Proximity sensor – Features, working principle and application

Proximity sensors are used to detect magnetic and non-magnetic metal objects (such as Aluminum, copper ..) using Inductivity Proximity Sensor and detecting non-metallic objects using sensor type. Capacitive Proximity Sensor. Or is it a familiar sensor form in every Smartphone, but so far many people still do not know what a proximity sensor is? What types of proximity sensors are there? What is the principle of operation, structure and application, what role does it play in modern electronic devices. In the following article, Electromechanical World would like to summarize all the content related to the proximity sensor as stated.

What is a proximity sensor?

Proximity sensors (also known as “Proximity Switches” or simply “PROX” in English, Proximity Sensors) react when an object is near the sensor. In most cases, this distance is only a few millimeters. The proximity sensor normally detects the end position of the machine part and the output signal of the sensor initiates another function of the machine. Especially this sensor works well even in harsh environments.

Proximity sensors convert signals about the motion or appearance of an object into an electrical signal. There are 3 detection systems to do this conversion: the system uses the eddy currents emitted in the metal object by electromagnetic induction, the system uses the change in capacitance when approaching objects to be detected, the system uses magnets and the magnetic addition switching system.

Proximity sensor characteristics

• Detect objects without contact, no impact on objects, the longest distance up to 30mm.
• Stable operation, good anti-vibration and shock resistance.
• Fast response speed, long life compared to limit switch.
• Small sensor head can be installed in many places.
• Can be used in harsh environments

Working principle of proximity sensor

Proximity sensor works on the principle of electromagnetic field emitted around the sensor with a maximum distance of 30mm and encounters an object, it will transmit a signal to the processor.

Working principle of magnetic induction proximity sensor

Magnetic proximity sensors consist of a coil wound around a magnetic core at the sensing end. High frequency waves passing through this core will create an electromagnetic field oscillating around it. This electromagnetic field is controlled by an internal circuit.

When the metal object moves towards this field, an electric current (eddy current) is generated in the object.
These currents cause transformer-like action, so the energy in the detection coil is reduced and the oscillation is reduced; the strength of the magnetic field decreases.

The monitoring circuit detects the oscillation level to decrease and then changes the output. object has been detected.
Since this operating principle uses an electromagnetic field, the proximity sensor is superior to the photoelectric sensor in terms of resistance to the environment. For example, oil or dust usually does not affect the operation of the sensor.

Output of Inductive Sensor

Today, most inductive sensors feature a transistor output with NPN or PNP logic. These types are also known as DC-3 wire models.

Some notes when using the proximity sensor

We must determine what we are measuring

• The processing speed of the sensor is fast or slow; and measurement area accuracy need high precision?
• Check the influence of the environment around the measuring area to see if there is a large magnetic field such as a magnet; to find solutions because this is one of the causes of sensor measurement errors
• Vibration measuring area or not?
• Is the ambient temperature high?
• What is the distance between the sensor and the object to be measured?

Depending on the needs of different factories, we should carefully check and choose to buy the right sensors to meet the needs to be measured.

Select Proximity Sensor

If you want to choose the right proximity sensor for an application, there are a few things to keep in mind:

• power supply,
• Sensor size, diameter,
• Output signal (PNP, NPN, NC, NO)
• Protected (flush) or non-transducer protection (Non-flush)
• M1 . plug or wire connection