Safety Considerations Guide for Trident v2 Systems - TUV ...

58 Chapter 4 Application Development
Defining Function Blocks
You can create your own user-defined function blocks for a safety-critical module.
Procedure
1 Copy the example EX02_CRITICAL_IO in the TdTUV.pt2 sample project provided with
the TriStation 1131 Developer’s Workbench.
2 Edit the lines following the comment “Include here all safety-critical I/O modules.”
Each line calls the safety-critical I/O (SCIO) function block for one safety-critical I/O
module.
Example
(*****************************************************************)
(* Include here all safety-critical I/O modules: *)
SCIO( IOP:=1,SLOT:=1, APP:=DE_ENERGIZED, RELAY_OK:=FALSE ): (*DI*)
SCIO( IOP:=1,SLOT:=2, APP:=RELAY, RELAY_OK:=RELAY1_OK); (*DO*)
SCIO( IOP:=1,SLOT:=3, APP:=ENERGIZED, RELAY_OK:=FALSE ); (*DO*)
(* IOP:=1,SLOT:=4, NOT CRITICAL) *) (*RO*)
3 Enter the correct IOP number, SLOT number, APP (application), and RELAY_OK
parameters for the safety-critical I/O module.
Table 15 Parameters for Safety-Critical Modules
Application Type
(App)
RELAY
(de-energized to trip
with relay)
RELAY
(de-energized to trip
with relay)
DE-ENERGIZED
(de-energized to trip
with no relay)
Relay_OK
Parameter
Safety Considerations Guide for Trident v2 Systems
Description
True A voter fault degrades the mode to dual.
The relay provides a third channel for
shutdown so that if an output voter fails,
two independent channels (relay and
other output voter channel) remain that
can de-energize the output.
False A voter fault degrades the mode to
single. A non-voter fault degrades the
mode to dual.
— A voter fault degrades the mode to
single. A non-voter fault degrades the
mode to dual.