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Additive Feeders Chapter 2: Functional Description 14 of 55
Safety Circuit Standards
Safety circuits used in industrial systems protect the operator and maintenance personnel
from dangerous energy. They also provide a means of locking out or isolating the energy for
servicing equipment.
Various agencies have contributed to the establishment of safety standards that apply to the
design and manufacture of automated equipment. The Occupational Safety and Health
Administration (OSHA) and the Joint Industrial council (JIC) are just a few of the
organizations that have joined with the plastics industry to develop safety standards.
Every effort has been made to incorporate these standards into the design of the additive
feeder; however, it is the responsibility of the personnel operating and maintaining the
equipment to familiarize themselves with the safety procedures and the proper use of any
safety devices.
Fail Safe Operation
If a safety device or circuit should fail, the design must be such that the failure causes a
“Safe” condition. As an example, a safety switch must be a normally open switch. The switch
must be held closed with the device it is to protect. If the switch fails, it will go to the open
condition, tripping out the safety circuit.
At no time should the safety device fail and allow the operation to continue. For
example, if a safety switch is guarding a motor, and the safety switch fails, the motor should
not be able to run.
Safety Device Lock-Outs
Some safety devices disconnect electrical energy from a circuit. The safety devices that are
used on these additive feeders are primarily concerned with electrical power disconnection
and the disabling of moving parts that may need to be accessed during the normal operation
of the machine.
Some of the safety devices utilize a manual activator. This is the method of initiating the
safety lock out. This may be in the form of a plug, lever or a handle. Within this lockable
handle, there may be a location for a padlock. Personnel servicing the equipment should
place a padlock in the lockout handle.
In addition to the safety devices listed above, these additive feeders are equipped with a line
cord plug. This allows the operator or maintenance personnel to unplug the additive feeder
from its power source and tag it out. The plug can then be tagged with any number of
approved electrical lockout tags available at most electrical supply stores.
WARNING! Always disconnect and lockout all electrical power and pneumatic (i.e. compressed air)
sources prior to servicing or cleaning the additive feeder. Failure to do so may result in
serious injury. No one but the person who installed the lockout may remove it.