Rockwell Automation T7411F ICS Regent+Plus Monitored Digital input Modules, Field powered (Type F) - Manual (Page 5)

Monitored Digital Input Modules, Type F (T7411F, T7418F)
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off failure modes. During testing the D/A converter generates
two reference voltages outside the normal operating range of
the field input voltages to test that the comparator output can
turn-off and turn-on. The I/O processors read the resulting
input status, line fault status, and reference voltage readings
for the test cycle to determine if there are faults in the input
circuits or the common data paths.
If the I/O processors detect a faulted input circuit, an I/O
module fault is indicated at the processor modules and the
Fault LED on the face of the input module is turned on.
Input Circuit Test Interval
The Regent processor modules schedule testing of the input
circuits on a background basis. The test interval for these
circuits may range from a few seconds to several minutes,
depending on the application program scan time and the size
of the I/O configuration. The equation below can be used to
estimate the test interval for monitored digital inputs.
TI = 172 * IOUQTY * TSCAN + 2
where:
TI = Test interval, seconds
IOUQTY = Quantity of I/O Units in the system (1 to 16)
TSCAN = The application program scan time, seconds
For example, for a system with 8 I/O units and an application
scan time of 60 milliseconds, the test interval would be:
TI = 172 * IOUQTY * TSCAN + 2 = 172 * 8 * 0.060 + 2
TI = 84.6 seconds
In this system, all of the monitored input modules would be
tested for stuck-on and stuck-off faults approximately every 85
seconds. This test interval can be used in reliability and
availability calculations to select the fault tolerant input
configuration that meet the application’s safety requirements.
Due to I/O processor fault filtering algorithms, it may take up
to four test intervals to report a failed input module as a
permanent fault
Note: