Electronic torque wrench

Claim 1

A torque wrench comprising, in combination: a wrench head; a handle structure including an internal cavity at one end thereof and a beam section secured to said wrench head at the other end thereof; a battery insertable into said internal cavity; a pair of strain gages respectively attached to the opposed lateral surfaces of said beam section including a first and second resistive element connected in series and adapted to register strain deformation of said beam section in the form of resistive change; resistive means connected across said first and second resistive elements to form a bridge circuit in combination therewith; excitation means connected to said bridge circuit and to said battery for electrical excitation of said bridge circuit in a first and second polarity; switching means connected to said excitation means for alternatively selecting said first or second excitation polarity according to the state of a received switching signal; a clock circuit connected to said battery for producing a sequence of timed pulses; counting means connected to said clock circuit for producing a plurality of binary signals indicative in combination to the accumulated count of said pulses; gate means connected to selected ones of said binary signals for producing said switching signal corresponding to the status thereof; connecting means connected to said bridge circuit, to said battery and to said counting means for alternatively passing a bridge balance signal produced by said bridge circuit or a fixed signal from said battery, selected according to the status of selected other ones of said binary signal; accumulating means connected to said connecting means for accumulating in a first direction said bridge balance signal and in a second direction said fixed signal connected to said counting means and said accumulating means; and readout means for displaying the accumulated count in said second direction.