Section 2 General - Parker H Series Installation & Service Instructions Manual

Safety Guidelines for the Application, Installation and Maintenance of Solid State Control
Section 2
General
(Sections 2 through 5 are classified as Authorized
Engineering Information 11-15-1984.)
Solid State and electro-mechanical controls can perform
similar control functions, but there are certain unique
characteristics of solid state controls which must be
understood.
In the application, installation and maintenance of solid
state control, special consideration should be given to the
characteristics described in 2.1 through 2.7.
2.1 Ambient Temperature
Care should be taken not to exceed the ambient
temperature range specified by the manufacturer.
2.2 Electrical Noise
Performance of solid state controls can be affected by
electrical noise. In general, complete systems are
designed with a degree of noise immunity. Noise immunity
can be determined through tests such as described in
3.4.2. Manufacturer recommended installation practices
for reducing the effect of noise should be followed.
General Comments
Solid state devices provide many advantages such as
high speed, small size, and the ability to handle extremely
complex functions.
electromechanical devices in the basic operating
characteristics and sensitivity to environmental influences.
In addition, solid state devices exhibit different failure
mechanisms when overstressed.
The comments which follow are intended to provide
additional information to help the reader better understand
the operating characteristics, environmental limitations,
and failure modes of industrial equipment that incorporates
solid state technology. Those who select, install, use,
and service such equipment should apply that knowledge
to make appropriate decisions that will optimize the
performance and safety of their applications.
C.2.1 Ambient Temperature
Temperature of the air immediately surrounding an open
solid state device is the ambient temperature which must
be considered. When equipment is installed in an
enclosure, the enclosure internal air temperature is the
ambient temperature which must be considered. Solid
state component manufacturers usually publish the
component failure rate for an ambient temperature of 40
degrees Celsius. A useful rule of thumb is: The failure rate
of solid state components doubles for every ten degrees
Celsius rise in temperature. This rule of exponential
increases in failure rate is a strong incentive for the user
to keep the ambient temperature as low as possible.
Also see sections 3.6.1, and 3.6.2.
C.2.2 Electrical Noise
Solid state devices are generally more susceptible to
electrical noise interference than their electromechanical
counterparts. The reasons are straightforward. The
operating mechanism for electromechanical devices
requires a deliberate input of electrical energy that can be
converted into a sustained mechanical force that is strong
enough to close the hard contacts and maintain the closure
for the duration on the ON cycle. Most random electrical
noise signals lack the energy content to produce that
magnitude of mechanical force.
The operating mechanism for solid state devices is totally
different. The deliberate electric energy input is used to
disturb the placement of the electrically charged particles
within the molecular structure.
displacement changes the electrical characteristic from
that of an insulator to that of a conductor or vice versa.
The required energy level is very low. In addition, a
sustained signal is not required for components such as
SCRs, triacs, and logic gates because these types are
self-latching. Most random electrical noise signals are of
the momentary low energy type. Since it is difficult to
separate deliberate signals from random noise, the devices
are thereby more susceptible. This is cause for special
concern regarding the electrical environment and possible
need for noise rejection measures.
Also see sections 3.4, 3.4.1, 3.4.2, 3.4.3.
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