Bolt load determining apparatus

摘要

A first signal at a first frequency which is a selected harmonic of the resonant frequency of a bolt in a first loaded condition is determined. Then there is determined a second signal at a second frequency being the same harmonic of the resonant frequency of the bolt in a second loaded condition. Both frequencies are multiplied by a factor M. The up input of a counter receives one of the signals for a predetermined duration, and the down input receives the other signal for the same duration. The number of pulses remaining in the counter is representative of the difference in load between the first and second loaded conditions.