高性价比两线制隔离智能温度变送模块的设计

Design of Isolated Intelligent Two-wire Temperature Transmit Module with High Cost Performance

介绍一种支持多种工业热电阻和热电偶传感器的两线制温度变送模块。采用微功率隔离电源供电;使用AD7705做输入信号处理和A/D转换电路;以P89LPC922为控制器,采用PWM式D/A输出,同时提供RS-232接口。软件中采用了数字校准和数字滤波技术,并具有软件温度补偿功能。设计中充分考虑了电磁干扰和环境温度的影响,变送模块在恶劣工况下具有很高的可靠性,精度优于0.1%,成本低廉。

A design of two-wire temperature transmit module supported lots of thermocouple and resistance thermometer sensors is presented. Micro-power isolated power supply is adopted. The input signals are preprocessed and A/D converted in AD7705. P89LPC922 is the processor and controls D/A converter by PWM, which also provides RS-232 port. The digital calibration and filter, temperature compensation are achieved by software. Because the influences of the electromagnetic interference and environment temperature disturbance are considered in design, the reliability of the transmit module is improved dramatically in bad working condition. The precision is higher than 0.1% and the price is low.