Programmable logic controllers are categorized according to the
a) number of I/O points.
b) current rating of I/O modules.
c) power rating of the I/O modules.
d) cost of the I/O modules.
The correct answer and explanation is :
The correct answer is:
a) number of I/O points.
Explanation:
Programmable Logic Controllers (PLCs) are industrial digital computers designed for automation and control applications. They are categorized based on several parameters, but the number of Input/Output (I/O) points is the primary classification criterion.
1. What Are I/O Points?
I/O points refer to the number of input and output devices a PLC can handle. Inputs include sensors, switches, and buttons, while outputs include relays, motors, and actuators. The number of I/O points determines the complexity of the system a PLC can control.
2. Classification of PLCs Based on I/O Points
- Small PLCs: Typically have fewer than 32 I/O points and are used for simple applications like small machinery automation.
- Medium PLCs: Handle between 32 and 128 I/O points, suitable for more complex processes.
- Large PLCs: Have 128 or more I/O points and are used in large-scale industrial automation like manufacturing plants and power stations.
3. Why Are I/O Points the Primary Criterion?
- Scalability: The number of I/O points determines how many devices a PLC can control.
- System Complexity: More I/O points mean the PLC can handle more complex automation tasks.
- Modularity: Many PLCs allow expansion by adding more I/O modules, increasing flexibility.
Why Not the Other Options?
- Current Rating of I/O Modules (b) and Power Rating (c) affect performance but are not primary classification factors.
- Cost of I/O Modules (d) varies based on design but does not define PLC categories.
Thus, PLCs are mainly categorized by their number of I/O points, which directly impacts their capability and application range.