Proximity sensors have endless applications.
In today's Arrow Product Insights, Arrow Engineer and sensors expert J.J. Meneu will give an overview of the most common proximity sensor technologies: hall effect sensors, inductive sensors, capacitive sensors, infrared sensors and time of flight. Some of the products featured in this video include:
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Today we’ll give an overview of the most common proximity sensors technology that are Hall Effect Sensors, Inductive Sensors, Capacitive Sensors, Infrared Sensors, and Time of Flight Sensors. Hall Effect sensors are designed to detect minutes in a short range. The Lorentz Force is the phenomena responsible for the Hall Effect. When electrons move along a direction in the magnetic field perpendicular to the current direction is applied, electrons undergo a force. Instead of going straight electrons is curved creating a voltage that can be measured. Hall Effect Sensor switch come in 3 configurations, Unipolar, which responds to north and south, but not both, Omnipolar configuration responds to north and south poles, the Bipolar configuration is similar to a latch.
Two fundamental parameters express in data sheets are BOP means magnetic count. It’s the magnetic first density at which a sensor output becomes active. BRP the magnetic release pump is the magnetic first density at which the sensor becomes inactive. For Unipolar and Omnipolar switches, BOP and BRP is the same sign, unlike the bipolar version, where BOP has the inverse sign of BRP.
A Hall Effect sensor is done to detect to close the distance of the magnet. The demo board from Allegro that integrates the A1569 and Omnipolar Hall Effects sensors with LED demonstrate the principle. As you can see if the magnet is close to the chip the LED turns off.
To detect proximity of other materials other techniques must be used. To detect the conductive material the inductive sensors is well suited. TI has a latch family of inductive digital converters. The physical phenomena is the following, the inductors digital converter uses an inductor in (??) capacitor to generate an AC magnetic fit. When a conductive target moves nearer for further from the inductor the magnetic created by the inductor generates 80 currents on the surface of the target. The 80 currents then create their own magnetic field which opposes the inductors fit. As the target closer the 80 current intensity increases creating a stronger opposing field. We end up with the inductance and the resistance which has functions to the distance between the inductance and the conductive material.
Inductive sensors are great for metal detection and for short range(?3:05). For detection of humans or other materials, the capacitance detection must be used. The capacitance value depends on permittivity dielectric, area of plates, and distance between plates. For proximity capacity censors, the distance and area are fixed, but inserting an object close to the capacity changes the dielectric value. For instance, with the FDC2214 from TI, the LED is turned on when my hand approaches turns on.
The capacitance sensors need a few square centimeters of copper . If space constraints exist for the design optical solutions are a better fit. The cheapest solution is infrared system. The principle is to send an infrared wave to a reflective object and detect the amount of light reflected. The VCNL4020 works on this principle. Moving my hand next to the sensors there is more reflections. The reflections depend on the type of material and this technology is not able to measure distance.
Let’s take a sheet of white paper, the return power is around 12000 at a small distance. With a gray foam it is around 1/3 of the previous power. The time of flight technology measures the distance. The principle is to aim is photons to a target and detect the same photons back to the sensor. The VL6180X was designed with this technology. Taking the same white paper and putting it on the Arduino we get we get a distance of 6mm, with the gray foam the distance is 6mm.
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