In an Active High PLC discrete input module, when is the input considered ON?

In an Active High PLC discrete input module, when is the input considered ON?

• A. An input is ON if voltage is applied to the input terminal
• B. An input is ON if voltage is absent
• C. An input is ON if voltage is negative
• D. An input is ON only above 100V

Answer: (A)

Active High means the input is considered ON when a valid positive voltage is applied to the input terminal. When you apply the designated supply voltage (within the module’s rated range), the input’s sensing circuit detects a high level and the discrete input is read as ON. If no voltage is present, the input is OFF. Voltages that are negative or far outside the specified range aren’t used to indicate ON and can damage the module. So, applying voltage turns the input ON, not the absence of voltage or a fixed high threshold like 100V.

Active High means the input is considered ON when a valid positive voltage is applied to the input terminal. When you apply the designated supply voltage (within the module’s rated range), the input’s sensing circuit detects a high level and the discrete input is read as ON. If no voltage is present, the input is OFF. Voltages that are negative or far outside the specified range aren’t used to indicate ON and can damage the module. So, applying voltage turns the input ON, not the absence of voltage or a fixed high threshold like 100V.