Psion Teklogix Vehicle-Mount Computer 8590 - Manual (Page 172)

Appendix D: Mechanical Dynamic Loading
Units Without Vibration Insulation (tuned to high frequency)
D-2 8580/8590 Vehicle-Mount Computer User Manual
(5)M1 Stationary Use
Operational environments with low energy vibrations and medium energy shocks as
well as very careful handling/transport compliant with:
• Operation class 5M1 according to DIN EN 60721-3-5.
• Examples: Vehicles with very good shock absorption: Car dashboard,
immobile mounting surfaces: Desk or wall.
D.2 Units Without Vibration Insulation (tuned to high
frequency)
Selection criteria: Stationary, partly mobile or fully mobile applications for which
components offering insulation against vibrations cannot be used or are not
required.
Important: The 8580/8590 system can vibrate and should therefore be
installed using the bracket as rigidly as possible.
With their variable mountings, the 8580/8590 units form a spring-mass system that
can result in excitation by one or more random vibrations or shocks from its
surroundings.
This system reacts with natural oscillations, the amplitudes of which can be up to 20
times greater than the excitation amplitudes (resonance effects). The goal is
therefore to remove resonance points of this kind or at least to tune the system to
such a high frequency that they fall within the range of low excitation amplitudes.
For an initial assessment, you can test the device by hand. Bring the system to
excitation by gently hitting it with your hand. If the 8580/8590 starts to visibly
oscillate and if the vibrations take a long time to die away, it is probable that the
natural frequency is too low. In this case, we recommend reinforcing the fixing
points to the maximum bending moments (through the use of rigid sections, for
example).
Practically speaking, natural frequencies above 100 Hz are sufficient. However,
those below 50 Hz are likely to lead to damaging amplitudes during resonance
which may result in fatigue fractures along the outer mounting parts or on the
internal electronic components or even a loosening of the connections.