Design And Implement Of PLC Based On IEC61131-3 Standard

Application of PLC(Programmable Logic Controller) in industrial control field is widespread; however the disunity in programming language causes inconvenience. The publication of IEC61131-3 provides standardization programming methods. It's very important to research programmable logic controller based on IEC61131-3 standard.Aiming at the features of industrial control system and field bus as well as the advantages of PLC, this paper designs programmable logic controller named PEC3000 based on IEC61131-3 standard, moreover forms the distributed field bus control system based on RS485 bus around PEC3000 controller. The communication model of the control system is also introduced, the physical layer adopts RS485 interface, the data link layer adopts modbus protocol, the application layer specifies communication services, bridge services and device management services, the management information base corresponds network devices to work in unity. The user layer supports IEC61131-3 standard programming language and provides open development enviroment for users.PEC3000 adopts ARM7TDMI-S CPU LPC2138, the controller can realize 4-channel high speed counter, 20-channel digital input, 1-channel PWM output, 18-channel digital output and 2-channel analog output. In order to measure the pulse number in interrupt method and count active signal frequence, each high speed counter channel is connected to the interrupt pin of CPU. Nonpolar switch state is imported through bipolar optocoupler in digital input, and Darlington transistor arrays with open connector are utilized to enhance output drive ability while outputting data. The internal timer output pulse signal which frequency is 100Hz and the duty cycle is modulatable, through segregating, filtering and amplifying, the signal is converted to 0-5V voltage signal, through series negative feedback circuit of current, the controller can output standard 4-20mA current signal. The accuracy of analog output can reach 0.1% by software calibration. In addition, PEC3000 extends 46-channel LED through SPI interface to indicate work state.Application of PEC3000 in the project of wave crest solder which extends TAC6000 temperature controller as slave device and successfully completes the control of temperature, speed, spray, counter, wave crest and stat, proves the opening and usability of programmable logic controller based on IEC61131-3 standard.