DE102008005821B4 - fire alarm - Google Patents

Abstract

Fire detector (1) for use in buildings, comprising at least one gas sensor (14) which emits an electrical signal depending on a change of state characteristic of a fire surrounding the gas sensor (14), the power supply of the fire detector (1) via the electrical installation network (6) of the building, and the fire detector (1) further comprises
- A backup battery (8) for redundant internal power supply of the fire detector (1) and
- A power failure detection device with a microprocessor, which detects an interruption of the mains power supply (6) and then causes the switching to the internal power supply through the backup battery (8), wherein the gas sensor (14) has a heated metal oxide semiconductor as the gas sensor element (18) and a heating element ( 16) for heating the metal oxide semiconductor, and the microprocessor (2) monitors the heating current through the heating element (16) as an indicator of an interruption of the mains power supply (6)

Description

The The invention relates to a fire detector for use in buildings, comprising at least one gas sensor depending on one for a fire characteristic change of state the gas surrounding the gas sensor emits an electrical signal.

The The invention further relates to a gas warning device for use in buildings, comprising at least one gas sensor, depending on the concentration of combustible gases in the air surrounding the gas sensor an electrical Signal issues, as well as a method for operating a fire alarm or gas detector.

The Most today in residential buildings Fire detectors used are smoke detectors that are sensitive to particles in the air surrounding the smoke detectors, as they smoke or soot, which arises in a fire, are present. They are predominant attached to indoor ceilings and are powered by a battery. These are typical low-price products that appeal to the end user judge. The charge status of the batteries is not displayed actively. If the battery charge is below one to operate the fire alarm yet If there is a risk of falling off, a short beep will sound at relatively long intervals, which can easily be overheard in everyday life. When the battery is complete then unloading takes place at all no indication. If the operator forgets then, the regular self-test of the fire detector, he does not realize that only a malfunctioning device at the Ceiling hangs, which can no longer trigger an alarm in the event of a fire.

The US Pat. No. 7,268,683 B2 shows in a smoke detector a circuit supplied with electrical energy from a primary energy source and arranged to receive the energy from a secondary energy source in the event of a failure of the primary energy source. The circuit is not described in detail, nor the way in which he recognizes the interruption of the primary power supply.

The US 5 574 436 A shows a smoke detector with a display device for displaying a failed primary power supply, comprising a monitoring circuit, which detects a failure of the power supply by detecting an undervoltage on the power line, and the undervoltage detection circuit used to deliver a warning signal.

The US 4,419,658 shows a portable combination of lamp, smoke detector and alarm device for indicating a failure of the supply voltage, comprising a standard power failure detection, so an additional circuit, without microprocessor, which detects the failure of the mains voltage and housed in the same housing as the device to be monitored and with the Power supply line is connected.

The US 4,380,760 shows a smoke alarm with a delayed alarm after switching to a backup power supply comprising an additional detector to detect a loss or failure of the supply voltage.

The US 5,694,118 shows a gas detection and alarm system to indicate gas, such as carbon monoxide, with a microprocessor-controlled measuring device, with a voltage converter that converts an AC supply voltage into a DC operating voltage, and with a redundant internal power supply.

It is therefore the object of the present invention, a generic fire detector so that its reliability and reliability is improved.

These Task is solved by a fire detector with the features of claim 1.

According to the invention thus takes place the power supply of the fire detector via the electrical installation network of the building, and the fire detector further comprises a backup battery for redundant internal power supply of the fire detector and a power failure detection device with a microprocessor interrupting the mains power supply detects and then switching to the internal power supply caused by the backup battery, wherein the gas sensor is a heated Metal oxide semiconductor as a gas sensor element and a heating element for Heating the metal oxide semiconductor includes, and the microprocessor monitors the heating current through the heating element, as an indicator of an interruption the mains power supply.

Advantageous It is that by the network operation of the fire detector regardless of its battery life is always ready for use. The risk of a Any power failure in the network is caused by the backup battery and the automatic switch to battery operation in case of a Power failure avoided.

According to a further advantageous embodiment, the fire detector comprises a display and alarm device, which is provided by the microprocessor can be controlled and emits an optical and / or audible alarm in case of interruption of the mains power supply of the fire alarm.

According to one further advantageous embodiment If the signal of the gas sensor is in a resistance change of the metal oxide semiconductor.

According to one further advantageous embodiment is a temperature sensor intended to determine the ambient temperature of the fire detector, which is connected to the microprocessor and its temperature reading is processed in the microprocessor for correction purposes.

According to one further advantageous embodiment is in the microprocessor a calibration characteristic deposited, based depending on the measured ambient temperature is a characteristic set value the sensitivity characteristic of the gas sensor element automatically is adjusted so that one compensated for environmental temperature influences Sensor signal can be determined.

According to one further advantageous embodiment the gas sensor is a CO sensor.

According to one further advantageous embodiment are next to the CO sensor and the temperature sensor at least an optical sensor and an infrared sensor available.

Further advantageous embodiments and improvements of the fire detector according to the invention and further advantages can be found in the dependent claims.

Based of the drawings, in which an embodiment of the invention is shown, the invention and further advantageous Embodiments and improvements of the invention explained in more detail and to be discribed.

It demonstrate:

1 a schematic block diagram of an embodiment of a fire detector according to the invention, and

2 schematically a calibration curve, as in the microprocessor of the fire detector according to 1 is deposited.

It will be first 1 considered. 1 schematically shows a fire alarm 1 whose housing is indicated by the dashed line. Inside the housing is a gas sensor 14 and a temperature sensor 22 for measuring the ambient temperature. The interior of the fire detector is located near the gas sensor via slots in the housing wall 14 and the temperature sensor 22 with the air surrounding the fire detector in connection, in particular, can via diffusion and / or gas flow, a rapid gas exchange between the air surrounding the fire detector and the gas sensor 14 respectively. This ensures that the gas sensor 14 the fire detector 1 the same gas composition looks like they are in the fire detector 1 ambient air prevails, and the temperature sensor the ambient temperature of the fire detector 1 can measure.

Furthermore, the fire detector includes 1 a microprocessor 2 , which includes the usual for a microprocessor peripheral circuit, which is not shown here for reasons of clarity. The gas sensor 14 is via sensor connection cables 20 with the microprocessor 2 connected, so that the sensor signal of the gas sensor 14 in the microprocessor 2 can be captured and processed. This includes the microprocessor 2 in the functional sense, all the necessary electronic circuits and assemblies such as amplifier circuits, current or constant voltage sources, comparators, etc, which can also be constructed on separate circuit boards.

Furthermore, the fire detector includes 1 a display and alarm device 4 that of the microprocessor 2 is controlled.

The power supply of the fire detector has a mains connection 6 over which the fire detector 1 in installation position with a power cord (not shown here) to the mains of the building in which it is installed, can be connected. The power supply can be done for example by means of a standard power cord with a power connector into a power outlet in the building's inner wall; It could also be a separate power cord under plaster led to the fire alarm and the fire alarm can then be connected. Other required for the production of a mains power supply modules, such as a rectifier or a switching power supply, are not shown in the figure for reasons of clarity, however, however, in the fire alarm 1 available.

The fire detector is in addition to the mains power supply 1 additionally via a battery 8th which is designed as a redundant power supply. It may be a rechargeable battery or a non-rechargeable primary cell.

The battery 8th is by means of a switch 10 , which is advantageously implemented as an electronic switch, connected to the power supply of the fire alarm when the Stromver supply via the mains supply 6 is interrupted. The mains power supply is also provided by the microprocessor 2 monitored, which in case of an interruption also via an action line 12 press the toggle switch and switch the power supply from mains to battery mode.

The fire detector 1 So normally it does not work with battery but directly on the building electricity network. In order to indicate the intact network operation, the display and alarm device is provided with a green ready display, for example a green LED, which lights up when the mains supply is intact.

Previously known fire detectors normally work with direct current, which they usually obtain via a battery, they do not have a mains connection. An example of such a fire detector is the Smart model from Honeywell. There is no active indication of sufficient battery voltage as this would itself consume power and reduce the life of the battery in the fire detector. Only when the battery charge has fallen below a just tolerable threshold, sounds a short periodic warning signal, which is easily overheard in everyday life. Thus, there is the danger in known fire detectors that one day only a functionless, because powerless, device depends on the building ceiling. This disadvantage overcomes the fire detector according to the invention 1 through the mains connection 6 ,

Through the backup battery 8th the fire detector works after 1 even if the power fails. In this case, the microprocessor recognizes 2 that no electricity is flowing anymore. Immediately he activates the switch 10 , and the backup battery 8th Adopts the internal power supply of the fire detector 1 , The fire alarm then works for at least one hour as intended in battery mode.

The microprocessor 2 also monitors the state of charge of the battery and continues to activate the display and alarm unit 4 so that at the end of battery life it will emit a visual and / or audible signal lasting for about a minute, signaling that the battery is soon depleted. The signal tone can be, for example, quickly pulsating and long-lasting, possibly accompanied by the illumination of a red warning light, for example an LED.

The beep is unmistakable and may be similar to the alarm sound used to indicate a fire alarm from the display and alarm unit 4 the fire detector 1 is delivered. It can have a volume of about 100 dB, at a frequency of about 3.5 kHz. Because the power failure could indeed have been caused by a short circuit in the pipeline network, which carries the risk of triggering a smoldering fire. Thus, the sound of the fire alarm gives the occupants of the building an indication to search for the causes of the power failure and eliminate the source of danger in a timely manner.

The gas sensor 14 is of a type of heated gas sensor. It includes a heater 16 , which via a power supply line 26 is also operated by the power supply of the fire alarm and a gas sensor element 18 heated to an operating temperature above room temperature. The heater can be operated in particular by the mains current after its rectification, thus by direct current. In the case of switching the power supply to the internal power supply through the backup battery 8th becomes the heater 16 then from the backup battery 8th operated. The capacity of the backup battery 8th is sized to the gas sensor 14 keep it at its working temperature for at least 1 hour and the intended functioning of the fire alarm 1 can ensure.

The heating current through the heater is above a current measuring resistor 24 tapped and the measured Heizstromwert the microprocessor 2 supplied as input signal. The microprocessor then monitors the correct current value of the heating current. If the microprocessor detects a sharp drop in heating current, it interprets this as a power failure and initiates the power failure signaling and power switching routine, as described above.

At the gas sensor 14 it is a gas sensor based on a heatable metal oxide semiconductor. The functional principle of semiconductor gas sensors, also known as Tagushi or Figaro gas sensors, based on the chemisorption of organic molecules on the surface of an oxide semiconductor, such as tin oxide (SnO2) and the associated change in the electron concentration. The higher the concentration of molecules in the atmosphere surrounding the sensor, the more molecules are chemisorbed, and the higher the electrical conductivity of the sensor becomes. The sensitivity of the sensor is thus a function of the gas partial pressure of the chemisorbable or gases.

Semiconductor gas sensors react more or less to a variety of reducing gases and are therefore very suitable as broadband detectors for the rapid detection of oxidizable gases. They can be isothermal at temperatures between 200 ° C and 450 ° C or with a programmed pe Riodisch heating and cooling are operated.

Semiconductor gas sensors have long been used in gas warning systems, smoke detectors and for workplace control used. By targeted doping of the semiconductor material can the selectivity for certain Gas types increased become. By doping with precious metals such as platinum or rhodium For example, the sensitivity for carbon monoxide (CO) or for hydrogen across from the sensitivity for other oxidizable gases increased become.

A fire detector with a semiconductor gas sensor is for example in the WO 93/08550 described. However, the semiconductor gas sensor used there is operated at ambient temperature, which makes it particularly susceptible to drift phenomena and cross sensitivities to ambient temperature variations and humidity changes of the ambient air.

Of the in the fire detector according to the invention used gas sensor is for example a sensor of the type Figaro TGS 813, specially for the detection of combustible gases has been optimized. His threshold is less than 300 ppm CO. He is at a working temperature from about 280 ° C operated.

In the 1 is a set of symbols in the microprocessor 30 deposited. Each characteristic of the crowd establishes a relationship between the measured electrical resistance of the sensor and the Gaskon concentration at a certain ambient temperature. The gas sensor in the fire detector described here 1 was calibrated to CO, therefore provides the family of characteristics 30 The relationship between the measured sensor resistance and the CO concentration. In accordance with other calibration could also be the hydrogen or the methane concentration or the concentration of another combustible gas detected.

It can be seen that as the gas concentration increases, the electrical resistance of the sensor R decreases with respect to a calibration value R ₀ . At constant gas concentration, the electrical resistance also decreases with increasing ambient temperature T. But also with increasing relative humidity of the atmosphere surrounding the sensor, the electrical resistance can decrease; the latter connection is not shown in the figure.

This is an expression of the well-known phenomenon that Semiconductor gas sensors in addition to the broadband sensitivity characterized by a certain temperature and humidity sensitivity. To get a stable sensor signal is a longer "break-in time" of two to five Days at the selected Operating temperature required within which the sensor into its chemical and physical equilibrium. Within the "break-in period" shifts the sensor characteristic is involved. To get a precise measurement during operation carry out to be able to It is necessary to shift the sensor characteristic during the Warm-up time and also later, if the ambient temperature changes, correct.

This is in the microprocessor 2 In addition to the sensitivity characteristics, a calibration curve in a function block for temperature compensation 28 deposited, see 2 , This links the ambient temperature with a set value for calibration of the sensitivity characteristic.

The setting value can be, for example, a test voltage applied to a specific measuring point of an electronic measuring amplifier circuit, which can be set via a variable resistor. The program stored in the microprocessor automatically checks by means of the temperature sensor 22 measured temperature value of the ambient temperature and the stored calibration curve, if the set value for the sensitivity characteristic is correct, and if detected deviations, the microprocessor automatically initiates appropriate corrective action. As a result, a sensitivity curve of the gas sensor which is automatically calibrated correctly with respect to the ambient temperature is always used in the fire detector according to the invention. Incorrect measurements are largely prevented.

A corresponding self-calibration with regard to the relative humidity of the atmosphere surrounding the sensor could, of course, also be carried out if the fire detector additionally comprised a humidity sensor which cooperates in a corresponding manner with the microprocessor in the same way as the temperature sensor 22 ,

in the The following are the advantages of the fire detector according to the invention over the state the technique described.

at A fire first produces highly toxic carbon monoxide in high concentrations Concentrations, especially in smoldering fires. Often the high CO concentration accompanied by a high concentration of hydrogen, namely hydrocarbons Materials burn, for example plastics. The particle-containing Fire smoke develops later. The toxic carbon monoxide is lighter than air, so it rises in a building quickly up to the ceiling and spreads throughout the house.

Conventional fire detectors, in particular those that are offered to the end user for easy retrofitting in apartments or residential buildings and are sold relatively cheaply in hardware stores, for example, can only detect particulate smoke or soot. In the time that must pass until in the case of a fire, the smoke has developed so strong that such a conventional smoke detector responds and emits an alarm, so may have already formed a dangerously high carbon monoxide concentration in the room air. However, this is not covered by conventional smoke detectors. However, the fire detector according to the invention reacts straight to the carbon monoxide, and therefore it triggers an alarm much earlier than conventional smoke detectors. The alarm threshold can be set below 500 ppm or 0.05 vol% CO.

Of the Mains operation and automatic switching to the backup battery in case of power failure, connected to the signal at approaching end of Battery charging reduces the risk of a malfunctioning, because they no longer supplied enough electrical energy, Fire alarm installed considerably.

The in the microprocessor stored calibration curve and the automatic Recalibration of the sensor characteristic with fluctuating ambient temperature elevated the measurement accuracy and thereby reduces the number of false alarms.

Even though the fire detector according to the invention especially advantageous for the detection of a home fire can be used, he can because of the high measuring accuracy and the low threshold also generally as a gas detector operate. As a gas warning device For example, it detects leaking gas from defective gas pipes in the house, be it a gas heater or a gas stove, or also carbon monoxide, which forms in a room through an exhaust gas backlog. An inventive fire detector can be dimensioned to meet the requirements of the DIN standard EN 50291 "Electric equipment for the Detection of carbon monoxide in homes ".

A possible Further development of the fire detector according to the invention may consist in that in addition to the CO gas sensor other sensors for Capture more for a fire characteristic change of state of the fire detector surrounding air are present. Because in a fire arises, how already mentioned, In addition to CO and smoke also hydrogen, it can also be steam arise; about that In addition, heat and heat are generated Infrared radiation.

So could the fire detector according to the invention in addition to the CO sensor still include an optical particle sensor. This would be then a combination of a fire detector according to the invention with a usual Smoke detector. Furthermore could an inventive fire detector also include an infrared sensor, for measuring the temperature or the IR radiation of a flame.

When CO sensors come in addition to the described semiconductor gas sensors also other heatable gas sensors in question, for example Pellistors, ie catalytically active gas sensors in which CO is catalytically oxidized and detects the resulting increase in temperature and metrologically evaluated, or gas sensors on the base of solid-state electrolytes, For example, zirconium dioxide sensors, which after the potentiometric Working principle, ie, depending on the CO concentration an electrical voltage between two as measuring and reference electrodes designated electrodes formed.

One particular advantage of the present invention is that these devices before delivery to the customers very accurately and easily calibrate.

1

fire alarm

2

microprocessor with periphery

4

display and alarm

6

mains connection

8th

Backup battery

10

switch

12

line of action

14

CO sensor

16

stoker

18

Gas sensor element

20

Sensor connection lines

22

temperature sensor

24

Current sense resistor

26

Power supply line

28

Temperaturkompenstion

30

Sensitivity curves the gas sensor element

Claims (15)

Fire detector ( 1 ) for use in buildings, comprising at least one gas sensor ( 14 ), which depends on a fire characteristic change of state of the gas sensor ( 14 ) emits an electrical signal, whereby the power supply of the fire detector ( 1 ) via the electrical installation network ( 6 ) of the building, and the fire detector ( 1 ) further comprises - a backup battery ( 8th ) to the redundant internal power supply of the fire detector ( 1 ) and - a power failure detection device with a microprocessor, which interrupt the Mains power supply ( 6 ) and then switching to the internal power supply by the backup battery ( 8th ), wherein the gas sensor ( 14 ) a heated metal oxide semiconductor as a gas sensor element ( 18 ) and a heating element ( 16 ) for heating the metal oxide semiconductor, and the microprocessor ( 2 ) the heating current through the heating element ( 16 ), as an indicator of an interruption of the mains power supply ( 6 ) Fire detector ( 1 ) according to claim 1, comprising a display and alarm device ( 4 ) generated by the microprocessor ( 2 ) is controllable and at an interruption of the mains power supply ( 6 ) of the fire detector ( 1 ) emits an optical and / or audible alarm. Fire detector ( 1 ) according to claim 1, wherein the signal of the gas sensor ( 14 ) consists in a change in resistance of the metal oxide semiconductor. Fire detector ( 1 ) according to claim 1, wherein a temperature sensor ( 22 ) is provided for determining the ambient temperature of the fire detector, with the microprocessor ( 2 ) and its temperature reading in the microprocessor ( 2 ) is processed for correction purposes. Fire detector ( 1 ) according to claim 4, wherein in the microprocessor ( 2 ) a calibration characteristic is deposited on the basis of which, as a function of the measured ambient temperature, a characteristic setting value of the sensitivity characteristic of the gas sensor element ( 18 ) is automatically adjusted so that a compensated for ambient temperature influences sensor signal can be determined. Fire detector ( 1 ) according to claim 1, wherein the gas sensor ( 14 ) is a CO sensor. Fire detector ( 1 ) according to claim 6, wherein besides the CO sensor ( 14 ) further sensors for detecting further changes of the fire detector characteristic of a fire ( 1 ) surrounding air are present. Fire detector ( 1 ) according to claim 7, wherein in addition to the CO sensor and the temperature sensor at least one optical sensor and an infrared sensor are still present. Gas warning device for use in buildings, comprising at least one gas sensor ( 14 ), which depends on the concentration of combustible gases in the gas sensor ( 14 ) emits an electrical signal, wherein the power supply of the gas warning device via the electrical installation network ( 6 ) of the building, and the gas warning device further comprises - a backup battery ( 8th ) to the redundant internal power supply of the gas detector, and - a power failure detection device with a microprocessor, which interrupt the power supply ( 6 ) and then switching to the internal power supply by the backup battery ( 8th ), wherein the gas sensor ( 14 ) a heated metal oxide semiconductor as a gas sensor element ( 18 ) and a heating element ( 16 ) for heating the metal oxide semiconductor, and the microprocessor ( 2 ) the heating current through the heating element ( 16 ), as an indicator of an interruption of the mains power supply ( 6 ). Gas warning device according to claim 9, comprising a display and alarm device ( 4 ) generated by the microprocessor ( 2 ) is controllable and at an interruption of the mains power supply ( 6 ) of the gas warning device emits an optical and / or audible alarm. Gas warning device according to claim 9, wherein the signal of the gas sensor ( 14 ) consists in a change in resistance of the metal oxide semiconductor. Gas warning device according to claim 9, wherein a temperature sensor ( 22 ) is provided for determining the ambient temperature of the fire detector, with the microprocessor ( 2 ) and its temperature reading in the microprocessor ( 2 ) is processed for correction purposes. Gas warning device according to claim 12, wherein in the microprocessor ( 2 ) a calibration characteristic is deposited on the basis of which, as a function of the measured ambient temperature, a characteristic setting value of the sensitivity characteristic of the gas sensor element ( 18 ) is automatically adjusted so that a compensated for ambient temperature influences sensor signal can be determined. Gas warning device according to one of claims 9 to 13, wherein the gas sensor ( 14 ) is a CO sensor. Method for operating a fire detector ( 1 ) or gas detector for use in buildings, whereby the fire detector ( 1 ) or the gas warning device at least one gas sensor ( 14 ), which in response to a characteristic change in state of the gas sensor ( 14 ) emits an electrical signal, whereby the power supply of the fire detector ( 1 ) or the gas detector via the electrical installation network ( 6 ) of the building, and the fire detector ( 1 ) or the gas warning device further comprises - a backup battery ( 8th ) to the redundant internal power supply of the fire detector ( 1 ) or the gas warning device and - a power failure detection device with a microprocessor, which interrupt the power supply ( 6 ) recognizes and then the Switching to the internal power supply through the backup battery ( 8th ), wherein the gas sensor ( 14 ) a heated metal oxide semiconductor as a gas sensor element ( 18 ) and a heating element ( 16 ) for heating the metal oxide semiconductor, characterized in that the heating element ( 16 ) flowing heating current of the gas sensor ( 14 ) is used as an indicator of an interruption of the mains power supply and by the microprocessor ( 2 ) is monitored.