Schaffner NSG 435 Generator
Electrostatic discharge (ESD*)
Under appropriate ambient conditions, both material objects
and even the Human
body itself can become charged with
electrical energy. This effect is due to "electrostatics*, a
phenomenon that has been known since the earliest times.
Thales von Milet (600 BC) noticed how amber attracted very
light particles when it was rubbed. Touching a charged item
against a conductive object leads to a charge equalisation
through a spark discharge which produces a brief but
powerful electro-magnetic field.
This effect can be explained as follows: Two insulating
substances with differing dielectric constants become
charged when rubbed together, i.e. one material gives
electrons to the other one. This effect is known as
electrostatic charging. The same can happen to a person.
When somebody walks around in a dry atmosphere on a carpet
with good insulating properties, a charge of several
thousand volts can be built up. If, now, that person comes
close to a conductive surface, the charge that he or she is
carrying flows away through a hefty spark discharge.
The high equalizing current that flows, and the associated
large electromagnetic field that hence results, can cause
electronic devices (computers, terminals, process
controllers, vehicle electronics, solid state devices,
credit or memory cards, etc.) to malfunction or even be
A systematic investigation of electronic equipment and
installations to determine their electromagnetic
compatibility (EMC) is, today, a necessity if one is not
prepared to suffer the economic disadvantages that could
otherwise ensue. As a logical consequence, appropriate
testing is now a legal requirement for the sale of
electronic products within the EC.
The ESD-test plays an important role in the range of
interference sensitivity tests. It simulates frequently
occurring effects and guides the development engineer to any
weak spots in an instrument or item of equipment through a
combination of high voltage and high frequency properties.
A simulation device must be constructed so that it
reproduces practical conditions realistically. Furthermore,
the results obtained (interference sensitivity threshold)
must be reproducible.
The interference immunity of an instrument is not only
dependent on its construction, it is also largely dependent
on the quality or the consistency of the mass production
techniques used. Knowing this has led to the demand for
individual testing or at least random sample testing.
Further weak spots, which could affect the overall
interference immunity, can arise through the assembly of
instruments into complete systems because of the
installation method used, the cabling and the earthing. An
ESD check on systems is therefore also prescribed. Such
tests provide valuable information about the immunity of the
system to effects that occur only sporadically under
operating conditions and hence represent difficult to detect
sources of disruption.
The most significant interference components of an
electrostatic discharge are of a high frequency nature. The
interference paths and effects have to be assessed in the
range from about 30 MHz to 1 GHz.
The extremely rapid rise time of a discharge affects an
object under test mostly through:
- magnetic HF-coupling between electrical conductors in the
electronics and the discharge current path.
- electrical coupling between the discharge current and
signal lines. A discharge current to the EUT flows
proportionally through all the associated conductors (earth,
mains, data lines, screening, etc.) according to their
Malfunctions in insufficiently immune electronic equipment
and systems make themselves apparentthrough:
- program crashes
- blocking of command sequences
- incorrect commands, statuses or data being processed
- partial system resets (e.g. only in peripheral modules
which lead to errors that the system does not recognize)
- disturbance or destruction of Interface
- destruction of insufficiently protected MOS components.
ESD (electrostatic discharge) testing usually shows up all
the weak spots in the HF-range of a piece of equipment
simultaneously. The uses to which the NSG 435
be put hence go way beyond those called for in
This instrument provides the engineer with a means to detect
sources of error caused by unsuitable earthing, poor ground
connections, insulation problems, etc.
also serves as a reliable aid for localizing
hidden wiring faults during acceptance trials on installations.
Use can also be made of the instrument as an insulation
tester to determine the breakdown voltage of switches, relay
contacts, insulators, etc.
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13 May 2017