Process Controls
CONTROL LOOP DIAGRAMS
CONTROL LOOP DIAGRAMS
A loop diagram is a "roadmap" that traces process fluids through the system and
designates variables that can disrupt the balance of the system.
EO 1.2
DESCRIBE the operation of a control loop diagram
including the following components:
a.
Controlled system
b.
Controlled elements
c.
Feedback elements
d.
Reference point
e.
Controlled output
f.
Feedback signal
g.
Actuating signal
h.
Manipulated variable
i.
Disturbance
EO 1.3
EXPLAIN
how
capacitance,
resistance,
and
transportation time affect a control system’s lag time.
Terminology
A block diagram is a pictorial representation of the cause and effect relationship between the
input and output of a physical system. A block diagram provides a means to easily identify the
functional relationships among the various components of a control system.
The simplest form of a block diagram is the block and arrows diagram. It consists of a single
block with one input and one output (Figure 5A). The block normally contains the name of the
element (Figure 5B) or the symbol of a mathematical operation (Figure 5C) to be performed on
the input to obtain the desired output. Arrows identify the direction of information or signal
flow.
Rev. 0
Page 7
IC-07
