Mechanism

Types Of Proximity Sensors

overview.

Inductive, Capacitive, Ultrasonic, IR? These are the common types of proximity sensors used today for varying applications. Picking one that’s easily connectable, accurate, and reliable is very much important for fulfilling your intended usages.

What are proximity sensors?

Proximity sensors are sensors that detect the movement/presence of objects without physical contact and relay that information captured into an electrical signal. It can also be defined as a proximity switch, a definition given by the Japanese Industrial Standards (JIS) to all contactless detecting sensors.

Where are Proximity Sensors used?

Proximity Sensors are widely used in industrial and manufacturing applications, especially for safety and inventory management applications. In an automated production line, for example, it is used for object detection, positioning, inspection and counting. It is also used for part detection in an industrial conveyor system.

Proximity sensors can also be found in consumer devices. In smartphones, proximity sensors are used to detect if a user is holding their phone near their face. They are also used as capacitive touch switches on consumer electronics products.

It is also used for many other different applications such as a diffuse sensor in a public washrooms or a collision detection sensor for robots!

Proximity Sensor Features.

To further understand what proximity sensor is all about, we’ll take a look at its features. The following is its features, with some uniquely seen as compared to traditional optical/contact sensors:

▪️Contactless sensing.Contactless proximity sensing allows for detection without touching the object, ensuring object stays well-conditioned.

▪️Unaffected by surface conditions.Proximity sensors are nearly unaffected by surface colors of objects since it mainly detects physical changes.

▪️Suitability for wide range of applications.

Proximity sensors are suitable for damp conditions and wide temperature range usage, unlike your traditional optical detection.

Proximity sensors are also applicable in phones as well, be it your Andriod or IOS devices. It consists of simple IR technology that switches on and off display accordingly to your usage. For example, it turns off your display when a phone call is ongoing such that you wouldn’t accidentally activate something while placing it near your cheeks!

▪️Longer service life.Since a proximity sensor uses semiconductor outputs, there are no moving parts dependent on the operating cycle. Thus, its service life tends to be longer as compared to other sensors!

▪️High speed response rate.

Compared to switches where contact is required for sensing, proximity sensors offer a higher-speed response rate.

Types of proximity sensor.

Here’s the rundown of the different proximity sensor types!

1.Inductive Proximity Sensors.

Inductive proximity sensors are contactless sensors used to only detect metal objects. It’s based on the law of induction, driving a coil with an oscillator once a metallic object approaches it.

It has two versions and comprises of 4 main components:

🔸Versions:

▪️Unshielded: Electromagnetic field generated by the coil is unrestricted, allowing for wider and greater sensing distances

▪️Shielded: Electromagnetic field generated is concentrated in the front, where sides of the sensor coil are covered up.

🔸Components:

▪️It comprises of 4 main components as seen in the picture; Coil, Oscillator, Schmitt Trigger, and output switching circuit.

How do Inductive Proximity Sensors work?

1. An alternating current is supplied to the coil, generating an electromagnetic detection field.

2. When a metal object comes closer into the magnetic field, eddy currents build-up, and result in coil inductance changes.

3. When coil inductance changes, the circuit that has been continuously monitoring, will trigger the sensor’s output switch.

*Note: Even when a target is not present, inductive sensors continue to oscillate. The switch is only triggered when an object is present.

🔸Common applications:

_Industrial usages.

▪️Production automation machines that count products, product transfers.

_Security usages.

▪️Detection of metal objects, armory, land mines, etc.

Advantages of inductive proximity sensors.

1. Contactless detection.

2. Environment adaptability; resistant to common conditions seen in industrial areas such as dust and dirt.

3. Capable and versatile in metal sensing.

4. Considerably cheap when it comes to price.

5. No moving parts, ensuring a longer service life.

Disadvantages of inductive proximity sensors.

1. Lack in detection range, averaging a max range of up to 80mm.

2. Can only detect metal objects.

3. Performance can be affected by external conditions; extreme temperatures,cutting fluids or chemicals.

2. Capacitive Proximity Sensors.

Capacitive proximity sensors are contactless sensors that detect both metallic and non-metallic objects, including liquid, powders, and granular. It operates by detecting a change in capacitance.

Similarly to inductive sensors, it consists of an oscillator, Schmitt trigger and output switching circuit. The only difference is it comprises of 2 charging plates (1 internal, 1 external) for capacitation:

▪️Internal plate connected to the oscillator.

▪️External plate (sensor electrodes) used as the sensing surface.

How do capacitive proximity sensors work?

1. Capacitive proximity sensor produces an electrostatic field.

2. When an object (conductive/non-conductive) approaches the sensing area, the capacitance of both plates increases, resulting in oscillator amplitude gain.

3. The resulted amplitude gain triggers sensor output switch.

*Note: Capacitive sensors only oscillate when the target object is present

🔸Common applications:

1. Industrial usages.

2. Production automation machines that count products, product transfers.

3. Filling processes, pipelines, inks, etc.

4. Fluid level, composition, and pressure.

5. Moisture control.

6. Non-invasive content detection.

7. Touch applications.

Advantages of Capacitive proximity sensors.

▪️Contactless detection.

▪️A wide array of materials able to be detected.

▪️Able to detect objects through non-metallic walls with its wide sensitivity band.

▪️Well-suited to be used in an industrial environment.

▪️Contains potentiometer that allows users to adjust sensor sensitivity, such that only wanted objects will be sensed.

▪️No moving parts, ensuring a longer service life.

Disadvantages of Capacitive proximity sensors.

1. Relative low range, though incremental increase from inductive sensors.

2. Higher price as compared to inductive sensors.

3. Ultrasonic Proximity Sensors.

ultrasonic proximity sensors, detecting the presence of objects through emitting high-frequency ultrasonic range. It does so through the conversion of electrical energy. Similarly to capacitive sensors, it can detect objects in solid, liquid, granular, or granular as well.

Probably the easiest among all, it only comprises an ultrasonic transmitter and an ultrasonic receiver.

How does Ultrasonic Proximity Sensor work?

1. The sonic transducer emits sonic waves.

2. Sonic waves bounces off the object.

3. The wave that bounced off is then returned to the sensor.

4. Time that it took to emit and receive sound waves is then used to determine distance/proximity.

Common applications.

▪️Distance measurement.

▪️Anemometers for wind speed and direction detection.

▪️Automation production processes.

▪️Fluid detection.

▪️Unmanned aerial vehicles (UAVs) for object monitoring.

▪️Robotics.

Advantages of ultrasonic proximity sensors.

▪️Contactless detection.

▪️Not affected by object color and transparency.

▪️Not affected by external environmental conditions, reliable solution.

▪️Works well in places with extreme conditions.

▪️Able to be used in dark environments.

▪️Low current consumption.

Disadvantages of an ultrasonic proximity sensors.

▪️Limited detection range though capable of higher range as compared to inductive and capacitive sensors.

▪️Doesn’t work in a vacuum since ultrasonic sensors operate via sound waves.

▪️Not able to measure the distance of Soft objects or ones with extreme textures.

4. IR Proximity Sensor.

IR, in short for infrared, detects the presence of an object by emitting a beam of infrared light. It works similarly to ultrasonic sensors, though instead of using sonic waves, IR is transmitted.

Infrared proximity sensors consist of an IR LED that emits, and a light detector for detection of reflection. It has an in-built signal processing circuit that determines an optical spot on the PSD.

How do IR proximity sensors work?

▪️Infrared light is emitted from the IR LED emitter.

▪️The beam of light hits the object and gets reflected back in an angle.

▪️The reflected light will reach the light detector.

▪️The sensor in the light detector determines the position/distance of reflective object.

Common applications.

▪️Distance measurement.

▪️Item counter; when object cuts the radiating light, it counts as one.

▪️Security systems such as surveillance, burglar alarms, etc.

▪️Monitoring and control applications.

▪️Advantages of IR proximity sensors.

▪️Contactless detection.

▪️Applicable for daytime and nighttime usages.

▪️Secured communication through a line of sight.

▪️Able to measure the distance to soft objects unlike ultrasound proximity sensors.

▪️Accuracy of the infrared sensor not affected by corrosion or oxidation.

Disadvantages of IR proximity sensors.

▪️Affected by environmental conditions and hard objects, implying inability fo usage through walls or doors.

▪️Requires line of sight between transmitter and receiver for communication.

▪️Performance dips over longer distances.

Reference:

“All about Proximity Sensors: Which type to use?”, seeedstudio

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