A novel signal conditioning circuit for push–pull-type resistive transducers

Abstract

A novel signal conditioning circuit suitable for push–pull-type resistive transducers is proposed. The circuit developed is capable of providing a linear output over a wide range of values of the measurand. Even when the transducer has an inverse relationship with the measurand, the circuit provides a linear output. The push–pull-type resistive transducer becomes an integral part of a relaxation oscillator, the duty cycle ratio of the output of which becomes proportional to the measurand. Since the output depends only on the relative sensitivity of the transducer and a pair of dc excitation voltages, it is possible to obtain very low errors. The various sources of error in the circuit are analysed and quantitative expressions to estimate such errors are derived. The circuit was set up in the laboratory and the results obtained from the prototype are presented. The prototype possessed an error of ±0.02% of the reading. It is seen that this circuit is not only simple but also produces errors which are much less than those from circuits currently mentioned in the literature.