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How 13 Smart Home Sensors Work

How 13 Smart Home Sensors Work


"Forbes" magazine: At present, and even in the next few decades, among the top 10 technological products that affect and change the world's economic structure and people's lifestyle, sensors are listed as the top 10 technological products, indicating that the spring of sensors has come!

The Internet of Things is a huge network formed by combining various information sensing devices and the Internet. The development of the Internet of Things requires technical support such as intelligent perception, identification and communication, and the key to perception is sensors and related technologies. The smart home control system is the "heart", and the sensor is the "context" of the entire control system, mastering the "central nervous system" of the entire system. The development of sensor technology plays an important role in the rapid development of smart homes.

From the perspective of the industrial chain, the upstream of the sensor is mainly various components to support the perception layer; the midstream is the transmission layer composed of optical transmission, communication equipment, network equipment, etc.; It is mainly based on applications, of which smart home is one of the extremely important sectors.

Smart home sensors are the "eyes, noses and ears" in the home, because the smart home is inseparable from the "humanized" data collection of the living environment, that is to say, the various physical quantities, chemical quantities, and biomass in the home environment are converted into Measurable electrical signaling devices and components.

The smart home field requires the use of sensors to measure, analyze and control system settings. The smart devices used in the home involve technologies such as position sensors, proximity sensors, liquid level sensors, flow and speed control, environmental monitoring, and security sensing.

Principles of home consumer sensor equipment

Temperature Sensor

The temperature sensor converts the temperature into a usable output signal by using the laws of various physical properties of substances changing with temperature. The temperature sensor is the core part of the temperature measuring instrument, and there are many varieties. According to the measurement method, it can be divided into two categories: contact type and non-contact type. According to the characteristics of sensor materials and electronic components, it can be divided into two categories: thermal resistance and thermocouple.

Although there are many types of temperature sensors, the general principle is to sense the change of temperature, so that the resistance of sensitive components such as thermistor, thermocouple, etc. changes, so that the output voltage changes in the circuit.

Two conductors of different compositions (called thermocouple wires or thermodes) are connected to form a loop at both ends. When the temperature of the two junctions is different, an electromotive force will be generated in the loop. This phenomenon is called the thermoelectric effect. This electromotive force is called thermoelectric potential. Thermocouples use this principle to measure temperature. One end that is directly used to measure the temperature of the medium is called the working end, also known as the measuring end, and the other end is called the cold end, also known as the compensation end; the cold end is connected to the display instrument or supporting instrument, The display meter will indicate the thermoelectric potential generated by the thermocouple.

Humidity Sensor

In the control of smart home, the control of humidity can improve the quality of life of users and provide users with a good living environment. In the humidity control of smart homes, humidity control is mainly achieved through humidity sensors.

The humidity sensor can display the specific changes of air humidity. Inside the integrated system, there are humidity sensors and amplifier circuits, which can convert the humidity information into voltage signals and transmit them to the computer system. humidifier.

Temperature and humidity sensor

In the control of smart home, the control of thermometer and humidity is an important indicator of environmental control, but only controlling a single indicator will waste more resources and prolong the calculation time, which needs to be analyzed by computer synthesis. Therefore, it is necessary to explore new sensor application methods.

The temperature and humidity sensor can realize the simultaneous adjustment of temperature and humidity, which is in line with the concept of smart home, and has the characteristics of small size and low power consumption. The temperature and humidity sensor is used to control the indoor temperature and humidity. The sensor chip can collect temperature and humidity information at the same time, calculate the two physical variables separately in an independent system, and convert them into electrical signals and transmit them to the corresponding control terminals to realize smart home. control purpose.

Visible light sensor: a component that converts the intensity change of visible light into a current or voltage change, and a photoelectric sensor is a sensor that uses a photoelectric element as a detection element. It first converts the measured changes into changes in optical signals, and then further converts the optical signals into electrical signals with the help of photoelectric elements. Photoelectric sensors are generally composed of three parts: light source, optical path and photoelectric element.

sound sensor

The principle of the sound sensor is very simple, mainly using an electric microphone with a frequency response similar to the human ear. The circuit amplifies the signal and transmits the signal to the telecommunication interface. The sound sensor acts as a microphone. It is used to receive sound waves and display the vibrating image of the sound. But the intensity of the noise cannot be measured.

In fact, the signal is sent to the data collector on 2 different lines. The sound sensor incorporates a sound-sensitive condenser electret microphone. The sound waves vibrate the electret film inside the microphone, causing a change in capacitance and a tiny voltage corresponding to the change. This voltage is then converted into a voltage of 0-5V, accepted by the data collector through A/D conversion, and transmitted to the computer.

gas sensor

Gas sensors can be used to measure the type, concentration and composition of gas, and can detect specific components in the gas and convert the component parameters into electrical signals. Also called gas sensor. It mainly includes semiconductor gas sensors, contact combustion gas sensors and electrochemical gas sensors, among which semiconductor gas sensors are the most used.

Gas sensors include electrochemical gas sensors, catalytic combustion gas sensors, semiconductor gas sensors, infrared gas sensors, and photoionization gas sensors, which can detect toxic gases (formaldehyde, CO2, CO, etc.), combustible gases (natural gas CH4), volatile organic compounds ( VOCs).

The specific principle is that the wave speed and frequency on the surface of the acoustic wave device will drift with the change of the external environment. The gas sensor uses this property to coat a gas-sensitive film on the surface of the piezoelectric crystal that selectively adsorbs a certain gas. When the gas-sensitive film interacts with the gas to be measured (chemical or biological action, or physical adsorption), When the film quality and conductivity of the gas-sensitive film change, the frequency of the surface acoustic wave of the piezoelectric crystal will drift; the gas concentration is different, and the degree of change in the film quality and conductivity is also different, that is, the frequency of the surface acoustic wave is changed. Also different. By measuring the change of the surface acoustic wave frequency, the accurate change value of the reaction gas concentration can be obtained.

The parameters of the gas sensor mainly include heating voltage, current, measurement loop voltage, sensitivity, response time, recovery time, voltage in the calibration gas (0.1% butane gas), load resistance value, etc.

The principle of air quality sensor

chemical principles

The polluted gas in the air is attached to the surface of the metal oxide, and the resistance of the metal oxide becomes lower, and the change of the resistance value is related to the concentration of the polluted gas. The metal oxide material of the air quality sensor is different from the working temperature. The metal oxide of this sensor is oxidized It has poor chemical selectivity and reacts to many polluting gases (formaldehyde, benzene, ammonia, cigarette smoke, perfume), and uses this comprehensive reaction to characterize air quality.

Infrared principle

Infrared gas sensor is a kind of gas sensing device based on the selective absorption characteristics of the near-infrared spectrum of different gas molecules, using the relationship between gas concentration and absorption intensity (Lambert-Beer law) to identify gas components and determine their concentration. When the infrared wavelength matches the absorption spectrum of the gas being measured, the infrared energy is absorbed. The attenuation of infrared light intensity after passing through the gas to be measured satisfies the Lambert-Beer law.

The greater the gas concentration, the greater the attenuation of light. Therefore, gas concentration can be measured by measuring the attenuation of infrared light by the gas. In order to ensure a linear relationship between the readings, when the concentration of the component to be measured is large, the measuring chamber of the analyzer is shorter, and the shortest is 0.3mm; when the concentration is low, the measuring chamber is longer, and the longest is >200mm. The light energy remaining after absorption is detected by an infrared detector.

Laser particle sensor

The photoelectric converter is converted into an electrical signal to measure the amount of particulate matter, which is more accurate than other ordinary infrared measurements, and can measure indoor PM2.5, PM1.0, and PM10 data in real time.

Water immersion sensor

The water immersion sensor is based on the principle of liquid conduction. The electrode is used to detect whether there is water, and then the sensor is converted into a dry contact output. Based on the principle of liquid conduction, the electrode is used to detect whether there is water, and then the sensor is converted into a dry contact output, which has two output states: normally open and normally closed.

Immersion sensors are divided into contact water immersion detectors and non-contact water immersion detectors.

Contact water immersion detector, using the principle of liquid conduction for detection. Normally, the two-pole probe is insulated by air; in the state of immersion in water, the probe is turned on, and the sensor outputs a dry contact signal. When the probe is immersed in water at a height of about 1 mm, an alarm signal is generated.

The non-contact water immersion detector uses the principle of refraction and reflection of light in different medium sections for detection. LEDs and photoelectric receivers are placed in the plastic hemisphere. When the detector is placed in the air, most of the LED photons are received by the photoelectric receiver due to total reflection; The incoming LED photons will be reduced, and thus the output will change. Suitable for deployment in general corrosive conductive liquid leakage locations.

door sensor

The wireless door sensor is composed of a wireless transmitter module and a magnetic block. There is a "steel reed pipe" component at the two arrows in the wireless transmitter module. When the distance between the magnet and the steel reed pipe is kept within 1.5 cm , the steel reed pipe is in the disconnected state, once the separation distance between the magnet and the steel reed pipe exceeds 1.5 cm, the steel reed pipe will be closed, causing a short circuit, and the alarm indicator light will be on and an alarm signal will be sent to the host. The wireless alarm signal of the wireless door sensor can transmit 200 meters in the open area and 20 meters in the general residence, which is closely related to the surrounding environment.

Image Sensor

In the smart home, the image sensor is also one of the important application components. Mainly because in modern construction, it is necessary to use monitoring equipment to achieve internal monitoring and monitoring of the surrounding residential areas. In traditional monitoring methods, cameras are mainly used for monitoring, and information cannot be transmitted to users. Destruction will cause the user to bear greater losses.

In the smart home system, through the monitoring of the PC, the information can be sent to the user's mobile phone or computer to realize remote monitoring. In the smart monitoring, the image sensor can be used for photoelectric conversion, which is mainly composed of CCD and CMOS sensors. composition, through which digital cameras can be made to achieve full control over the smart home.

Infrared sensor

The infrared sensor is based on the principle of infrared reflection. When a certain part of the human body is in the infrared region, the infrared light emitted by the infrared transmitting tube is reflected to the infrared receiving tube due to the human body blocking, and the signal is sent to the pulse solenoid valve through the integrated circuit, and the solenoid valve receives the signal. Then control the spool according to the specified command.

The infrared sensor includes three parts: optical system, detection element and conversion circuit. Optical systems can be divided into transmission type and reflection type according to different structures. The detection element can be divided into thermal detection element and photoelectric detection element according to the working principle. The most common thermal detection element is the thermistor. When the thermistor is exposed to infrared radiation, the temperature rises, and the resistance changes, which is converted into an electrical signal output through the conversion circuit.

smoke sensor

Fire prevention is achieved by monitoring the concentration of smoke. The interior of the smoke alarm adopts ionic smoke sensing. The ionic smoke sensor is an advanced technology, stable and reliable sensor, and is widely used in various fire alarm systems. Much better than gas-sensing resistance fire alarms.

human presence sensor

Using the law of black body radiation, that is, all objects above absolute zero are constantly radiating energy outward, and the magnitude of the outward radiated energy of an object and its distribution by wavelength are closely related to its surface temperature. The higher the temperature, the more powerful the infrared radiation emitted. To quickly and reliably detect the human body entering the effective area, the sensor fully supports mainstream communication protocols to achieve the effect of equipment linkage, which can be widely used in smart buildings, hotels, energy conservation and emission reduction and smart home security monitoring.

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