電流信號被廣泛應用于儀表信號的輸出。為了給智能儀表提供廉價標準電流信號輸出
接口，可以使用RC低通濾波器，從PWM中分離出與占空比成正比的線性直流電壓信號。此電壓信號經過由放大器組成的壓/流轉換產生穩定的標準電流信號。同時，為了方便量程校準，儀表采用軟件和硬件相結合的方法，對表征輸出電流信號大小的電壓進行數模轉換，用軟件的方法確定量程的上下限。從而使整個標準電流輸出電路對所用元件的參數不敏感且結構簡單、校準方便、也降低了成本。
關鍵字：自動化儀表；標準電流信號源；脈寬調制；自動校準

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