说明：  PWM经过RC滤波产生电压,经过XTR115产生4-20mA电流输出,要点是XTR115的电压输入问题,自身为两线制,+5V输出提供不了较大电流,需要用DCDC,RC滤波采用钽电容和4.7k-4.9k的低温漂电阻能得到较高线形度,PWM输出为AVR单片机16位,模式15,不分频
(PWM voltage generated through RC filter, after XTR115 have 4-20mA current output, the key points of the voltage input XTR115 problems, their own two-wire system,+ 5V output can provide a larger current, need to DCDC, RC filter using tantalum capacitors and 4.7k-4.9k resistor at low temperature drift can be a higher degree of linear, PWM output for the AVR Singlechip 16, mode 15, regardless of the frequency)