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Appendix D: Mechanical Dynamic Loading
Determining Insulating Effects
D-8 8580/8590 Vehicle-Mount Computer User Manual
Based on this table, we can clearly expect very good insulation for excitation
frequencies that are twice as high as the system's natural frequency.
Consequently, the amplitude of the reaction accelerations of the 8580/8590 still only
reaches 66% of the amplitude of the excitation accelerations, which actually have an
effect twice that of the natural frequency.
The table also demonstrates the costs of achieving this, namely that all excitation
frequencies below the natural frequency are amplified - to a maximum when
resonance occurs.
Implication For Designing Computer Mounts:
• If high energy excitation frequencies mainly occur in the region of the
natural frequency of the 8580/8590 with its mounting, which can be found,
for example, in a vehicle chassis tuned to a low frequency. In this case a
spring mounting of the 8580/8590 should be avoided.
• However, if high energy excitation frequencies mainly occur above the
natural frequency, it is recommended that you use passive vibration insula-
tion for the computer. This applies to unsprung fork lifts with solid rubber
tires or for unbalanced machines with relatively constant and correspond-
ingly high operating speed.
Random samples of fork lift rotors were taken and the field excitations measured:
Excitation Frequency Natural Frequency Degree Of Insulation
10Hz 20Hz 0.5 -33% Warning! Amplification
20Hz 20Hz 1
Warning!Resonance, approx. – 500%
and greater! High amplification!
Approx. 28Hz
20Hz 2 0, no insulation
40Hz 20Hz 2 66%
60Hz 20Hz 3 88%
80Hz 20Hz 4 93%