61 77 476 D 3495
12
D 3495
.
201.01.02
.
02
08.2007
2
Warning and safety information
Sirona Dental Systems GmbH
About the physics of electrostatic charges
Operating Instructions and Installation
XIOS USB
Formation of an electrostatic charge
Electrostatic charges generally build up whenever two bodies are rubbed
against each other, e.g. when walking (shoe soles against the floor) or driving
a vehicle (tires against the street pavement).
Amount of charge
The amount of charge depends on several factors:
Thus the charge is higher in an environment with low air humidity than in one
with high air humidity; it is also higher with synthetic materials than with
natural materials (clothing, floor coverings).
The following rule of thumb can be applied to assess the amount of transient
voltages resulting from an electrostatic discharge.
An electrostatic discharge is:
z
perceptible at 3,000 V or higher
z
audible at 5,000 V or higher (cracking, crackling)
z
visible at 10,000 V or higher (arc-over)
The transient currents resulting from these discharges have a magnitude of
10 amperes. They are not hazardous for humans because they last for only
several nanoseconds.
Background information
Integrated circuits (logical circuits and microprocessors) are used in order to
implement a wide variety of functions in dental/X-ray/CEREC systems.
The circuits must be miniaturized to a very high degree in order to include as
many functions as possible on these chips. This leads to structure
thicknesses as low as a few ten thousandths of a millimeter.
It is obvious that integrated circuits which are connected to plugs leading
outside of the unit via cables are sensitive to electrostatic discharge.
Even voltages which are imperceptible to the user can cause breakdown of
the structures, thus leading to a discharge current which melts the chip in the
affected areas. Damage to individual integrated circuits may cause
malfunction or failure of the system.
To prevent this from happening, the ESD warning label next to the plug warns
of this hazard. ESD stands for
E
lectro
S
tatic
D
ischarge.
NOTE:
Electrostatic discharge must be preceded by electrostatic charging.
