Inductive sensor uses Eddy Current Killed Oscillator (EKCO) principle to detect the presence of metal object. A detecting coil driven by an oscillator circuit produces high frequency magnetic field at the sensor front. When metal objects approach to the magnetic field, eddy current is generated in metal objects to magnetic energy attenuation, when metal objects close to the sensor sensing surface, energy is absorbed and caused attenuation, when the decay reaches to a certain extent, the trigger circuit switches output signal, so as to achieve non-contact detection of metal objects.
Capacitive sensorsensing element is comprised of two co-axial metalic poles that formed into one capacitor and this capacitor is in series with the RC oscillator circuit. When the power is connected, RC oscillator circuit is not active, however when the target is approaching to the sensing face, the capacitance increases and causing the ocillilator circuit to oscillate corresponding. The oscillation signal is processed and triggered into and ON state to repersent the presence of an object. Capacitive sensor can detect ferrous and non-ferrous objects and it has the maximum sensing distance with ferrous material. For non-ferrous material, the sensing distance is determined by the dielectric constant of the material; the larger the material's dielectric constant, the longer the sensing distance.
It is the installation methods of the sensor. The flash mounting allows the sensor to be buried inside a metallic mounting block in an application. For flush mounting, the sensor is not allowed to be buried inside the metallic mounting block. By comparision, the sensing distance is longer with the non-flush mounting version. In flush mounting: the sensor is completely buried inside the mounting block and effective sensing face is mounted flushed with the mounting block. For non-flush mounting, the sensor is not allowed to be completely buried inside the mounting block, the effective sensing face must maintain a certain distance from the mounting block. For sensors with the same specifications, the non-flash mounting version can achieve the longest sensing distance. A flush mounting sensor has the following advantages: it has better mechanical protection and it has stronger interference property when compared to the non-flash mounting sensor. However, the sensing distance is only 69% of the non-flash mounting sensor.
When the sensor is connected or disconnected to the power supply, whether the sensor is in sensing or non-sensing condition, the output state of the sensor is always at OFF state. Especially when the power is connected, for a moment the output goes OFF state, and it is called initial reset. But in this case, the output will go into a momentarily ON (OFF), and the period is directly proportional to the sensing distance and is about 10 - 100 ms. When the sensor is connected to counter and programmable controller, since there is a initial reset circuit inside the counter and programmable controller, there would be no problem with this condition. On other occasions, please pay attention to avoid the following condition: ◇ Target object near the detection area of the sensor. ◇ For DC voltage and DC switching type sensor, in its power on (off) period, it will exhibit a condition with a sharp rise (fall) time constant. ◇ For AC switching type sensor, in its power on (off), there will be a self-excitation and noise conditions.
Sensing distance is subjected to the changes of environmental factors as temperature, voltage and the slight change in the surrounding conditions. Therefore, in order to ensure the sensor works reliably, making sure that the maximum detection distance is smaller than the sensor's specified sensing distance. In application, setup the detection point at 80% below the specified sensing distance. In addition, if the detection target size is less than the standard target size or the use of targets beyong iron material, the effective sensing distance will be shortened, so correspondingly, the actual detection distance must also be reduced during setup.
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