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The SMT surface mounting line is generally composed of screen printing machine, SMD mounting machine and reflow oven.
Lead-free reflow soldering technology is the most important welding process in current surface mounting technology. There is a heating circuit inside the equipment, which heats air or nitrogen to a high enough temperature and then blows to the circuit board where the components have been affixed, so as to melt the solders on both sides of the components and bond the components to the main board.
The advantage of this process is that the temperature is easy to control, the oxidation can be avoided in the welding process, and the manufacturing cost is easier to control. The difficulty of control is how to quickly raise the temperature to a set value with small temperature fluctuation.
2 System configuration
1. System configuration and description
The system requires 60-point IO and 28-way temperature control. It is equipped with one Megmeet MC100 series PLC, three MTC-08-NT (8-way temperature control module), one MTC-04-NT (4-way temperature control module), and one computer monitor. The configuration diagram is as follows:
1> The computer and PLC are connected by RS232, and adopt MODBUS communication protocol.
2> The MC100 series PLC is connected with four MTC temperature control modules and four variable frequency drives through its own RS485, and adopts standard MODBUS communication protocol.
2. Key control points
1> MTC temperature control: MTC assistant software is provided for debugging. Control function setting: select sensor type, set value, and control output cycle (as shown in the figure below):
2> Chart / table monitoring: self-tuning operation, automatic adaptation to PID parameters, no need to explore. Self-tuning: The self-tuning function is enabled by the internal self-tuning algorithm of the thermostat to simulate the temperature rise process of the equipment. After self-tuning, the proportional band, integral time and differential time of the channel PID control parameter unit will be changed to the self-tuning control parameters (as shown in the figure below):
3> The MC100 series PLC uses MODLINK form to communicate with four MTCs and four variable frequency drives without the need of complex programming, which is easy and convenient (as shown in the figure below).
After using Megmeet MC100 series PLC and MTC, the equipment runs steadily and reliably, which greatly saves the customer debugging and maintenance time. The specific advantages are as follows:
1. MTC multi-channel intelligent temperature control module, self-tuning PID parameters, easy to achieve multi-temperature zone control, the accuracy can reach up to ±1˚C;
2. The MC100 series PLC is equipped with 2 communication ports, 1 computer, 1 temperature control and variable frequency drive to save cost;
3. The MODLINK simplified table-filling instructions can easily realize the communication between PLC and multiple temperature controllers and variable frequency drives through MODBUS without taking up scanning time;
4. It provides DLL of MODBUS protocol, which is convenient to use VB, VC and other high-level languages to call, and is easy to read and write PLC data;
5. In MC100, the data saving upon power off is realized through internal capacitors, so there is no need of battery and user needs not worry about battery maintenance. (Top)