Siemens S5-155U System Manual page 6

ESD Guidelines
Guidelines for Handling
Electrostatically Sensitive Devices (ESD)
1 What is ESD?
VSLI chips (MOS technology) are used in practically all SIMATIC and TELEPERM modules.
These VLSI components are, by their nature, very sensitive to overvoltage and thus to
electrostatic discharge:
They are therefore defined as
Electrostatically Sensitive Devices: "ESD"
"ESD" is the abbreviation used internationally.
The following warning label on the cabinets, subracks and packing indicates that electrostatically
sensitive components have been used and that the modules concerned are susceptible to touch:
ESDs can be destroyed by voltage and energy levels which are far below the level perceptible
to human beings. Such voltages already occur when a component or a module is touched by a
person who has not been electrostatically discharged. Components which have been subjected
to such overvoltages cannot, in most cases, be immediately detected as faulty; the fault occurs
only after a long period in operation.
An electrostatic discharge
– of 3500 V can be felt
– of 4500 V can be heard
– must take place at a minimum of 5000 V to be seen.
But just a fraction of this voltage can already damage or destroy an electric component.
The typical data of a component can suffer due to damage, overstressing or weakening caused
by electrostatic discharge; this can result in temporary fault behavior, e.g. in the case of
– temperature variations,
– mechanical shodks,
– vibrations,
– change of load.
Only the consequent use of protective equipment and careful observation of the precautions for
handling such components can effectively prevent functional disturbances and failures of ESD
modules.
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C79000-D8076-C333-01