Uncertainty in resistance measurements based on microcontrollers with embedded time counters
José Jordana Barnils, Ferran Reverter, Ramon Pallas-Areny · 2004
Microcontrollers with embedded time counters can measure resistance by determining the time needed to charge or discharge a given capacitor C. This paper analyzes the uncertainty and error in resistance measurements based on measuring the discharging interval depending on the value of C. Using the internal Timer1 of the PIC16F874, two calibration resistors, and averaging 1000 measurements, the relative error for resistors from 825 /spl Omega/ to 1540 /spl Omega/ and C = 220 nF, 1.5 /spl mu/F, and 4.7 /spl mu/F is below 0.2%, and the standard deviation for C = 1.5 /spl mu/F, and 4.7 /spl mu/F is below 0.3 /spl Omega/. Power supply noise greatly influences the uncertainty, which makes it essential to use power supply decoupling capacitors.