Which statement is true about Source Input?

Which statement is true about Source Input?

• A. Source Input is Active High; on positive side; voltage flows from PLC to device; If enabled no voltage at PLC terminal.
• B. Source Input is Active Low; on ground side; voltage flows from device to PLC; If enabled voltage at PLC terminal.
• C. Source Input uses an optocoupler.
• D. Source Input cannot be used with DC loads.

Answer: (A)

Source Input is designed to be activated by a high signal on the positive side of the circuit. When the input is energized, the external device provides the positive voltage to the input line and current flows through the input path accordingly. In this arrangement the input is considered ON at a high level, and the internal circuitry of the PLC is wired so that, in that active state, the PLC terminal can appear at low potential relative to the PLC’s reference, which is why you might read no voltage at the PLC terminal once the input is enabled. This wiring, with the positive-side connection and a high-level trigger, is what distinguishes a Source Input as active high. In practice, many PMMI PLCs use an optocoupler to isolate the external device from the PLC’s internals, which aligns with common input designs but isn’t the whole defining feature. Also, Source Inputs can be used with DC loads, so the statement that they cannot is not correct. So the true statement reflects that Source Input is active high, connected on the positive side, and the on-state behavior can result in the PLC terminal not showing voltage relative to the PLC reference, with isolation typically provided by an optocoupler.

Source Input is designed to be activated by a high signal on the positive side of the circuit. When the input is energized, the external device provides the positive voltage to the input line and current flows through the input path accordingly. In this arrangement the input is considered ON at a high level, and the internal circuitry of the PLC is wired so that, in that active state, the PLC terminal can appear at low potential relative to the PLC’s reference, which is why you might read no voltage at the PLC terminal once the input is enabled. This wiring, with the positive-side connection and a high-level trigger, is what distinguishes a Source Input as active high.

In practice, many PMMI PLCs use an optocoupler to isolate the external device from the PLC’s internals, which aligns with common input designs but isn’t the whole defining feature. Also, Source Inputs can be used with DC loads, so the statement that they cannot is not correct.

So the true statement reflects that Source Input is active high, connected on the positive side, and the on-state behavior can result in the PLC terminal not showing voltage relative to the PLC reference, with isolation typically provided by an optocoupler.