Controllers, Control Loops, and Complex Control Loops Study Guide

Primary Measuring Elements and Principles

• The most common element used for measuring flow is a/n rifice place. It functions by creating a differentil pressure ($DP$).

• The primary element for measuring level is a/n $D/P$ Cell. It operates by comparing the total pressure of the bottom of the vessel (calculated as liquid head pressure I vapor pressure @ the tap) to the valor Tren Pressure of the top of the vessie (known as the Vapor Space).

• The most common element for measuring temperature is a/n Thermocouple.

Functional Differences Between Indicators and Controllers

• Indicators are designed to provide the user with a meesurem.
• Controllers are designed to exert control over a flow.

Controller Faceplate and Process Information

A controller faceplate, such as those found on a Simtronics board, provides three specific pieces of information about the process:

• $PV$: This stands for Processe veniable and represents the Actual Reading/measurement of the process.
• $SP$: This stands for Setpoint and represents the Desired reading measurement for the process.
• $OP$: This stands for Output and represents the Valve Position.

Controller Operating Modes

A controller can be set to any of the following three modes:

• Automation: In this mode, the Operator controls the $SP$.
• Manual: In this mode, the Operator controls the $OP$.
• Cascade: In this mode, another controller determines its $SP$.

Cascade Control Loop Mechanics

• A cascade control loop is composed of two (2) Controllers and one (1) Valve.
• The primary controllers' $OP$ determines the $Sp$ of the Secondary controller.

Impact of Pressure on Liquid State

• The relationship between pressure and liquid behavior is dictated by the principle: Higher Pressure =

Control Loop Component Identification and Naming

The variable controlled by a control loop is identified by the first letter of its components:

• F: The control loop is controlling flow.
• L: The control loop is controlling level.
• P: The control loop is controlling pressure.
• I: The control loop is controlling temporcue.
• A: The control loop is controlling Anctical. While this commonly refers to Composition, it can also refer to other factors such as pH or Conductivity.

Process Composition and Loop Components

• Composition is defined as the ingredients or make-up of something.

Basic Flow Control Loop Components and Functionality

A basic flow control loop consists of the following elements, each with specific definitions and roles:

• Flow Element (E): Defined as the component used to measure flow.

• Flow Transmitter (T): Defined as the component that translates the flow measurement to the $FIC$.

• Flow Indicating Controller ($FIC$): This component compares the $Pv$ (the actul measurement obtained from the $FI$) to the $SP$ (the desired op/valve Position or desired measurement received from the board op). It then sends a command to adjust the $Op$ Valve Position in order to achieve or maintain the $SP$.

• Flow transducer ($FV$): Defined as the device used to Convert Something like energy or a messge into Grother form.

• Flow Control Valve ($Fev$): Defined as the assembly that Open / Closes to a just flow.