Proportional, Integral, And Derivative (Pid); Function Sequence Table (Fst) - Emerson ROC809 Instruction Manual

1.5.7 Proportional, Integral, and Derivative (PID)

1.5.8 Function Sequence Table (FST)

Revised July-2017
▪ The design of the PM-30 and PM-24 power modules does not
include the low voltage cutoff feature present in the PM-12
module: should power fall below the set LoLo alarm (a default
of 10.1V), the PM-12 module ceases to provide power to the
backplane. Thus, the module shuts down CPU operations. For
the PM-24 and PM-30 modules, when power falls below the
LoLo alarm point, the CPU goes into sleep mode. In sleep mode,
the backplane still receives power, the DO modules continue to
hold their logic, but nothing controls I/O at this point. If you
need both the increased power capacity offered by the PM-30
and low voltage cutoff, refer to the options provided in the
description of the PM-30 module in Chapter 3 of this manual.
The PID Control applications firmware provides Proportional, Integral,
and Derivative (PID) gain control for the ROC800 and enables the
stable operation of 16 PID loops that employ a regulating device, such
as a control valve.
The firmware sets up an independent PID algorithm (loop) in the
ROC800. The PID loop has its own user-defined input, output, and
override capability.
The typical use for PID control is to maintain a Process Variable at a
setpoint. If you configure PID override control, the primary loop is
normally in control of the regulating device. When the change in output
for the primary loop becomes less or greater (user-definable) than the
change in output calculated for the secondary (override) loop, the
override loop takes control of the regulating device. When the
switchover conditions are no longer met, the primary loop regains
control of the device. Parameters are also available to force the PID into
either loop or force it to stay in one loop.
The Function Sequence Table (FST) applications firmware gives analog
and discrete sequencing control capability to the ROC800. This
programmable control is implemented in an FST, which defines the
actions the ROC800 performs using a series of functions. You use the
FST Editor in ROCLINK 800 software to develop FSTs
The function is the basic building block of an FST. You organize
functions in a sequence of steps to form a control algorithm. Each
function step can consist of a label, a command, and associated
arguments. Use labels to identify functions and allow branching to
specific steps within an FST. You select commands from a library of
mathematical, logical, and other command options. Command names
consist of up to three characters or symbols. Finally, arguments provide
access to process I/O points and retrieve real-time values. A function
may have zero, one, or two arguments.
General Information
ROC800-Series Instruction Manual
1-19