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Gravimetric Batch Blenders w/Mitsubishi Control Chapter 2: Functional Description 26
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 the Slide Gate/Auger Blenders are primarily concerned with pneumatic and 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 blenders are equipped with a line cord
plug (Shown in figures 11 and 12). This allows the operator or maintenance personnel to
unplug the unit 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.
Figure 12: Electrical Disconnect Plug