TUTORIALS 1839

Sensor Temperature Compensation Using the Four DAC Signal Conditioning Architecture


Abstract: Resistive element pressure sensors, most notably the Wheatstone bridge configured piezoresistive devices, have dominated the low- to medium-accuracy pressure sensing industry since the early 1980s. The principal source of measurement error with these devices is changing sensitivity and output offset with temperature. Signal conditioning and calibration provide greater accuracy and lower cost. One of the most effective solutions to this basic requirement is the analog path conditioning architecture using four digital-to-analog converters (DACs) to provide the necessary temperature corrections. The temperature sensitivity of the gain of piezoresistive sensors stems from thermal coefficient of sensitivity (TCS) and the thermal coefficient of resistance (TCR). TCS effects arise from dimensional and stiffness changes in the sensor over temperature. TCS is usually negative (sensitivity reducing with increasing temperature). TCR describes the change in sensor bridge resistance with temperature and is normally positive. Most resistive element sensors are designed to make best use of the opposing signs of these two thermal coefficients. The aim is to produce a sensor with TCS slightly lower in magnitude than TCR. This results in a sensor which, when driven from a constant current source; exhibits a much-reduced total temperature sensitivity and allows external temperature compensation to be easily applied.