Uncertainty in Resistance-to-Code Converters Based on Microcontrollers Measuring Time Intervals

Abstract

This paper analyses the effect of trigger noise and quantization on the uncertainty of time intervals measured with Timerl of the PIC16F874 microcontroller. The time intervals result from charging and discharging a capacitor through a resistive sensor and two reference resistors. The uncertainty is described by the standard deviation and frequency distribution of the time counts. The uncertainty comes from quantization and trigger noise due to both the input channel noise and signal noise, which depends on the slew rate of the signal, and can be reduced by multiple time-interval averaging. Because of that uncertainty, a large capacitor does not necessarily yield a small relative uncertainty.