Force signal alignment in dynamic testing machine calibration applications

• Cross-correlation can help time-align the signals in dynamic force calibration. • Signal synchronisation improves the testing machine calibration error results. • Tested on 20 kN and 1000 kN testing machine calibration examples. • Signal clock-rates should be matched before delay correction. Calibration of force in measuring systems where the force is time dependent i.e. dynamically changing, introduces additional complexities versus quasi-static calibration conditions. Time variable force signals necessitate accurate time alignment between concurrent signals – measurement series from unit under test and the measurement series from the reference standard need to be synchronised. Different unsynchronised measuring systems are typically used for acquisition of each calibration signal and they need to be time aligned in post-processing to eliminate as much as possible the influence of the sample misalignment from the resulting testing machine indication error. The paper focuses on the time synchronization of measurement series by using cross-correlation to determine the necessary time correction when calibrating testing machines with dynamic cyclic force excitation. Measurements are presented for calibration signals in the examples of 20 kN testing machine compression calibration for 5 kN ± 1 kN cycling force with 1 Hz, 5 Hz, and 10 Hz cycling frequencies, and 1000 kN testing machine tensile calibration for 500 kN ± 100 kN cycling force with 1 Hz cycling frequency. The standard deviation of the error distribution after time correction and clock rate compensation was below 0.2 % for both, 20 kN testing machine calibration, and 1000 kN testing machine calibration.