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2.2.4 Safety Guidelines
This section presents recommended installation practices, and procedures. Since no two
applications are identical, these recommendations should be considered as guidelines.
Hardware Considerations WARNING!
The system designer should be aware that devices in Controller systems could fail and thereby
create an unsafe condition. Furthermore, electrical interference in an operator interface, such as an
NP-610X, can lead to equipment start-up, which could result in property damage and/or physical
injury to the equipment operator.
If you, or your company, use any programmable control systems that require an operator or
attendant, you should be aware that this potential safety hazard exists and take appropriate
precautions. Although the specific design steps depend on your particular application, the
following precautions generally apply to installation of solid-state programmable control devices.
In addition, these precautions conform to the guidelines for installation of Controllers as
recommended in the NEMA ICS 3-304 Control Standards.
Programming Considerations
To conform with ICS Safety Recommendations, checks should be placed in the controller to
ensure that all writable registers that control critical parts of plant or machinery have limit checks
built into the program, with an out-of-limit safe shut down procedure to ensure safety of
personnel.
ICS 3-304.81 Safety Recommendations:
Consideration should be given to the use of an emergency stop function, which is independent
of the programmable controller.
Where the operator is exposed to the machinery, such as in loading or unloading a machine
tool, or where the machine cycles automatically, consideration should be given to the use of an
electromechanical override or other redundant means, independent of the programmable
controller, for starting and interrupting the cycle.
If provision is required for changing programs while the equipment is in operation,
consideration should be given to the use of locks or other means of assuring that only authorized
personnel can make such changes.
These recommendations are intended as safeguards against the failure of critical components
and the effects of such failures or the inadvertent errors that might be introduced if programs are
changed while the equipment is in operation. *