1756-RM001B-EN-P, Using ControlLogix in SIL2 ... - Tuv-fs.com

6-14 ControlLogix I/O Modules• Choose Floating Point Data Format During ModuleConfiguration: ControlLogix analog input modules perform ahost of on-board alarm processing to validate that the inputsignal is within the proper range for the application. However,these features are only available in Floating Point mode.• Examine the Appropriate Module Fault, Channel Fault andChannel Status Bits to Initiate Fault Routines: Each modulewill communicate the operating status of each channel to thecontroller during normal operation. Application logic mustexamine the appropriate bits to initiate a fault routine for a givenapplication. For more information on faults, see Chapter 7,Faults in the ControlLogix System.• Compare Analog Input Data and Annunciate Miscompares:When wiring sensors to two inputs channels, the values fromthose channels must be compared to each other for concurrencewithin an acceptable range for the application before actuatingan output. Any miscompare between the two inputs outside theprogrammed acceptable range must be annunciated as a fault.In Figure 6.11, a user-defined percentage of acceptabledeviation (that is, tolerance) is applied to the configured inputrange of the analog inputs (that is, range) and the result is stored(that is, delta). This delta value is then added to and subtractedfrom one of the input channels; the results define an acceptableHigh and Low limit of deviation. The second input channel isthen compared to these limits to determine if the input areworking properly.The input’s OK bit preconditions a Timer run that is preset toaccommodate an acceptable fault response time and anycommunication filtering lags in the system. If the inputsmiscompare for longer than the preset value, a fault is registeredwith a corresponding alarm.Publication 1756-RM001B-EN-P - October 2003