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Inductive Proximity Switch Schematic Circuit Diagram

Inductive Proximity Switches: Applications and Benefits

Inductive proximity switches play a crucial role in various applications, such as measuring motor speeds or determining the position of metal objects. What sets them apart is their immunity to mechanical wear and the absence of sparking contacts. This attribute becomes particularly significant in environments where explosive materials are stored.

Construction of Commercial Proximity Switches: Operational Principle

The vast majority of commercial proximity switches adhere to the construction illustrated in Figure 1. The sensor in these switches is an inductor integrated into the resonant circuit of an oscillator. As a conducting object enters the magnetic field of the coil, eddy currents are induced in the inductor, causing damping in the resonant circuit and subsequently dropping the voltage across it. Monitoring this voltage drop is achieved through a Schmitt trigger. When objects approach the inductor closely enough, leading to a significant voltage drop, the Schmitt trigger changes its state. Following the trigger, an output stage completes the operational sequence.

Inductive proximity switch Schematic diagram

Object Proximity Sensing with IC1: Translating Object Approach into Current Variation

In this circuit, the sensor IC1 plays a pivotal role by translating the approach of an object into a decrease in current through the sensor. In the absence of any object, the current maintains a level of approximately 4 mA. However, when an object comes within 4 mm of the sensor, the current sharply decreases to 1 mA.

Voltage Conversion and Proximity Detection: Utilizing Schmitt Trigger C2

R1 converts the sensor current into a voltage, which is then applied to the non-inverting input of Schmitt trigger C2. Despite functioning more like a comparator due to its small hysteresis, the trigger compares the voltage across R1 with that across R3. When an object is within the 5 mm proximity limit of the sensor, the potential across R3 surpasses that across R1, leading to a high logic output from IC2.

Supply Voltage Considerations and Sensor Characteristics

The potential across R3 is influenced by the supply voltage, yet it is within the specified range in the diagram. It consistently remains greater than the smallest drop across R1 and consistently smaller than the largest drop across R1. This meticulous design ensures the accurate switching of IC2 under all circumstances. The output potential of the circuit is the only parameter impacted by the supply voltage. The sensor utilized is a Type IFR10-82-01 from Baumer Electric, measuring 10 mm in diameter and 5 mm in length.

 

Inductive proximity switch Schematic diagram

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