Siren (device)
A siren is a device for acoustic alarms or warnings , usually by means of a characteristic increasing and decreasing howling sound .
Sirens are used in public areas to alert the fire brigade or to warn the civilian population in the event of a disaster .
The siren got its name in 1819 from Charles Cagniard de la Tour , who linked it to the siren from mythology .
Types
Based on the design and sound generation, a distinction is made between mechanical (or motorized ), pneumatic and electronic sirens . The last two types, but mostly only the pneumatic sirens, are referred to as high-performance sirens (HLS) in Germany .
Mechanical sirens
A mechanical siren (also known as a motor siren ) consists of a paddle-wheel-like drum (the so-called rotor ) and an interrupted housing that surrounds it (the so-called stator ). By rotating the drum, e.g. B. by an electric motor , the resulting air flow is continuously cut off and generates a sound.
The pitch depends on the speed and the number of blades, the so-called ports of the drum. The pitch of a siren in Hertz is calculated from the revolutions per second multiplied by the number of ports. In order to ensure a simultaneous interruption of the air flow at all ports, the stator has the same number of openings.
The starting and stopping of the motor results in a higher and lower tone. But this can also be prevented by using a flap instead of a sheet metal hood that has a fixed distance from the rotor. B. is lifted off with an electromagnet and closes the opening of the rotor when switched off. Such types are used predominantly in the United States as special alarm sirens.
If the rotor shaft is usually arranged upright, there is also a (rarer) type in which a drum is attached to the horizontal rotor shaft on both sides of the motor. Two different paddle wheels can also be attached, which produce a double tone with one another.
The standard siren of the type E 57 with 9 ports (originally West German standard siren) used in Germany howls with a volume of 101 dB (A) at a distance of 30 m and a pitch of (420 ± 16.5) Hz at (2800 ± 110) revolutions per minute. Their tone can be heard in rural (sparsely populated) areas at a distance of 600 m with around 70 dB (A). In densely built-up areas such as industrial zones or in regions with multi-storey buildings, the E 57 can only achieve a range of around 350 m with the same volume.
The siren type DS 977 was installed in East Germany as well as in the Soviet Union, Hungary and the ČSSR during the GDR. It was also used to warn the population and to alert the fire brigades (using a manual trigger, and later via the control center). This siren has 8 ports, has a nominal speed of 2880 / min and is driven by an electric motor with 3.5 kW. It takes one second longer than the E 57 to reach the required speed and generates an audio frequency of 384 Hz. This type weighs around 100 kg and was manufactured by the VEM electric motor combine.
In Austria there is a dense network of (as of 2019) around 8,200 sirens of various types, the operation of which is transferred from the respective municipalities to the individual fire departments. In Lower Austria alone there is a network of 2,400 sirens for around 600 municipalities.
Since most sirens are installed outdoors on the one hand, and on the other hand are not used very often, a bird protection grille is installed in many cases to prevent nesting in the paddle wheels.
In the United States during the Cold War, very large and powerful motorized sirens powered by a V8 internal combustion engine were installed in metropolitan areas.
There are also small hand-operated sirens that can be used independently of a power supply. There is a hand crank on these hand sirens. Here, too, the pitch depends on the speed.
Pneumatic sirens
Pneumatic sirens generate their sound similar to a mechanical siren by cyclical interruption of the air flow, which also takes place by an electric motor-driven rotor in the siren head. In contrast to the mechanical siren, in which the air flow is created by centrifugal force , here compressed air with around 16 bar is fed to the siren head from a storage container under the siren mast . After the rotor, which consists of a perforated disc (hence the name perforated disc siren), which periodically opens or closes the outlet openings, the air is directed into several horns .
The advantage of this solution consists on the one hand in the immediately available compressed air supply, which is continuously refilled by a compressor , and on the other hand in the much greater power of this type of siren. For a model with a head height of 20 m, the sound pressure on the floor 20 m from the siren is about 130 dB.
The siren head sits on a mast or occasionally on buildings. The compressor and air tanks are usually located in an underground engine room. The compressor is driven by a diesel engine, partly also by an electric motor. The rotor in the siren head draws its energy from accumulators .
In the years from 1990 onwards, i.e. after the Cold War , many of the approximately 500 copies of these sirens in Germany were replaced by electronic versions or removed without replacement due to reduced requirements. The lattice masts, which were once the carriers of the HLS, often still serve today as carriers for antennas (e.g. for radio or cellular networks).
When the high-performance sirens were being developed, the systems were often large and clumsy. The Pintsch-Bamag "Anlage 1" and "Anlage 2" z. B. sat on a large steel pole, which was attached to the ground with a large concrete foundation. The inside of the mast was hollow in “Plant 1” so that maintenance work could be carried out. The technicians were given access through a door at the base of the mast and a ladder inside the mast.
In "Plant 2", the mast also serves as a compressed air reservoir.
The successor model from the 1970s, Type 273, was significantly smaller and more compact. The large head of the earlier sirens was designed to be more open, so that only the rotor and exit horns sit on the mast. The paneling that gave the earlier heads their clumsy appearance was almost completely dispensed with.
A variant of pneumatic sirens is still common in the United States. It differs in the air supply that occurs through the compressor during the alarm. There is no air tank with this variant. Another difference is that some models have rotors with two or more rows of ports and corresponding stators. This allows a double tone to be generated. The two tones can also be given alternately by means of solenoid valves .
Hörmann
F71
Hörmann
HLS 273
Head of an
HLS 273
Pintsch-Bamag
Annex 2
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Electronic siren
Electronic sirens produce the sound with a loudspeaker and an electronic amplifier . With a control you can also feel the swelling and swelling of the mechanical siren. The advantage of the electronic sirens is that they have no moving parts. This reduces weight, maintenance effort and power consumption. This type of siren is also partially independent of the electricity network by supplying it with a rechargeable battery that can be charged by solar cells or the power grid. The individual horns can be turned in the desired directions in order to fill certain areas with more or less sound. Voice announcements can also be made with electronic sirens.
In 2020, a siren about 6.20 m long mounted on a truck trailer, rotatable through 360 °, was presented in China. This device, which generates 130 dB at a distance of 35 m, is mainly intended for use in civil defense.
Electronic siren (fire brigade)
Electronic siren with 2.4 kW power from the Höchst industrial park
Hörmann ECL 400, one of the first electronic sirens of the 1970s
Siren control
Today sirens are mainly triggered by radio, occasionally via manual call points.
The manual call points have a direct wire connection between the detector and the siren control unit. If someone triggers the manual call point, the siren starts immediately with the corresponding siren signal (usually a fire alarm with public sirens ). The person giving the alarm should then be at the manual call point to brief the fire brigade.
In order to trigger sirens remotely and or at the same time (usually via control centers), a telecontrol receiver is installed that reacts to radio signals, for example. Existing alarm technology is used depending on availability, so-called 5-tone sequences are the most common in analog radio networks and the POCSAG protocol in digital networks . Triggering via cellular networks, especially in the GSM standard, is also possible; individual voice messages can then also be transmitted.
The programming can be done in such a way that the siren triggers at the same time as the radio alarm receivers of fire brigade members or is controlled independently. Different siren signals can be controlled via the technologies available depending on the transmission technology, for example fire alarm , warning the population or the all-clear .
Uses
Alerting the fire brigade
In some, mostly rural areas , sirens still alert volunteers of the fire brigade to their operations (also known as loud alarms ). In cities and more densely populated regions in particular, however, since the 1970s more and more fire departments have switched to so-called silent alarms using radio receivers and, in some cases, also by SMS .
Disadvantages of the siren when alerting rescue workers are the great noise nuisance of the uninvolved population, especially at night, the attraction of onlookers and the insufficient or excessive acoustic range, depending on the weather (especially wind). It can happen that the siren is not heard everywhere even in one's own location or, conversely, that the sound is carried so far that it scares the fire fighters in several locations, as it is difficult to assign an exact location. In addition, the siren does not allow specific alerting of individual emergency services with special training (e.g. respiratory equipment wearers, dangerous goods specialists) or functions (e.g. executives, specialist advisors) required at the emergency location, nor is it variable to those at the emergency location required number of forces (full alarm for everyone, small alarm for some of the fire fighters in a fire brigade or department) can be received. See also article Alarm systems of the fire brigade .
However, the siren, which is set up on exposed points, is also experiencing a return, since electronic, "silent" alarm systems (e.g., via radio receiver or SMS), for example, show a considerable susceptibility to failure in the event of a large-scale power failure. The city of Trossingen, for example, which shut down its sirens when the Cold War subsided, wants to reinstall ten such alarm devices.
Sirens, which are used to alert the fire brigade, are usually checked for functionality at regular intervals by means of test alarms. A very common time for this is every first Saturday of the month at 12:00 noon. But there are also municipalities that test their sirens at different times or at different intervals. In North Rhine-Westphalia there is a so-called warning day every six months, on which all alarm systems are tested at the same time.
In Austria, in addition to a short weekly test run on Saturdays at noon, all siren signals are tested on the first Saturday in October.
Disaster warning
Further
Sirens, like compressed air whistles or horns, are occasionally used by larger companies to indicate the start of work and break times and to announce blasting at construction sites or quarries.
In companies, but increasingly also in private houses, small sirens are installed in connection with alarm systems against burglary or fire .
The alarm systems with an electronic siren are also used in motor vehicles .
It is used at fairgrounds, for example to announce the arrival or departure of rides.
In some countries, an alarm siren is also used on emergency vehicles alone instead of or in combination with the secondary horn .
The sirens are not used every day in Tulln in Lower Austria, where the sirens sound instead of the church bells on Good Friday at the hour of Jesus Christ's death at 3 p.m. This custom also takes place in the Salzburg municipality of Thalgau and in the municipality of Greinbach near Hartberg.
A siren powered by the airflow was attached to each of the two landing gear panels of the German Junkers Ju 87 dive fighter aircraft . These devices, called Jericho trumpets , were intended to demoralize the opponent on the ground during a fall attack.
literature
- The Physics book. Springer Verlag, 2013, pp. 290f. (on-line)
Individual evidence
- ^ Encyclopaedia Britannica, 1911, quoted from Wikisource
- ↑ Data sheet from the manufacturer of the E 57: http://www.hoermann-gmbh.info/pdf/Downloads/01-Sirendatenblaetter/E57-de.pdf
- ↑ Joachim Schmidt: Interest group warning service and sirens for VEM DS977. (wiki.ig-wasi.de)
- ↑ REMINDER: civil defense test alarm on October 5, 2019. Accessed on October 19, 2019 .
- ↑ The civil defense test alarm on October 1, 2011 was successfully accessed on October 13, 2011 on the Lower Austria state government's website.
- ↑ Website about the 180 hp Chrysler Air Raid Siren (English) ( Memento from November 6, 2010 in the Internet Archive )
- ↑ It's the biggest siren in the world. December 22, 2017, accessed January 21, 2020 .
- ^ Franz-Josef Sehr : Development of fire protection . In: Freiwillige Feuerwehr Obertiefenbach e. V. (Ed.): 125 years of the Obertiefenbach volunteer fire brigade . Beselich 2005, ISBN 3-926262-03-6 , p. 114-119 .
- ↑ The good old siren is seeing a return. In: Südwestpresse - Neckar spring. November 27, 2018. (nq-online.de)
- ↑ Test alarm: When the sirens wail. Vorarlberg Online from October 2, 2017. (vol.at)
- ↑ Siren signal on Good Friday. Tulln City Fire Brigade, accessed on February 16, 2020 .
