76 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 4 Diagnostic Module Features
Diagnostic output modules list a minimum load current specification
(1756-OA8D = 10 mA & 1756-OB16D = 3 mA). In the On state, the module
must be connected to a load that will draw a minimum current equal to these
values.
If a connected load is sized in accordance with the minimum load current
specification, diagnostic output modules are capable of sensing current through
the optoisolator and the load when the output point is Off.
Follow these steps to enable no load detection.
1. On the Module Properties dialog box, click the Configuration tab.
2. Do one of the following in the No Load column:
• To enable the feature for a specific point, check the corresponding
checkbox.
• To disable the feature for a specific point, clear the corresponding
checkbox.
3. Click OK.
This feature has a corresponding tag that can be examined in the user program in
the event of a fault. For more information on these tags, see Appendix
B.
Field-side Output Verification
Field-side output verification informs you that logic-side instructions consumed
by the module are accurately represented on the power side of a switching device.
For each output point, this feature confirms that the output is On when it is
commanded to be On.
The diagnostic output module can tell a controller that it received a command
and whether the field-side device connected to the module has executed the
command. For example, in applications that need to verify that the module has
accurately followed the processor’s instructions, the module samples the field-side
state and compares it to the system-side state.
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