The current loop: A measurement circuit topology alternative to the Wheatstone bridge

An analog measurement circuit topology is presented that significantly outperforms the Wheatstone bridge in many measurement and control applications. The initial output level can be simply adjusted to zero volts. Using active subtraction, the topology can provide greater measurement accuracy than the Wheatstone bridge, especially for measurements in difficult environments. When compared to a Wheatstone bridge arrangement of variable impedance elements, some of the advantages of this measurement circuit topology are: double the electrical output for the same sensor element power dissipation, the quantity of sensor elements may be reduced by one half, nearly 6db improvement in single-to-noise ratio, ratiometric operation, even random lead wire variations are typically irrelevant, linear electrical output even for large changes in a single impedance element, fewer wires from the observing electronics to impedance elements, transducers can have any number of electrical elements (each with different initial impedances), outputs are presented from each individual sensor impedance element as well as an aggregate output from any subset of elements, sensor calibrations can be any function of each individual sensor element change, and temperature at the various monitored impedances can he indicated without additional lead wires.