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.
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.
Check the sensor's wiring when using buzzer, lights in the applications, they may produce high voltage, large current. So please do not use this kind of detection method.
A photoelectric sensor emits a beam of light (visible or infrared) from its transmitter. A reflective type photoelectric sensor is used to detect the light beam reflected from the target and the thrubeam type is used to measure the change in light quantity caused by the target crossing the beam.
From the specifications sheet one must verify the key spec as shape and dimensions, sensing distance, operating voltage and output configuration (NPN/PNP), output states （NO/NC). In addition, the wiring types (Cable wiring/Connector), cable length, switching frequency, temperature requirement, water ingress protection (IP Level). In some special sensing applications, a special sensor will be needed. Take Meijidenki sensor as an example, options available include high pressure, high temperature, high switching frequency, high magnetic field immune, analog outpout, namur and Factor 1 sensors.
First of all, verify for correct wiring connections and the power suppy is stable. When installing a sensor, need to take into consideration for possible interference, ensuring proper spacing between sensors and in some case, selection of shielded sensor to obain a better interference effect.
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