Integration of MODBUS/TCP master monitoring and control system using python for high power RF system

Ion Cyclotron Resonance Heating (ICRH) Data Acquisition Control system (DAC) for high power RF system has been conceptualized for experimental activities in tokamak. As per the requirement of DAC, it needs 32 analog inputs, 32 digital inputs, 16 digital outputs and 16 analog outputs channels for monitoring and control of the system. For the same reason Delta automation PLC (AH500 series) has been procured. It provides interface with MODBUS which is an open standard protocol that can build into equipment without paying any license fees. MODBUS provides memory maps for read and write coils for digital I/O interaction and 16 bit registers to read and write analog registers as required by DAC. MODBUS protocol is widely used in the industrial control field because of its excellent reliability, flexibility, real-time performance etc. MODBUS follows a master and slave architecture where a master (PC) transmits a request to a slave (PLC) and waits for the response. Pymodbus library allows reading of data from PLCs and writing of data to PLCs over Ethernet using specified MODBUS addresses in two way communication. Pymodbus uses asynchronous communication over TCP/IP connections that reduces the amount of code, and has good debugging and connection management. This paper describes the integration scheme and control structure of PLC with MODBUS/TCP installed on Windows based computer. It is decided to use EPICS as control system which uses python for logic implementation. Python would be the better choice as it provides both pymodbus and pyepics libraries for single platform interface.