SCADA and DCS: 100 Objective Questions and Answers

1. What does SCADA primarily stand for?

A. System Control And Data Access
B. Supervisory Control And Data Acquisition
C. Sensor Control And Data Application
D. Supervisory Communication And Device Automation
Correct Answer: B
Explanation: SCADA stands for Supervisory Control and Data Acquisition, used for remote monitoring and supervisory-level control.

2. A DCS is mainly used for:

A. Wide-area remote monitoring
B. Real-time, closed-loop process control
C. Retail shop automation
D. Email communication
Correct Answer: B
Explanation: DCS handles continuous, closed-loop control within large industrial plants.

3. Which component of SCADA displays real-time plant data to operators?

A. PLC
B. RTU
C. HMI
D. Router
Correct Answer: C
Explanation: The HMI (Human-Machine Interface) is used to visualize real-time data, trends, alarms, and control functions.

4. A PLC used in SCADA usually acts as:

A. A data storage server
B. A field controller
C. An alarm historian
D. A network switch
Correct Answer: B
Explanation: PLCs act as field controllers that execute logic and send data to SCADA systems.

5. Which communication protocol is most commonly used in SCADA systems?

A. HTTP
B. SMTP
C. Modbus
D. POP3
Correct Answer: C
Explanation: Modbus (RTU/TCP) is widely used due to simplicity and compatibility with industrial devices.

6. A key difference between SCADA and DCS is:

A. SCADA is only for temperature measurement
B. DCS is used for geographically spread-out systems
C. SCADA handles supervisory control; DCS handles process control
D. SCADA uses no communication network
Correct Answer: C
Explanation: SCADA provides supervisory control; DCS provides tight process control and automation.

7. RTU stands for:

A. Remote Terminal Unit
B. Remote Transmission Utility
C. Real-Time Unit
D. Ring Terminal Utility
Correct Answer: A
Explanation: An RTU collects field data and communicates it to SCADA.

8. Which of the following is usually NOT part of a SCADA system?

A. RTU
B. Historian
C. PLC
D. Pump
Correct Answer: D
Explanation: Pumps are field equipment, not a SCADA subsystem.

9. In DCS, controllers are typically:

A. Distributed across the plant
B. Installed only in one control room
C. Stored in cloud servers
D. Wireless-only devices
Correct Answer: A
Explanation: DCS controllers are distributed, enabling faster and local control.

10. SCADA systems usually operate over:

A. Short-distance point-to-point links
B. Long-distance communication networks
C. Mobile phone apps only
D. No communication network
Correct Answer: B
Explanation: SCADA supports wide-area communication using fiber, radio, GSM, satellite, etc.

11. A DCS controller is mainly responsible for:

A. Database management
B. Closed-loop process control
C. Email notifications
D. Operating web servers
Correct Answer: B
Explanation: DCS handles local, continuous process control using dedicated controllers.

12. An HMI displays alarms using:

A. Trend charts
B. Alarm summary and banner
C. Network topology maps
D. File explorer
Correct Answer: B
Explanation: HMIs show alarms in an alarm banner and alarm summary window.

13. A historian server in SCADA is used for:

A. Program editing
B. Long-term data storage
C. Motor control
D. Network switching
Correct Answer: B
Explanation: The historian stores trends, logs, and production history.

14. Which one is TRUE for SCADA?

A. It performs high-speed control
B. It focuses on supervisory-level monitoring
C. It has no remote communication
D. It replaces PLCs
Correct Answer: B
Explanation: SCADA is primarily for supervisory monitoring, not high-speed control.

15. A typical DCS is preferred for:

A. Pipelines spread over hundreds of kilometers
B. Batch or continuous process control
C. Home automation
D. Smartphone gaming
Correct Answer: B
Explanation: DCS is ideal for continuous and batch processes like refineries and chemical plants.

16. SCADA alarms are triggered when:

A. The operator presses the alarm button
B. A process value crosses a predefined limit
C. The HMI restarts
D. Data logging stops
Correct Answer: B
Explanation: Alarms are activated when a measurement exceeds high/low limits.

17. Which network architecture is widely used in SCADA?

A. Star network
B. Tree network
C. Ring network
D. All of the above
Correct Answer: D
Explanation: SCADA may use star, ring, mesh, or tree depending on reliability needs.

18. The main advantage of a DCS is:

A. High-speed centralized architecture
B. Distributed controllers enabling reliability
C. It uses no programming
D. Works only without communication
Correct Answer: B
Explanation: Distributed control improves fault tolerance and system reliability.

19. Which of the following is an example of a SCADA communication medium?

A. Fiber optic cable
B. Satellite
C. Radio
D. All of the above
Correct Answer: D
Explanation: SCADA supports all major long-distance communication mediums.

20. SCADA systems are commonly used in:

A. Social media companies
B. Petroleum pipelines and power grids
C. Grocery stores
D. Hospitals only
Correct Answer: B
Explanation: SCADA is heavily used in pipelines, power transmission, water supply, and remote utilities.

21. In SCADA, polling is used to:

A. Store data in the historian
B. Regularly request data from field devices
C. Reset alarms
D. Tune PID loops
Correct Answer: B
Explanation: SCADA masters poll RTUs/PLCs at fixed intervals to acquire updated process values.

22. Which type of system uses a master–slave communication architecture?

A. DCS
B. SCADA
C. HVAC
D. CCTV
Correct Answer: B
Explanation: SCADA typically uses master–slave communication where the master polls field units.

23. The primary purpose of an RTU in SCADA is to:

A. Run complex batch algorithms
B. Collect field data and transmit it to the master
C. Display HMI to operators
D. Replace PLC controllers
Correct Answer: B
Explanation: RTUs are designed to collect and transmit field data over long distances.

24. A DCS controller communicates with field devices mostly using:

A. Wireless LAN
B. Serial RS-232
C. Fieldbus protocols
D. Telephone lines
Correct Answer: C
Explanation: DCS systems widely use Foundation Fieldbus, Profibus PA, and HART for process control signals.

25. Which SCADA element provides real-time and historical data storage?

A. RTU
B. SCADA Historian
C. PLC
D. Switchgear
Correct Answer: B
Explanation: The historian stores both real-time and historical process data for analysis.

26. In a DCS, the redundancy of controllers is used to:

A. Increase power consumption
B. Improve system reliability
C. Increase operator workload
D. Slow down process control
Correct Answer: B
Explanation: Redundancy ensures control continues even if one controller fails, improving reliability.

27. The HMI screen in SCADA generally shows:

A. Only alarms
B. Only equipment status
C. Process graphics, trends, alarms, and controls
D. Operating system controls
Correct Answer: C
Explanation: HMIs provide a complete operator interface including graphics, trends, alarms, and controls.

28. Which of the following is a major advantage of SCADA?

A. No need for communication networks
B. Remote monitoring over large distances
C. Complete elimination of hardware
D. Requires no programming
Correct Answer: B
Explanation: SCADA is ideal for large, geographically distributed processes like pipelines and power grids.

29. In DCS, the main function of the Engineering Workstation (EWS) is:

A. Data logging
B. Controller programming and configuration
C. Alarm acknowledgment
D. Field wiring
Correct Answer: B
Explanation: EWS is used for configuring controllers, HMI graphics, and system databases.

30. Which of the following protocols is MOST associated with SCADA remote communication?

A. OPC-UA
B. DNP3
C. Ethernet/IP
D. PROFINET
Correct Answer: B
Explanation: DNP3 is widely used in SCADA for robust, secure, long-distance communication.

31. The trending feature in SCADA helps operators:

A. Print PLC logic
B. Visualize parameter changes over time
C. Reset communication settings
D. Tune wireless networks
Correct Answer: B
Explanation: Trends show historical and live changes in process parameters.

32. A DCS system typically uses which type of control strategy?

A. Time-based control
B. Centralized control
C. Distributed and hierarchical control
D. Manual-only control
Correct Answer: C
Explanation: DCS uses distributed controllers with a hierarchical structure for efficient process control.

33. A ‘hot standby’ controller in DCS means:

A. The controller is powered off
B. The controller is used only for heating operations
C. A backup controller takes over automatically if primary fails
D. It requires manual switching
Correct Answer: C
Explanation: Hot standby redundancy enables automatic switchover during controller failure.

34. The primary goal of alarm management in SCADA/DCS is to:

A. Increase alarm frequency
B. Reduce nuisance alarms and improve operator response
C. Disable all alarms
D. Make graphics more colorful
Correct Answer: B
Explanation: Alarm management ensures important alarms stand out, preventing overload.

35. SCADA systems in water distribution mainly control:

A. Human resources
B. Chemical dosing, pumps, and reservoir levels
C. Accounting data
D. Building doors
Correct Answer: B
Explanation: SCADA helps manage pumps, dosing systems, and storage levels in water utilities.

36. A key advantage of a DCS over PLC + SCADA in large plants is:

A. More social media connectivity
B. Integrated process control with seamless communication
C. Better home automation features
D. Lower reliability
Correct Answer: B
Explanation: DCS provides tight integration between control, HMI, and engineering.

37. In SCADA, radio telemetry is mainly used when:

A. Fiber is easily available
B. Low-distance connections are sufficient
C. Remote sites are difficult to reach
D. Industrial robots are used
Correct Answer: C
Explanation: Radio communication is ideal for remote, difficult, or inaccessible locations.

38. In a DCS, the operator station is used for:

A. Equipment installation
B. Plant operation, alarm acknowledgment, and monitoring
C. Cable routing
D. PLC programming
Correct Answer: B
Explanation: Operator stations allow monitoring and controlling the process and managing alarms.

39. Which topology is commonly used for DCS controller communication?

A. Bus topology
B. Ring or redundant Ethernet topology
C. Line topology only
D. Manual patching
Correct Answer: B
Explanation: Redundant Ethernet rings increase uptime and ensure fault tolerance.

40. SCADA systems are widely used in which of the following?

A. Banking
B. Gas pipelines, power transmission, water supply
C. Retail stores
D. Social networking
Correct Answer: B
Explanation: SCADA is popular in critical infrastructure such as utilities and pipelines.

41. Which device typically converts analog signals to digital data in SCADA?

A. Router
B. RTU/PLC
C. HMI
D. DCS Operator Station
Correct Answer: B
Explanation: PLCs and RTUs have A/D converters to convert analog field signals (4–20 mA, 0–10 V) into digital data.

42. In DCS architecture, field devices are usually connected to:

A. Operator station
B. Historian
C. Local controller or I/O modules
D. Alarm server
Correct Answer: C
Explanation: Field instruments connect to local DCS controllers or distributed I/O for real-time process control.

43. SCADA systems allow operators to control equipment:

A. Only manually on site
B. Remotely through the HMI
C. Using mobile games
D. Without permission levels
Correct Answer: B
Explanation: SCADA HMIs allow remote operation such as starting/stopping pumps, opening valves, etc.

44. Which feature of SCADA is crucial for predictive maintenance?

A. Printer logs
B. Historical trend analysis
C. Manual operation
D. Wi-Fi password
Correct Answer: B
Explanation: Trends help identify equipment degradation, enabling predictive maintenance.

45. A DCS is preferred over SCADA in a refinery because:

A. It is cheaper
B. It supports continuous, high-integrity process control
C. It requires no engineering effort
D. It only stores historical data
Correct Answer: B
Explanation: Refineries need continuous, closed-loop control, which is better handled by DCS.

46. OPC stands for:

A. Operator Process Console
B. Open Platform Communications
C. Offline Process Control
D. Output Process Controller
Correct Answer: B
Explanation: OPC is a universal interface standard for industrial communication.

47. In SCADA, remote sites use UPS systems mainly to:

A. Improve internet speed
B. Provide backup power during outages
C. Control the HMI screen
D. Increase data logging size
Correct Answer: B
Explanation: UPS ensures continuous data transmission and control even during power failures.

48. Which one of the following is TRUE about DCS graphics?

A. They are fixed and cannot be customized
B. They allow dynamic animations, trends, alarms, and navigation
C. They are created by PLC hardware
D. They are only black and white
Correct Answer: B
Explanation: DCS HMIs support dynamic, customizable graphics and control interfaces.

49. SCADA master station is also known as:

A. Field controller
B. Control center
C. DCS node
D. Power management unit
Correct Answer: B
Explanation: The SCADA master is the central control station where operators monitor the system.

50. DCS systems generally use time-synchronized clocks for:

A. Screen brightness
B. Accurate event logging and sequence-of-events
C. Email notifications
D. Music alarms
Correct Answer: B
Explanation: Precise time synchronization ensures accurate event logs and SOE (Sequence of Events).

51. The communication between DCS controllers and HMIs is usually:

A. Wireless only
B. Ethernet-based
C. Manual
D. Done through USB drives
Correct Answer: B
Explanation: Modern DCS systems use high-speed Ethernet for controller-to-HMI communication.

52. RTUs are commonly used instead of PLCs when:

A. Applications require rugged outdoor performance
B. High-speed logic is needed
C. Indoor factory automation is required
D. No communication is needed
Correct Answer: A
Explanation: RTUs are designed for harsh, remote, and outdoor environments.

53. SCADA redundancy improves:

A. Data loss
B. System uptime and reliability
C. Power consumption
D. Operator workload
Correct Answer: B
Explanation: Redundant servers and networks improve system reliability and reduce downtime.

54. Which of the following devices is commonly used for level-1 control in DCS?

A. Field instruments
B. Local controllers
C. HMI stations
D. Routers
Correct Answer: B
Explanation: Level-1 control in DCS is performed by local controllers close to the process.

55. A common DCS application in a power plant is:

A. Employee attendance
B. Boiler control and turbine control
C. CCTV monitoring
D. Website hosting
Correct Answer: B
Explanation: DCS is essential for boiler, turbine, and heat balance control in power plants.

56. Which of the following best describes telemetry in SCADA?

A. Manual measurement
B. Remote measurement and data transmission
C. Offline calibration
D. Local-only control
Correct Answer: B
Explanation: Telemetry refers to remote measurement and transmission of data to a central system.

57. DCS batch control is defined as:

A. Continuous flow control
B. Step-by-step recipe-based control
C. Only level measurement
D. Manual mode operation
Correct Answer: B
Explanation: Batch control uses recipes and sequences to produce batches in chemical, pharma, etc.

58. A SCADA alarm message usually shows:

A. IP address of the server
B. Tag name, description, timestamp, and priority
C. PLC wiring number
D. User password
Correct Answer: B
Explanation: Alarm messages contain tag name, time, priority, and description.

59. Which system typically uses long-distance protocols like radio, GSM, and satellite?

A. DCS
B. SCADA
C. Building management system
D. Office LAN
Correct Answer: B
Explanation: SCADA is designed for long-distance remote monitoring.

60. The main role of a system integrator in SCADA/DCS projects is to:

A. Manufacture sensors
B. Configure, install, program, and commission the system
C. Provide internet
D. Operate the plant
Correct Answer: B
Explanation: System integrators handle design, programming, graphics, testing, and commissioning.

61. Which layer of the automation pyramid does SCADA mainly operate in?

A. Field level
B. Control level
C. Supervisory level
D. Enterprise level
Correct Answer: C
Explanation: SCADA belongs to the supervisory layer, handling monitoring, data acquisition, and high-level control.

62. In a DCS, the control loops are usually executed:

A. In the HMI
B. In the local controller
C. In the historian
D. In the web server
Correct Answer: B
Explanation: DCS local controllers execute PID loops for fast and reliable control.

63. Which feature of SCADA allows operators to return equipment to known states after a fault?

A. Automatic reset
B. Event replay
C. Sequence-of-events (SOE)
D. Command scripts
Correct Answer: C
Explanation: SOE logs help operators understand the sequence leading to a fault.

64. In DCS, “scan time” refers to:

A. Time to load HMI graphics
B. Time to read inputs, execute logic, and update outputs
C. Time to backup the historian
D. Time for operator login
Correct Answer: B
Explanation: Scan time is the controller cycle for inputs → logic → outputs.

65. SCADA systems generally use which type of servers?

A. Basic home computers
B. Industrial-grade redundant servers
C. Gaming PCs
D. Battery-powered devices
Correct Answer: B
Explanation: SCADA requires rugged, redundant, fault-tolerant servers.

66. DCS communication networks are designed for:

A. High-speed and deterministic control
B. Email traffic
C. Social media browsing
D. Occasional manual entry
Correct Answer: A
Explanation: DCS networks support real-time, deterministic data exchange for control loops.

67. In SCADA, which device is MOST likely to be installed at a remote wellhead?

A. DCS controller
B. RTU
C. HMI terminal
D. Ethernet switch
Correct Answer: B
Explanation: RTUs are built for remote, isolated, harsh outdoor locations such as wellheads.

68. A “tag” in SCADA/DCS refers to:

A. A network cable
B. A variable or data point representing a field measurement
C. An electrical terminal
D. A barcode
Correct Answer: B
Explanation: Tags represent process variables such as pressure, flow, level, or status.

69. SCADA event logging is essential because it helps:

A. Reduce graphics load
B. Track all actions and process changes
C. Reduce controller scan time
D. Increase electricity bills
Correct Answer: B
Explanation: Event logs record operator actions, alarm changes, and status updates.

70. DCS systems are preferred in chemical plants mainly because:

A. They support long-distance communication
B. They provide tight, reliable, and safe process control
C. They require no training
D. They are cheaper than PLCs
Correct Answer: B
Explanation: Chemical plants require continuous, reliable, safety-oriented control, which DCS provides.

71. In SCADA, HMI “faceplates” are used for:

A. Network configuration
B. Operator control of individual field devices
C. Resetting controllers
D. Editing PLC programs
Correct Answer: B
Explanation: Faceplates give operators control buttons and live data for each device.

72. Which SCADA communication protocol supports encryption and secure authentication?

A. Modbus RTU
B. DNP3 Secure
C. RS-232
D. 4–20 mA
Correct Answer: B
Explanation: Secure DNP3 provides modern cybersecurity features for SCADA.

73. In DCS, the term “integration” refers to:

A. Combining control, HMI, and databases into one platform
B. Mixing chemicals
C. Connecting printers
D. Allowing internet browsing
Correct Answer: A
Explanation: DCS integrates control, visualization, historians, alarms, and configuration seamlessly.

74. Which device handles interlock logic in a SCADA + PLC system?

A. UPS
B. PLC
C. HMI
D. Operator
Correct Answer: B
Explanation: Interlock and safety logic run inside PLCs, not SCADA.

75. SCADA is typically used for batch processes when:

A. Operator presence is mandatory
B. Remote visibility of multiple sites is required
C. No field instrumentation exists
D. Manual control is preferred
Correct Answer: B
Explanation: SCADA suits multi-site batch operations where remote monitoring is needed.

76. DCS “redundant power supplies” are used to:

A. Save energy
B. Ensure the system stays operational during power supply failure
C. Reduce controller size
D. Provide high voltage
Correct Answer: B
Explanation: Redundant supplies prevent system shutdown during a power failure.

77. SCADA systems commonly use GSM/4G communication for:

A. Short-range motor control
B. Remote data transfer from distributed locations
C. Video streaming
D. Local PLC programming
Correct Answer: B
Explanation: GSM/4G is ideal for wide-area wireless SCADA communication.

78. In DCS, “graphics navigation hierarchy” helps operators:

A. Change programs
B. Move between plant overview and detailed screens
C. Adjust brightness
D. Set network addresses
Correct Answer: B
Explanation: Hierarchical navigation lets operators go from overview → area → unit → detail screens.

79. The main purpose of SCADA trending alarms is to:

A. Notify calibration
B. Alert changes in rate of increase/decrease
C. Change controller logic
D. Reset the historian
Correct Answer: B
Explanation: Trending alarms detect abnormal rate-of-change, predicting failures early.

80. Which system is more suitable for real-time furnace temperature PID control?

A. SCADA only
B. DCS
C. Cloud dashboard
D. Mobile app
Correct Answer: B
Explanation: DCS is built for fast, real-time PID loop control, essential for furnace applications.

81. Which SCADA component is responsible for executing logic at the field level?

A. Historian
B. RTU/PLC
C. HMI
D. Modem
Correct Answer: B
Explanation: PLCs/RTUs execute control logic, read inputs, and control outputs at the field level.

82. DCS systems achieve deterministic communication by using:

A. Token passing
B. High-speed industrial Ethernet
C. Telephone lines
D. Bluetooth
Correct Answer: B
Explanation: DCS uses industrial Ethernet that guarantees real-time data delivery.

83. SCADA is MOST suitable for which of the following industries?

A. Retail
B. Remote oil & gas wells
C. Cafeterias
D. Education institutes
Correct Answer: B
Explanation: SCADA excels in remote and geographically spread-out operations.

84. In DCS, the term “control module” refers to:

A. A complete PLC
B. A small software unit used for logic and control
C. A network cable
D. A power supply
Correct Answer: B
Explanation: Control modules are software objects used to structure logic in DCS systems.

85. Which feature of SCADA allows the operator to view previous alarm conditions?

A. Alarm Summary
B. Alarm History
C. System Logs
D. Backup files
Correct Answer: B
Explanation: Alarm history shows all past alarms, timestamps, and acknowledgments.

86. A DCS controller must have which important feature for critical processes?

A. Music playback
B. Hot standby redundancy
C. High graphics capability
D. Bluetooth connectivity
Correct Answer: B
Explanation: Redundancy ensures uninterrupted control even when one controller fails.

87. Which network device is commonly used in SCADA communication systems?

A. Video Switch
B. Industrial router
C. Gaming hub
D. Smartphone
Correct Answer: B
Explanation: Industrial routers handle WAN/LAN connectivity, VPN, and secure communication.

88. DCS logic design is usually done using:

A. Ladder logic only
B. Function blocks and sequential charts
C. Text messages
D. Barcode programming
Correct Answer: B
Explanation: DCS uses function block diagrams and SFCs for advanced process control.

89. SCADA operators typically access the system through:

A. Engineering stations
B. Operator workstations
C. Alarm server
D. PLC cabinet
Correct Answer: B
Explanation: Operators use HMI-based workstations to monitor and control the plant.

90. Utility companies use SCADA mainly for:

A. Employee tracking
B. Billing
C. Monitoring power grids and substations
D. Social media updates
Correct Answer: C
Explanation: SCADA helps supervise substations, feeders, transmission lines, and load control.

91. In DCS, the “I/O subsystem” handles:

A. System backups
B. Connecting field devices to controllers
C. Sending email notifications
D. User management
Correct Answer: B
Explanation: The I/O subsystem interfaces sensors, transmitters, and actuators with the controller.

92. What type of alarm is triggered when a value reaches a dangerous level?

A. System alarm
B. High-high alarm
C. Tune alarm
D. Execution alarm
Correct Answer: B
Explanation: High-high or low-low alarms indicate critical limits requiring immediate action.

93. SCADA’s trending function helps in:

A. Plant security
B. Predicting abnormal process behavior
C. Networking
D. Controller programming
Correct Answer: B
Explanation: Trends reveal patterns and deviations, preventing failures.

94. The main reason DCS is used in pharmaceutical industries is:

A. Payroll integration
B. Batch production automation with strict accuracy
C. Social media scheduling
D. Inventory printing
Correct Answer: B
Explanation: Pharma production requires recipe-based batch control, ideal for DCS.

95. In SCADA, a communication failure alarm usually indicates:

A. Controller logic error
B. Loss of communication with an RTU/PLC
C. Wrong password
D. Incorrect wiring
Correct Answer: B
Explanation: This alarm occurs when SCADA cannot communicate with a remote device.

96. Which DCS component handles operator commands and visual displays?

A. Controller
B. Operator workstation
C. Modem
D. UPS
Correct Answer: B
Explanation: Operators use workstations to view graphics, trends, alarms, and issue commands.

97. SCADA cybersecurity focuses mainly on:

A. Reducing graphics
B. Protecting communication and servers from cyber threats
C. Increasing scan time
D. Improving HMI colors
Correct Answer: B
Explanation: Cybersecurity ensures secure communication and protected control centers.

98. Foundation Fieldbus is mainly used in:

A. SCADA for remote sites
B. DCS systems for smart instrumentation
C. Mobile phones
D. HVAC systems
Correct Answer: B
Explanation: Foundation Fieldbus is widely used in DCS for smart digital instrumentation.

99. SCADA “control scripts” are used to:

A. Tune controller scan time
B. Automate repetitive tasks
C. Update firmware
D. Create user accounts
Correct Answer: B
Explanation: Scripts automate routine control actions, improving efficiency.

100. A major benefit of DCS is:

A. No need for communication networks
B. Complete integration of control, graphics, alarms, and data
C. It requires no operator
D. No redundancy
Correct Answer: B
Explanation: DCS provides fully integrated process automation, improving reliability and performance.