ABB Triguard SC300E Safety Manual

Also see for Triguard SC300E: User manual

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ABB Triguard SC300E Safety Manual Manual pdf 14 page image

Issue 5 - September 2006 Page 14 of 65The field analogue signal is wired to the Analogue Input Termination Card. Where the safetyintegrity levels require that more than one transmitter be used to monitor a safety parameter,then the additional analogue input signals should be wired to separate Termination Cards wherepractical. The Simplex circuitry on the termination card must be considered for reliability as partof the transmitter loop (eg fuses and monitoring resistors where fitted). Refer to Figure 2.The signal is connected from the termination card to the Triguard SC300E input module via astandard system cable, which connects to the socket on the appropriate Hot Repair AdapterCard (THR) or chassis connector.Through the Hot Repair Adapter Card, where required, and the chassis backplane connectorthe input signal is connected to the appropriate configured analogue input module slot position,where an appropriate Analogue Input Module would be located.All the chassis slot and, where required, their hot repair partner slots configured for theAnalogue module must also have the coding blocks fitted and configured for this type of moduleas specified in the Module and Chassis User Manuals.Figure 2 Current to Voltage ConversionWhere separate transmitters are used to monitor the same safety parameters to meet increasedintegrity levels these should be configured to separate Analogue Input Modules where practical.Switch inputs with end of line and series line-monitoring resisters fitted may be connected asanalogue inputs. These line-monitored inputs provide increased diagnostic information to thesafety system giving discrete analogue values (step changes) for open circuit, switch open,switch closed and short circuit conditions.3.3.1.3 Fail Safe Analogue ProcessingFor each Analogue Input variable received by the system three values are generated, one fromeach channel. Under normal operation (transparent to the application) a mid-value selectionalgorithm is used selecting the middle value (assuming all three values are within the healthwindow) to be passed on to the application. It is this mid-value that the user operates on withinthe application, all three processing channels now using this selected mid-value.When one of the three analogue channel values presented to the processors falls outside of thehealth window the processors flag it as bad by converting it to a negative number. If now thetwo remaining values diverge by more than the health window these are also flagged as bad byconverting them to negative numbers. The effect is to present to the application a negativevalue when 2 or more channels are bad.