ABSTRACT
This chapter focuses on relatively small departures of the measurand with respect to its nominal value and the corresponding linearized response of the sensor, starting with the linearized thermistor and the response of a voltage divider when using the approximate linear thermistor response. An important part of the chapter is designing transducer circuits based on bridge circuits, starting with the balanced source divider, and continuing with Wheatstone bridges, including quarter-bridge, half-bridge, and full-bridge. The latter is illustrated using strain gages and their application to soil tensiometers. After discussing more details on transducer specifications, namely dynamics and environmental specifications, we cover electrochemical sensors, piezoelectric sensors, and applications to environmental monitoring. The last part of this chapter is devoted to signal conditioning, and a detailed explanation of operational amplifiers and their use to linearize bridge circuits, as well as to amplify transducer output. Several other signal-conditioning topics included are common-mode rejection, noise, shielding, and current loop methods.
