About The Physics Of Electrostatic Charges - Sirona CEREC AC Connect Operating Instructions For The Acquisition Unit

Sirona Dental Systems GmbH
Operating Instructions for the Acquisition Unit CEREC AC Connect
What is an electrostatic charge?
Formation of an electrostatic charge
Amount of charge
Background
63 20 134 D3492
D3492.201.04.15.02 10.2018
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
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