scope:

External calibration of the torque sensor of a performance test station is no replacement for calibrating the measuring chain when the sensor is installed. From this follows the necessity of generating torque for comparative calibration with a reference measuring system.

The present guideline applies to performance test stations with an integrated torque measuring device in the shafting between drive and loading system (for example, engine or transmission test beds) in which the torque is defined by measurement of the elastic change in shape of a deformation body or a measured quantity proportional to the torque. It applies to performance test stations in which the torque to be measured is picked up in the shafting.

For performance test stations of different designs it will be necessary in addition to take other measurement uncertainties into consideration (for example, the effects of bearing friction).

Torque calibration is used for detecting as many as possible of the effects which determine the measurement uncertainty of torque measurement in test stations. Calibration in the test station takes into account more influencing variables than calibration of the torque sensor in an external torque calibration facility. Influences relating to installation include, for example, flanges, restraints, adapters.

Further influences arise from changing the instrumentation amplifier and analysis unit when carrying out an external calibration. If, instead of calibrating in the test station, calibration takes place in an external calibration facility, these influences must be taken into consideration in the measurement uncertainty appraisal for torque measurement in test station operation. The advantages and disadvantages of the two methods should be weighed up against each other.

This guideline applies to the stepwise static and rotation-free calibration of torque measuring devices in their fitted state in the shafting. Methods of calibration are described in which the measurement uncertainty is determined.

Note: In the case of integrated sensors this guideline covers only the sensors themselves in conjunction with measured data collection in the non-rotating state.

Stepwise calibration is a purely static loading of the calibration object. Here, suitable loading times should be observed for each step to pay due regard to creeping effects of the calibration object.

In the measurement result the calibration procedure described does not take into consideration operational conditions which differ from the calibration conditions (for example, temperatures between the shafting and the torque pickup), their changes over time during operation (for example, temperature gradients) and different environment conditions. Nor are modifications to the mechanical configuration and the measuring chain as compared with the original configuration of the test station taken into consideration. These influences shall be taken into consideration in the measurement uncertainty budget for the application.