All commercial ultrasonic fastener load measurement equipment uses a “pulse-echo” meaurement technique. When a voltage is applied to the ultrasonic transducer, a longtitudinal ultrasonic wave is generated that travels down the length of the fastener, reflects off the end, and returns to the transducer. This is the “time-of-fight”, which is measured at zero load and continously during tightening. The change in “time-of-flight” provides for direct measurement and control of load, allowing automatic shut-off at the predetermined and designated clamp load.
