Inductive sensors
Inductive sensors
Inductive sensors are non-contact sensors that respond only to metals. They can directly send signals to relays, solenoid valves, measuring systems, and electronic control circuits such as PLCs.
Operating Principle and Structure of Inductive Sensors:
The structure of these sensors consists of four main stages.
The core of these sensors consists of a high-frequency oscillator that can be influenced by metallic objects. This oscillator generates an electromagnetic field in the sensor's sensing area. When a metal object approaches, eddy currents are induced in the object, which absorb energy from the field, resulting in a reduction in the oscillator's amplitude.
Since the demodulator stage detects the oscillator's amplitude, the reduction in amplitude is transmitted to the Schmitt Trigger stage, which in turn activates the output stage.
Standard object:
It is a square-shaped piece of ST37 steel used for testing the switching distance.
(according to IEC 947-5-2 standard)
The thickness of the piece is 1 mm, and the side length of this square can be in the following sizes.
- Equal to the diameter of the sensor
- Three times the nominal switching distance of the sensor (3Sn)
Correction Factors:
The switching distance will change with smaller dimensions of the standard piece or when using a metal other than ST37 steel.
The table below shows the correction factors for different metals.
|
Correction Factors |
Metal type |
|
1.0 |
Steel ST37 |
|
0.9 |
Nickel |
|
0.5 |
Brass |
|
0.45 |
Copper |
|
0.4 |
Aluminum |
For example, if a sensor performs the switching operation at a distance of 10 mm in front of steel, the same sensor will perform the switching operation at a distance of 4.5 mm in front of copper.
Switching Frequency:
The maximum number of on/off cycles a sensor can perform in one second. (This unit is expressed in Hertz, Hz)
This parameter is measured according to the DIN EN 50010 standard under the following conditions.
Switching Distance (S):
The distance between the standard target and the sensor's sensitive surface during the switching operation. (EN 50010 Standard)