ABSTRACT
Calibration is an important part of any measurement application. Accelerometers are the most used sensors for all kinds of shock and vibration measurements. Accelerometer calibrations may be sinusoidal tests to determine the frequency response, or shock tests to determine the suitability for shock measurements. PCB Piezotronics* has developed and offered for sale a convenient pneumatic shock calibrator Model 9155C-525. This device makes an interesting study in system dynamics because it includes thermodynamics, fl uid mechanics, and mechanical motion aspects. It uses the back-to-back method of comparing the response of the accelerometer to be calibrated with that of a standard (reference) accelerometer known to be much more accurate and thus usable as a transfer standard. In this method, the two accelerometers are fastened to an “anvil” in a back-to-back fashion. The anvil is subjected to an impact from a “projectile” launched from a pneumatically driven “gun.” If the assembly of anvil and two accelerometers behaves essentially as a single rigid mass, then the two accelerometers will feel the same acceleration pulse and we can easily compare the two dynamic response voltages from the instruments, taking the reference accelerometer signal as perfect. By adjusting the parameters of the calibrator, shock pulses of various magnitudes and time durations may be selected, thus exercising the tested accelerometer over a range of conditions. Most purchasers and users of this calibrator have little interest in the design or analysis of the device; they just use it according to the instrument’s instruction manual. Since a more complete understanding of the device develops our capability for the design of instrumentation systems in general, we will pursue a detailed analysis and simulation. Although PCB could not, for proprietary reasons, supply such an analysis, they were very helpful in providing certain details.
