An efficient digitization scheme for resistive sensors interfaced through quarter bridge

This paper presents a new and efficient approach to obtain a linear quasi-digital/ digital output from a resistive sensor that is interfaced through a quarter bridge, whose output characteristic is fundamentally non-linear. A simple feedback technique, which does not require the use of any multiplier, is employed to accomplish automatic self-balancing of the bridge, every time the parameter being measured changes. The output of the self-balancing circuit is: (a) linear, i.e., directly proportional to the change in the sensor resistance, (b) quasi-digital in nature, (c) independent of the variation in the bridge excitation voltage, (d) independent of the values of the lead wire resistances and its variation. A prototype of the proposed converter has been developed and tested. The maximum non-linearity noted in the output is less than 0.25%, in the experimental studies conducted on a prototype. For the prototype developed, the typical time required for one measurement under steady state is 10 ms, which can be improved.