Allen-Bradley 1756-L6 Series, Reference Manual, Page: 72 / 134

72 Rockwell Automation Publication 1756-RM001I-EN-P - May 2012
Chapter 6 FLEX I/O Modules
Requirements When Using FLEX I/O Analog Output Modules
Follow these general application considerations when applying the analog output
modules in a SIL2 application:
• Proof tests - Periodically (for example, once every several years) a System
Validation test must be performed. Manually, or automatically, test outputs
to make sure that all outputs are operational. Channel data should be
varied over the full operating range to make sure that the corresponding
field signal levels vary accordingly.
• Calibrate outputs periodically, as necessary . FLEX 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
their FLEX I/O modules are properly calibrated for their specific
application.
You can employ tests in application program logic to determine when a
module requires recalibration. For example, to determine whether an
output module needs to be recalibrated, a user can determine a tolerance
band of accuracy for a specific application. You can then measure output
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 output be calibrated at least every 3 years
to verify the accuracy of the input signal and avoid nuisance application
shutdowns.
• For typical emergency shutdown (ESD) applications, outputs must be
configured to De-energize . When configuring any FLEX I/O output
module, each output must be configured to de-energize in the event of a
fault and in the event of the controller going into program mode.
• Wire outputs back to inputs and examine output data feedback signal.
You must wire an analog output to an actuator and then back to an analog
input to monitor the output’s performance. (The use of feedback
transmitters to verify an output’s performance is acceptable.) The
application logic must examine the Data Feedback value associated with
each output point to make sure that the requested output command from
the controller was received by the module. The value must be compared to
the analog input that is monitoring the output to make sure the value is in
an acceptable range for the application.