33 PLC, SCADA & Instrumentation questions from the Electrical Design bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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A.digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
B.DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
C.RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
D.graphical PLC language of rungs with contacts and coils mimicking relay wiring, one of the five IEC 61131-3 languages (LD, FBD, ST, IL, SFC)
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2. Which term means: "graphical PLC language of rungs with contacts and coils mimicking relay wiring, one of the five IEC 61131-3 languages (LD, FBD, ST, IL, SFC)"?
Junior
A.Ladder logic
B.Modbus RTU vs TCP
C.Profibus DP vs Profinet
D.PLC scan cycle
Answer + AI explanation with Pro
3. Which statement is correct?
Junior
A.Ladder logic — read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed
B.Ladder logic — controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
C.Ladder logic — digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
D.Ladder logic — graphical PLC language of rungs with contacts and coils mimicking relay wiring, one of the five IEC 61131-3 languages (LD, FBD, ST, IL, SFC)
Answer + AI explanation with Pro
4. What is PLC scan cycle?
Junior
A.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
B.operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
C.RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
D.read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed
Answer + AI explanation with Pro
5. Which term means: "read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed"?
Junior
A.PLC scan cycle
B.DCS vs PLC vs SCADA
C.Loop check
D.Profibus DP vs Profinet
Answer + AI explanation with Pro
6. Which statement is correct?
Junior
A.PLC scan cycle — remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
B.PLC scan cycle — graphical PLC language of rungs with contacts and coils mimicking relay wiring, one of the five IEC 61131-3 languages (LD, FBD, ST, IL, SFC)
C.PLC scan cycle — read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed
D.PLC scan cycle — RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
Answer + AI explanation with Pro
7. What is 4–20 mA loop?
Junior
A.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
B.RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
C.live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
D.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
Answer + AI explanation with Pro
8. Which term means: "live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance"?
Junior
A.PLC scan cycle
B.4–20 mA loop
C.Loop check
D.DCS vs PLC vs SCADA
Answer + AI explanation with Pro
9. Which statement is correct?
Junior
A.4–20 mA loop — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
B.4–20 mA loop — live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
C.4–20 mA loop — remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
D.4–20 mA loop — RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
Answer + AI explanation with Pro
10. What is HMI?
Junior
A.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
B.digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
C.operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
D.live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
Answer + AI explanation with Pro
11. Which term means: "operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View"?
Junior
A.Ladder logic
B.HMI
C.DCS vs PLC vs SCADA
D.Modbus RTU vs TCP
Answer + AI explanation with Pro
12. Which statement is correct?
Junior
A.HMI — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
B.HMI — remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
C.HMI — live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
D.HMI — controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
Answer + AI explanation with Pro
13. What is Modbus RTU vs TCP?
Mid
A.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
B.DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
C.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
D.remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
Answer + AI explanation with Pro
14. Which term means: "master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502"?
Mid
A.Profibus DP vs Profinet
B.DCS vs PLC vs SCADA
C.Modbus RTU vs TCP
D.Ladder logic
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.Modbus RTU vs TCP — live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
B.Modbus RTU vs TCP — pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
C.Modbus RTU vs TCP — master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
D.Modbus RTU vs TCP — DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
Answer + AI explanation with Pro
16. What is Profibus DP vs Profinet?
Mid
A.controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
B.live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
C.RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
D.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
Answer + AI explanation with Pro
17. Which term means: "RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation"?
Mid
A.RTU
B.Ladder logic
C.Profibus DP vs Profinet
D.Safety PLC
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
A.Profibus DP vs Profinet — RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
B.Profibus DP vs Profinet — digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
C.Profibus DP vs Profinet — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
D.Profibus DP vs Profinet — DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
Answer + AI explanation with Pro
19. What is DCS vs PLC vs SCADA?
Mid
A.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
B.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
C.operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
D.DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
Answer + AI explanation with Pro
20. Which term means: "DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs"?
Mid
A.HMI
B.Safety PLC
C.4–20 mA loop
D.DCS vs PLC vs SCADA
Answer + AI explanation with Pro
21. Which statement is correct?
Mid
A.DCS vs PLC vs SCADA — graphical PLC language of rungs with contacts and coils mimicking relay wiring, one of the five IEC 61131-3 languages (LD, FBD, ST, IL, SFC)
B.DCS vs PLC vs SCADA — read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed
C.DCS vs PLC vs SCADA — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
D.DCS vs PLC vs SCADA — DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
Answer + AI explanation with Pro
22. What is RTU?
Mid
A.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
B.RS-485 fieldbus at up to 12 Mbit/s versus industrial Ethernet with real-time classes, both from the Siemens-led PI organisation
C.digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
D.remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
Answer + AI explanation with Pro
23. Which term means: "remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station"?
Mid
A.RTU
B.HMI
C.HART protocol
D.Safety PLC
Answer + AI explanation with Pro
24. Which statement is correct?
Mid
A.RTU — digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
B.RTU — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
C.RTU — read inputs, execute the program top to bottom, write outputs and repeat every few milliseconds; an input pulse shorter than one scan can be missed
D.RTU — remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
Answer + AI explanation with Pro
25. What is Loop check?
Mid
A.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
B.pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
C.controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
D.DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
Answer + AI explanation with Pro
26. Which term means: "pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms"?
Mid
A.RTU
B.HART protocol
C.Loop check
D.HMI
Answer + AI explanation with Pro
27. Which statement is correct?
Mid
A.Loop check — controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
B.Loop check — operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
C.Loop check — pre-commissioning verification of each instrument loop from field device to HMI by injecting 0, 25, 50, 75 and 100% and confirming indication and alarms
D.Loop check — remote terminal unit at a substation or feeder collecting I/O and reporting over IEC 60870-5-104 or DNP3 to the SCADA master station
Answer + AI explanation with Pro
28. What is HART protocol?
Mid
A.controller with redundant self-diagnosing channels certified to IEC 61508 SIL 2 or 3 for emergency shutdown and burner management
B.master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
C.digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
D.operator interface panel or software showing graphics, alarms and trends from PLC tags, such as Siemens WinCC or Rockwell FactoryTalk View
Answer + AI explanation with Pro
29. Which term means: "digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value"?
Mid
A.Safety PLC
B.HART protocol
C.Loop check
D.Profibus DP vs Profinet
Answer + AI explanation with Pro
30. Which statement is correct?
Mid
A.HART protocol — live-zero current signal where 4 mA is 0% and 20 mA is 100%, allowing open-circuit detection and immunity to line resistance
B.HART protocol — master-slave serial protocol on RS-485 with up to 247 nodes versus the same register model carried over Ethernet on port 502
C.HART protocol — DCS gives integrated continuous process control, PLC fast discrete logic, and SCADA supervisory software over geographically spread RTUs and PLCs
D.HART protocol — digital FSK signal superimposed on the 4–20 mA loop that carries device configuration and diagnostics without disturbing the analogue value
Answer + AI explanation with Pro
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