Rockwell Automation T8019 Trusted Process Control Algorithms - Manual

SDS-8019
Trusted
TM Industrial Control System
Trusted TM Process Control Algorithms-T8019
Issue 5 Jan 2006
DESCRIPTION
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 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.
ERROR STATISTICS
Several of the basic control
algorithms may generate error
conditions at run-time as all function
parameters are variable. This may
result in reversed parameters, e.g.
max < min, overflow and underflow
conditions, divide by zero errors, etc.
For each function, the required output
under these conditions is defined and
error counters are incremented.
These error counters are available to
the application programmer using the
error statistics function block..
FUNCTIONS
‘Functions’ algorithms currently
supported are listed below:
Square Root Extraction
BCD Translation
Analogue Select
Multiple Value Averaging
Drum Level Control
Mass Flow Computation
The Mass Flow Computation
algorithm is shown overleaf.
FUNCTION BLOCKS
‘Function Blocks’ currently supported
are listed below:
Analogue Scaling
Analogue value Clamping
Low Value Select
High Value Select
Median Value Select
PID Function
Deviation Alarm
Manual tracking
Time Averaged Value
Rate Of Change Detection
Analogue Value Slew
The Deviation Alarm algorithm is
shown overleaf.