Allen-Bradley 1756-L6 Series, Справочное руководство, Страница: 89 / 134

Rockwell Automation Publication 1756-RM001I-EN-P - May 2012 89
Faults in the ControlLogix System Chapter 8
In Figure 49 on page 88 , the Get System Value (GSV) instruction interrogates
the STATUS attribute of the CONTROLLERDEVICE object and stores the
result in a word called KEYSTATE, where bits 12 and 13 define the state of the
keyswitch as shown in
Table 4 .
If bit 13 is ever ON, then the keyswitch is not in the RUN position. Examining
bit 13 of KEYSTATE for an ON state will generate a fault.
It is your responsibility to determine appropriate behavior when a fault is present.
For more information on the accessing the CONTROLLERDEVICE object, see
the Logix5000 Controllers General Instructions Reference Manual, publication
1756-RM003 .
Examining an 1756 Analog
Input Module’s High Alarm ControlLogix analog modules perform processing and comparison of field data
values right on the module, allowing for easy examination of status bits to initiate
a fault.
For example, the 1756-IF8 module can be configured with user-defined alarm
values that, when exceeded, will set a status bit on the module which is then sent
back to the controller. You can examine the state of these bits to initiate a fault as
shown in
Figure 50 .
Figure 50 - High Alarm Bit to Trigger Fault
In the example above, the High Alarm bits for channels 1 and 2 are being
examined for a condition to initiate a fault. During operation, as the analog input
module processes analog signals from the field sensors, if the value exceeds the
user-defined value for High Alarm, the alarm bit is set and a fault is declared.
It is your responsibility to determine appropriate behavior when a fault is present.
Table 4 - Keyswitch State Bits
Bit 13 Bit 12 Description
0 1 Keyswitch in Run position
1 0 Keyswitch in Program position
1 1 Keyswitch in Remote position
Alarm to
Operator
Ch1HAlarmA
Fault
Fault
Ch1HAlarmB Module A Module B
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