1. What is the difference between DCS and PLC?
Answer:
- DCS is used for complex and large-scale process control, mainly in continuous processes.
- PLC (Programmable Logic Controller) is used for discrete, fast control, mostly in manufacturing or machine control.
- DCS handles analog inputs better, has better redundancy, and is more suited for process industries.
2. Name a few popular DCS manufacturers.
Answer:
- Honeywell (Experion PKS)
- Siemens (PCS 7)
- Yokogawa (Centum VP)
- Emerson (DeltaV)
- ABB (800xA)
3. What are the main components of a DCS system?
Answer:
- Engineering Station
- Operator Station (HMI)
- Controller (Process station)
- Input/Output Modules (I/O cards)
- Communication Network (e.g., Ethernet, Fieldbus)
4. What is a redundant system in DCS?
Answer:
Redundancy in DCS means having backup hardware/software for critical components like controllers and power supplies. If one fails, the backup takes over without interrupting the process.
5. What is the role of a controller in DCS?
Answer:
The controller performs PID control, logic operations, alarms, and event handling. It processes field inputs and controls outputs in real-time.
6. Explain the term ‘scan time’ in DCS.
Answer:
Scan time is the time it takes for a controller to read inputs, execute logic, and update outputs. It affects system response and performance.
7. How does DCS communicate with field devices?
Answer:
DCS uses protocols like:
- Modbus
- Profibus
- Foundation Fieldbus
- HART
- Ethernet/IP
8. What is HMI in DCS?
Answer:
HMI (Human-Machine Interface) is the operator interface for monitoring and controlling the plant. It provides graphical displays, trends, alarms, and reports.
9. What is interlocking?
Answer:
Interlocking is a safety control strategy that prevents unsafe operation. For example, a motor cannot start unless a valve is closed.
10. How are alarms handled in DCS?
Answer:
DCS generates alarms when process values go beyond set limits. Operators get visual and audio alerts, and can acknowledge or take corrective actions.
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