Modifying relay-type process control circuits usually involves changing the a) circuit wiring. c) output circuit modules. b) input circuit modules. d) circuit operating voltage levels.
Which of the following is not an advantage that PLCs offer over the conventional relay-type of control system? a) Smaller size c) Higher current capacity b) Less expensive d) More reliable
The correct answer and explanation is:
Correct Answers:
- a) Circuit wiring
- c) Higher current capacity
Explanation:
1. Modifying Relay-Type Process Control Circuits
Relay-based control systems use physical wiring to define logic operations. If a modification is needed, the wiring must be changed, which can be time-consuming and labor-intensive. This is why the correct answer is “a) circuit wiring.” Unlike programmable logic controllers (PLCs), which can be reprogrammed with minimal effort, relay systems require physical rewiring whenever a process change is required. This increases downtime and makes them less flexible for modern automation needs.
2. Advantages of PLCs Over Relay-Based Systems
PLCs have largely replaced relay-based control systems because they are more efficient, reliable, and cost-effective. However, one aspect where conventional relay-based systems still hold an advantage is higher current capacity. The correct answer to this question is “c) Higher current capacity.”
- PLCs are smaller, cheaper, and more reliable than relays because they use microprocessors and software-based logic rather than physical contacts that wear out over time.
- PLCs are more flexible and easier to modify since changes can be made through programming rather than rewiring.
- Relays can handle higher current loads, whereas PLCs usually require additional contactors or relays to control high-power devices.
In industrial settings, high-current applications often require supplementary relays or motor starters to work alongside PLCs, making PLCs less advantageous in this regard. However, their advantages in efficiency, space-saving, and troubleshooting capabilities far outweigh this limitation, making PLCs the preferred choice for modern automation systems.
Now, I’ll generate an image representing a comparison between a PLC and a relay-based control system.
Here is the image comparing a traditional relay-based control system with a modern PLC control system. It visually highlights the differences in wiring complexity and space efficiency. Let me know if you need any modifications or further explanations!
