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