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            "Smoke detectors" past and present, how smoke detectors work
            Source: Hyman Technology Release time: 2019-08-12 Clicks:

            Fire is one of the most frequent disasters in the world today. According to relevant statistics, an average of more than 10,000 fires occur every day in the world, causing hundreds of deaths. And the damage caused by the fire has doubled exponentially over time.

            As a result, there is an urgent need for automatic fire detection technology, and in particular, fire smoke detection technology has also made considerable progress and is widely used.

            How Smoke Detectors Work

            Smoke detectors, also known as smoke alarms , implement fire prevention by monitoring the concentration of smoke. They are powered by a bus, networked and communicated with a fire alarm controller to form an alarm system. According to the type of sensor used, fire smoke detectors can be divided into ion smoke alarms and photoelectric smoke alarms.

            History of smoke detectors

            Smoke detectors have gone through a history of more than 100 years since their birth.

            The first automatic fire detector that used electricity was patented in 1890 by Edison's partner, American physicist and mathematician Francis Robbins Upton. Unfortunately, his achievement is often overlooked.

            This was caused by a bluff incident at the time-his patent was incorrectly labeled as "Portable Electric Tire-Alarm", and the correct one should be "Portable Electric Fire-Alarm" Portable electric fire alarm.

            Then in 1902, British engineer George Andrew Darby applied for a patent for the first European electrothermal detector in Birmingham, England. His invention was called the "Butter Sentinel" and was considered the precursor to modern smoke detectors.

            The structure of his invention is very simple: two electric plates with a piece of butter sandwiched between them. When the smoke rises, they will melt the butter and cause the two electric plates to contact each other to form a path, thereby triggering an alarm. Rather than detecting smoke, it is detecting temperature.

            This is a very clever design, and unfortunately there are many disadvantages: First, it is easy to falsely report. In the hot summer, the alarm may ring continuously; moreover, the installation of butter is very inconvenient, It's dripping everywhere. Later, many inventors succeeded and failed to find a better solution. Therefore, this problem is dragged on for 30 years.

            Until the late 1940s, Swiss physicist Walter Jaeger accidentally invented a real smoke detector. The plan started with the design of an alarm for the mine to detect gas poisonous gas.

            They designed a "ionization chamber" based on the principle that the ionized ions are affected by smoke particles and will reduce the ionization current. The air in this chamber is ionized by radioactive materials into various suspended ions. These ions can communicate with the circuits on both sides to keep the current at a stable level.

            He expected that the gas entering the sensor would bind to ionized air molecules, altering the current in the instrument's circuit. Unexpectedly, small concentrations of gas have no effect on the conductivity of the sensor. His equipment does not meet its design goals. Jaeger lit a cigarette in frustration, but unexpectedly found that the meter on the instrument had recorded a drop in current. The smoke particles in his cigarette apparently have done what the gas gas could not do.

            In the same period in 1939, Swiss physicist Ernst Meili designed an ionization chamber device capable of detecting combustible gases in a mine. The experiments of Walter Jaeger and Ernst Meili paved the way for the birth of modern smoke detectors, and based on this, established a complete automatic fire alarm system.

            The international fire protection community generally uses this as a new starting point for automatic fire alarm systems. After about a decade of research, manufacturing, and improvement, the smoke detector was put on the market in 1951 and first sold in the United States. However, it is only used in large factories and commercial centers because it is expensive, bulky, and the corresponding lines need to be laid during installation.

            In 1965, the first low-cost home-use smoke detector was developed by American entrepreneur Duane D. Pearsall. This is an easily replaceable, battery-powered unit. And began mass production of these household smoke detector devices in 1975.

            Donald Steele and Robert Emmark invented the photoelectric (optical) smoke detector by the Electronic Signal Laboratory in 1972 and were patented in 1972.

            Photoelectric Smoke Detector Technology Introduction

            Because ionization smoke technology uses radioactive materials and causes environmental pollution, although the use process is safe, it is very difficult in terms of production, storage and disposal. With the invention of photoelectric smoke detection technology, the tendency of photoelectric smoke detection technology to gradually replace ion smoke detection technology is becoming more and more obvious. Because the photoelectric smoke detector has the advantages of no radioactive pollution, little influence by wind flow and environmental humidity changes, low cost, high reliability and so on.

            Photoelectric smoke detectors are smoke detectors based on the principle that smoke particles scatter, absorb (or block) light. Dimmed (or light-shielded) photoelectric smoke detectors have fewer applications.

            Most of the domestic and foreign production and application are scattered light photoelectric smoke detectors, which are based on the principle of light scattering: most of the photoelectric smoke detection technology works with the principle of scattered light, the basic principle is: no smoke particles exist in sensitive spaces When the ambient light outside the detector housing is blocked by the labyrinth, it cannot basically enter the sensitive space. The infrared photodiode can only receive the background light formed by the infrared beam reflected in the sensitive space multiple times, so no photocurrent is generated. Under normal working conditions.

            When the smoke particles enter the sensitive space surrounded by the labyrinth, the smoke particles absorb the incident light and emit light at the same wavelength to the surroundings. After the scattered light is received by the infrared photodiode, the impedance of the light receiving element is changed to form a photocurrent, thereby The function of converting the smoke signal into an electric signal is realized. When the photocurrent reaches a certain level, the detector sends out an alarm signal.

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