Application of S7-200 PLC to the monitoring system of strip steel temperature

This paper presents the communication method realized through RS485 bus and RTU protocol of Modbus in strip steel temperature monitoring system of the hot dip galvanizing unit. The emphasis is to analyze the design of S7-200 communication program using the protocol library of Modbus RTU slave station. S7-200 PLC is designed as a slave station which receives message from the industrial personal computer, so as to control acousto-optic alarm circuit for indicating the temperature condition of hot dip galvanizing unit. Meanwhile, it reads the strip steel weld signals which are necessary for the industrial personal computer.