Honeywell SmartPAC 2 User Manual page 39

SmartPAC 2 with WPC Integration
Green Special
CAUTION
GREEN SPECIAL SENSOR MAY NOT PREVENT DAMAGE
Use the green special sensor type with caution. It is not foolproof. It is possible that an
undesirable number of slugs could stack up in an ejection hole, while still satisfying a green
special sensor's requirements. See the example at the end of this section.
Failure to comply with these instructions could result in property damage.
Green special sensors are specifically designed to effectively monitor slug ejection. They are
generally used to detect slugs excessively stacking up in a slug ejection hole. When slugs are
ejected through the bottom of the die, they do not necessarily discharge on every stroke. It is
normal for several strokes to occur with the slugs sticking in the hole before they finally
break free and all fall out of the bottom of the die. If the slugs jam and too many stack up in
the hole, the die can be damaged.
Slug stacking is virtually impossible to monitor with a standard green sensor. A red or
yellow sensor is equally ineffective because the slugs must come out at some time and will
cause the sensor to change state. Instead of happening once per stroke like a typical green
sensor, the green special must actuate at least once during a preset number of strokes. Rather
than setting a ready signal, you set the maximum number of strokes that the press can make
without this sensor actuating.
Here is how it works: You install a sensor so that it will actuate when a slug passes through
the slug ejection hole. In this example, assume that the die clears all the slugs out of this
particular ejection hole about every four strokes. You know that something is wrong if the
press makes six stokes without ejecting a slug. You would set the sensor type to "Green
Special" and set the number of stokes to six. If no slugs are ejected after six strokes, the
press will stop.
Example: How a green special sensor may not detect a problem
Referring to the example above, assume that the press makes five strokes without ejecting a
slug. On the sixth stroke, one slug ejects and actuates the sensor. The green special sensor
is satisfied and the press continues to run (remember, there are still five slugs in the ejection
hole). The press then makes five more strokes without ejecting a slug. There are now ten
slugs stuck in the hole. Using this logic, it is conceivable that an infinite number of slugs could
stack up in the hole without the press stopping. Luckily, the laws of physics make this scenario
unlikely. When slugs jam, it is usually because the bottom one is stuck. If the bottom slug
ejects, it is very likely that the rest will soon follow.
Introduction to SmartPAC 2 Chapter 1
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page 17