Allen-Bradley 1756-L6 Series, Reference Manual, Page: 48 / 134

48 Rockwell Automation Publication 1756-RM001I-EN-P - May 2012
Chapter 5 ControlLogix I/O Modules
Calibrate Inputs
Analog input modules should be calibrated periodically, as their use and
application requires. ControlLogix I/O modules ship from the factory with a
highly accurate level of calibration. However, because each application is
different, you are responsible for making sure your ControlLogix I/O modules
are properly calibrated for your specific application.
You can employ tests in application program logic to determine when a module
requires recalibration. For example, to determine whether an input module needs
to be recalibrated, you can determine a tolerance band of accuracy for a specific
application. You can then measure input values on multiple channels and
compare those values to acceptable values within the tolerance band. Based on
the differences in the comparison, you could then determine whether
recalibration is necessary.
Calibration (and subsequent recalibration) is not a safety issue. However, we
recommend that each analog input be calibrated at least every three years to verify
the accuracy of the input signal and avoid nuisance application shutdowns.
Use the Floating Point Data Format
ControlLogix analog input modules perform on-board alarm processing to
validate that the input signal is within the proper range. These features are only
available in Floating Point mode. To use the Floating Point Data format, select
the Floating Point Data format in the Module Properties dialog box.
Program to Respond to Faults Appropriately
When programming the SIL 2 system, verify that your program examines the
appropriate module fault, channel fault, and channel status bits and responds by
initiating the appropriate fault routine.
Each module communicates the operating status of each channel to the controller
during normal operation. Application logic must examine the appropriate bits to
initiate a fault routine for a given application. For more information on faults, see
Chapter 8 , Faults in the ControlLogix System on page 87 .
Program to Compare Analog Input Data
When wiring sensors to two input channels on different modules, the values from
those channels must be compared to each other within the program for
concurrence within an acceptable range for the application, before an output is
actuated. Any miscompare between the two inputs outside the programmed
acceptable range must be annunciated as a fault.