Esd Protective Measures; About The Physics Of Electrostatic Charges - Sirona Cerec 3 Operating Instructions Manual

4 Safety
Electrostatic charges
ESD
Training
What is an electrostatic charge?
Formation of an electrostatic charge
Amount of charge
Background
14
4.3.2

ESD protective measures

ESD stands for ElectroStatic Discharge.
We therefore recommend that all persons working with this system be
instructed on the significance of this warning label. Furthermore, they also
should receive training in the physics of electrostatic discharges which can
occur in the practice and the destruction of electronic components which may
result if such components are touched by electrostatically charged USERS.
The content of this training is explained in the Chapter "About the physics of
electrostatic charges" [ 14].
4.3.3

About the physics of electrostatic charges

An electrostatic charge is a voltage field on and in an object (e.g. a human
body) which is protected against conductance to ground potential by a
nonconductive layer (e.g. a shoe sole).
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).
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).
NOTE:
Electrostatic discharge must be preceded by electrostatic charging.
The following rule of thumb can be applied to assess the transient voltages
resulting from an electrostatic discharge.
An electrostatic discharge is:
perceptible at 3,000 V or higher
audible at 5,000 V or higher (cracking, crackling)
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.
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.
Sirona Dental Systems GmbH
Operating Instructions for the Acquisition Unit CEREC 3
D 3344.201.01.25.23 01.2011
63 22 700 D 3344