Method for determining the magnitude of the output torque and a power wrench

A method of verifying a magnitude of a delivered output torque during a tightening operation of a threaded joint performed by a hand held power wrench comprising a housing, a motor, an output shaft, and a power transmission connecting the motor to the output shaft, wherein the method comprises:

• tightening the threaded joint;
• monitoring a magnitude of a direct torque acting along the power transmission during said tightening by at least one direct torque indicating sensor;
• monitoring a magnitude of a reaction torque transferred via the housing during said tightening by at least one reaction torque sensor;
• comparing the monitored magnitude of the direct torque with the monitored magnitude of the reaction torque;
• and
• determining, based on said comparison, whether the accuracy of the delivered output torque is acceptable.

A power wrench comprising:

• a housing;
• a motor;
• an output shaft;
• a power transmission connecting the motor to the output shaft;
• and
• at least one direct torque indicating sensor provided in the power transmission to monitor a magnitude of a direct torque delivered by the power wrench during a tightening operation,
• wherein:
• at least one reaction torque sensor is arranged to monitor a magnitude of a reaction torque during the tightening operation, and
• a control unit is arranged to compare the monitored direct torque with the monitored reaction torque, and based on said comparison, to determine whether an accuracy of the tightening operation is acceptable.