Rockwell Automation Safety Guidelines for the Application, Installation, and Maintenance of Solid-State Control - Manual (Page 4)

Publication SGI-1.1 - August 2009
4 Section 2: General Authorized Engineering Information
Section 2: General Authorized Engineering
Information
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.
General: Comments
Solid-state devices provide many advantages such as high speed, small
size, and the ability to handle extremely complex functions. However, they
differ from 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.
2.1 Ambient Temperature Care should be taken not to exceed the ambient temperature range specified by
the manufacturer.
Comments: 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 40º C. A useful rule of thumb is: The failure rate of
solid-state components doubles for every 40º C 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.
See also sections 3.6.1, and 3.6.2.
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.