Shock Pulse Duration in Calibration

ISO 16063-22:2005 standard covers different methods for the calibration of shock transducers by comparison to a reference transducer. During shock calibration, almost as important as being able to produce the required acceleration peak magnitude is to make sure the shock pulse duration is long enough compared to the natural period (inverse of resonant frequency) of the transducer under test. Pulse duration is a critically important aspect that can be easily overlooked during shock calibration and the standard does a good job recommending the half-sine pulse duration of the applied shock pulse to be at least a factor of five times larger than the natural period of the test transducer to eliminate potentially excessive overshoot and “ringing” due to resonance excitation.

Shock calibration involves submitting the test sensor to different shock peak magnitudes. The following picture shows an example of a shock sensor being tested at approximately of 6276 m/s² or 640 g_n (peak)^[1]. Is the pulse duration in the below photo long enough to avoid sensor “ringing” issues? The question can be easily answered by first checking the manufacturer’s specification for the resonant frequency of the test sensor and validating it against the ISO 16063-22 guidelines. In this particular example, the resonant frequency of the test sensor is 20 kHz and therefore the sensor’s natural period is 0.05 ms (the recommended shortest pulse duration should be at least five times that, i.e. greater than 0.25 ms) which fortunately was the case as shown below.

Figure 1: Typical transient data acquired with a pneumatically operated piston shock calibration system. The test sensor and the reference transducer were both submitted to an acceleration of 6276 m/s² or 640 g_n (peak). Per ISO 16063-22, pulse duration is measured at 10% of the peak value.

Once the measurements at a particular shock level are validated, the calibration process moves on to the next acceleration magnitude level. Shock pulses in the 0.05 ms to 8.0 ms range are typically applied to both sensor under test and reference sensor during the process and amplitude linearity is measured for different high acceleration levels. 

^[1] The acceleration peak magnitude may be expressed in terms of the standard acceleration due to gravity, symbol gn (1 g_n = 9.80665 m/s²; 1.5 km/s² ≈150 g_n).

Click here to download a white paper on methods for the calibration of vibration and shock transducers.