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The head restraint must be fitted and tested on the seat of the vehicle for which it is intended. The seat must be firmly secured to the test bench so that it does not move under impact.
The recording instruments used must be such that measurements can be made with the following degrees of accuracy:
accuracy: ± 5 % of the real value,
frequency response: up to 1 000 Hz
cross-axis sensitivity: < 5 % of the lowest point on the scale.
accuracy: ± 2·5 % of the real value,
sensitivity: 0·5 km/h.
the instrumentation must enable the action to be recorded throughout its duration and readings to be made within one thousandth of a second,
the beginning of the impact at the moment of first contact between the headform and the head restraint being tested is noted on the recordings used for analyzing the test.
In tests carried out by the above procedure, the deceleration of the headform must not exceed 80 g continuously for more than three milliseconds. The deceleration rate is taken as the average of the readings on the two decelerometers.
The relationship of the reduced mass ‘mr’ of the pendulum to the total mass ‘m’ of the pendulum at a distance ‘a’ between the centre of percussion and the axis of rotation and at a distance ‘l’ between the centre of gravity and the axis of rotation is given by the formula: ·