Maple Systems OIT Family - Manual (Page 124)

Alarms
How Many Alarms are Supported?
Each OIT can store and display up to 500 screens (250 on the OIT5400). Of these 500
screens, any or all can be alarms.
How are Alarms Displayed?
The PLC requests an alarm screen by placing the number that corresponds to that screen in the
Message Request Register (MRR). When the OIT reads the number in the MRR, the OIT
displays the corresponding alarm screen, sounds the audible alert, and blinks the alarm LED.
Refer to the Alarm Screens section in CHAPTER 3: Stored Screens for more information.
What Happens When the OIT Operator Pushes the Alarm Ack Key?
The audible alert is silenced, the alarm LED is cleared, and the Acknowledge Alarm
status coil is set. If the alarm stack contains additional alarms, the next alarm in the stack
is displayed. Otherwise, the prior non-alarm screen is displayed.
Is There an Alarm Stack?
Yes, but only for pending alarms. Once the OIT operator acknowledges an alarm screen,
the alarm request is terminated and discarded.
Alarms are Cleared Before the OIT Operator Acknowledges Them
Possible Cause:
• The PLC is setting the Clear Alarm or Clear Alarm Stack status coil.
Possible Solution:
• Modify the PLC program so that the PLC does not set the Clear Alarm or Clear Alarm Stack
status coils. From the starting PLC address for the status coils, the Clear Alarm status coil is
offset 7 bits and the Clear Alarm Stack status coils is offset 8 bits. To determine the starting PLC
address for the status coils, press F4 in OITware-200. The OIT - Controller Settings dialog box
appears. The Status Coils group box contains the starting PLC address for the status coils.
When the PLC Requests the Same Alarm Twice the Alarm is Not
Displayed
Possible Cause:
• If the MRR already contained the screen number that the PLC requested, the OIT would
not recognize the screen request.
Possible Solutions:
• Modify the PLC program so that when the MRR already contains the screen number that
the PLC is requesting, the PLC writes a zero to the MRR before writing the screen number.
This allows the OIT to recognize the alarm request and does not clear the OIT’s display.
• If using an OIT3160, OIT3165, OIT3175, OIT3185, OIT4160, OIT4165, OIT4175, or
OIT4185, activate the Clear Register/Bit After Receiving Screen Request feature. Refer
to the Configuring the MRR with Enhanced Features section in CHAPTER 5: Displaying
Stored Screens.
Troubleshooting 124
1010-0099, Rev. 07