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Inductive sensors detect metal using a magnetic field and are used in various applications. They consist of an oscillator, iron core or coil, sensing circuit, and output processor. They are preferred over mechanical switches due to their durability and lack of physical contact. They can detect various metals, but calibration may be required for non-ferrous metals.
An inductive sensor is an electronic device that detects the presence of metal. These devices were introduced in the 1960s and quickly replaced mechanical switches, especially in dirty or wet environments. Inductive sensors, also known as proximity sensors, use a magnetic field influenced by nearby metals. When metal is present, electronic circuits detect changes in the field and send out a signal that can be used to operate other machinery. The effect of metal on a magnetic field is called the induction effect, and a sensor uses an induction loop.
Four main parts make up an inductive sensor. An oscillator changes direct current (DC) to alternating current (AC), although some sensors are powered by alternating current and do not need this part. An iron core or coil wrapped in wire creates a magnetic field that will be affected by the presence of metal. The sensing circuit monitors the magnetic field and detects field changes caused by metal passing nearby. An output processor takes the information from the sensing circuit and sends a signal to other equipment.
Inductive sensors have a wide range of uses. These sensors are normally manufactured as normally open or normally closed devices. A normally open inductive sensor will not allow electric current to flow unless the sensor is triggered. A simple example of this is a garage door opener, where the proximity sensor will stop the door motor when the opener assembly gets close to the motor hanging from the ceiling.
In contrast, normally closed sensors allow current to flow until metal is sensed, which causes the switch to open, cutting off the flow. They are used when a metal object needs to turn on a circuit or operate machinery. Applications may include remote valve position sensors, sorting machinery to separate metal from other materials, or car washes where the passing car or drive roller spins on the car wash equipment.
An inductive sensor is preferred over mechanical switches for several reasons. They have no moving parts and require no preventative maintenance. There is no physical contact between the metal object and the inductive sensor, so the products will not be damaged during manufacturing or assembly operations. Inductive sensors are rugged and are unaffected by a wide range of temperatures or environmental conditions, including dirt or chemicals.
Iron is most sensitive to the magnetic field created by an inductive sensor, but other metals can also be detected. Stainless steel, brass and even aluminum can be detected, but magnetic field effects are less with these metals and calibration may be required to ensure signal reliability. Sensors used for non-ferrous metals may need to be placed very close to the metal object, which may reduce their advantages over other types of sensors.
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