Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 71)

Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 71
Diagnostic Module Features Chapter 4
The following table lists possible diagnostic faults on the 1756-OB16D module.
Features Specific to
Diagnostic Input Modules The table below lists features specific to ControlLogix diagnostic digital input
modules.
Diagnostic Change of State for Input Modules
If the diagnostic change of state feature is enabled, a diagnostic input module
sends new data to the owner-controller when one of the events described in the
table occurs.
Table 10 - 1756-OB16D 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)
1. Output Data Echo returns the state of the output as Off.
(4)
2. Pulse Test fails.
(5)
Output is shorted to GND.
1. Output Data Echo returns the state of the output as On.
2. Pulse Test fails 1. Output Data Echo returns the state of the output as Off.
2. No Load bit is set.
3. Pulse Test passes. One of the following could be the cause.
1. No Load.
2. Output shorted to DC+.
3. No power at module.
1. Output Data Echo returns the state of the output as On.
(2)
2. Output Verify sets a bit.
(3)
1. Output Data Echo returns the state of the output as Off.
2. Pulse Test fails. Hardware point damage.
(6)
(1) The electronic protection of this module has been designed to provide protection for the module from short-circuit conditions. The protection is based on a thermal cutout principal. In the event of a
short-circuit condition on an output channel, that channel will limit the current within milliseconds after its thermal cutout temperature has been reached. Other channels could produce a false error on
the output verify fault signal due to the supply dropping below the minimum detect level of 19.2V DC. The output channels that are affected by this phenomena will continue to operate as directed by the
module master (CPU, bridge, and so forth). What this means is that the output verify fault signals of the other channels should be checked and reset if a short-circuit on one channel occurs.
(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 point is turned Off and the fault appears in the Off state until that point is reset.
(5) When the pulse test is executed, it is normal operation to see a momentary pulsation on the module display.
(6) During normal operating conditions, hardware damage should not be possible. An output shorted to GND may temporarily cause a hardware point fault. See output shorted to GND as a possible cause.
Topic Page
Diagnostic Change of State for Input Modules 71
Open Wire Detection 73
Field Power Loss Detection 74
Event Description
RPI A user-defined rate at which the module updates the information sent to its
owner-controller. This is also known as Cyclic Data Transfer.
Change of State Configurable feature that, when enabled, instructs the module to update its
owner-controller with new data whenever a specified input point transitions from
On to Off and Off to On. The data will be sent at the RPI rate where there is no
change of state. By default, this setting is always enabled for input modules.
Diagnostic Change of State Information updates when any change in the diagnostics for an input module
occurs.