Output Configurations in Inductive Sensors: NO, NC, and NO+NC (Antivalent)

Choosing the correct output logic is as critical as selecting the sensing range or switching frequency. The proper configuration determines not only how the PLC controller interprets signals but, more importantly, affects process safety and system diagnostics. As a manufacturer, we offer a full spectrum of solutions: from standard NO and NC sensors to advanced antivalent models (NO+NC).

1. NO Output (Normally Open) – The Detection Standard

The NO (Normally Open) output, also known as a "make contact," is the most commonly used configuration in automation.

• Operating Principle: In the idle state (no metal in the sensing field), the output circuit remains open. The circuit only closes and allows current to flow when an object is detected.
• When to Use: This is the optimal choice for counting processes, part positioning, and applications where a signal should be generated only at the moment an event occurs. Check our range of NO inductive sensors.
• Advantages: Intuitive logic ("object present = signal present"), energy efficiency in systems where detection occurs sporadically.

2. NC Output (Normally Closed) – Safety Logic

The NC (Normally Closed) output, or "break contact," operates with inverted logic, which is crucial in systems requiring high reliability.

• Operating Principle: The sensor constantly transmits a signal in its idle state. Introducing metal into the sensing zone breaks the circuit, causing the signal to disappear.
• When to Use: Limit functions, monitoring machine guards, and collision prevention. View available models: NC inductive sensors.
• Safety Aspect (Fail-Safe): NC models allow for automatic detection of cable breakage. If the cable is damaged, the signal disappears, which the controller interprets the same as the sensor being triggered, immediately stopping the process.

3. NO+NC Output (Antivalent) – Complete Control

Antivalent sensors are advanced 4-wire devices that combine both logics in a single housing. They feature two independent switching outputs.

• Operating Principle: At the moment of detection, one output changes state from low to high (NO), while the other simultaneously changes from high to low (NC).
• Applications:
  • Systems requiring signal redundancy.
  • Applications where one sensor must control two different processes.
  • Advanced diagnostics: if the state is identical on both outputs (e.g., 0 and 0), the system immediately identifies a failure of the sensor itself.
• Explore our most versatile solutions: NO+NC inductive sensors.

Operating Characteristics Comparison

FAQ – Technical Knowledge Base

How can I tell a NO sensor from an NC sensor without power?

Every sensor has a wiring diagram on its label. A contact symbol with a gap indicates NO. A contact symbol with a cross-line or solid line indicates NC. In antivalent models, you will see both symbols assigned to different pin numbers.

Can a NO+NC sensor replace a standard 3-wire sensor?

Yes. NO+NC sensors are the most universal. You can use only one of the available outputs (isolating the unused wire), which helps reduce inventory—one sensor model can serve as either NO or NC depending on how it's connected.

What is the difference between PNP and NPN in the context of NO/NC?

NO/NC defines the logic (whether the circuit opens or closes), while PNP/NPN defines the switching method. PNP provides a positive potential to the output, whereas NPN provides a negative potential (ground). The choice depends on the input type of your PLC.

As a manufacturer, we provide full support in selecting the right control logic. We encourage you to explore our offer: