CA1204838A - Chimney fire alarm device - Google Patents
Chimney fire alarm deviceInfo
- Publication number
- CA1204838A CA1204838A CA000466491A CA466491A CA1204838A CA 1204838 A CA1204838 A CA 1204838A CA 000466491 A CA000466491 A CA 000466491A CA 466491 A CA466491 A CA 466491A CA 1204838 A CA1204838 A CA 1204838A
- Authority
- CA
- Canada
- Prior art keywords
- chimney
- temperature
- input
- voltage
- lead
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B17/00—Fire alarms; Alarms responsive to explosion
- G08B17/06—Electric actuation of the alarm, e.g. using a thermally-operated switch
Abstract
ABSTRACT
The invention is a device for detecting a fire in a chimney, the device having one means for producing a first signal proportional to the temperature of combustion gases at the outflow end of the chimeny, another means for producing a second signal proportional to the temperature of combustion gases at the inflow end of the chimney, and means for comparing the first and second signals and for activating an alarm when the chimney outflow end combustion gas temperature exceeds the chimney inflow end combustion gas temperature. The device may also have means for producing a third signal proportional to a selected temperature, and means for comparing the second and third signals and for activating an alarm when the chimney inflow end temperature exceeds the selected temperature.
The invention is a device for detecting a fire in a chimney, the device having one means for producing a first signal proportional to the temperature of combustion gases at the outflow end of the chimeny, another means for producing a second signal proportional to the temperature of combustion gases at the inflow end of the chimney, and means for comparing the first and second signals and for activating an alarm when the chimney outflow end combustion gas temperature exceeds the chimney inflow end combustion gas temperature. The device may also have means for producing a third signal proportional to a selected temperature, and means for comparing the second and third signals and for activating an alarm when the chimney inflow end temperature exceeds the selected temperature.
Description
~2~ 33~
This invention relates to a fire detection device for a building, and more particularly, to a device that electronically monitors the temperature of combustion gases passing through the chimney of a building for detecting a fire within the chimney.
Wood burning stoves have regained popularity in recent years. One byproduct of combustion of wood in such stoves is creosote. Due to the high efficiency of modern wood burning stoves and the relative lack of experience of the general public in using such stoves, a larger amount of the creosote produced by combustion is being carried from the combustion chamber by the combustion gases. A creosote lining often forms on the inner surface of the stove chimney, and it is common for such creosote linings to ignite. The result is that a fire will burn in the stove chimney, which fire may not only damage the integrity of a chimney but may also present a danger to the rest of the building. Such fires may give few signs for their detection; the first sign of such a fire may come too late to prevent more serious damage.
The subject invention recogni~es that a temperature inversion exists in a chimney when a chimney fire is present.
Normally, combustion gases passing through a chimney from a stove to the exterior of the building will experience a decrease in temperature as they pass through the chimney.
The decrease in temperature might be small due to insulation surrounding the chimney, but without a chimney fire being present it would not be expected that combustion gases would leave a chimney at a higher temperature than that at which they entered the chimney. When reference is made henceforth to combustion gases entering a chimney that reference to a chimney should be understood to mean the duct means that conveys the combustion gases from the point at which they leave the stove to the point at which ~, they are exhausted from the building.
The sub~ect invention recognizes that an indicator of a chimney fire is a combustion gas temperature at the outflow end of a chimney exceeding thP combustion gas temperature at the inflow end of the chimney. By positioning means for measuring the temperature of the combustion gases at the inflow and outflow ends of a chimney and by comparing those temperatures, the subject invention detects a chimney fire and proceeds to activate an alarm. Measurement of the combustion gas temperatures is conveniently done by thermocouples mounted in probes which are extended into the interior of the chimney. The signals_output from the thermocouples are connected to the two inputs of an electronic comparator which has the alarm connected to its output. Means may be utilized to amplify the signal levels from the thermocouples prior to their input into the comparator. Additionally, a means for reducing the amplitude of the signal from the thermocouple at the outflow end of the chimney may be connected to the one input of the electronic comparator. This arrangement acts to ensure that the alarm activated by the output of the comparator is only activated when the temperature of the combustion gases leaving the chimney is above the temperature of the combustion gases entering the chimney.
In a further form of the invention, the temperature of the combustion gases entering the chimney from the stove is compared to a reference temperature selected by the operator of the sub~ect device. The comparison is accomplished by a second electronic comparator which has an alarm connected to its output to indicate when the combustion gases leaving the stove have a temperature above the selected temperature. When that second alarm is activated the occupant of the building may decide to reduce the size of the fire in the stove;
in turn, the second alarm becomes deactivat~d when ~0~83B
the temperature of combustion gases leaving the stove drop below the selected temperature. The alarms may be in the form of light emitting diodes each connected in parallel with a tone generator to create both a visible and audible alarm.
The subject invention will now be more fully described by means of a preferred embodiment utilizing the accompanying drawings in which:
Figure 1 is a schematic drawing of the Plectronic circuit utili~ed in the preferred embodiment of the subject invention.
Figure 2 is a perspective view of a housing holding the electronic circuitry schematically illustrated in Figure 1.
Figure 3 is a sectioned side view of a first building having the preferred embodiment of the sub~ect invention installed in a first type of chimney.
Figure 4 is a perspective view of a second building having a preferred embodiment of the sub~ect invention installed in a second type of chimney.
With reference to the schematic circuit of Figure 1, the leads from a thermocouple positioned at the combustion gas outflow end of a chimney are designated 11 and 12, 11 being a grounded lead and 12 being a lead having a positive voltage that varies according to the temperature sensed by the thermocouple. The corresponding pair of leads from the combustion gas inflow end of the chimney are designated 13 and 14, 13 being a grounded lead and 14 being a lead bearing a positive voltage varying with the temperature sensed by the associated thermocouple. The two thermocouples are identical and o~-tput the same voltage levels when acted upon by the same temperatures. The two thermoouples each have a linear response wi~h temperature, each producing a potential difference across its leads of i,o microvolts per degree Centrigrade above 0C. For ins~ance, if either thermocouple sensed a temperature o~ 600 C., .
~9`~ 3 that thermocouple would have a 24 millivolt potential difference across its leads.
Operational amplifiers 16 and 17 amplify the voltage on thermocouple leads 12 and 14, respectively.
Each of the operational amplifiers 16 and 17 produce a voltage gain of 150; to accomplish that voltage gain, the value of resistors 19 and 20 are selected to be 802 Kohms and the value of resistors 21 and 22 are selected to be 5.42 Kohms. The value of resistors 23 and 24 are selected to be 2.2 Kohms so as to reduce the input current to the operational amplifiers to the level of microamperes. The particular operational amplifiers utilized are a pair located on a single integrated circuit chip, that chip being a LM358N.
The result of the voltage amplification is that output lines 27 and 28 of the combustion gas outflow and inflow ends, respectively, of the chimney each have a voltage of 3O5 volts when the respective thermocouples are sensing a temperature of 600C. Output line 27 enters diode ~0 29, and the voltage on output line 30 from that diode is always approximately 0.2 volts lower than the voltage on output line 27. The reason for reducing the voltage on line 30 below that on line ~8 when the thermocouples at the inflow and outflow ends of the chimney are sensing the same temperature is to ensure that the temperature at the outflow end of the chimney is greater than the temperature at the inflow end of the chimney when the voltage on line 30 is the same or greater than the voltage on line 28. Diode 29 is the type lN4002; the voltage drop of approximately 0.2 volts across diode 29 corresponds to a temperature diference Df approximately 35C.; in other words, the voltage on line 30 only exceeds the voltage on line 28 when the thermocouple connectPd to leads 11 and 12 (located at the outflow end of the chimney) senses a temperature at least 35 C. above the temperature sensed by the thermocouple having leads 3~3 13 and 14 (the thermocouple positionedat the inflow end of the chimney).
The voltages on lines 28 and 30 are input to a comparator 35. The comparator 35 maintains a low level output voltage on its output line 36 when the voltage on line 28 is higher than the voltage on line 30; that is the case when the temperature of the combustion gases leaving the chimney is less than 35 C. above the temperature of the combustion gases entering the chimney, as would be the case except when a fire is present in the chimney. A low voltage level on comparator output line 36 produces insufficient current across resistor 37 to activate light emitting diode 38. Also, insu~ficient current passes through diode 39 to activate tone generator 40. On the other hand, a high output voltage on comparator output line 36 is sufficient to generate enough current to activate light emitting diode 38 as well as tone generator 40. That high level voltage is generated on comparator output line 36 when the temperature of the combustion gases leaving the chimney is more than 35 C. above the temperature of the combustion gases entering the chimney. The comparator 35 is constructed from an operational amplifier of the type LM358N.
Output line 28 from operational amplifier 17 is passed to the positive input of a second comparator 42.
The purpose of the second comparator 42 is to compare the temperature of the combustion gases flowing into the chimney with a preselected temperature set by the operator' of the device. As can be seen from Figure 19 the voltage on the negative input to second comparator 42 is ad~ustable, with resistor 43, potentiometer 44 9 and resistor 45 acting as a voltage divider, and potentiometer 44 being tapped for the negative input voltage. The values of resistors 43 and 45, and potentiometer 44 9 are selected with a view to the voltages produced on line 28 when various temperatures are sensed by the thermocouple at the ~ ~04~3~3 combustion gas inflow end of the chimney. The circuit of Figure 1 is operated by a six volt battery, and the value of resistors 43 and 45, and the total resistance of potentiometer 44, have been chosen to be 1 Megohm, 2 Megohms, and
This invention relates to a fire detection device for a building, and more particularly, to a device that electronically monitors the temperature of combustion gases passing through the chimney of a building for detecting a fire within the chimney.
Wood burning stoves have regained popularity in recent years. One byproduct of combustion of wood in such stoves is creosote. Due to the high efficiency of modern wood burning stoves and the relative lack of experience of the general public in using such stoves, a larger amount of the creosote produced by combustion is being carried from the combustion chamber by the combustion gases. A creosote lining often forms on the inner surface of the stove chimney, and it is common for such creosote linings to ignite. The result is that a fire will burn in the stove chimney, which fire may not only damage the integrity of a chimney but may also present a danger to the rest of the building. Such fires may give few signs for their detection; the first sign of such a fire may come too late to prevent more serious damage.
The subject invention recogni~es that a temperature inversion exists in a chimney when a chimney fire is present.
Normally, combustion gases passing through a chimney from a stove to the exterior of the building will experience a decrease in temperature as they pass through the chimney.
The decrease in temperature might be small due to insulation surrounding the chimney, but without a chimney fire being present it would not be expected that combustion gases would leave a chimney at a higher temperature than that at which they entered the chimney. When reference is made henceforth to combustion gases entering a chimney that reference to a chimney should be understood to mean the duct means that conveys the combustion gases from the point at which they leave the stove to the point at which ~, they are exhausted from the building.
The sub~ect invention recognizes that an indicator of a chimney fire is a combustion gas temperature at the outflow end of a chimney exceeding thP combustion gas temperature at the inflow end of the chimney. By positioning means for measuring the temperature of the combustion gases at the inflow and outflow ends of a chimney and by comparing those temperatures, the subject invention detects a chimney fire and proceeds to activate an alarm. Measurement of the combustion gas temperatures is conveniently done by thermocouples mounted in probes which are extended into the interior of the chimney. The signals_output from the thermocouples are connected to the two inputs of an electronic comparator which has the alarm connected to its output. Means may be utilized to amplify the signal levels from the thermocouples prior to their input into the comparator. Additionally, a means for reducing the amplitude of the signal from the thermocouple at the outflow end of the chimney may be connected to the one input of the electronic comparator. This arrangement acts to ensure that the alarm activated by the output of the comparator is only activated when the temperature of the combustion gases leaving the chimney is above the temperature of the combustion gases entering the chimney.
In a further form of the invention, the temperature of the combustion gases entering the chimney from the stove is compared to a reference temperature selected by the operator of the sub~ect device. The comparison is accomplished by a second electronic comparator which has an alarm connected to its output to indicate when the combustion gases leaving the stove have a temperature above the selected temperature. When that second alarm is activated the occupant of the building may decide to reduce the size of the fire in the stove;
in turn, the second alarm becomes deactivat~d when ~0~83B
the temperature of combustion gases leaving the stove drop below the selected temperature. The alarms may be in the form of light emitting diodes each connected in parallel with a tone generator to create both a visible and audible alarm.
The subject invention will now be more fully described by means of a preferred embodiment utilizing the accompanying drawings in which:
Figure 1 is a schematic drawing of the Plectronic circuit utili~ed in the preferred embodiment of the subject invention.
Figure 2 is a perspective view of a housing holding the electronic circuitry schematically illustrated in Figure 1.
Figure 3 is a sectioned side view of a first building having the preferred embodiment of the sub~ect invention installed in a first type of chimney.
Figure 4 is a perspective view of a second building having a preferred embodiment of the sub~ect invention installed in a second type of chimney.
With reference to the schematic circuit of Figure 1, the leads from a thermocouple positioned at the combustion gas outflow end of a chimney are designated 11 and 12, 11 being a grounded lead and 12 being a lead having a positive voltage that varies according to the temperature sensed by the thermocouple. The corresponding pair of leads from the combustion gas inflow end of the chimney are designated 13 and 14, 13 being a grounded lead and 14 being a lead bearing a positive voltage varying with the temperature sensed by the associated thermocouple. The two thermocouples are identical and o~-tput the same voltage levels when acted upon by the same temperatures. The two thermoouples each have a linear response wi~h temperature, each producing a potential difference across its leads of i,o microvolts per degree Centrigrade above 0C. For ins~ance, if either thermocouple sensed a temperature o~ 600 C., .
~9`~ 3 that thermocouple would have a 24 millivolt potential difference across its leads.
Operational amplifiers 16 and 17 amplify the voltage on thermocouple leads 12 and 14, respectively.
Each of the operational amplifiers 16 and 17 produce a voltage gain of 150; to accomplish that voltage gain, the value of resistors 19 and 20 are selected to be 802 Kohms and the value of resistors 21 and 22 are selected to be 5.42 Kohms. The value of resistors 23 and 24 are selected to be 2.2 Kohms so as to reduce the input current to the operational amplifiers to the level of microamperes. The particular operational amplifiers utilized are a pair located on a single integrated circuit chip, that chip being a LM358N.
The result of the voltage amplification is that output lines 27 and 28 of the combustion gas outflow and inflow ends, respectively, of the chimney each have a voltage of 3O5 volts when the respective thermocouples are sensing a temperature of 600C. Output line 27 enters diode ~0 29, and the voltage on output line 30 from that diode is always approximately 0.2 volts lower than the voltage on output line 27. The reason for reducing the voltage on line 30 below that on line ~8 when the thermocouples at the inflow and outflow ends of the chimney are sensing the same temperature is to ensure that the temperature at the outflow end of the chimney is greater than the temperature at the inflow end of the chimney when the voltage on line 30 is the same or greater than the voltage on line 28. Diode 29 is the type lN4002; the voltage drop of approximately 0.2 volts across diode 29 corresponds to a temperature diference Df approximately 35C.; in other words, the voltage on line 30 only exceeds the voltage on line 28 when the thermocouple connectPd to leads 11 and 12 (located at the outflow end of the chimney) senses a temperature at least 35 C. above the temperature sensed by the thermocouple having leads 3~3 13 and 14 (the thermocouple positionedat the inflow end of the chimney).
The voltages on lines 28 and 30 are input to a comparator 35. The comparator 35 maintains a low level output voltage on its output line 36 when the voltage on line 28 is higher than the voltage on line 30; that is the case when the temperature of the combustion gases leaving the chimney is less than 35 C. above the temperature of the combustion gases entering the chimney, as would be the case except when a fire is present in the chimney. A low voltage level on comparator output line 36 produces insufficient current across resistor 37 to activate light emitting diode 38. Also, insu~ficient current passes through diode 39 to activate tone generator 40. On the other hand, a high output voltage on comparator output line 36 is sufficient to generate enough current to activate light emitting diode 38 as well as tone generator 40. That high level voltage is generated on comparator output line 36 when the temperature of the combustion gases leaving the chimney is more than 35 C. above the temperature of the combustion gases entering the chimney. The comparator 35 is constructed from an operational amplifier of the type LM358N.
Output line 28 from operational amplifier 17 is passed to the positive input of a second comparator 42.
The purpose of the second comparator 42 is to compare the temperature of the combustion gases flowing into the chimney with a preselected temperature set by the operator' of the device. As can be seen from Figure 19 the voltage on the negative input to second comparator 42 is ad~ustable, with resistor 43, potentiometer 44 9 and resistor 45 acting as a voltage divider, and potentiometer 44 being tapped for the negative input voltage. The values of resistors 43 and 45, and potentiometer 44 9 are selected with a view to the voltages produced on line 28 when various temperatures are sensed by the thermocouple at the ~ ~04~3~3 combustion gas inflow end of the chimney. The circuit of Figure 1 is operated by a six volt battery, and the value of resistors 43 and 45, and the total resistance of potentiometer 44, have been chosen to be 1 Megohm, 2 Megohms, and
2.2 Megohms, respectively. Therefore, the negative input to second comparator 42 can vary between approximately 1.1 volts and
3.5 volts, which corresponds approximately to a temperature range between 200C. and 600C. As mentioned~ the particular value of the voltage at the negative input of second comparator 42 depends upon the setting of potentiometer 44. If the temperature measured by the thermocouple at the combustion gas inflow end of the chimney is above the tempPrature correspondin~ to the setting on potentiometer 44 then the output line 46 of second comparator 42 assumes a high voltage level which is sufficient to produce enough current across resistor 47 to activate light emitting diode 48 and also activate tone generator 40. Diode 49 serves the same purpose a diode 39, namely, to prevent the output line of either comparator 35 or 42 feeding current into each other. Comparators 35 and 42 can be constructed from a single operational amplifier chip, the LM358~.
Switch 50 may be incorporated into the circuit in association with zener diode 51forbattery testing.
Zener diode 51 is of the type lN4730, which drops 3.9 volts and is sufficient to simulate the voltage losses across the operational amplifiers when the circuit is operating. With switch 50 closed the tone generator 40 is thereby sub;ect to a load corresponding to that when one of the output lines 36 and 46 assumes a high voltage level. I~the battery is low the tone generator 40 will produce a correspondingly low audible signal. To test comparator 35 a switch may be positioned between thermo-couple lead 12 and resistor 23; when that switch is opened the positive input of operational amplifier 16 will assume a high level and output line 36 of comparator 35 will assume a high voltage level output.
~20~3~
A similar test can be conducted with respect to comparator 42 by incorporating into the circuit a means for selectively connecting the ground voltage to the negative input of that comparator (for instance, by shorting across resistor 43), the output line 46 thereby being driven to a high voltage level. With respect to diodes 39 and 49, they are of the type lN5819.
An integrated circuit board having the circuit schematically illustrated in Fi~ure 1 can conveniently be mounted into the housing 55 illustrated in Figure 2. The tone generator 40 is mounted in housing 55 behind the perforations 56. The outer tips of light emitting diodes 38 and 48 extend through the front panel of housing 55. Light emitting diode 38 is red in colour so as to indicate the more dangerous condition it represents in comparison to light emitting diode 48, which is yellow in colour. Slidable control arm 57 is connected to potentiometer 44 to set the maximum selected temp-erature for combustion gases leaving the stove and entering the chimney. As previously mentioned, the word "chimney"
as used in this document refers generally to the path of combustion gases from the point at which they leave the stQve to the point at which they are exhausted from the building. Control arm 57 has a lower discrete position in which the negative input of second comparator ~2 is connected to ground for testing the effectiveness of the circuit that measures the temperature of combustion gases entering the chimney. The button 58 is depressed to open the connection between thermocouple lead 12 and resistor 23; light emitting diode 38 and tone generator 40 will be activated by depression of that button since it creates a simulation of a high temperature condition at the outflow end of the chimney. Thermocouple leads ll and 12 are connected to screw terminals 60 and 61, and thermocouple leads 13 and 14 are connected to screw terminals 62 and 63. A button (not shown) is mounted on housing 55 for activating battery test switch 50.
Figures 3 and ~ illustrate two types of buildings in which the preferred embodiment of the fire alarm system 83~1 of the sub~ect invention may be installed. In Figure 3, probe 65 housing a thermocouple is inserted into the combustion gas inflow end of a chimney generally designated as 66. A pair of ther~ocouple leads 67 extend from probe 65 to the screw terminals 62 and 63. Similarly, a probe 68 is secured to the chimney so as to extend into the chimney at a position proximate of where the combustion gases leave the chimney. A pair of thermocouple leads 69 extend from the thermocouple contained within probe 68 to connect with the screw terminals 60 and 61 on housing 55. Figure 4 illustrates a second building have a fireplace 70 and an integral chimney 71. One probe 72 has been inserted through the wall of the building above the fireplace70 such that the thermocouple in probe 72 is exposed to combustion gases entering chimney 71. A probe 73 has been fixed to the upper end of the chimney such that a thermocouple in the probe can measure the temperature of combustion gases leaving the chimney. The thermocouple in probe 72 is connected to housing 55 by a pair of thermocouple leads 74, and the thermocouple in probe 73 is connected to housing 55 by~..a pair of thermocouple leads 75.
Switch 50 may be incorporated into the circuit in association with zener diode 51forbattery testing.
Zener diode 51 is of the type lN4730, which drops 3.9 volts and is sufficient to simulate the voltage losses across the operational amplifiers when the circuit is operating. With switch 50 closed the tone generator 40 is thereby sub;ect to a load corresponding to that when one of the output lines 36 and 46 assumes a high voltage level. I~the battery is low the tone generator 40 will produce a correspondingly low audible signal. To test comparator 35 a switch may be positioned between thermo-couple lead 12 and resistor 23; when that switch is opened the positive input of operational amplifier 16 will assume a high level and output line 36 of comparator 35 will assume a high voltage level output.
~20~3~
A similar test can be conducted with respect to comparator 42 by incorporating into the circuit a means for selectively connecting the ground voltage to the negative input of that comparator (for instance, by shorting across resistor 43), the output line 46 thereby being driven to a high voltage level. With respect to diodes 39 and 49, they are of the type lN5819.
An integrated circuit board having the circuit schematically illustrated in Fi~ure 1 can conveniently be mounted into the housing 55 illustrated in Figure 2. The tone generator 40 is mounted in housing 55 behind the perforations 56. The outer tips of light emitting diodes 38 and 48 extend through the front panel of housing 55. Light emitting diode 38 is red in colour so as to indicate the more dangerous condition it represents in comparison to light emitting diode 48, which is yellow in colour. Slidable control arm 57 is connected to potentiometer 44 to set the maximum selected temp-erature for combustion gases leaving the stove and entering the chimney. As previously mentioned, the word "chimney"
as used in this document refers generally to the path of combustion gases from the point at which they leave the stQve to the point at which they are exhausted from the building. Control arm 57 has a lower discrete position in which the negative input of second comparator ~2 is connected to ground for testing the effectiveness of the circuit that measures the temperature of combustion gases entering the chimney. The button 58 is depressed to open the connection between thermocouple lead 12 and resistor 23; light emitting diode 38 and tone generator 40 will be activated by depression of that button since it creates a simulation of a high temperature condition at the outflow end of the chimney. Thermocouple leads ll and 12 are connected to screw terminals 60 and 61, and thermocouple leads 13 and 14 are connected to screw terminals 62 and 63. A button (not shown) is mounted on housing 55 for activating battery test switch 50.
Figures 3 and ~ illustrate two types of buildings in which the preferred embodiment of the fire alarm system 83~1 of the sub~ect invention may be installed. In Figure 3, probe 65 housing a thermocouple is inserted into the combustion gas inflow end of a chimney generally designated as 66. A pair of ther~ocouple leads 67 extend from probe 65 to the screw terminals 62 and 63. Similarly, a probe 68 is secured to the chimney so as to extend into the chimney at a position proximate of where the combustion gases leave the chimney. A pair of thermocouple leads 69 extend from the thermocouple contained within probe 68 to connect with the screw terminals 60 and 61 on housing 55. Figure 4 illustrates a second building have a fireplace 70 and an integral chimney 71. One probe 72 has been inserted through the wall of the building above the fireplace70 such that the thermocouple in probe 72 is exposed to combustion gases entering chimney 71. A probe 73 has been fixed to the upper end of the chimney such that a thermocouple in the probe can measure the temperature of combustion gases leaving the chimney. The thermocouple in probe 72 is connected to housing 55 by a pair of thermocouple leads 74, and the thermocouple in probe 73 is connected to housing 55 by~..a pair of thermocouple leads 75.
Claims (14)
1. An electronic device for detecting a fire in a chimney carrying combustion gases from a stove, the device comprising:
(a) means for producing a first signal varying as a function of the temperature at a first position inside of the chimney, the first position being proximate of the outflow end of the chimney;
(b) means for producing a second signal varying as a function of the temperature at a second position inside of the chimney, the second position being proximate of the inflow end of the chimney; and, (c) means for comparing the first and second signals, and for activating a first alarm when the comparison of signals indicates that the temperature at the first position in the chimney exceeds the temperature at the second position.
(a) means for producing a first signal varying as a function of the temperature at a first position inside of the chimney, the first position being proximate of the outflow end of the chimney;
(b) means for producing a second signal varying as a function of the temperature at a second position inside of the chimney, the second position being proximate of the inflow end of the chimney; and, (c) means for comparing the first and second signals, and for activating a first alarm when the comparison of signals indicates that the temperature at the first position in the chimney exceeds the temperature at the second position.
2. An electronic device as in claim 19 wherein the first and second signal means each comprise a thermocouple, each of the two thermocouples being selected so as to output the same voltage differential when acted upon by the same temperature.
3. An electronic device as in claim 1, and also comprising third signal means selectively adjustable by an operator of the device for producing a third signal, and further comprising means for comparing the second signal to the third signal and for activating a second alarm when the comparison of those two signals indicates that the temperature at the second position in the chimney exceeds a temperature value selected by the operator of the device and corresponding to the third signal.
4. An electronic device as in claim 3, wherein the first and second signal means each comprise a thermocouple, each of the two thermocouples being selected so as to output the same voltage differential when acted upon by the same temperature.
5. An electronic device as in claim 2, wherein the one lead of each thermocouple is connected to a common ground and wherein the other lead of each thermocouple is connected to a respective input of a first electronic comparator, the first alarm being connected between the output of the first electronic comparator and the common ground.
6. An electronic device as in claim 4, wherein the one lead of each thermocouple is connected to a common ground and wherein the other lead of each thermocouple is connected to a respective input of a first electronic comparator, the first alarm being connected between the output of the first electronic comparator and the common ground, and wherein the other lead of the thermocouple of the second signal means is also connected to an input of a second electronic comparator, the other input to the second electronic comparator being a voltage differential from the common ground corresponding to the temperature value selected by the operator of the device, the second alarm being connected between the output of the second electronic comparator and the common ground.
7. An electronic device as in claim 5 or 6, wherein the other lead of the thermocouple of the first signal means is indirectly connected to the respective input of the first electronic comparator, that other lead being connected to the comparator through a voltage reducing element, the voltage reducing element acting to reduce the voltage at the one input of the first electronic comparator compared to that at the other input when the temperatures acting on the first and second thermocouples are the same, the presence of the voltage reducing element acting to ensure that the first alarm is activated only when the temperature at the first position in the chimney exceeds the temperature at the second position.
8. An electronic device as in claim 5 or 6, wherein the other lead of each of the thermocouples is indirectly connected to the respective input of the first electronic comparator, each of the other leads being connected to the input of a respective voltage amplifying means, the output of each voltage amplifying means being connected to the respective input of the first electronic comparator.
9. An electronic device as in claim 5 or 6, wherein the other lead of each of the thermocouples is indirectly connected to the respective input of the first electronic comparator, each of the other leads being connected to the input of a respective voltage amplifying means, the output of the voltage amplifying means connected to the other lead of the thermocouple of the first signal means being connected to one input of the first electronic comparator, the output of the voltage amplifying means connected to the other lead of the thermocouple of the second signal means being connected to the other input of the first electronic comparator through a voltage reducing element, the voltage reducing element acting to reduce the voltage at the one input of the first electronic comparator compared to that at the other input when the temperatures acting on the first and second thermocouples are the same, the presence of the voltage reducing element acting to ensure that the first alarm is activated only when the temperature at the first position in the chimney exceeds the temperature at the second position.
10. An electronic device as in claim 5, wherein the first alarm comprises a light emitting diode connected in a parallel circuit with a tone generator.
11. An electronic device as in claim 6, wherein the first alarm comprises a first light emitting diode connected in a parallel circuit with a first diode and a tone generator, and wherein the second alarm comprises a second light emitting diode connected in a parallel circuit with a second diode and the tone generator.
12. A method for detecting a fire in a chimney carrying combustion gases from a stove, the method comprising the steps of:
(a) measuring the temperature at a first position inside of the chimney proximate of the outflow end of the chimney;
(b) measuring the temperature at a second position inside of the chimney proximate of the inflow end of the chimney;
(c) comparing the temperature at the first position in the chimney with the temperature at the second position in the chimney; and (d) activating an alarm if the temperature at the first position in the chimney exceeds the temperature at the second position.
(a) measuring the temperature at a first position inside of the chimney proximate of the outflow end of the chimney;
(b) measuring the temperature at a second position inside of the chimney proximate of the inflow end of the chimney;
(c) comparing the temperature at the first position in the chimney with the temperature at the second position in the chimney; and (d) activating an alarm if the temperature at the first position in the chimney exceeds the temperature at the second position.
13. A method for detecting a fire in a chimney as in claim 12, wherein the temperatures at the first and second positions are measured by means of thermocouples, the thermocouples each having one lead connected to a common ground and another lead connected to a respective input of a first electronic comparator.
14. A method for detecting a fire in a chimney as in claim 13, wherein the other lead of the thermocouple at the second position in the chimney is connected to one input of a second electronic comparator, the other input of the second electronic comparator being connected to a voltage means capable of selective voltage adjustment.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000466491A CA1204838A (en) | 1984-10-29 | 1984-10-29 | Chimney fire alarm device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000466491A CA1204838A (en) | 1984-10-29 | 1984-10-29 | Chimney fire alarm device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1204838A true CA1204838A (en) | 1986-05-20 |
Family
ID=4129020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000466491A Expired CA1204838A (en) | 1984-10-29 | 1984-10-29 | Chimney fire alarm device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1204838A (en) |
-
1984
- 1984-10-29 CA CA000466491A patent/CA1204838A/en not_active Expired
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| MKEX | Expiry |