A loop diagram is a "roadmap" that traces process fluids through the system designates variables that can disrupt the balance of the system.

and

EO 1.2DESCRIBE the operation of a control loop 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 diagram

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 513) 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.

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Figure 5 Block and Arrows

Although blocks are used to identify many types of mathematical operations, operations of addition and subtraction are represented by a circle, called a summing point. As shown in Figure 6, a summing point may have one or several inputs. Each input has its own appropriate plus or minus sign. A summing point has only one output and is equal to the algebraic sum of the inputs.

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Figure 6 Summing Points

A takeoff point is used to allow a signal to be used by more than one block or summing point (Figure 7).

Figure 7 Takeoff Point