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    Tag: proximity sensor

    Difference between Limit Switch and Proximity Sensor

    The difference between limit switch and proximity sensor:

    1. Proximity sensors are non-contact switches with a long life and are suitable for passing objects. Limit switches are contact switches. Due to the internal contacts, the working life is relatively shorter.
    2. Limit switches are used for position detection in one direction. For two-way position detection, using a proximity sensor is better.
    3. Use limit switch for protection function. Use a proximity sensor to detect when an object passes a certain point.
    4. The limit switch usually has 1 NO + 1 NC contacts. Generally only one group of contacts is used, so there are 2 wires. Proximity sensors generally adopt 2-wire, 3-wire and 4-wire, so they have more wires than limit switches. Some proximity sensors have to confirm it is PNP or NPN based on the connected equipment.
    How to Connect NPN/PNP Proximity Sensor to PLC?

    In PLC control system, we mostly use DC proximity sensors. And in DC circuit, the proximity sensors used include 2-wire proximity sensor, 3-wire proximity sensor and 4-wire proximity sensor. And they can be further divided into NPN type and PNP type. Generally, people in the United States and Japan usually use NPN proximity sensor, while in the Europe use the PNP proximity sensor.
    The difference of NPN proximity sensor and PNP proximity sensor lies in the conduction situation. NPN proximity sensor belongs to the low level conduction and PNP proximity sensor belongs to the high level conduction. In other words, signal of the NPN proximity sensor flows from the load to the proximity sensor, while that of the PNP proximity sensor flows from the proximity sensor to the load.
    We will take FX3U PLC and S7-200 PLC as examples to explain how is the NPN proximity sensor and PNP proximity sensor connected to PLC.

    Proximity Sensor Selection Guide

    Proximity sensor belongs to the non-contact static position switch. When an object approaches it at a certain distance, the proximity switch gives an action signal. Different from the mechanical position switch that needs to be applied with mechanical force, the proximity switch acquires signal by the change of medium energy between the probe and the object under test. The proximity switch is widely used and has exceeded its scope of limit and protection, and common applications include speed measurement, liquid level control, and metal detection. When you are going to buy a proximity sensor but without any suggestion of others, you will be clear after reading this article.

    Proximity Sensor Price List

    The proximity sensor is a position sensor or switch that can have operation on the moving parts without mechanical contact. When the object gets close to the sensing surface of the sensor to the working distance (detection distance), the proximity sensor can operate without mechanical contact and pressure, thereby provide control instructions to the computer or PLC.
    There are two main types of ATO proximity sensors: inductive proximity sensors and capacitive proximity sensors. Inductive proximity sensors are specifically designed to detect metal, and capacitive proximity sensors are primarily used to detect dielectric, such as conductors, insulating liquids or powders. According to output methods and wiring, the proximity sensors can be divided into DC 2-wire NO/NC, DC 3-wire NPN/PNP type NO/NC, DC 4-wire NPN/PNP type NO+NC, AC 2-wire NO/NC and AC 3-wire NO+NC.