Page 104 of catalogue Control systems for mobile vehicles of ifm Electronic GmbH

Sensors for mobile applications

Inductive sensors

System description

Inductive sensors In all automated processes sensors are absolutely necessary to provide the plc with information. They supply the necessary signals on positions, limits or serve as pulse pick-ups for counting tasks or for monitoring rotational speed. In comparison with mechanical switches they offer almost ideal conditions: operation without contact and wear as well as high switching frequencies and accuracy. In addition, they are not affected by vibration, dust and moisture. Inductive proximity switches detect all metals without contact. Operating principle of inductive sensors Inductive sensors take advantage of the physical effect of a change in the quality factor of a resonant circuit caused by eddy current losses in conductive materials. This is how it works: An LC tuned circuit generates a high-frequency electromagnetic field. This field is emitted from the active face of the sensor. If a conductive material passes through this field, eddy currents are formed in accordance with the law of inductance which take energy away from the oscillator. This reduces the oscillation amplitude. This change is converted into a switching signal. The operating principle permits detection of all metals irrespective of whether they are moving or not. Important: The high-frequency field causes no measurable heat in the object nor is there any magnetic interference. So the sensors operate without interaction. The distance to the active face at which an electrically conductive material leads to a signal change in the sensor is called sensing range. The sensing range of an inductive sensor is defined by means of a target made of mild steel. If the sensor is damped by other metals, e.g. aluminium or copper, it changes. By means of correction factors which exist for every kind of metal the user can calculate the sensing range expected. Modular sensors A special series of inductive sensors are the application sensors which are called “efectorm”– The “m” stands for modular technology. It is based on a new mechanical concept, new assembly methods and an innovative sealing system. It is based on an O ring (made of Viton / EPDM) which is in the front cap and in the plug area. In addition, these areas are sealed using a special cast resin. The reinforced housing provides additional mechanical stability. A high degree of automation is reached in manufacturing. This new production technology provides high quality sensors. During production all components and the individual production steps are subjected to a continuous function check. This severe quality testing guarantees permanent reliable operation even under extreme conditions. The common feature of these sensors is an increased sensing range. It permits use where standard units meet their limit.

standard setting in practice

adjustment with setting LED

80 100 sensing range [%]

standard sensing range increased Sn safe setting range increased Sn unsafe setting range

In practice that means sensing ranges more than 2.4 times greater than using standard sensors.

Quick set-up: The set-up LED helps to send the optimum sensing range.

High-frequency electromagnetic field: The inductive sensor detects all metals.

Cable drum of a mobile crane: An inductive sensor type M18 monitors and signals the end of the cable.

An inductive sensor serves for position monitoring in a Hydraulic system.

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