What is Smoke Detector?

Ⅰ. What is Smoke Detector?

One day at 7:46 in the morning, the G63 high-speed train from Jinan to Wenzhou ran smoothly on the track, but after a while, some passengers noticed that the train was slowing down, "The speed dropped from more than 200 kilometers per hour to more than 100 kilometers per hour. ." Mr. Chen who was in the car said so. Later, after investigation, it turned out that a passenger smoking in the toilet in the carriage caused the train to slow down.

Smoke detectors, or we can call smoke sensors, are frequently found in automobiles, trains, and airplanes. If the smoke sensor detects the presence of smoke while moving trains and trains, it will transmit an alarm signal to the cab for the first time. At the same time, the train's in-car control system will limit or even stop the train's speed. The event that led to the circumstance.

The smoke sensor detects whether or not there is smoke in the environment, as well as the concentration of smoke, such as sensing intense smoke during a fire. When the smoke probe comes into contact with smoke or another gas, its internal resistance changes, and an analog value is created to regulate it. To provide the corresponding analog signal of the smoke concentration to the host, the smoke sensor exploits the idea that the concentration of smoke (primarily combustible particles) affects the resistance value of the smoke-sensitive element.

Ⅱ. The Types of Smoke Detector

Smoke sensors mainly include ionized smoke sensors, photoelectric smoke sensors, and gas-sensitive smoke sensors.

Ionic smoke sensor

Inside the smoke alarm is an ionization smoke sensor. The ionized smoke sensor is a type of sensor that has sophisticated technology and operates in a steady and dependable manner. It is widely utilized in various fire alarm systems.

The inner and outer ionization chambers each have a radioactive source of americium 241, and the positive and negative ions created by ionization migrate to the positive and negative electrodes, respectively, under the force of the electric field. The current and voltage of the inner and outer ionization chambers are steady under typical conditions. Outside the ionization chamber, smoke begins to escape. Because the current and voltage are disrupted by interfering with the normal movement of charged particles, the balance between the internal and external ionization chambers is disrupted, so the wireless transmitter sends out a wireless alarm signal to notify the remote receiving host to transmit the alarm information. 

After ionization of uncharged particles, this type of detector creates charged particles (ions), hence the name "ion-type" smoke detector.

A DC voltage modulates the air between the electrodes, which is generated by the radiation source to form ions and generate electric current. The current signal weakens when the smoke particles connect to the ions, and this signal change is proportional to the number of smoke particles. The ion detector is effective at detecting open fires.

Photoelectric smoke sensor

The photoelectric smoke alarm, which is equipped with an infrared pair tube, has an optical labyrinth. The infrared receiving tube cannot receive the infrared light emitted by the infrared emitting tube when there is no smoke. The receiving tube receives infrared light through refraction and reflection when smoke enters the optical labyrinth. When the intelligent alarm circuit detects light, it determines whether the threshold has been exceeded, and if it has, an alert is triggered.

Photoelectric smoke detectors can be divided into dimming type and scattered light type:

1. Dimming photoelectric smoke detector

The detector's detection chamber is outfitted with light-emitting and light-receiving components. The light-receiving device receives a certain amount of light emitted by the light-emitting device under normal circumstances; however, when there is smoke, the light emitted by the light-emitting device is blocked by the smoke, reducing the amount of light received by the light-receiving device, the photocurrent, and the detector sending an alarm signal.

2. Scattered light photoelectric smoke detector

Light-emitting and light-receiving devices are also included in the detector's detecting chamber. The light-receiving device cannot receive the light emitted by the light-emitting device in normal circumstances, hence no photocurrent is generated. When smoke enters the detection room during a fire, the light emitted by the light-emitting device is diffused due to the effect of smoke particles. The light-receiving device receives this dispersed light, which modifies the impedance of the device and generates a photocurrent. The task of transforming smoke signals into electrical signals has been completed. The detector receives the signals and determines whether or not an alert signal is required.

This type of sensor has an optical sensor built into the interior structure (detection cavity) (transmitting light source and photoelectric receiver). When smoke enters the sensing cavity, it blocks light emission and causes scattering, and the photoelectric receiver receives the signal that changes as a result of the light scattering. After that, make a change to the present signal.

Gas-sensitive smoke sensor

A gas sensor is a device that detects the presence of a certain gas. The most common types of gas sensors are semiconductor gas sensors, contact combustion type gas sensors, and electrochemical gas sensors, with semiconductor gas sensors being the most common. Carbon monoxide gas detection, gas gas detection, gas detection, freon (R11, R12) detection, ethanol detection in breath, human oral malodor detection, and other applications are among them.

It translates information about the kind of gas and its concentration into electrical impulses. Information about the presence of the gas to be measured in the environment can be obtained based on the strength of these electrical signals, allowing it to be detected, monitored, and alarmed; it can be combined with an interface circuit and a computer to form an automatic detection, control, and alarm system.

Among them, the gas sensor has the following types:

1. Range hoods, leak alarms, and air cleaners all use the combustible gas sensor, which contains various alkane and organic vapor (VOC) gases.

2. Carbon monoxide gas sensor, which may be utilized in industrial production, environmental protection, autos, homes, and other carbon monoxide leakage and incomplete combustion detection and warning applications.

3. Oxygen sensors are a type of sensor that detects the presence of oxygen. In the domains of environmental protection, medicinal treatment, metallurgy, and transportation, oxygen sensors are widely employed and in high demand.

4. Toxic gas sensors are mostly used to detect pollutants such as flue gas, exhaust gas, and exhaust gas in the environment.

The MQ-2 gas sensor is a common model of gas-sensitive smoke sensor. The sensor is commonly used in gas leak detection equipment in homes and companies, and it can detect liquefied gas, butane, propane, methane, alcohol, hydrogen, smoke, and other gases.

Ⅲ. Comparison between Smoke Detectors

Comparison of Ionic Smoke Sensor and Photosensitive Smoke Sensor

Forward-facing photoelectric smoke alarms are more sensitive to larger smoke particles and have poor response to gray and black smoke. Ionic smoke alarms are more sensitive to microscopic smoke particles and respond to diverse smoke energies in a balanced manner. some. There are more microscopic particles of smoke in the air when a fire is blazing, and there are more smoke particles that are slightly larger in the air when it is smoldering.

The ion smoke alarm will sound before the photoelectric smoke alarm if a large amount of small smoke particles are created following a fire. Although there is a short time difference between these two types of smoke alarms, this form of fire spreads swiftly. In such areas, it is preferable to install ionization smoke alarms. A huge number of somewhat larger smoke particles are formed after another sort of smoldering fire occurs. Ionizing smoke alarms will sound before photoelectric smoke alarms. Photoelectric smoke alarms should be installed in such areas.

Comparison of Gas-Sensitive Smoke Detector and Ion-Type Smoke Detector

Smoke from a fire is a mixture of gas, liquid, and solid particles with volume, mass, temperature, and electric charge. Ion-type smoke detectors detect smoke particles by measuring voltage changes induced by an ionization chamber, which functions as a smoke-sensitive resistor. The ionization state of the air in the ionization chamber is changed when smoke particles enter it, and the macroscopic appearance is that the equivalent resistance of the ionization chamber increases and the voltage across the ionization chamber increases, determining the smoke condition in the air.

The gas sensor detects specific combustible gas components in the air, therefore its performance in terms of fire detection is inferior to that of the ion sensor. Detect the presence of flammable gas in the atmosphere. Detect the presence of various combustible gases, such as coal gas, liquefied petroleum gas, natural gas, carbon monoxide, and so on. It is appropriate for industrial companies such as petroleum, chemical industry, coal, electric power, metallurgy, electronics, and other areas where combustible gases are produced and stored, as well as gas plants, liquefied petroleum gas stations, hydrogen stations, and other places.

Ⅳ. The Applications of Smoke Detector

Application of smoke sensor in fire prevention networked system

To work consistently and dependably, the networked smoke alarm uses a photoelectric or ion-type smoke sensor, and its performance is significantly superior to that of gas-sensitive resistance fire alarms. The networked smoke alarm can be used to detect smoke from a variety of early fires. The product is compact and can combine wireless communication with fire smoke sensors in a natural way. Hotels, warehouses, hotels, restaurants, hostels, industries, oil field well teams, mobile dwellings, and other public areas employ networked smoke alarms.

It is possible to utilize the networked smoke alarm on its own. Install the mounting base on the ceiling of the room to be monitored, then connect the battery to the alarm and screw it into the mounting base. When the smoke concentration and duration of the preventive space reach the alert value in the working state, the buzzer will immediately sound an alarm. When a networked smoke alarm is combined with a wireless anti-theft alarm system, the installation and operation are identical to when the two systems are used separately.

When a networked smoke alarm goes off, it sends a wireless signal to the wireless anti-theft alarm host. Regardless of whether the alarm is armed or disarmed, the alarm host will respond to it. As a result, the alarm range is expanded, and the fire alarm can be detected even when no one is home, allowing for immediate response.

The application of smoke sensor in hotel fire automatic alarm system

Domestic and international tourists can stay, eat, and hold various meetings and banquets at the hotel. The majority of modern hotels are multi-functional and comprehensive. They combine food, lodging, entertainment, and shopping, all of which can easily result in fires. The automatic fire alarm system serves a critical role in the early identification and control of fires, reducing the number of casualties, economic losses, and negative social consequences.

Smoke detectors and temperature detectors are selected to establish a regional fire detector network for hotel buildings in order to precisely forecast the location of the fire and limit the false alarm rate of the detectors. Detectors with buzzer bases are used in the guest room's bedroom, study, dining room, and reception rooms, and any area detector in the guest room transmits a fire alarm signal to the control room and activates the buzzer to alert visitors who are sleeping or working to evacuate swiftly.

A smoke-sensing fire detector responds to the smoke aerosol (solid or liquid particles) created by combustion and/or pyrolysis suspended in the surrounding atmosphere using a tiny smoke sensor. Ionic and photoelectric smoke detectors are the most common types.

Take, for example, a photoelectric smoke detector. A smoke detector having a light source and a photosensitive element is known as a photoelectric smoke detector. In most cases, light from the light source is unable to illuminate the photosensitive element; but, when smoke enters, the light is scattered in the smoke, and a portion of it reaches the photosensitive element. The more light is diffused on the photosensitive element, the denser the smoke. The light signal is subsequently converted into an electrical signal by the photosensitive element, which is then sent to the fire controller.

The key application of on-board smoke sensor in automobile fire prevention

Automobile fire accidents have occurred more frequently in recent years, resulting in significant losses to the country's and people's lives and property. The lessons are life-changing. Automobile fire incidents have recently become the focus of media and public opinion, with all segments of society paying close attention.

People are in a somewhat closed environment, especially in urban buses and long-distance buses, due to the usage of air-conditioning systems, which causes a great deal of inconvenient fire management and personnel escape. Controlling the occurrence of fires and providing early warning are critical. To do a good job in fire prevention, we must rely on the use of high-tech fire prevention devices in the automobile industry to identify, control, and eradicate hazards as soon as possible.

Smoke sensors and temperature sensors are commonly used to monitor fire smoke, with ion type, photoelectric type, and gas-sensitive type smoke sensors being the most common.

With the advancement of gas sensing technology in recent years, detection technology combining gas sensors with classic fire detectors has become increasingly popular in the field of a car fire and smoke detection.

CO is a unique indication of very early fires since the gaseous combustion products are primarily CO and CO2. CO levels in the air are typically relatively low, but in the course of a fire, practically every substance must be created. CO that has fully combusted, especially if the fire is still smoldering.

CO underwent a regular change process from start to finish, from small to large, and then steadily declined, from the gestation of the fire to the furious combustion. Furthermore, because CO has a lower density than air, it is easier for it to float earlier and provide early warning. As a result, CO is appropriate for early fire detection, which is critical for obtaining fire data at an earlier stage.