SCADA vs DCS vs PLC comparison in SCADA systems - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Primary Function Differences

Which system is mainly designed for centralized control and monitoring of large industrial processes?

A PLC

B SCADA

C All three systems equally

D DCS

💡 Hint

Think about which system integrates control and monitoring tightly in one platform.

DCS (Distributed Control System) is designed for centralized control and monitoring of complex industrial processes, integrating control and monitoring in one system.

🧠 Conceptual

intermediate

System Architecture

Which system typically uses a distributed architecture with multiple controllers connected over a network?

A SCADA

B DCS

C PLC

D None of the above

💡 Hint

Consider which system spreads control tasks across multiple controllers.

DCS uses a distributed architecture where control functions are spread across multiple controllers connected via a network.

💻 Command Output

advanced

PLC Program Scan Cycle Output

Given a PLC program that reads an input, processes logic, and sets an output, what is the typical output after one scan cycle if the input is ON and the logic is to invert the input state?

SCADA systems

Input = ON
Output = NOT Input

What is Output?

A Input state unchanged

B ON

C OFF

D Error: Undefined variable

💡 Hint

Inversion means the output is the opposite of the input.

If the input is ON (true), and the logic inverts it, the output will be OFF (false).

❓ Troubleshoot

advanced

SCADA Communication Failure

A SCADA system is not receiving data from remote RTUs. Which of the following is the most likely cause?

A RTUs are powered off

B PLC program logic error

C DCS controller overload

D SCADA software license expired

💡 Hint

Check the physical status of remote devices first.

If RTUs (Remote Terminal Units) are powered off, SCADA cannot receive data from them.

✅ Best Practice

expert

Choosing Control Systems for Safety-Critical Applications

For a safety-critical chemical plant requiring fast response and high reliability, which system is best suited?

A DCS with redundant controllers and safety protocols

B SCADA system alone

C PLC with manual override only

D Standalone PLC without network connection

💡 Hint

Consider systems designed for reliability and safety with built-in redundancy.

DCS with redundant controllers and safety protocols provides fast response and high reliability needed for safety-critical plants.