基于MODBUS协议的4～20mA电流输出智能模块

Design of 4 to 20mA Current Output Intelligent Module Based on Modbus Protocol

针对现场设备的组态控制,介绍了基于Modbus协议的4～20 mA电流输出智能模块的硬件和软件设计。该智能模块具有RS-485接口,支持标准Modbus串行协议,可以连接到测控系统进行设备组态,并且可按照Modbus命令输出4～20 mA电流来控制现场设备。利用该智能模块,可以将传统的4～20 mA执行器变成Modbus智能设备。系统以ATmega168微控制器为核心,通过PWM方式产生变化电压,该变化电压经XTR111转换得到4～20 mA的电流。该模块可以降低系统升级的成本,具有较强的现场抗干扰能力,可以提高测控系统的智能化水平。

This paper introduced the hardware and software design of an intelligent module with 4 to 20 mA current output based on Modbus protocol. This intelligent module has a RS -485 interface, which can support the standard Modbus serial protocol to realize equipments configuration by connecting to measurement and control system. It also can be integrated into DCS system and output 4 to 20 mA current to control the field equipments. By using this module, traditional 4 to 20 mA actuator can be transformed into current signal of 4 to 20 mA intelligent equipment. Microcontroller ATmega168 is the core of the system, which obtains a variable voltage signal by the way of PWM. The voltage signal is converted into current signal of 4 to 20 mA by XTR111. With a strong anti-interference ability, this module can reduce the cost of system upgrades and can improve the intelligent level of measurement and control system.