Computer Control Systems Chapter 6 Quiz

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Questions and Answers

What should be expected regarding maintenance requirements for a SCADA system over time?

They will consistently increase without any drops.

They will be high initially and then drop to a lower plateau. (correct)

They will decrease initially and then stabilize at a high level.

They will remain uniform from installation to end of life.

Why might maintenance requirements for sensors and actuators be higher initially?

Solid-state equipment requires more frequent maintenance than process interface devices.

Sensors and actuators are built to last without any initial issues.

They undergo wear and tear at a consistent rate immediately after installation.

New equipment goes through its early mortality stage, leading to early failures. (correct)

What design considerations should be taken into account for SCADA maintenance?

Installation of more complex systems to enhance functionality.

Increased protection against environmental factors.

Ease of access and temporary isolation for maintenance tasks. (correct)

Construction of larger facilities to accommodate equipment.

How does the failure rate of process interface devices compare to solid-state equipment?

They fail at a higher rate than solid-state equipment. Signup and view all the answers

What issues might arise during the early mortality stage of new equipment?

Manufacturing defects such as loose contacts and pinched wires. Signup and view all the answers

What is often overlooked as a significant cost in SCADA projects?

Sensors and actuators Signup and view all the answers

By how much can the cost of sensors, actuators, and wiring exceed the cost of RTUs and communications equipment?

They typically cost 3-4 times more. Signup and view all the answers

Which of the following is a key consideration when selecting and installing sensors and actuators?

Special considerations of process and ambient conditions Signup and view all the answers

Which part of a SCADA project is typically highly visible?

Master Terminal Units Signup and view all the answers

What percentage of the total SCADA project cost may be attributed to engineering, development, and documentation costs?

50 percent Signup and view all the answers

What type of systems is SCADA used in?

In a wide range of industries Signup and view all the answers

What aspect of a SCADA project can overshadow its more basic components?

The MTU and communications system Signup and view all the answers

What is a significant challenge in the food processing industry regarding SCADA systems?

Preventing equipment contamination Signup and view all the answers

What might happen if a company frequently changes suppliers for process end devices?

Increased risk of inferior quality Signup and view all the answers

How many sensors, actuators, and analyzers can a SCADA site potentially have?

As many as 250 Signup and view all the answers

What is one of the learning objectives regarding the cost of process interface equipment?

It can be significantly high. Signup and view all the answers

What type of costs in a SCADA project are typically three to five times higher than in a non-SCADA project?

Engineering costs Signup and view all the answers

Which issue is NOT mentioned as a special consideration for the chemical processing industry?

High voltage isolation Signup and view all the answers

Which of the following statements about market changes is true concerning sensor and actuator manufacturers?

Market conditions affect pricing among manufacturers. Signup and view all the answers

What type of field equipment is crucial in hydrocarbon fluid transportation?

Sensors that prevent fires Signup and view all the answers

Why might there be extra charges in SCADA system implementation?

To cover the complexity and special considerations required. Signup and view all the answers

What is the purpose of the junction boxes in a SCADA system?

To terminate wires from multipair cables and connect to individual instruments Signup and view all the answers

Which component serves as a large junction box located at the RTU site?

Marshaling panel Signup and view all the answers

What factors can overshadow small price savings in a SCADA system?

Increased costs of documentation and warehousing Signup and view all the answers

What might be housed within a marshaling panel in a SCADA system?

Status lights, power relays, and calibration circuitry Signup and view all the answers

What should be considered in addition to the fitness of a manufacturer's sensors and actuators?

The financial stability of the manufacturer Signup and view all the answers

What is the role of terminal strips found in junction boxes?

To enable wiring connections and facilitate checks for correctness Signup and view all the answers

Why are replacement parts for sensors and actuators considered more critical than for MTUs and RTUs?

Sensors and actuators have moving parts that wear out Signup and view all the answers

What type of cables may be connected to a junction box?

Multipair cables and smaller ones with one or two pairs Signup and view all the answers

What is the acceptable timeframe for the availability of replacement parts after sensors and actuators cease to be marketed?

Ten years Signup and view all the answers

What is a characteristic of MTUs and RTUs compared to sensors and actuators?

They have no moving parts Signup and view all the answers

What is commonly found at the marshaling panel aside from wiring connections?

Power relays and control power fuses Signup and view all the answers

Why are junction boxes necessary for process instruments?

To provide a connection site for various multipair cables Signup and view all the answers

What aspect of maintenance is considered unique in a SCADA system?

Calibration and validation of communications equipment Signup and view all the answers

What is typically not found in a marshaling panel?

Field termination boxes Signup and view all the answers

What should the planning for a SCADA project include regarding maintenance?

Provision for maintenance of sensors and actuators Signup and view all the answers

What common failure mode might MTUs and RTUs experience during initial installation?

Infant mortality failures Signup and view all the answers

What is a key difference between sensors designed for SCADA systems and those meant for human operators?

SCADA sensors require additional engineering effort for integration. Signup and view all the answers

Why might a temperature transmitter for a SCADA system cost more than a standard thermometer?

Temperature transmitters output signals in specific formats. Signup and view all the answers

What type of wire is commonly used to connect sensors and actuators in a SCADA system?

Copper wire Signup and view all the answers

What is the purpose of shielding on copper wire in a SCADA system?

To prevent electromagnetic interference or noise from corrupting the signal. Signup and view all the answers

What must be done to protect copper wires in a SCADA system from corrosive environments?

They should be encapsulated in fluid-proof, flexible plastic. Signup and view all the answers

What form of physical protection may be used for unarmored cables in SCADA systems?

Installation within flexible conduits or cables trays. Signup and view all the answers

Which feature distinguishes a SCADA sensor from a traditional sensor?

A SCADA sensor interfaces directly with a control system. Signup and view all the answers

What additional component is required to ensure the safety of wires in corrosive or hazardous environments?

A fluid-proof jacket. Signup and view all the answers

Study Notes

Selective Course 1 (Computer Control Systems)

Course is taught by Assoc. Prof. Ahmed M. ElMahalawy and Dr. Bassam Wasfi
Part of the Communications and Computers Engineering Department

Chapter 6: Introduction to SCADA System - Sensors, Actuators, and Wiring

SCADA (Supervisory Control and Data Acquisition) is a significant system in various industries
The cost of sensors, actuators, and wiring within a SCADA system is often substantial, often three to four times more than the RTU, UPS, and communications equipment.

Master Terminal Units (MTUs)

Process interface equipment can be expensive
Special consideration for process and ambient conditions when selecting and installing sensors and actuators is necessary

Table of Contents (Agenda)

Overview
A Forgotten Cost
Special Considerations
Standardization
Maintenance

Overview

Project details can be overshadowed by prominent highlights
SCADA projects often emphasize MTUs, communications systems, or RTUs
Limit switches, valve actuators, and equipment analyzers are critical components and typically represent a large portion of a SCADA project's capital cost

A Forgotten Cost

SCADA is widely used, but the crucial parts (sensors, actuators, wiring) are often overlooked
These components can cost three to four times more than the RTU, UPS, or communications equipment at a site
Costs of components at a simple RTU site are detailed in a table (costs vary between different components)

Sensors, Actuators, and Wiring

Considerations for applying sensors and actuators
Devices may not be different from those used in similar automated plants
However, they are designed for operator reading (differing from machine-read instruments)
Years of effort is going into improvement for operator input
Sensors are considerably cheaper when they can be read using a human operator, but more expensive when read by machines (e.g. $50 thermometer vs. $600 temperature transmitter)

Junction Boxes

Process instruments may be too small to house multiple wires
Junction boxes (field termination boxes) address this for easier connection (shown in image)
Smaller cables connect the instrument to the junction box

The Marshaling Panel

Process configuration sometimes requires multiple cables, necessitating large junction boxes (marshaling panels) located at the RTU location.
These panels allow instruments and cabling to be checked before RTUs are deployed
Supports critical components like power relays, circuit breakers, calibration equipment, and additional instruments like flow meters

Data Storage

The marshaling panel can include status lights, manual controls and, in some cases, locally read meter outputs used on the panel

Engineering Cost of SCADA System

Specifying technical equipment is crucial
Installation drawings, system documentation, licenses, software, and operating instructions need to be developed.
Engineering of the field installation is crucial
SCADA engineering costs are generally higher than for non-SCADA projects (often 3-5x) for the complexity of the system

Special Considerations

Different industries require unique process conditions and considerations
Production and transportation of hydrocarbon fluids need to avoid explosions and fires
Chemical processes need to address corrosion, atmosphere pollution and isolation of instruments from electric fields
Food industry needs to worry that instruments prevent contamination of food

Standardization

Only rare sensor/actuator types are made by a single manufacturer
Choosing to change suppliers must be considered carefully because changes may lead to increased warehousing costs, personnel training and changes to documentation
Early survey of potential parts suppliers is crucial
Financial stability and support history of manufacturers is important, in addition to functionality

Standardization -cont.

Spares for each part should be available for the system's lifetime
Replacement parts for sensors and actuators should be available for a minimum of 10 years
Sensors and actuators are more susceptible to wear because they have more moving parts and are exposed to various external factors (i.e., process chemicals, temperature, vibrations)
Maintenance planning should focus on sensors and actuators more than other components

Maintenance

SCADA maintenance requirements are generally comparable to other high-technology controls
Special equipment & training for communications hardware is needed
Initial maintenance requirements may be high, then stabilise
Sensors and actuators need more consideration to maintain operation and functionality due to being more prone to damage or wear and tear

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Description

This quiz covers Chapter 6 of the Computer Control Systems course, focusing on the Introduction to SCADA Systems and the role of sensors, actuators, and wiring. It explores the costs and special considerations involved in the selection and installation of process interface equipment within SCADA systems. Test your understanding of these critical components and their impact on project success.