Proximity Sensors: definition, types, the future

A proximity sensor is a sensor used to detect the presence of nearby objects in a non-contact nature. These sensors then convert the information about presence or movement of an object into an electrical signal

Technical Definition and Meaning of Proximity Sensors

The essence of Proximity sensors is detecting the movement/presence of objects without physical contact and converting that data into an electrical signal. Therefore, all sensors that perform non-contact detection are included in the category of proximity sensors. Proximity sensors are also commonly referred to as “proximity switches” (by the Japanese Industrial Standards), and include all the sensors that non-contact detect objects within the general vicinity of the sensor.

The two main types of proximity sensors are Inductive and Capacitive. The first ones use the eddy currents, generated in metallic objects by electromagnetic induction, and the second ones detect changes in electrical capacity in both metallic and non-metallic objects when approaching them with the sensor.

There are other types of conventionally and commercially used proximity sensors as well, that may use magnets, reed switches, ultrasonic, photoelectric sensing, etc.

General Advantages and Features of Proximity Sensors

To further identify the specific added values of proximity sensors we ought to recognize their features and advantages. An honest heads-up is that the conventional users of these sensors chose them for their advantages over the traditional optical or contact sensors.

Contactless sensing

This gives vast opportunities on its own, as extensive amounts of contact sensors force compromised the design of the original applications – no contact usually means no design changes.

Additionally, as proximity sensors need no contact to affect service life (due to semiconductors usage) the general lifetime of these sensors is increased.

Relatively high resistance in physical environments

Unlike optical detection methods, proximity sensors are usually not affected by oily, dusty, or generally wet surroundings. On top of that, these sensors can be used in temperatures ranging from –40 to 200 °C.

Unaffected by surface conditions

Proximity sensors are not compromised by colors or other surface visuals conditions of the objects as main detected quantities are within the physical changes of the subject.

Response speed

Unlike contact-requiring switches, the proximity sensors offer `higher speed detection.

Proximity Sensor: Types and their characteristics

Let’s go ahead and do a quick deep-dive into the most commonly known and used proximity sensor types, to try and understand the current trends this market offers to satisfy the demand of the measurement needs. As it is known, the devil hides in plain sight: so with all the advantages and added values we went through – it is fair to also point out the potential downsides that the available proximity sensors will “offer”.

What is Inductive Proximity Sensor?

Inductive proximity sensors are used to detect metallic objects such as iron, copper, aluminum, brass, etc. These sensors essentially detect the loss of magnetic properties due to eddy currents generated on a conductive surface, by external magnetic fields.

These are composed of four main components: ferrite core with coils, oscillator, Schmitt Trigger, and output switching circuit. The operating principle is rather creative, yet not too complicated: first, an alternative current travels to the coil, which generates an electromagnetic field, so when a metallic object is close to the magnetic field – eddy current builds up and inductive changes are reflected through coils.

The inductive proximity sensor creates a symmetrical oscillating magnetic field even when a metallic object isn’t present, however, it is only triggered when the target metallic object appears in the vicinity.

Inductive proximity sensors are widely used in applications where metallic objects need to be detected, such as security-related applications, or product counting, sorting applications especially for automation purposes, however, these sensors have narrow limitations when it comes to further applications.

Disadvantages (limitations) of Inductive Proximity Sensors

Detecting only metallic objects, the length of the detection range, severe effects on performance by external objects such as other sensors, extreme temperatures, chemicals and physically unstable harsh environments. Unfortunately, these drawbacks are sufficient deal breakers for most applications, whether considering the shielded or unshielded versions of these sensors.

Capacitive

The next widely used type of proximity sensor is the capacitive type sensor: these detect metallic and non-metallic objects alike (i. e. liquids, resins, powders, etc.). Fundamentally capacitive sensors detect the capacitance (the ratio of the amount of electric charge stored on a conductor to a difference in electric potential) in between the sensing object and the sensor.

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 (like inductive sensors, these plates are linked to an oscillator, a Schmitt trigger, and an output amplifier).

Due to the advantages over the inductive proximity sensors – the capacitive sensors have a wider range of applications too: moisture control, non-destructive sensing, as well as generally wide acceptance within industrial applications, due to production automation, fluid level/composi­tion/pressure detection, etc.

These also have lawyer current consumption than the inductive type proximity sensors and are resistant to the higher pressure of the physical environment, however, being better than the inductive type, unfortunately, doesn’t remove the limitations as such – the same drawbacks connected to law range of sensing, and in addition, the above mentioned improvements come with a higher price in comparison.

There are also higher range proximity sensors like Ultrasound, IR, Photoelectric etc. To showcase some of their specific characteristics let’s start with the IR Proximity Sensors.

IR Proximity Sensor

IR (infrared), is a sensor that emits a beam of infrared light through which it detects the presence of an object. Infrared proximity sensors consist of an infrared emitting LED and a light detector that essentially detects the reflection (this happens through the signal processing circuit that identifies the optical spot on PSD).

Working principle: Infrared light is emitted from the IR LED emitter, The beam of light hits the object and gets reflected back into an angle, the reflected light will reach the light detector, the sensor in the light detector determines the position/distance of the reflective object.

Some common applications of IR proximity sensors are:

• distance measurement,
• providing a count, when the objects cut the radiating light – it counts as one,
• security systems such as surveillance, burglar alarms, etc.,
• monitoring and control applications.

It is surely advantageous to use these sensors, especially because of the contactless detection, daytime and nighttime usability, distance measurements of soft objects (unlike ultrasound proximity sensors), no effects of corrosion or oxidation on the accuracy, and many more features. At the same time, there are considerable disadvantages of these systems too, that serve as dealbreakers for applications with diverse measurement demands.

Main Disadvantages of IR Proximity Sensors

• affected by environmental conditions – inability to detect through physical obstacles (doors, walls, dust, etc.);
• requires clear visibility between transmitter and receiver to ensure detection and communication;
• performance is compromised over longer distances.

Ultrasonic proximity sensors

Another honorable mention is the ultrasonic proximity sensors. These detect the presence of objects through the emission of high-frequency ultrasonic ranges, which happens through conversion of electric energy.

Working principle is following:

• the sonic transducer emits sonic waves;
• the waves then “bounce” off of the object;
• the wave returns back to the sensor;
• the distance or the proximity is identified as per the time it took to send and receive the bounced sonic wave.

The most common applications are:

• distance measurement;
• automation production processes;
• fluid detection, etc.

Ultrasonic Proximity Sensors as well give opportunities of contactless detection, without being affected by object color and transparency, aren’t compromised by places with extreme conditions and even detect in dark environments with low current consumption.

Disadvantages of Ultrasonic Proximity Sensors

are vital red flags for many use cases. These can be the Limited detection range (comes up especially in comparison to inductive and capacitive sensors); Doesn’t work in a vacuum (due to the sound waves, essential for the detection); not able to measure the distance of objects with extreme textures (as the sound waves are effected and too complicated to capture).

Future of Proximity Sensing: what is on the horizon?

The companies in need of proximity sensing, meaning a contactless system that will easily provide reliable data – have gradually increased awareness of the competitive advantage a better though through non-destructive system grants.

Unfortunately, in many cases, the companies have to combine multiple of the above-mentioned systems, spend a round sum to engineer and set up the combined system in the physical space as well as ensure communication into the software, test the system, and develop additional maintenance activities to ensure the quality of the engineered measurement system is always working.

For instance, a company that requires detection of a subject as well as real-time precise data of temperature – may need to choose IR and Capacitive Proximity sensors to ensure one of these sensors “covers” for the drawbacks of the other. And even in this case – should the environment be dusty – the temperature data will be compromised.

To be fair – we also need to take into account the costs coming with the power consumption, setting up and maintenance of this system – making it hard for the company to take the risk, and as a lot of their competitors, they chose to proceed blindly, leaving the hope of reactive maintenance strategies.

This surely is nothing short of unsustainable ways of things, and the Proximity Sensor market is a vital body that is more needed to react. This can come in the form of R&D , AI, and through sponsorship of EU, Governments, and unions of individual countries, as well as international corporations – the proximity sensor market is to step up and give this matter the deserved attention.

Our approach (contactless measurements)

We at RVmagnetics truly believe that science, size, accuracy, and versatility matter. Fundamentally a Research & Development company, we introduce to the market our own MicroWire sensors to provide Proximity Sensing with one system that covers multiple measurements, as well as overcomes the current Proximity Sensing flows, which have negatively affected user decisions about data thus far.

Our system is custom developed based on the exact use case our customers are challenged with. Based on the local physical environment, the required resolution, sensitivity, physical quantities, and other KPIs defined by the client – we aim to customize a Proof of Concept, a Prototype – and finally launch the perfectly adjusted MicroWire sensor(s) with the sensing head, and the customized software accordingly.

With our solutions – the clients can collect massive local data(due to the sensing frequency of up to 10.000×/sec) which can be fed to software to enable AI, Machine Learning, Predictive Maintenance, etc.

Surely our system is aimed for the specific demand looking to integrate an economic advantage – a huge added value over their current available system, and naturally, over the competition. With this in mind, however, it is important to notice that MicroWire sensors are fairly inexpensive to produce (from a gram of metallic alloy up to a kilometer of sensors), and even with the electronics – the final price/unit of our sensor solutions are largely competitive, to say the least.

This is why we believe that the urge to boost the proximity sensor market with our – more versatile solution is an obvious benefit for the market players, from consumer goods in international volumes all the way to industrial “precision applications”.