A survey of torque transduction methodologies for industrial applications

The measurement of direct shaft torque and its transduction to various forms of signal is a primary interest of many electric machine builders and process application end users. Since torque multiplied by the instantaneous shaft rotational speed is the instantaneous power being delivered to the product and its integration over time the delivered process energy, the use of torque transduction to indicate everything from delivered mass of product to the energy change necessary to produce the proper change of state in a mix has increased dramatically. This paper reviews the basic methods and applications of torque sensing and transduction in industrial applications and provides comparison of their relative operational characteristics and performance. Nondirect methods such as inferred torque (i.e., reaction strain gage) are compared to direct methods such as "torduction". It is shown that the recent advances in noncontact types of direct torque measurement have made them a more practical choice for many industrial applications where speed of response is a dominant consideration, but the indirect methods must be carefully considered in comparison because of higher steady state accuracy, durability, and reduced cost.