About The Physics Of Electrostatic Charges - Dentsply Sirona CEREC AC Notice D'utilisation

Dentsply Sirona
Operating Instructions for the Acquisition Unit
What is an electrostatic charge?
Formation of an electrostatic charge
Amount of charge
Background
66 37 461 D 3492
D 3492.201.06.27.02 09.2017
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).
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 to
implement a wide variety of functions in dental/X-ray/CAD/CAM 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 ElectroStatic Discharge.
Connector pins or sockets bearing ESD warning labels must not be
touched or interconnected without ESD protective measures.
4 Safety
17