| Analog sensors: Sensor for Every Need |
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Analog sensors – Some applications can only be implemented with sensors using analog output signals. Analog sensors with intelligent evaluation can even replace considerably more expensive measuring devices. |
Some innovations are launched on the market with a large amount of advertising but are then soon forgotten immediately afterwards. There are also those which only attract the attention of many users slowly, but which nevertheless maintain a continuous presence because they cover a wide range of possible applications. TURCK, the sensor specialists from Mülheim/Ruhr, have now developed an innovation of this kind: An analog sensor that can not only detect the presence of a metal but at the same time its composition, irrespective of the distance between the sensor and the object.
Well-established measuring principle
The technology of the new sensor is based on the eddy current principle by which inductive proximity switches also operate: If an electrical conductor is present in a time varying magnetic field, or if this type of conductor is moved in a magnetic field, a voltage is induced in the conductor, thus producing an eddy current. This in turn generates an opposing magnetic field to the original magnetic field, which is superimposed on the inducing field. The impedance of the coil changes as a result, and this can be measured as a voltage change at the output of the sensor.
Eddy current sensors react to different influences such as the electrical conductivity or magnetic permeability of the material measured. The sensitivity of an inductive proximity switch consequently depends on the material to be detected. This means that the measuring result has to be adjusted with a so-called material factor – the correction factor. St37 mild steel thus allows the maximum switching distance, whilst the permissible switching distances for other metals are smaller. The correction factor indicates the fraction of the maximum switching distance to which the possible distance is reduced when other metals are used. Typical correction factor values for brass are between 0.35 and 0.5, 0.25 and 0.45 for copper, 0.35 and 0.50 for aluminium and between 0.6 and 1 for stainless steel...
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