The specific calibration for each tool is set by comparing the internal and external torque indicators which are indicated on a tool controller readout. 30 sample readings are taken to ensure that the tool’s internal and external readings are consistently in agreement. The calibration factor is affected by the transducer gauge, the gear ratios in the tool, and the efficiency of the gears. It is the change in gear efficiency throughout the life of the tool that will have the greatest effect on the specific calibration factor value. Often the gears will become more efficient after some use and then near the end of their life, the efficiency will begin to decrease.
Once the tool has been put into service, torque calibration should be validated and adjusted at regular intervals, either time-based or cycle-based. A variation greater than the values for new tools is expected and does not necessarily mean a transducer is defective. To allow for normal wear and associated efficiency changes, we recommend setting a limit from the nominal torque calibration value.