智能仪表标准电流信号输出电路设计

电流信号被广泛应用于仪表信号的输出。为了给智能仪表提供廉价标准电流信号输出
接口，可以使用RC低通滤波器，从PWM中分离出与占空比成正比的线性直流电压信号。此电压信号经过由放大器组成的压/流转换产生稳定的标准电流信号。同时，为了方便量程校准，仪表采用软件和硬件相结合的方法，对表征输出电流信号大小的电压进行数模转换，用软件的方法确定量程的上下限。从而使整个标准电流输出电路对所用元件的参数不敏感且结构简单、校准方便、也降低了成本。
关键字：自动化仪表；标准电流信号源；脉宽调制；自动校准

Abstract：The current signal is widely used for the instrument’s output signal. To provide
intelligent instruments with the cheap interface of the standard current sign, the RC low pass filter is used for producing a voltage signal which is proportion to PWM`s duty rate from PWM. This voltage signal generates the standard current signal via V/I convert. And, to make the instrument’s calibration convenient, the software is combined with the hardware. The ADC of the instrument sample the voltage signal which is represents the current signal. And the software calculates upper and lower limits of measure range. By this means, the system with the low price and the simple structure isn’t sensitivity to the component’s parameter, and measure range can be adjusted conveniently.
Keywords: automatization instrument, standard current signal source, PWM, spectral analysis; automatization calibrate