Sensors are complex devices often used to detect and respond to electrical or optical signals. The device converts a physical parameter (temperature, blood pressure, humidity, speed) into a signal that can be measured by the device.
Classification of sensors in this case may be different. There are several basic parameters for the distribution of measuring devices, which will be discussed further. Basically, this separation is due to the action of various forces.
This is easy to explain using temperature measurement as an example. Mercury in a glass thermometer expands and compresses the liquid to convert the measured temperature, which can be read by an observer from a calibrated glass tube.
Selection criteria
There are certain features to consider when classifying a sensor. They are listed below:
- Accuracy.
- Environmental conditions - usually sensors have limitations in temperature, humidity.
- Range - limitsensor measurements.
- Calibration - required for most measuring instruments as readings change over time.
- Cost.
- Repeatability - Variable readings are measured repeatedly in the same environment.
Distribution by category
Sensor classifications are divided into the following categories:
- Primary input number of parameters.
- Principles of transduction (using physical and chemical effects).
- Material and technology.
- Destination.
The principle of transduction is a fundamental criterion followed for effective information gathering. Typically, logistical criteria are selected by the development team.
Classification of sensors based on properties is distributed as follows:
- Temperature: thermistors, thermocouples, resistance thermometers, microcircuits.
- Pressure: Fiber Optic, Vacuum, Flexible Fluid Gauges, LVDT, Electronic.
- Flow: electromagnetic, differential pressure, positional displacement, thermal mass.
- Level sensors: differential pressure, ultrasonic radio frequency, radar, thermal displacement.
- Proximity and displacement: LVDT, photovoltaic, capacitive, magnetic, ultrasonic.
- Biosensors: resonant mirror, electrochemical, surface plasmon resonance, light-addressable potentiometric.
- Image: CCD, CMOS.
- Gas and chemistry: semiconductor, infrared, conduction, electrochemical.
- Acceleration: gyroscopes, accelerometers.
- Others: humidity sensor, speed sensor, mass, tilt sensor, force, viscosity.
This is a large group of subsections. It is noteworthy that with the discovery of new technologies, the sections are constantly replenished.
Assignment of sensor classification based on direction of use:
- Control, measurement and automation of the production process.
- Non-industrial use: aviation, medical devices, automobiles, consumer electronics.
Sensors can be classified according to power requirements:
- Active sensor - devices that require power. For example, LiDAR (light detection and rangefinder), photoconductive cell.
- Passive sensor - sensors that do not require power. For example, radiometers, film photography.
These two sections include all devices known to science.
In current applications, the assignment of sensor classification can be grouped as follows:
- Accelerometers - based on microelectromechanical sensor technology. They are used to monitor patients who turn on pacemakers. and vehicle dynamics.
- Biosensors - based on electrochemical technology. Used to test food, medical devices, water, and detect dangerous biological pathogens.
- Image sensors - based on CMOS technology. They are used in consumer electronics, biometrics, traffic monitoringtraffic and security, as well as computer images.
- Motion detectors - based on infrared, ultrasonic and microwave/radar technologies. Used in video games and simulations, light activation and security detection.
Sensor Types
There is also a main group. It is divided into six main areas:
- Temperature.
- Infrared.
- Ultraviolet.
- Sensor.
- Approach, movement.
- Ultrasound.
Each group may include subsections, if the technology is even partially used as part of a particular device.
1. Temperature sensors
This is one of the main groups. The classification of temperature sensors unites all devices that have the ability to evaluate parameters based on the heating or cooling of a particular type of substance or material.
This device collects temperature information from a source and converts it into a form that other equipment or people can understand. The best illustration of a temperature sensor is mercury in a glass thermometer. Mercury in glass expands and contracts with changes in temperature. The outdoor temperature is the starting element for measuring the indicator. The position of the mercury is observed by the viewer to measure the parameter. There are two main types of temperature sensors:
- Contact sensors. This type of device requires direct physical contact with the object or carrier. They are in controltemperature of solids, liquids and gases over a wide temperature range.
- Proximity sensors. This type of sensor does not require any physical contact with the measured object or medium. They control non-reflective solids and liquids, but are useless for gases due to their natural transparency. These instruments use Planck's law to measure temperature. This law concerns the heat emitted by the source to measure the benchmark.
Work with various devices
The principle of operation and classification of temperature sensors are divided into use of technology in other types of equipment. These can be dashboards in a car and special production units in an industrial shop.
- Thermocouple - modules are made of two wires (each - from different homogeneous alloys or metals), which form a measuring transition by connecting at one end. This measuring unit is open to the studied elements. The other end of the wire ends with a measuring device where a reference junction is formed. Current flows through the circuit because the temperatures of the two junctions are different. The resulting millivolt voltage is measured to determine the temperature at the junction.
- Resistance Temperature Detectors (RTDs) are types of thermistors that are made to measure electrical resistance as temperature changes. They are more expensive than any other temperature detection devices.
- Thermistors. They are another type of thermal resistor in which a largechange in resistance is proportional to a small change in temperature.
2. IR sensor
This device emits or detects infrared radiation to detect a specific phase in the environment. As a rule, thermal radiation is emitted by all objects in the infrared spectrum. This sensor detects the type of source that is not visible to the human eye.
The basic idea is to use infrared LEDs to transmit light waves to an object. Another IR diode of the same type should be used to detect the reflected wave from the object.
Operation principle
Classification of sensors in the automation system in this direction is common. This is due to the fact that the technology makes it possible to use additional tools for assessing external parameters. When an infrared receiver is exposed to infrared light, a voltage difference develops across the wires. The electrical properties of the IR sensor components can be used to measure the distance to an object. When an infrared receiver is exposed to light, a potential difference occurs across the wires.
Where applicable:
- Thermography: According to the law of radiation of objects, it is possible to observe the environment with or without visible light using this technology.
- Heating: Infrared can be used to cook and reheat food. They can remove ice from aircraft wings. Converters are popular in industrialfields such as printing, plastic molding and polymer welding.
- Spectroscopy: This technique is used to identify molecules by analyzing constituent bonds. The technology uses light radiation to study organic compounds.
- Meteorology: measure the height of clouds, calculate the temperature of the earth and the surface is possible if meteorological satellites are equipped with scanning radiometers.
- Photobiomodulation: used for chemotherapy in cancer patients. Additionally, the technology is being used to treat the herpes virus.
- Climatology: monitoring the exchange of energy between the atmosphere and the earth.
- Communication: An infrared laser provides light for optical fiber communication. These emissions are also used for short distance communication between mobile and computer peripherals.
3. UV sensor
These sensors measure the intensity or power of incident ultraviolet radiation. A form of electromagnetic radiation has a longer wavelength than X-rays, but is still shorter than visible radiation.
An active material known as polycrystalline diamond is used to reliably measure ultraviolet. Instruments can detect various environmental impacts.
Device selection criteria:
- Wavelength ranges in nanometers (nm) that can be detected by ultraviolet sensors.
- Operating temperature.
- Accuracy.
- Weight.
- Rangepower.
Operation principle
An ultraviolet sensor receives one type of energy signal and transmits another type of signal. To observe and record these output streams, they are sent to an electric meter. To create graphs and reports, the readings are transferred to an analog-to-digital converter (ADC) and then to a computer with software.
Used in the following appliances:
- UV phototubes are radiation-sensitive sensors that monitor UV air treatment, UV water treatment and solar exposure.
- Light sensors - measure the intensity of the incident beam.
- UV Spectrum Sensors are charge-coupled devices (CCDs) used in laboratory imaging.
- UV light detectors.
- UV germicidal detectors.
- Photostability sensors.
4. Touch sensor
This is another large group of devices. The classification of pressure sensors is used to assess the external parameters responsible for the appearance of additional characteristics under the action of a certain object or substance.
The touch sensor acts like a variable resistor according to where it is connected.
Touch sensor consists of:
- A fully conductive material such as copper.
- Insulated intermediate material such as foam or plastic.
- Partly conductive material.
At the same time, there is no strict separation. The classification of pressure sensors is established by selecting a specific sensor, which evaluates the emerging voltage inside or outside the object under study.
Operation principle
The partially conductive material opposes the flow of current. The principle of the linear encoder is that the current flow is considered to be more opposite when the length of the material through which the current is to pass is longer. As a result, the material's resistance changes by changing the position in which it comes into contact with a fully conductive object.
Classification of automation sensors is based entirely on the described principle. Here, additional resources are involved in the form of specially developed software. Typically, software is associated with touch sensors. Devices can remember "last touch" when the sensor is disabled. They can register the "first touch" as soon as the sensor is activated and understand all the meanings associated with it. This action is similar to moving a computer mouse to the other end of the mouse pad to move the cursor to the far side of the screen.
5. Proximity sensor
Increasingly, modern vehicles use this technology. The classification of electrical sensors using light and sensor modules is gaining popularity with automotive manufacturers.
Proximity sensor detects the presence of objects that are almost without anypoints of contact. Since there is no contact between the modules and the perceived object and no mechanical parts, these devices have a long service life and high reliability.
Different types of proximity sensors:
- Inductive proximity sensors.
- Capacitive proximity sensors.
- Ultrasonic proximity sensors.
- Photoelectric sensors.
- Hall sensors.
Operation principle
The proximity sensor emits an electromagnetic or electrostatic field or a beam of electromagnetic radiation (such as infrared) and waits for a response signal or changes in the field. The object being detected is known as the target of the registration module.
Classification of sensors according to the principle of operation and purpose will be as follows:
- Inductive devices: there is an oscillator at the input that changes the loss resistance to the proximity of an electrically conductive medium. These devices are preferred for metal objects.
- Capacitive Proximity Sensors: These convert the change in electrostatic capacitance between the detection electrodes and ground. This occurs when approaching a nearby object with a change in the oscillation frequency. To detect a nearby object, the oscillation frequency is converted into a DC voltage, which is compared to a predetermined threshold. These fixtures are preferred for plastic objects.
The classification of measuring equipment and sensors is not limited to the above description and parameters. With the adventnew types of measuring instruments, the total group is increasing. Various definitions have been approved to distinguish between sensors and transducers. Sensors can be defined as an element that senses energy in order to produce a variant in the same or a different form of energy. The sensor converts the measured value into the desired output signal using the conversion principle.
Based on the received and created signals, the principle can be divided into the following groups: electrical, mechanical, thermal, chemical, radiant and magnetic.
6. Ultrasonic sensors
The ultrasonic sensor is used to detect the presence of an object. This is achieved by emitting ultrasonic waves from the head of the device and then receiving the reflected ultrasonic signal from the corresponding object. This helps in detecting the position, presence and movement of objects.
Because ultrasonic sensors rely on sound rather than light for detection, they are widely used in water level measurement, medical scanning procedures and in the automotive industry. Ultrasonic waves can detect invisible objects such as transparencies, glass bottles, plastic bottles and sheet glass with their reflective sensors.
Operation principle
Classification of inductive sensors is based on the scope of their use. Here it is important to take into account the physical and chemical properties of objects. The movement of ultrasonic waves differs depending on the shape and type of medium. For example, ultrasonic waves travel straight through a homogeneous medium and are reflected and transmitted back to the boundary between different media. The human body in the air causes significant reflection and can be easily detected.
The technology uses the following principles:
- Multioreflection. Multiple reflection occurs when waves are reflected more than once between the sensor and the target.
- Limit zone. The minimum sensing distance and the maximum sensing distance can be adjusted. This is called the limit zone.
- Detection zone. This is the interval between the surface of the sensor head and the minimum detection distance obtained by adjusting the scan distance.
Devices equipped with this technology can scan various types of objects. Ultrasonic sources are actively used in the creation of vehicles.
