Parker H Series, Installation & Service Instructions Manual

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Safety Guidelines for the Application, Installation and Maintenance of Solid State Control E116P
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3.6.2 Contaminants
Moisture, corrosive gases and liquids, and conductive
dust can all have adverse effects on a system that is not
adequately protected against atmospheric contaminants.
If these contaminants are allowed to collect on printed
circuit boards, bridging between the conductors may result
in malfunction of the circuit. This could lead to noisy,
erratic control operation, or at worst, a permanent
malfunction. A thick coating of dust could also prevent
adequate cooling on the board or heat sink, causing
malfunction. A dust coating on heat sinks reduces their
thermal efficiency.
Preventive measures include a specially conditioned room
or a properly specified enclosure for the system.
3.6.3 Shock and Vibration
Excessive shock or vibration may cause damage to solid
state equipment. Special mounting provisions may be
required to minimize damage.
3.7 The Need for Education –
Knowledge Leads to Safety
Planning for an effective solid state circuit requires enough
knowledge to make basic decisions that will render the
system safe as well as effective.
Everyone who works with a solid state control should be
educated in its capabilities and limitations. This includes
in-plant installers, operators, service personnel, and
system designers.
C.3.6.2 Contaminants
Modules for solid state systems usually consist of electronic
devices mounted on printed circuit boards with relatively
close spacing between conductors. Moisture in the form
of humidity is one of the atmospheric contaminants which
can cause failure. If moisture is allowed to condense on a
printed circuit board, the board metallizations could
“electroplate” across the conductor spacings when voltage
is applied. In low impedance circuits, this conductive path
would immediately burn open, then reform to be burned
open again. This action can lead to erratic operation. In
high impedance circuits, a short circuit may appear resulting
in a permanent malfunction. Specifications for equipment
often include a relative humidity exposure limit, but
appropriate precautions should be taken to prevent
condensation. Failures due to moisture are often
accelerated in the presence of corrosive gases or vapors.
These increase the conductivity of the moisture layer
allowing electromigration to occur more rapidly and at
lower potentials.
C.3.6.3 Shock and Vibration
Solid state systems usually have good resistance to shock
and vibration since they contain no moving parts. However,
at relatively high levels of shock or vibration, circuit boards
may disengage from mating connectors if not restrained
sufficiently. Circuit boards can crack, components can
come out of sockets or component leads can break loose
from a solder connection to the board. Mounting position
is usually of little significance to solid state devices except
in instances where air flow is required for cooling.