EGE-Elektronik Spezial-Sensoren GmbH - Special-Sensors for Automation

Inductive proximity switches - Terminology

Operating Principal
An inductive proximity switch works with a high frequency oscillating circuit that creates an alternating electromagnetic field on the active sensor surface by means of a coil. When a metallic object nears this field a damping occurs in the oscillating circuit. If this damping exceeds a threshold value, a switching signal is generated.

Operating distance
The operating distance is the distance between an object and the active sensor surface at which a switching signal is generated. The operating distance depends on the diameter of the coil. Therefore larger sensors are required for longer operating distances. On some of the EGE sensors the operating distance is adjustable. If a metal object dampens only a part of the alternating field, the operating distance decreases; a larger object increases it. The following approximate values are derived from a standard rectangular measurement plate made of steel ST 37 with an edge length that corresponds to the diameter of the sensor coil or three times the rated operating distance, whichever is greater.

Sensitivity proximit switches

The operating distance is influenced by the material of the object: Constant dimensions for different materials against steel ST 37 yield a changed operating distance. The following table lists approximate values for the material dependent reduction factors. In practical applications variations could occur due to different alloying, for example.

Material influence proximity switches

Rated operating distance sn
The rated operating distance is a device parameter that does not take into account sample variances and external influences such as temperature and supply voltages.

Effective operating distance sr The effective operating distance is the operating distance at nominal voltage and a nominal temperature of 23°C. It is between 90 % and 110 % of the rated operating distance.

Usable operating distance su
The usable operating distance lies in the entire allowable temperature and voltage range between 90 % and 110 % of the effective operating distance.

Assured operating distance sa The assured operating distance takes into account all the external influences and sample variances and lies in the range from 0 % to 80 % of the usable operating distance. Within this range a guaranteed switching is ensured.

Switch point drift
The operating distances are given for an ambient temperature of 23°C. In the permissible temperature range the operating distance varies by less than 15 % from the value at 23°C. The temperature of the measured object has no influence on the switch point.

Hysteresis H
The switching hysteresis describes the distance between the turn-on point while approaching an object and the turn-off point during the separation of it from the sensor. The hysteresis brings about a stable switching signal even when there are vibrations, temperature drift, or electrical variations. The hysteresis is defined in EN60947-5-2 as a maximum 20 % from the effective operating distance, and carries a value of typically 10 % from the effective operating distance sr for EGE sensors.

Repeating accuracy R
The repeating accuracy describes the maintenance of the switching point after the repeated approach of an object under specified circumstances. EGE sensors have typical tolerances of less than 3 % of the effective operating distance.

Switching frequency
The maximum switching frequency of the sensor is determined at half rated operating distance sn with standard measurement plates to EN 60947-5-2

Operating voltage
The operating voltage is the voltage range within EGE sensors function safely. For a constant voltage supply it is important to make sure that the limits are still observed when the residual ripple is included.

Current carrying capacity
This current gives the maximum long-term current for the switching output of the sensor at an ambient temperature of 25 °C and ohmic load. At an elevated ambient temperature, the current load capability decreases.
For analog outputs, the boundary values given in the appropriate technical data, and particularly the permissible values for resistance loads, must be observed.

Short circuit protection
The short circuit protection ensures the sensor against destruction through a short circuit on the output. After removal of the fault, the output is reactivated. Where a maximum overload current is listed, this should not be exceeded.

Excess-current release
This value indicates the median value of current at which the short circuit protection responds with a tolerance of ± 20 %.

Reverse polarity protection
The reverse polarity protection prevents destruction of the sensor by a reversal of the polarity of the voltage supply.

Voltage drop Ud
The voltage drop arises at the internal resistance of semiconductor elements, which are in the current-path of the output. It is dependent of the load-current and is declared for a mean current of 200 mA.

Residual current Ir
The residual current flows in the load current circuit when the output is blocked. The residual current must be considered when switching sensors in parallel.

Minimum load current Im
The minimum load current is necessary for flawless operation with two-wire devices.

Current consumption
The current consumption is the maximum value of the noload current Io that the sensor can absorb without a load.

Ambient temperature
The ambient temperature indicates the maximum allowable temperature range for the sensor.

Electromagnetic compatibility EMC
The EMC class is a measure of the noise immunity of the sensor against external electrical and magnetic influences. The information is based on the standard EN 61000-6-2.

Switch-on impulse suppression
EGE sensors have a switch-on impulse suppression that blocks the output during the switch-on phase, when the operational voltage is applied.

Protective system
The protective system indicates the protection of the sensors against penetration of foreign bodies and water to EN 60529.

EGE sensors with yellow light-emitting diodes indicate the switching status optically.

Housing material
The housing material determines the chemical resistance of the sensor against external influences. For special applications, other housing materials are available.

The connection of the sensors is accomplished through plugin connections or cables. Different cable types and lengths are available upon request.

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