Pulse width compensated resistive bridge algorithms

A Wheatstone resistance bridge is modified, adding a capacitor and a switch. The switch allows alternately the charge and discharge of the capacitor through, respectively, the first and second resistors in the reference resistor branch. The command for the switch is a logical signal, with constant frequency and variable duty factor. The voltage on the capacitor is compared to the voltage generated by the bridge´s measuring branch. The result is a square wave with its duty factor dependent on the unbalance of the bridge. The command signal duty factor is modified in such a way as to bring the comparator output duty factor to 0.5. This means that the bridge is balanced, and the duty factor of the command signal represents the transducer branch resistor ratio. When the transducer is located far away from the measuring point, long connection cables interfere with the measurement through both significant parasitic impedance and high noise susceptibility. The controller algorithm needs to allow, beside high resolution (precision) and reasonable balancing (measuring) time, noise attenuation and connection wires compensation. The adaptive algorithms have been tested by simulation. They can be easily implemented in a microcontroller program to build an embedded measuring system.