Inductive (proximity) proximity sensors are used for non-contact detection of metal objects. Its working principle is based on a coil and oscillator that creates an electromagnetic field in the immediate vicinity of the sensing surface. The presence of a metal object in the work area causes the oscillation amplitude to decrease. The rise or fall of this oscillation is defined by a threshold circuit that changes the output of the sensor. The working distance of the sensor depends on the shape and size of the metal and is strictly dependent on the nature of the material.

     Inductive sensors work on the basis of Faraday's Law. One way of stating Faraday's Law is that a change in magnetic flux in a coil of wire will cause a voltage in a nearby coil. The sensor itself contains an oscillator circuit and a coil through which an electromagnetic field propagates and induces eddy currents in any metal object nearby. Eddy currents have the effect of reducing oscillations from the amplifier. This reduction in oscillations is recorded as the presence of a metallic object.

Inductive proximity sensors can only detect metal targets.

     They do not detect non-metal targets such as plastic, wood, paper and ceramics. Unlike photoelectric sensors, this allows an inductive proximity sensor to detect a metal object through opaque plastic.

     Inductive proximity sensors are widely used in many automation applications. They are used to detect the presence of objects and do not require physical contact with the detected target or object, so they are often called non-contact sensors. Common types of proximity sensors include photoelectric, capacitive, and inductive (proximity) sensors.

   Properties:
   Non-contact detection

Unlike a limit switch, it detects an object without any mechanical contact. Therefore, there is no possibility of the sensing object or sensor being damaged by contact.

  Can be used in harsh environments

water, etc. Reliable detection is possible even in adverse conditions where it can come into contact with Most of the sensors have IP67 protection and oil resistant construction.
   High sensitivity
It is suitable for precise object positioning due to its very high repeatability.
   Short response time
Stable detection is possible even with fast moving objects due to the high response frequency (max. 3.3 kHz).
   Long working performance
Due to its non-contact output, it is long-lasting and requires almost no maintenance.

 However, it also has the following disadvantages.
Metal detection only
It cannot detect non-metals where current is not flowing because detection relies on thermal losses due to induced current.
(Also, metals such as ferrite that do not allow current flow cannot be detected.)

Short sensing distance
Although there are various methods to improve the sensing range, such as increasing the sensing coil size, using unshielded sensor heads, the sensing range is still smaller than that of photoelectric sensors.

2-wire DC: These sensors contain an output amplifier with NO or NC function that can drive a load connected in series. In this system, a residual current flows through the load even when it is on, and a voltage drop occurs to the sensor when it is in the off state. These restrictions should be considered when selecting relays or electronic controls to be used with these sensors. Compatible with PLC units. What is 2 wire sensor ? >

3- and 4-wire DC: These powered DC sensors include an output amplifier. They are supplied as 3 wires with NO or NC function and 4 wires with complementary outputs (NO + NC) in types NPN and PNP. The standard version is short-circuit protected, protected against polarity and peaks generated by disconnecting inductive loads. Compatible with PLC Units

Analog and Linear: With these 3-wire powered sensors, the current or voltage output changes proportionally to the distance between the sensor and a metallic object. Analog sensors >


NAMUR: These are non-amplified 2-wire sensors whose current changes in the presence of a metallic object. The difference between these sensors and conventional sensors is the absence of amplifier trigger stages. Current and voltage limits allow use in hazardous (explosive) environments when used with approved amplifiers. In standard applications (normal atmospheres) the sensor should be used with ALNC, ALN2 or similar amplifier units. What is NAMUR Sensor ? >

AC Voltage:

2-wire AC: These are two-wire sensors with a thyristor output amplifier. In this system, a residual current flows through the load even when it is on, and a voltage drop occurs to the sensor when it is in the off state. Consideration should be given to minimum switching current, residual current and voltage drop when selecting low consumption relays or high impedance electronic controls to be used with these sensors. Compatible with PLC Units. 2 Wire sensor pages >

Definitions:

NO (normally open): A switch output that closes when an actuator is not present and allows current to flow when an actuator is present.

NC (normally closed): A switch output that allows current to flow when an actuator is not present and blocks current flow when an actuator is present.

NPN Output: Transistor output that passes the common or negative voltage to the load. The load is connected between the positive supply and the output. When the switch output is open, current flows from the load from the output to ground. Also known as current reduction or negative switching.

PNP Output: Transistor output that passes the positive voltage to the load. The load is connected between the output and the common. When the switch output is open, current flows from the device output to the ground to the load. Also known as current source or positive switching.

Working Distance (Sn): The maximum distance from the sensor to a square piece of Iron (Fe 37) whose side = 1 mm thick and will trigger a change in the diameter of the sensor face. The distance will decrease for other materials and shapes. The tests are carried out with a constant voltage supply at 20 voltsC. This distance includes ±10% manufacturing tolerance.

Power Source: The supply voltage range in which the sensor will operate. Power supply main page >

Maximum Switching Current: The amount of continuous current allowed to flow through the sensor without damaging the sensor. It is given as the maximum value.

Min Switching Current: It is the minimum current value that must flow through the sensor to guarantee operation.

Maximum Peak Current: The maximum peak current indicates the maximum current the sensor can handle in a limited time.

Residual Current: The current flowing through the sensor when it is on.

Power Drain: The amount of current required to power a sensor.

Voltage Drop: The voltage drop across a sensor while driving its maximum load.

Short Circuit Protection: Protection against damage to the sensor if the load is shorted.

Operating Frequency: The maximum number of on/off cycles the device can take in one second. According to EN 50010, this parameter is shown in Fig. It is measured by the dynamic method shown in Fig. When 1 sensor is in positions (a) and (b). S is the working distance and m is the diameter of the sensor.

Repeatability (% Sec): The difference between any operating distance value measured over an 8 hour period is a supply voltage of 15 to 30ºC and a deviation of <= 5%.

Hysteresis (%Sn): The distance between the "on" point of the actuator approach and the "off" point of the actuator retraction. This distance reduces false triggering. Its value is given as a percentage of the run distance or distance. 

Flush Mount: For side-by-side mounting of flush mount models, see Fig. Figure 4a. Flush-mount models can be embedded in metal according to Figure 4b. For side by side, see sec. 4c. Sn = working distance.

Degree of Protection: According to IEC (International Electrotechnical Commission), the protection class is as follows:
IP 65: Dustproof. Protection against water jets.
IP 67: Dustproof. Protection against immersion effects

What is the difference between inductive and capacitive sensors?

 
    Inductive sensors use a magnetic field to detect objects. Capacitive sensors use an electric field. An object must be conductive in order to be detected by an inductive sensor. This limits suitable targets for metal objects (mostly). The target does not have to be conductive to be detected by a capacitive sensor. A capacitive sensor will respond to an object acting as a dielectric material and a conductive object. This makes metal and non-metal objects suitable targets. What is capacitive sensor?