Abstract: A portable air tool for applying torque to a workpiece includes a built in strain gauge transducer for measuring applied torque and a built in potentiometer adjustment mechanism for balancing or calibrating the transducer in unloaded condition. The transducer and potentiometer adjustment mechanism are electrically connected by leads passing from the tool to an electrical circuit containing the power supply and a millivolt meter or computer. To balance the transducer in unloaded condition, the end of a screwdriver or other tool may be inserted through a housing aperture and into the air tool to turn an adjustment screw on the enclosed potentiometer until the millivolt meter reads zero indicating balance in the transducer circuit. Alternatively, the potentiometer could be mounted in a threaded sleeve forming the handle of the tool, with adjustment access to the potentiometer being provided when the handle is unthreaded and axially moved relative to the tool to expose the potentiometer.

Abstract: A shutoff mechanism for a pneumatic tool such as a nut runner senses both the instantaneous speed and the instantaneous rate of change of speed of the drive components of the tool. The mechanism controls the flow of air to the motor and terminates such flow as the drive speed decreases while approaching a stall condition. The mechanism comprises a main air valve operated by a centrifugal governor having a plurality of pivoted weights with their pivot axes oriented at acute angles to radial lines intersecting the centers of the weights rather than oriented at right angles to such radial lines as in conventional governor assemblies. So oriented, the weights sense both instantaneous speed and instantaneous rate of change of speed of the drive components.