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Operating Distance as Central Characteristic

A magnetic field sensor switches at a certain distance from a material to be detected. This distance is referred to as the "operating distance." The operating distance is potentially the most important characteristic of a proximity sensor. The operating distance that can be achieved by a magnetic field sensor depends on the size and the magnetic flux density of the actuating magnet. The reference value for determining the operating distance (sn) is the permanent magnet DM60 as a damping element.

The permanent magnet DM60 has a diameter of 31 mm and a height of 15 mm with a remanence flux density Br of 380 ⁠– 400 mT. With this permanent magnet, numerous magnetic field sensors from Pepperl+Fuchs achieve an operating distance of 60 mm.

A polarity-dependent response curve is obtained when the surface of the sensor is crossed sideways. The response curve represents the sensing range of the sensor.

Note: Observe the orientation of the permanent magnet.

A bipolar orientation of the magnet creates a two-hump response curve, a "double switch point," which is usually not required.

Figure: Two-hump response curve with a bipolar orientation of the magnet

Unipolar orientation of the magnet creates a central sensing range with lateral side humps.

Due to these side humps, a certain minimum distance between the magnet and the sensor must be maintained for defined and clear switching characteristics

Figure: Central sensing range (1) with side humps with unipolar orientation of the magnet

Operating Distance ("Rated Operating Distance") sn

The operating distance sn, or "rated operating distance," according to EN 60947-2-5, is a conventional variable for determining the operating distance. This type of operating distance does not take into account manufacturing tolerances or changes caused by external influences such as voltage and temperature.

Effective Operating Distance sr

The effective operating distance sr is the operating distance of a single sensor measured under the following conditions:

  • Ambient temperature of +23 ± 5 °C
  • Voltage within the operating voltage range
  • Within the specified installation conditions

0.9 · sn ≤ sr ≤ 1.1 · sn

Assured Operating Distance sa

The assured operating distance sa is the distance from the sensing face, within which actuation of the sensor is assured under set conditions:

0 < sa ≤ 0.81 · sn

Hysteresis H

The hysteresis H is the distance between the switch points when the permanent magnet approaches the sensor and moves away from it again. The hysteresis is specified relative to the effective operating distance sr. This distance is measured at an ambient temperature of +23 °C ± 5 °C and at the rated operating voltage.

H ≤ 0.2 · sr

The typical hysteresis of magnetic field sensors from Pepperl+Fuchs is 5 % … 10 % of the effective operating distance sr.


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