Safety Documentation; Guarding Against Unauthorized Operation; Labeling, Guarding, And Lighting Issues; Equipment Accessibility Issues - GE 90-30 PLC Series Installation And Hardware Manual

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Safety Documentation

Guarding Against Unauthorized Operation

Keylock switches and passwords are frequently used for this purpose.

Labeling, Guarding, and Lighting Issues

Equipment Accessibility Issues

The equipment should be laid out so as to give operators sufficient room to perform their tasks
safely. Also, sufficient clearance should be provided so that maintenance personnel have safe
access to electrical panels, control boxes, etc. These minimum clearances are specified in the NEC
and OSHA requirements.
12-10 Series 90-30 PLC Installation and Hardware Manual – August 2002
PLC Program Documentation. Thorough documentation will help you and others who work
on the equipment remember and understand how the safety circuits and features work. (In
some industries, applicable regulations may require this type of documentation.) The PLC
programming software gives you extensive documentation abilities.
For example, you can create Nicknames such as "PSTOP," Descriptions such as "Program
Stop Coil," and Comments such as "This coil is used to stop the program cycle, but it does not
turn off power to the main hydraulic circuit. However, if the operator opens the safety gate,
the Safety Gate Interlock switch will open and shut off the hydraulic pump." These
Nicknames, Descriptions, and Comments become part of the PLC program and can be viewed
with the applicable software.
As an alternative to ladder logic programming, the State Logic programming language makes
it easier to document PLC program design because it uses "Natural Language" expressions
instead of ladder logic symbols.
Electrical and mechanical prints should contain notations pertaining to safety issues.
Written operating and maintenance instructions as well as training should be provided to
operators and maintenance personnel. These should address any applicable safety issues.
Labeling. Operator devices such as pushbuttons, switches, or on-screen (software) buttons
should be clearly labeled as to their function.
Guarding. Operator devices should be guarded, where applicable, to prevent them from being
activated accidentally. Recessed pushbutton designs or pushbuttons with surrounding guard
rings might help prevent the pushbutton from being depressed if, for example, a tool were
dropped or laid upon it. Mounting pushbutton stations to vertical surfaces also may help avoid
this problem.
Lighting. Illumination levels in the working area should be adequate so that all labels can be
clearly seen.
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