AADvance Safety Manual - Tuv-fs.com

Chapter 5 AADvance Functional Safety SystemImplementationInput modules support redundancy when configured for dual or triple operation usingthe appropriate termination assembly. Redundant input modules may be inserted orremoved at any time without any impact on the safety function of the system.Redundant input modules operate independently providing independent values of theinput values to the processor module.Input module termination assembliesThe termination assemblies are safety critical and provide termination for 16 channels.They connect the field signals to the input modules. The simplex version connects eachinput channel to one input module, the dual TA routes them to two input modules andthe triple TA to three input modules.A digital input TA circuit has fuse protection and a 4.99k high reliability inputtermination for each channel. The analogue input TA has fuse protection for eachchannel and a high reliability 120 ohm input termination for each channel.Input Module Safety AccuracyThe I/O input modules determine the channel state and the line fault state bycomparing the input reported values with user programmed threshold values. Whentriple analogue input modules are used and active, the system adopts the median value.When dual modules are used, the lowest reported value is used. The discrepancybetween the redundant channels' measurements are monitored to determine if theyare within the safety accuracy limit.When the safety accuracy within a channel is detected outside the following limits thenthat channel is set to a fail-safe state. Digital Input Module = 4% Analogue Input Module = 1%When the safety accuracy between channels exceeds the following limits then adiscrepancy alarm is set for the input channel Digital Input Module = 8% Analogue Input Module = 2%in both situations the following safe values are reported by the variables:Digital input modules Input state = FALSE Line fault = TRUE Discrepancy= TRUE Channel fault = TRUEand the voltage value is 0mVDocument number 553630 Issue 7: February 2010 5-21