Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 70)

70 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 4 Diagnostic Module Features
8-Point AC/16-Point DC
Diagnostic I/O modules provide various grouping of points on different
modules. The eight-point AC modules and 16-point DC modules provide
additional flexibility when designing module applications. The greater number of
points allows for more field devices to be attached to I/O modules to boost
efficiency.
Point-level Fault Reporting
Diagnostic I/O modules set bits to indicate when a fault has occurred on a
point-by-point basis. The following fault conditions generate their own unique
fault bits.
Using these bits in tandem with data echo and manually performing a pulse test
can help to further isolate the fault.
Table 9 lists possible diagnostic faults on the
1756-OA8D module.
Table 8 - Unique Fault Bits for I/O Points
Input Points Output Points
These conditions can set a fault bit for an input point:
• Open wire
• Field power loss (1756-IA8D only)
These conditions can set a fault bit for an output point:
• Fuse blown
• No load
• Output verify
• Field power loss (1756-IA8D only)
Table 9 - 1756-OA8D Point-level Fault Scenarios
Ladder commands output to be On Ladder commands output to be Off Possible cause of fault
1. Output Data Echo returns the state of the output as Off.
2. Fuse Blown bit is set. 1. Output Data Echo returns the state of the output as Off.
(4)
2. Pulse Test fails.
Output is shorted to L2.
1. Output Data Echo returns the state of the output as On.
2. Pulse Test fails.
(1)
1. Output Data Echo returns the state of the output as Off.
2. No Load bit is off. No Load or output is shorted to L1.
1. Output Data Echo returns the state of the output as Off.
2. No Load shows a fault.
3. Field Power Loss shows a fault.
4. Pulse Test fails. 1. Output Data Echo returns the state of the output as Off.
2. No Load bit is set.
3. Field Power Loss is set.
4. Pulse Test fails. L1 or L2 are disconnected or outside the 47-63 Hz
frequency range.
1. Output Data Echo returns the state of the output as On.
(2)
2. Output Verify bit is set.
(3)
1. Data Echo returns the state of the output as Off.
2. Pulse Test fails. Hardware point damage.
(5)
(1) When pulse test is executed, it is normal operation to see a momentary pulsation on the module display.
(2) The output cannot turn On due to hardware point damage.
(3) Depending on the characteristics of an applied short-circuit, an output verify fault could be set until the short- circuit is detected by the module and the output is turned Off.
(4) It is not possible to create a fuse blown fault in the Off state. If a short-circuit occurs, the output point is turned Off and the fault appears in the Off state until the point is reset.
(5) During normal operating conditions, hardware damage should not be possible. An output shorted to L2 may temporarily cause a hardware point fault. See output shorted to L2 as a possible cause.