How to Wire a Two-Wire Induction Sensor

How to Wire a Two-Wire Induction Sensor

Induction sensors, also known as proximity sensors, have many different wiring configurations. The most common are 2-wire and 3-wire. Two-wire devices wire in series with the load; in a 3-wire device, two of the three leads supply power while the third switches the load. Both types can be wired strategically, in series or parallel configurations, to conserve inputs or perform logic.

When it comes to proximity sensors, one of the most common questions is what type to use. The answer to this question depends on what your application requires.

There are many kinds of induction sensors, including those that rely on a magnetic field or an electric field to detect objects. These include the following:

High-frequency oscillation sensor

This type of induction sensor incorporates a circuit that changes its frequency when a metal target approaches it. It is designed to detect nonferrous metals such as copper and aluminum as well as ferrous metals such as iron.

Its operating distance (Sn) is typically 1mm to 1.5mm for iron and less than that for other materials and shapes. The maximum distance will vary depending on the shape of the sensor and its manufacturing tolerances.


Inductive sensor outputs come in the form of NO or NC switch outputs. NO is an open switch output that prohibits current flow and NC is a closed switch output that allows current to flow.

The switch outputs can have a low voltage level to trigger the mosfet switching process, or they can have higher voltage levels for use in applications where triggering is not important. In addition, it is a good idea to keep an ohm-resistance between the switch and the input to protect against possible leakage current during operation.

Unlike mechanical switching contacts, two-wire induction sensors require current and voltage at all times, even when the sensor is closed. Because of this, they cannot be easily compared to switches and will not have clear “open” or “closed” states.

If you want to operate a two-wire induction sensor on modern digital inputs, it is best to choose ones that have a low residual current. This is because it will minimize power dissipation and heat waste during the sensor’s operations.

For this reason, Pepperl+Fuchs offers a large selection of induction sensors that can be operated on DSI 2 inputs. It is also recommended to choose ones with a high output impedance to limit input currents.

When it comes to wiring a two-wire induction sensor, it is important to be sure to remove only one wire at a time and do not disconnect both at the same time. This will help to prevent shorts and ensure the safety of the system.

For example, if you need to replace a 3-wire PNP sensor with a 2-wire sensor that has an NPN output, simply connect the Blue wire of the new sensor to the 0V common on the sensor’s circuit and then the Brown wire of the sensor to the +24V source on the PLC block. Once you have completed this, the new sensor will work just as the old sensor did.

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