ircon Modline 4, Installation And Operation Manual

Page: 83 / 88

Appendix
A–4
Precautions should be taken to prevent the off-
state current of an output device which is in the off-
state from energizing an input device.
3.6 AVOIDING ADVERSE ENVIRONMENTAL
CONDITIONS
3.6.1 Temperature
Solid state devices should only be operated within
the temperature ranges specified by the manufac-
turer. Because such devices generate heat, care
should be taken to see that the ambient tempera-
ture at the device does not exceed the tempera-
ture range specified by the manufacturer.
The main source of heat in a solid state system is
the energy dissipated in the power devices. Since
the life of the equipment can be increased by
reducing operating temperature, it is important to
observe the manufacturer’s “maximum/minimum
ambient temperature” guidelines, where ambient
refers to the temperature of the air providing the
cooling. The solid state equipment must be
allowed to stabilize to within the manufacturer’s
recommended operating temperature range before
energizing control functions.
When evaluating a system design, other sources
of heat in the enclosure which might raise the
ambient temperature should not be overlooked.
For example, power supplies, transformers, radiat-
ed heat, sunlight, furnaces, incandescent lamps,
and so forth should be evaluated.
In instances where a system will have to exist in a
very hot ambient environment, special cooling
methods may have to be employed. Techniques
that are employed include cooling fans (with ade-
quate filtering), vortex coolers, heat exchanges,
and air conditioned rooms.
Over-temperature sensors are recommended for
systems where special cooling is employed. Use of
air conditioning should include means for preven-
tion of condensing moisture.
3.6.2 Contaminants
Moisture, corrosive gases and liquids, and conduc-
tive dust can all have adverse effects on a system
that is not adequately protected against atmo-
spheric contaminants.
If these contaminants are allowed to collect on
printed circuit boards, bridging between the con-
ductors may result in malfunction of the circuit.
This could lead to noisy, erratic control operation
or, at worst, a permanent malfunction. A thick coat-
ing of dust could also prevent adequate cooling on
the board or heat sink, causing malfunction. A dust
coating on heat sinks reduces their thermal effi-
ciency.
Preventive measures include a specially condi-
tioned 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 provi-
sions may be required to minimize damage.
3.7 THE NEED FOR SAFETY–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 limita-
tions. This includes in-plant installers, operators,
service personnel, and system designers.
Section 4: APPLICATION GUIDELINES
4.1 INSTALLATION AND WIRING PRACTICE
4.1.1 Proper installation and field wiring practices
are of prime importance to the application of solid
state controls. Proper wiring practice will minimize
the influence of electrical noise, which may cause
malfunction of equipment.
Users and installers should familiarize themselves
with and follow installation and wiring instructions
in addition to requirements of all applicable codes,
laws, and standards. The manufacturer of the
device or component in question should be con-
sulted whenever conditions arise that are not cov-
ered by the manufacturer’s instructions.