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

ControlLogix I/O Modules 6-21• Choose Floating Point Data Format During ModuleConfiguration: ControlLogix analog output modules perform ahost of on-board alarm processing to validate that the outputsignal 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.• For typical emergency shutdown (ESD) applicationsoutputs must be configured to De-energize: Whenconfiguring any ControlLogix output module, each output mustbe configured to de-energize in the event of a fault and in theevent of the controller going into program mode. For exceptionsto the typical ESD applications, see Chapter 1, SIL Policy.• Wire Output Back to Input and Examination of OutputData Echo signal: Users must wire an analog output to anactuator and then back to an analog input to monitor theoutput’s performance, as shown in Figure 6.17. The applicationlogic must examine the Data Echo value associated with eachoutput point to make sure that the requested output commandfrom the controller was received by the module. The value mustbe compared to the analog input that is monitoring the output tomake sure the value is in an acceptable range for theapplication.In the ladder diagram in Figure 6.16, a user-defined percentageof acceptable deviation (that is, tolerance) is applied to theconfigured range of the analog input and output (that is, range)and the result is stored (that is, delta). This delta value is thenadded to and subtracted from the monitoring analog inputchannel; the results define an acceptable High and Low limit ofdeviation. The analog Output Echo is then compared to theselimits to determine if the output are working properly.The output’s OK bit preconditions a Timer run that is preset toaccommodate an acceptable fault response time and anycommunication filtering, or output, lags in the system. If themonitoring input value and the Output Echo miscompare forlonger than the preset value, a fault is registered with acorresponding alarm.Publication 1756-RM001B-EN-P - October 2003