Maple Systems OIT Family - Manual (Page 63)

If the OIT determines that the current value in the set point address is below the low limit
or above the high limit, then the appropriate screen is displayed on the OIT. The screen
displayed can be an alarm, message, recipe, or menu.
Once an out-of-range condition has occurred, the set point screens cannot be activated
again until the set point address value comes back into range. For example, suppose a set
point has been configured to monitor PLC address ADD1. The set point is configured to
display Screen #1 if ADD1 falls below -100 and Screen #2 if ADD1 rises above 100. The
PLC address starts with a value of 0 (in range). Then ADD1 falls to -200 (low limit range
exceeded) causing the OIT to display Screen #1. If the next value of ADD1 is 200 (high
limit range exceeded) the OIT will not display Screen #2, because ADD1 did not go back
into range (-100 to 100) after the low limit range was exceeded. However, if ADD1 had
changed from -200 to 10 to 200, Screen #2 would have been displayed.
NOTE:Depending on the poll rate (number of set points), data may change many times before
being detected by the OIT.
In addition to the possible delay based on the poll rate, the response time of low limit or
high limit violations can vary depending on the communications speed and the amount of
data overhead of each PLC protocol. Therefore, if the set points are used as alarms, they
should be treated as auxiliary alarms and placed at priorities 3 and 4 while PLC generated
alarms are placed at priorities 1 and 2.
NOTE:Under no circumstances should set points be used to monitor safety critical processes or
limits!
To configure a set point:
1. From the Configuration menu, choose Setpoints Editor. The Set Points Editor dialog
box appears.
PLC Register Monitors 63
1010-0099, Rev. 07