Rockwell Automation T8019 Trusted Process Control Algorithm Software Package - Manual

Trusted TM
PD-T8019
Issue 8 Sep 07 PD-T8019 1
Trusted
TM
Process Control Algorithm
Software Package
Introduction
The system architecture of the Trusted TM is intended to cover as large a cross section of control and
interlock applications as is possible. The control algorithms detailed in this Product Description are
primarily intended to support the limited process control capabilities required for Floating Production,
Storage and Offloading (FPSO) installations. The algorithms may also be used for other process
control applications as required.
Control functions require the use of floating point values. This ultimately limits the integrity that can be
attributed to these functions because of the introduction of an element of “loss of precision” and the
general inability to exhaustively verify floating-point capabilities.
The functions are integrated into the IEC1131 TOOLSET execution environment. This environment is
“Commercial-Off-The-Shelf (COTS)” and designed to commercial standards. The overall system
achieves higher levels of integrity by the use of additional on-line monitoring and internal state control.
The combination of the above factors indicate that the target integrity for the basic process control
functions should be SIL1 (AK3). These functions should therefore NOT be used within elements of
application programs intended for SIL3 (AK6) use.
The control algorithms are executed within the Trusted TM Controller as part of the standard application
program and are divided into ‘functions’ and ‘function blocks’.
‘Functions’ are those algorithms with no internal state, or time dependent operation, i.e. they have no
storage element. The functions process the defined number of parameters and return a single
resultant state or value. Functions, therefore, have only a single operating mode, always performing
the same operation.
The ‘function blocks’ include retentive information and may return multiple values. Function blocks will
have an initial state or value for each of their outputs. The initial value may be maintained for a single
or multiple application iterations, depending on the detail of the algorithms.