Volume 22, Issue 1 (January 1994)
Practical Aspects of Dynamic Verification of Extensometers: Part II—Actual Examples
Verification and calibration of an extensometer requires operation at multiple points within the desired operating range. Whereas static calibrations observe changes in sensitivity at different levels within the transducer operating range, dynamic calibrations require duplicating that range of test levels for a range of operating frequencies. Additionally, although the static accuracy of an extensometer is relatively independent of the test machine, dynamic accuracy was believed to be quite dependent.
Test results for dynamic verification of several extensometers are presented. The focus of the tests was to gain an understanding of the advantages and disadvantages of different methods of verification. Testing was generally in accordance with ASTM E 467, Practice for Verification of Constant Amplitude Dynamic Loads in An Axial Load Fatigue Testing Machine. Two excitation methods were used: discrete frequency and pseudo-random. Evaluation of a proposed revision to ASTM E 467 is included. Use of a computer to provide an efficient, high-accuracy method of verifying the calibration of an extensometer was explored. Further testing is recommended to determine if extensometer dynamic verification must be done on the actual test setup, and to what extent it is repeatable.