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ROC800-Series Instruction Manual

Revised Jul-14

General Information

1-19

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.

1.5.7 Proportional, Integral, and Derivative (PID)

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.

1.5.8 Function Sequence Table (FST)

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.

The FST Editor provides a workspace into which you can enter—for

each FST—

either

a maximum of 500 lines

or

a maximum of 3000