基于占空比测量的铂电阻数字化接口研究

Investigation of the Digital Interface for Platinum Resistance Based on the Duty Cycle Measurement

定时器 5 5 5组成的经典多谐振荡电路可以实现R/F转换 ,由于RC振荡电路中的电容元件容量受环境温度影响 ,引起输出频率很大的变化 ;将测量脉冲频率改为测量脉冲占空比能有效地消除这一误差。由经典公式计算得出的占空比与实测数据存在差异 ,其原因主要在于 5 5 5内部放电用MOS管导通电阻的存在。根据电路理论 ,给出了修正的方程并估算了环境温度和电源电压等因素对占空比测量造成的误差。最终得出一种基于占空比测量的铂电阻接口方法 ,它入机方式简便、经济、低功耗。

The classical multi vibrator circuit formed by timer 555 can play a role of R/F conversion,but the frequency output is influenced to a great extent by the varying value of capacity in the RC circuit due to ambient air temperature,the errors are reduced well by the change of measure mode from frequency to cycle duty. The test data are not accorded with the classical formula, theory analysis show that the errors mainly originate from the on state resistance R ON of the MOSFET inner 555 during discharge,a modified formula is given and the degree of errors is estimated that caused by the changes of ambient temperature and power voltage etc. As a result, a practical interface for Pt1 000 transducer to MCU based on duty measure is provided,it features simple,economical, to be low voltage and dissipation and also precise in wide range.