Siemens S5-135U/155U appendix What is ESD?, Definition

Guidelines for Handling Electrostatically-Sensitive Devices (ESD)

B.1	What is ESD?
Definition		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.

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These Electrostatically- Sensitive Devices are commonly referred to by the abbreviation ESD.

Electrostatically-sensitive devices are labeled with the following symbol:

Caution

Electrostatically-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 or the electrical connections of a 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.

B-2	System Manual
	C79000-G8576-C199-06