How Inductive Sensors Work
Inductive sensors detect metallic objects contactlessly and measure the distance between the sensor and the object to be measured by electromagnetic induction. To do this, a current is conducted through a coil, creating an electromagnetic field around the coil. If an electrically conductive object such as steel or aluminum approaches the magnetic field, this is changed. The inductive sensor recognizes the change in the magnetic field and evaluates it to determine whether there is a metallic object in the vicinity.
Various Switching Outputs
A signal is present on the digital switching output as soon as the sensor has detected an electrically conductive object. The distance can be output via an analog output as a proportional voltage signal – either as a current value of 4 mA…20 mA or as a voltage value of 0 V…10 V. In the case of inductive sensors with an IO-Link interface, the switching outputs (NPN, PNP or push-pull) can be configured as normally closed or normally open contacts as well as the switching distances.
Switching Distances with Inductive Sensors
The switching distance is the distance at which a standard target, which is approaching the sensing face of an inductive sensor, triggers a signal change. The standard target is a grounded, square plate made of steel with a thickness of d = 1 mm. If an object moves away from the sensing face, the sensor remains switched on longer. In contrast, the sensor switches sooner if the object moves towards the sensing face. The difference between the switch-on and switch-off point as a percentage relative to the switching distance is called switching hysteresis. The switching distance is further subdivided into the variables nominal switching distance (Sn), real switching distance (Sr), useable switching distance (Su) and working distance (Sa).
Correction Factor 1
Influence of Different Materials on the Switching Distance
The correction factor of an inductive sensor refers to the specified switching distance for an object made of steel (EN 60947-5-2). If an object made of another material needs to be detected, the switching distance has to be adjusted by an amount equal to the specified correction factor. Inductive sensors with correction factor 1 have the same switching distance for all metals. The correction factor 1 is of great importance in applications where the material of the object to be detected can vary. For inductive sensors, the correction factor is specified in the data sheet.
Switching Frequency for Inductive Sensors
The switching frequency corresponds to the maximum possible number of switching operations per second if the distance between the objects to be detected is equal to the size of the individual object in Hertz (Hz), i.e. with a pulse duty factor of 1:2.
Installation Situations of Inductive Sensors
Inductive sensors are used in a wide range of applications and enable reliable detection of the smallest parts as well as reliable detection of end positions. Since the inductive sensors react to electrically conductive objects and materials, sufficient distance to metallic objects must be maintained during installation to avoid unintentional switching of the sensor. The installation conditions can be found in the data sheet of the relevant sensor.
Flush Sensors
Flush sensors can be mounted in electrically conductive materials without protruding because they have a metallic ring around the sensor head that protects the sensor from influences from the surrounding material. This shielding reduces the electromagnetic field and thus reduces the switching distance. Flush mounting protects the sensor from damage and prevents objects passing by from getting caught on the sensor. This makes them particularly suitable for tight installation situations.
Non-Flush Sensors
In the case of non-flush sensors, the sensing face is not enclosed by a metallic housing. As a result, the generated magnetic field is not shielded by the housing and a larger field can build up. Inductive sensors with non-flush mounting have the largest switching distance, but protrude significantly from the surrounding surface. These sensors can only be flush-mounted in non-conductive materials.
weproTec and Alternative Frequency
weproTec is the abbreviation for wenglor proximity switch technology, a wenglor technology for inductive sensors. Inductive sensors with weproTec can be mounted very close next to each other, or opposite one another in the distance range B1 . The sensors do not influence each other in this range. This is achieved by the sensors synchronizing with each other and pulsed with a time delay.
Alternative frequency is a simpler form of weproTec technology in which an alternative working frequency can be parameterized. This means that two sensors in the immediate vicinity do not interfere with each other if the alternative frequency is activated for one of them and not for the other. They each work at a different frequency.
Overview of Inductive Sensors
Difference Between Inductive Sensors and Photoelectronic Sensors
Both inductive and optical sensors enable identification solutions in process automation. Different functional principles and associated advantages enable a wide variety of applications that meet a wide range of requirements.
