Chapter 38

Question 1

What is a Digital Controller?

Answer 1

Digital Controller-

A controller that uses microprocessor technology and special programming to perform the controller functions.

Question 2

Why are Digital Controllers preferred?

Answer 2

Digital controllers offer lower costs, smaller size, greater accuracy, self tuning and intercommunication between controllers and other systems.

Question 3

Explain the term “small”.

Answer 3

“small”-

Refers to those digital devices that are more economical for use with small process systems.

Question 4

Explain the term “large”.

Answer 4

“large”-

Refers to those digital devices that are the most economical for use with large process systems.

Question 5

What is a Stand Alone Controller?

Answer 5

Stand Alone Controller-

A general type of microprocessor-based controller with all required operating components enclosed in one housing.

Question 6

What is a configuration?

Answer 6

Configuration-
The selection of programmed software packages embedded in a controller representing available features that can be chosen.

Question 7

How many controller functions does a Stand Alone Controller have? How many inputs and outputs?

Answer 7

Stand-alone controllers usually have only one controller function and one output, but may have two or more inputs.

Question 8

What is a Direct Computer Control System?

Answer 8

Direct Computer Control System-

A control system that uses a computer as the controller.

Question 9

What is a Distributed Control System (DCS)?

Answer 9

Distributed Control System (DCS)-
A control system where the individual functions that make up a control system are distributed among a number of physical pieces of equipment that are connected by a high-speed digital communication network.

Question 10

What is Scan Speed?

Answer 10

Scan Speed-

The time it takes to access all the I/O points and gp through the configuration program.

Question 11

What is a Programmable Logic Controller (PLC)?

Answer 11

Programmable Logic Controller (PLC)-
A control system with an architecture very similar to that of a DCS, with self-contained power supplies, distributed inputs and outputs, and a controller module all connected on high-speed digital communication networks.

Question 12

What are the two common categories of electric controllers?

Answer 12

The two-
most common categories of electric controllers are null-balance and analog output controllers. Null-balance electric controllers were the first ones to be developed. Analog controllers were developed with transistors became more common.

Question 13

What is a Null-Balance Controller?

Answer 13

Null-Balance Controller-
An electric controller that generates an output signal to a final control element based on a measurement from a process and requires a proportional feedback signal representing the position of the final element.

Question 14

What is an Analog Output Controller?

Answer 14

Analog Output Controller-

An electric controller that has a 4 mA to 20 mA DC electric current as the output.

Question 15

What does an Analog Output Controller do>

Answer 15

Analog Output Controllers contain adjustable setpoints, process measurements, derivative action on the measurement signal, direct and reverse controller action, PID controller actions, and auto/manual output selection.

Question 16

What is an Operator Interface?

Answer 16

Operator Interface-

A view into a digital control system through which an operator can observe and control process.

Question 17

What is a Stand-Alone Display System?

Answer 17

Stand-Alone Display System-
A display system designed for use with smaller digital control systems and has the electronics and display packaged together in a panel-mounted enclosure.

Question 18

What is a PC-based Display System?

Answer 18

PC-based Display System-
A display system that used standard personal computer hardware and special software to display full graphics, control functions, alarms, trends, etc.

Question 19

What is a Digital Recorder?

Answer 19

Digital Recorder-
A device that uses local memory to record process data, which is then displayed on digital display screens that can have the appearance of the old style strip chart recorders.

Question 20

What is a Configuration Format?

Answer 20

Configuration Format-
One of the various programming methods that have been developed to provide a simplified method for instructing the various digital control systems on how to control a process.

Question 21

Configuration Format choice include…

Answer 21

The choices may include the number and type of inputs, input engineering units, type of control functions, controller tuning, math functions, and the number and types of outputs.

Question 22

What is Pick and Choose?

Answer 22

Pick and Choose-

A configuration format where the configuration is selected from a list of available functions.

Question 23

When is a Pick and Choose format most used?

Answer 23

With Stand-Alone Digital Controllers.

Question 24

What is Function Block Configuration?

Answer 24

Function Block Configuration-

A configuration method that uses a library of functions provided by the manufacturer.

Question 25

What is a Function Block?

Answer 25

Function Block-
A Stand-alone procedure designed to perform a specific task and can be linked with other function blocks to form complex control strategies.

Question 26

What is Ladder Logic?

Answer 26

Ladder Logic-
A configuation method that consists of two vertical rails, the left one being the source and the right one being the end, and the sequential rungs of logic between the two.

Question 27

What is a disadvantage of Ladder Logic?

Answer 27

A disadvantage of Ladder Logic formats is that they are more difficult to understand and ti troubleshoot than any other configuration methods.

Question 28

What is Structured Text?

Answer 28

Structured Text-

A type of configuration that is very similar to Microsoft Visual Basic or older structured programming languages.

Question 29

What is a Sequential Function Chart?

Answer 29

Sequential Function Chart-
A type of configuration format consisting of a series of conditional statements, parallel paths, and action blocks, which begins with a Start command and ends with an existing scan.