operation interface is very friendly and easy to operate.
3.2 Reversing part of the furnace
The commutation of the furnace is divided into three modes: manual, semi-automatic, and automatic. Manual operation is performed on the control cabinet; semi-automatic and automatic are both controlled by PLC. Under normal circumstances, they operate under fully automatic reversing state. No manual intervention is required, as long as the reversing time is set on the upper computer, the PLC will automatically reversal according to the given time. And PLC can automatically recognize the direction and display it on the host computer. At the same time, it can ensure that there is no disturbance switching between the three states of active/semi-automatic/automatic.
3.3 Communication between PLC and inverter
Fieldbus is an advanced technology that has entered the field of industrial field control in recent years. In this project, we adopted DeviceNet open fieldbus to realize the communication between PLC and inverter. DeviceNet has many characteristics; 1. It is an open field bus network, and machines of various domestic and foreign manufacturers that conform to the DeviceNet bus standard can be connected. 2. It supports a wide range of data processing operations, from the usual ON/OFF data processing to the data bit operation of the bar code reader. 3. DeviceNet guarantees a baud rate of 125kbps and a maximum data transmission distance of 500m between nodes, so it is simple and convenient to apply on a longer production line. When a certain PLC model is used, it can use up to 2048 I/O points and 63 slave stations. In the past, we all used an analog signal (4-20mA or 0-10v) to control the output frequency of the inverter, so as to achieve the requirements of energy saving or speed regulation. However, whether the analog signal is a 4-20mA current signal or a 0-l0v voltage signal, even if it is digitally processed, it is still transmitted as an analog signal during the transmission process, which is susceptible to interference. At the same time, the accuracy of the analog signal is relatively high. Low, can only be used in systems with low accuracy requirements. In systems with high accuracy requirements, analog signals are also susceptible to interference, causing system instability. We use communication to control the output frequency of the inverter. , Is a purely digital control, that is, digital processing adopts digital processing, and the transmission is purely digital transmission with high precision, which can make the output frequency of the inverter very stable. At the same time, the operating status and fault information of the inverter can be displayed on the host computer.
After the system is applied to a certain glass production line, it runs stably and reduces the labor intensity of the operator. It is well received by the production branch. Before the system was reformed, the oil flow control could not be automatic, and it was in manual control state for a long time. It was necessary to adjust the opening of the flow valve very frequently, and the workload was very large. After the transformation, automatic control can be fully realized. Moreover, the operation of the system is very convenient. All the parameters that need to be modified can be directly input on the host computer, such as the start/stop of the inverter, the reference frequency, the parameter value of each PID control loop, etc. In addition, the system has low price and low investment, which reduces product costs and has significant benefits.