Analog Wheatstone bridge-based automatic interface for grounded and floating wide-range resistive sensors

In this paper we present a suitable use of Wheatstone bridge-based circuits to employ a novel interface for both grounded and floating wide range resistive sensor estimation. The proposed topology is very simple and, through the use of only analog blocks in a feedback configuration, allows the automatic and continuous detection and quantification of the sensor resistance. Two circuit variations are proposed: both of them implement the commercial component analog multiplier AD633 as voltage controlled resistor placed in the feedback loop to compensate the sensor variations. Electrical measurement results, conducted on a prototype PCB, have shown that, even if the bridge autobalancing operation works in only 1.6 decades depending on the employment of the AD633, through a two-voltage-reading technique, it is possible to estimate up to 5-decades resistive variations, whose range is also settable, with a relative error within 1.5% and with a higher and supply-independent sensitivity, when compared to traditional bridge. This fact, together with its high resolution, has also allowed, in experimental tests performed by using an air quality resistive sensor, to reveal few ppm carbon monoxide particles.