As shown in the illustrated block diagram for a programmable logic controller system, what functional component is used to convey signals from switches, counters, and various sensors to the processor? See illustration EL-0225.
• Look at how inputs and outputs are labeled in the PLC diagram. • Think about whether switches, counters, and sensors are devices that send signals to the PLC or receive signals from it. • Compare the roles of the processor module, power supply module, and the various I/O (input/output) modules.
• On the illustration, which modules are physically connected to field devices like switches and sensors, and how are they labeled? • Do switches and sensors normally control what the PLC does, or do they act on commands from the PLC—are they inputs or outputs? • Which choice specifically mentions the types of signals (DC, AC, analog) that you would expect from sensors and counters going into the PLC?
• Verify which side of the PLC rack in the diagram is handling field inputs versus field outputs. • Check that the component you choose is clearly marked as handling signals coming into the processor, not signals going out. • Confirm that your choice includes the same types of signals shown next to the switches, counters, and sensors (e.g., DC, AC, analog).
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