Bridge measuring circuit

Claim 1

A voltage measuring circuit comprising a bridge having output terminals which have the same potential when said bridge is balanced, a null detector connected to said output terminals, and a single power supply means for said null detector and for polarizing said bridge, said null detector comprising a voltagE sensing circuit and means for connecting said voltage sensing circuit to said output terminals including semiconductor switching means and gate means for rendering said semiconductor switching means conductive to energize said voltage measuring circuit from said bridge through a path including said semiconductor switching means, gating circuit means for applying a gating signal to said gate means, said gate means having a high input impedance which effectively isolates said gating circuit means from said path whereby the power supply for said bridge and said null detector are not independent of each other, said semiconductor switching means including a pair of MOS fieldeffect transistors each having a gate electrode comprising said gate means, said oscillating circuit connected to the gate electrodes of said MOS field-effect transistors to render the latter alternately conductive to alternately connect said null detector to different ones of said terminals to enable said voltage measuring circuit to alternately sense the potential of said output terminals, said null detector and said bridge having a common ground.