The amount of capacitance varies depending on the size and distance of the sensing object. An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the capacity of the two plates is detected.
One of the plates is the object being measured with an imaginary ground , and the other is the Sensor's sensing surface. The changes in the capacity generated between these two poles are detected. The objects that can be detected depend on their dielectric constant, but they include resin and water in addition to metals.
The reed end of the switch is operated by a magnet. Page top page-top Omron uses cookies to improve your experience on this website. Lead Contents Proximity Sensors. The rise or fall of such oscillation is identified by a threshold circuit that changes the output of the sensor.
The operating distance of the sensor depends on the actuator's shape and size and is strictly linked to the nature of the material Table 1. In this system a residual current flows through the load even when in the open state and a voltage drop occurs to the sensor when it is in the closed state.
Attention must be paid to these restrictions when selecting relays or electronic controls to be used with these sensors. They are compatible with P. They are supplied as 3 wire with function N. Standard version include protected against short circuit, protected against polarity and peaks created by the disconnection of inductive loads. NAMUR: These are 2 wire non-amplified sensors whose current varies in the presence of a metallic object. The difference between these sensors and traditional sensors is the absence of amplifier trigger stages.
Their current and voltage limits allow them to be used in hazardous explosive environments when used with approved amplifiers. Attention must be paid to the minimum switching current, residual current and voltage drop when selecting low consumption relays or high impedance electronic controls to be used with these sensors. NO normally open : A switch output that is open prohibiting current flow when an actuator is not present and closes allowing current flow when an actuator is present.
NC normally closed : A switch output that is closed allowing current flow when no actuator is present and opens prohibiting current flow when an actuator is present. NPN Output: Transistor output that switches the common or negative voltage to the load. The load is connected between the positive supply and the output. Current flows from the load through the output to ground when the switch output is on. Also known as current sinking or negative switching.
PNP Output: Transistor output that switches the positive voltage to the load. These non-contact proximity sensors detect ferrous targets, ideally mild steel thicker than one millimetre. They consist of four major components: a ferrite core with coils, an oscillator, a Schmitt trigger, and an output amplifier.
This sensor has 2 main versions and they are,. The oscillator creates a symmetrical, oscillating magnetic field that radiates from the ferrite core and coil array at the sensing face. An inductive proximity sensor has the frequency range from 10 to 20 Hz in ac, or Hz to 5 kHz in dc.
Because of magnetic field limitations, inductive sensors have a relatively narrow sensing range like from fractions of millimetres to 60 mm on an average.
Due to this, load will be caused on the sensor that decreases the electromagnetic field amplitude. If the metal object moves towards the proximity sensor , the eddy current will increase accordingly. Thus, the load on the oscillator will increase, which decreases the field amplitude.
The schmitt trigger block monitors the amplitude of the oscillator and at particular level predetermined level the trigger circuit switches on or off the sensor. If the metal object or target is moved away from the proximity sensor, then the amplitude of the oscillator will increase. The above image shows the waveform of the inductive proximity sensor oscillator in the presence of the target and in the absence of the target. Nowadays, inductive proximity sensors are available with different operating voltages.
Hope this article will help you to understand the complete inductive proximity sensor working principle.
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