Which statement best contrasts Active High and Active Low input module operation?

Which statement best contrasts Active High and Active Low input module operation?

• A. Active High: ON when voltage present; Active Low: ON when voltage absent
• B. Active High: ON when voltage absent; Active Low: ON when voltage present
• C. Both are ON only when voltage present
• D. Active High uses AC; Active Low uses DC

Answer: (A)

Active High means the input is considered ON when voltage is present on that input. Active Low means the input is considered ON when the voltage is low (near ground) or effectively absent. In a simple 24V DC PLC setup, wiring a switch to supply +24V to the input makes it ON for Active High when the switch is closed; wiring the switch to connect the input to ground makes it ON for Active Low when the switch is closed. The key contrast is what condition activates the ON state: voltage present for Active High, voltage absent (low) for Active Low. The other options mix up this relationship or introduce AC/DC as the defining factor, which isn’t the core distinction.

Active High means the input is considered ON when voltage is present on that input. Active Low means the input is considered ON when the voltage is low (near ground) or effectively absent. In a simple 24V DC PLC setup, wiring a switch to supply +24V to the input makes it ON for Active High when the switch is closed; wiring the switch to connect the input to ground makes it ON for Active Low when the switch is closed. The key contrast is what condition activates the ON state: voltage present for Active High, voltage absent (low) for Active Low. The other options mix up this relationship or introduce AC/DC as the defining factor, which isn’t the core distinction.