Siemens SIMATIC S5-100U System Manual page 518

Active and Passive Faults in Automation Equipment
Guidelines for Handling Electrostatic Sensitive Devices (ESD)
What is ESD?
All electronic modules are equipped with large-scale integrated ICs or components. Due to their
design, these electronic elements are very sensitive to overvoltages and thus to any electrostatic
discharge.
These Electrostatic Sensitive Devices are commonly referred to by the abbreviation ESD.
Electrostatic sensitive devices are labelled with the following symbol:
Caution
!
Electrostatic sensitive devices are subject to voltages that are far below the voltage
values that can still be perceived by human beings. These voltages are present if you
touch a component module without previously being electrostatically discharged. In most
cases, the damage caused by an overvoltage is not immediately noticeable and results in
total damage only after a prolonged period of operation.
C-2
S5-100U
EWA 4NEB 812 6120-02b