IE72463B1 - A process of monitoring and ensuring the safe operation of unvented stoves particularly kerosene stoves and apparatus for practising said process - Google Patents

Description

A PROCESS OF MONITORING AND ENSURING THE SAFE OPERATION OF UNVENTED STOVES. PARTICULARLY KEROSENE STOVES, AND APPARATUS FOR PRACTISING SAID PROCESS invention relates to a process of monitoring and sate operation of an unvented stove5particularly ensuring of a ke~ „ rosene heater in an indoor space both in the normal heating condition in which the height of the flame produced by the burner is within a predetermined range which is monitored by radiation-response means to detect flame heights outside said range, as well as in operation outside said normal heating condition, wherein flame heights higher and lower than said predetermined range causing corresponding control signals to be'generated and to be coupled to an electronic control circuit so as to enable the normal heating condition to be re15 stored or, if the burner consistently operates outside said predetermined flame height range for more than a predetermined period of time, to generate a warning signal and to automatically shut down the burner after a corresponding timeout delay .

Further, the invention relates to a safety apparatus for monitoring and ensuring the safe operation of an unvented oven and particularly of a kerosene heater for practicing the inventive process as stated in the preamble of patent claim 12.

The European countries have recently tightened safety regula25 tions relative to indoor air pollution caused by unvented ovens and particularly by kerosene heaters with one- or twostage burners - to be monitored strictly operation (see U.S. Patent 4,390,003). tor sare There have been known safety systems for ovens and particularly for kerosene heaters (WO-A-86058S0) in which, once the oven or heaters has attained its normal operation, the height of the flames the burner produces may exceed a predetermined range and/or the heating means as well as the burner head and the associated piping may heat up to the point where the oven assumes an undesirable operating condition. The prior safety apparatus includes sensing means for detecting flame heights higher than a predetermined maximum and for providing a corresponding measuring and/or control signal which is coupled to actuating means responsive thereto to return the kerosene heater to the desired operating state or to shut it down. For a kerosene heater with a one-stage burner, the sensing means in the prior safety apparatus comprises two light sensors or thermal radiation detecting sensors each associated with an upper or lower limit of said predetermined range of flame heights in the normal operation of the kerosene heater. The burner's wick is re-adjusted manually or in accordance with the measuring signals generated by the light sensors as the flame height exceeds the predetermined flame height range: alternatively the burner is shut down positively by means of a drop bar as soon as the flame height has exceeded the predetermined flame height range continuously for a pre-determined period of time.

This prior safety 30 radiation-responsive it does not satisfy number of inherent burner is operated height, this condit sensor associated predetermined flame apparatus is detection of based solely on a flame height. However, latest safety regulations as it has a uncertainties. For example, if the from the beginning at the lowest flame ion will not be detected by the light with the lower limit of the height range. Once the burner has - 3 burned at its lowest flame height for an extended period of time because the user has forgotten to shut down the heater, for example, there exists a great danger of the indoor space air containing inadmissible levels of CO2 since the absence of a light-responsive minimum flame height detection feature prevents the heater from being shut down automatically.

Since the wick fabric always includes irregularities, it is possible for the burner flame in normal heater operation to temporarily exceed the top limit of the predetermined flame height range - which may cause the prior safety apparatus to prematurely automatically shut down the burner although the maximum permissible CO2 level in the indoor air has not yet been reached. In an oven or heater equipped with the prior safety device, such preliminary burner shut down results in the emission of foul smell and soot, since the hot burner piping does not have enough time to cool down sufficiently to prevent the kerosene still present in the wick fabric from being burned by the heat the burner pipe will radiate so that an intensive smell will be emitted.

In indoor spaces where an unvented kerosene heater is being operated and air ventilation is not sufficient, the CO2 will increase and the O2 concentration decrease (CH4 425 2Ο9 -> CC>2 + 2^0) . A lack of oxygen results in incomplete combustion, however, which results in increased CO and CO-? levels. As a consequence, there exists a direct relationship between the 02 and C02 or CO concentrations on the one hand and between the CO2 and CO concentrations on the other. As the CO2 level rises, so will the CO level.

Gas sensors of the type used in conjunction with microcomputers for automatically controlling air cleaning equipment /. «s·» or fans to which detect via electric resistance changes the amount of CO, and a number of other organic components in gaseous environments such as kitchen vapors, cigarette smoke or automobile exhaust gases have been known per se (Figaro Eng. Inc., type TGS 800).

US-A-4,449,919 describes a process and an apparatus of monitoring an unvented stove using an 0j sensor which responses to a definite flame height and then delivers a shut down signal to the burner.

Also in medicine, it has been known to use 02 sensors for monitoring the oxygen enrichment level in artifical respiration apparatus (US-A-4,495,051) . Such an 07 sensor may have the form of a galvanic cell, for example, comprising a lead anode, an oxygen cathode made of gold and a weakly acidic electrolyte.

The object underlying the invention is to provide a process of the nature specified above as well as an apparatus for practicing that process which avoid the drawbacks stated above and which answer today's stringent safety requirements. In particular, kerosene ovens or heaters are to be monitored and to be operated safely in a manner not necessarily dependent on a radiation-response detection of flame height.

In accordance with the ixxvention, the object underlying the invention is achieved by sensitively detecting the O2 percentage in the burner off-gases inside the kerosene heater and using it as a measure for monitoring the amount of C0? in the burner off-gases and converted to a voltage signal forming said control signalseffecting burner operation outside the predetermined flame height range the sensitive O2 detection under program control both for restoring the normal heating condition and for monitoring bur- 5 ner operation at minimum flame height, and using the electronic control circuit to generate the alarm signal and to » automatically shut down the burner after a delay at predetermined first and second 09 concentrations- in the burner off-gases each corresponding to a predetermined C07 concentration in the indoor air. said second concentration being lower than said first concentration.

Patent claims 2 to 11 relate to advantageous further developments of the inventive process. Ιθ In accordance with a preferred practice of the invention the warning signal is generated and the burner shut down automatically when the θ£ in the burner off-gas has reached the level corresponding to the permissible maximum of 0.8 % in the indoor air.

Prefereably, burner shut-down is 90 sec. after the warning signal of 0^ or too high a CO-CC^ level effected automatically e.g. indicating too low an amount has been issued.

The inventive safety apparatus for monitoring and ensuring of an unvented oven and particularly of a kerosene heater according to the preamble of claim 12 is used for practicing the process of the invention according to claims 1 to 11 and characterized by the sensor means additionally comprising an O^sensor coupled to a microprocessor, said sensor being mounted within housing of kerosene heater in the bottom housing position, detecting the (^percentage in the burner off-gases and converted to a voltage signal forming said control signal in the electronic control circuit coupling said control signal to the wick adjusting means, the warning means and shut down means for the burner, each 3θ of them are connected with the electronic control circuit, wherein, when the burner is operating outside said predetermined ϊ latte height range, the voltage signal of the O2 sensor is causing the wick adjusting means to re-establish the normal heating condition of the kerosene heater and is serving to monitor the opex-ation of the burner at the lowest flame height in a manner,that with predetermined first snd second 02 concentration in the off-gases of burner warning means and the automatic shut down means of burner ere operated by the electronic control circuit wirh said second concentration being lower than said first concentration, and chat a vibration protection means is provided.

Advantageously, a CO sensor may additionally be provided on an electronic circuitry card mounted on a bracket in a top corner of the kerosene heater housing behind a screen reflecting the heat radiated by the burner and having an opening such that a small portion of the off-gas stream passing through the opening in the reflecting screen may contact the CO sensor.

Using the inventive process and the inventive apparatus for practicing it, it is possible to operate unvented ovens and particularly kerosene heaters in indoor spaces and to correctly and consistently meet safety parameters even more stringent than the official safety regulations presently in force. In particular, accurate CO2 monitoring does not necessarily have to rely on a detection of the burner's flame height.

For example, if the oxygen concentration in the air of an indoor space decreases, so will the flame height, meaning that e.g. in a two-stage burner kerosene heater the second burner stage does not operate any more, causing high CO emission and an increased CO2 concentration in the indoor air. The inventive safety apparatus directly and accurately detect a - 7 decrease of the oxygen concentration inside the housing of the kerosene heater so that an increase of the CO2 in the indoor air will be precisely detected. At the same time, the inventive safety apparatus is capable of accurately and directly detecting an increased CO concentration already in the interior of the housing of the kerosene heater and thus ensures an accurate monitoring of the minimum flame height of the kerosene heater's burner.

The inventive safety apparatus measures the O2 concentration in the burner off-gases in the housing of the kerosene heater to detect the CO2 concentration in the indoor air and converts the O2 concentration to a voltage signal. The set value is the voltage corresponding to the maximum permissible CO2 concentration in the indoor air, which for the inventive safety apparatus is defined as being 0.8%. When the CO2 concentration in the indoor air exceeds 0.8% (according to the rating established by the TUV (Technical Inspection Association in West Germany), the maximum permissible level is 1%), the shut-down feature in the inventive safety apparatus automatically deactivates the burner. This means that the inventive safety apparatus operates well below the limit stipulated by applicable safety regulations.

The amount of CO2 in the indoor air is measured by means of an O2 sensor in the form of a galvanic cell which is mounted on circuit board supported by the housing of the kerosene heater.

The following procedures are used to check the CO2 concentration: - 8 1 . CO2 is measured after a delay of e.g. 4 min. following the activation of the kerosene heater so as to allow the sensor voltage to settle. 2. Any alarm is delayed for e.g. 30 seconds to prevent transients from triggering the feature. 3. An intermittent buzzer signal, which may comprise three tones and lasts a maximum of 90 seconds is generated to indicate an excess CO-CO2 concentration in the indoor air. Within that period, indoor ventilation may be improved (e.g. by opening a door or a window) so as to reduce the CO-COj level. 4. Deactivation of the kerosene heater by means of a solenoid in case such ventilation has failed to improve the indoor air within 90 seconds.

C>2 sensor malfunction due to the operation thereof at very low temperatures of towards the end of its useful life result in a sensor output voltage Usensor lower than 30 mV; this condition is indicated by an intermittent buzzer signal comprising e.g. seven beeps for a duration of 90 seconds after the kerosene heater has been (deactivated.

The O2 sensor used in the inventive safety apparatus has the following advantages : 1. An extremely long service life (5 to 10 years). 2» In sensitivity to CO2 and other sour components. 3. Enhanced reliability and accuracy because of the relationship existing between an O2 decrease and a CO/CO2 increase due to combustion taking place in poorly ventilated indoor spaces. 4. A possibility exists for setting the alarm voltage Ua of the O2 sensor. - 9 10 . Self-contained power supply of the C>2 sensor forming a galvanic cell, so that a 3V DC voltage of the electronic control circuit in the kerosene heater can be maintained.

The only aspect to be kept in mind is that the difference between operating voltage Uo and the voltage corresponding to 0.8% CO2 in the indoor air may be rather slight. As will be seen in the test results shown in the following Table 1, the O2 sensor's alarm voltage Ua is 2 mV. For this reason, stability, a high signal-to-noise ratio as well as a low level of sensitivity to temperature fluctuations call for a high-quality operational amplifier operating at a Ua gain (K) of 100. The accuracy of CO2 control action depends mainly on voltage drift of the O2 sensor and in the hardware of the electronic control circuit inside the kerosene heater. The O2 sensor in the inventive safety apparatus is rated at 2% of average voltage drift per year.

Assuming a O2 sensor output of 50 mV, the above rating amounts to a drift of one millivolt per year. At Ua = 2 mV, and an operating voltage UQ fixed at the factory by means of a potentiometer, the C02 control action can be expected to be highly reliable over a period of one year.

Inside the test period, the operating voltage Uo will fluctuate slightly on a day to day basis. When the kerosene heater equipped with an O2 sensor is activated in a well-ventilated indoor space, temperature effects will cause the sensor voltage Usensor to rise to approx. 2 mV within a period of 90 min.

The use of a microprocessor in the control system of the inventive safety apparatus enables the aforesaid problems to be solved. With the aid of the microprocessor, it is possible after each burner activation inside the kerosene heater ‘30 -10co determine operating voltage Ue as a maximum voltage level before a poor ventilation of the indoor space causes the sensor voltage to decrease. The sensor voltage is checked every 4 minutes and compared to the preceding value. Fol5 lowing determination of the operating voltage Uo , sensor alarm voltage Ua results from the relationship U.1 = Uo “AU. . 'able 1 (Analysis of the test results obtained with a type ΧΞ-50 oxygen sensor coupled to the microprocessor of the electronic control circuit circuit in the inventive safety apparatus) Test No .Uo (mV) U 0,3 $ (mV) AU 0,3 (mV) * (mV) Λ U *- a (mV) C02 % Φ “Sensor On 1 45,70 4-5,85 1 ,87 4-5,71 1,99 0,875 17-57 2 45,52 - - 45,59 2,15 0,77 29-45 5 ^6,53 44,52 2,06 44,52 2,06 0,30 9-24 Zi 4-6,85 - - 44,95 1,90 0,725 8-21 5 4-6,67 - - 44,70 1,97 0,75 1p-«xp o 4-7,55 45,1 2,^5 44,15 5,59 1,18 5-25 7 4-5,39 44,0 7>G 4-5,35 1,56 1,09 - 8 47,25 45,2 2 7 0 p op 2,58 0,95 5-21 Q y 4-5,30 44,6 1 ,20 4^.,23 1,52 1,15 - 10 4-5,52 /i /1 X| ..,1 Ί zxP 45,90 1,62 0,8^ - 11 4-5,76 44,17 *** ι -''-i 44,12 1,64 0,845 — Aver ace : 1,75 2,01 0,905 Test % (J 0,3 >3 U 0,3 2 JiCL— 7a 4-5,53 42,84 2,52 9a 44,97 4-2,70 2,27 10a 45,41 45,40 2,01 A determination of operating voltage Uo following each burner activation is advantageous in that it eliminates the influence of any voltage drift on CC>2 monitoring. However, problems may arise if the ventilation of an indoor space has not improved after an excessive CO2 level has caused the burner to be turned off and the kerosene heater has recklessly been reactivated though the CO2 level in the indoor air was still too high. In that case, the corresponding sensor voltage, which differs from the voltage resulting from a well ventilated condition of the indoor space, would then be used as the operating voltage Uo in a disadvantageous manner. As a result, shut-down due to an excessive C02 level would result in a further increase thereof after each activation of the kerosene heater.

This problem may be solved by setting the operating voltage Uo to a fixed level for a period of 45 minutes in case an excessive CO2 level in the indoor air has caused the burner to be shut down. If the burner is re-activated within this period, CO2 control will be based on that fixed operating voltage Uo. It is assumed that the CO2 concentration will have returned to its normal level after 45 minutes so that the operating voltage Uo is again determined in the manner described above.

When the burner flame exceeds its predetermined height range, soot or smoke may be generated and the fire hazard increases. The inventive safety apparatus includes a light sensor associated with the maximum permissible flame size which is located at a corresponding level in the vicinity of the combustion chamber of the kerosene heater. This sensor cooperates with the electronic control circuitry in the inventive safety apparatus to provide the required control functions such as: 1. A timeout of about 3 seconds to override transients; 2. Generation of an intermittent acoustic alarm signal (such as 5 tones) if the height of the burner flame exceeds the top limit of the predetermined flame height range; and 3. Automatic burner shut-down if the flame height has not returned to the predetermined flame height range within a period of e.g. 60 seconds following the triggering of an alarm signal.

In a poorly ventilated indoor space, operation of the kerosene heater with too high a burner flame causes an oxygen deficiency, incomplete combustion and thus increased CO-CO2 levels in the indoor air. In this situation, the 02 sensor included in the inventive safety apparatus provides a monitoring action in addition to that effected by the light sensor.

When the burner is shut down automatically, it is important to prevent the smoke and the accompanying smell the heaters equipped with conventional safety devices generate.

The inventive process and the inventive safety guarantee an automatic shut down of burner in that the minimized. generation oa the aforesaid smell apparacus a manner will be The inventive safety apparatus ensures automatic shut-down of the burner sequence of steps: The rotary knob of adjusting device is set to a very low by the following the burner's wick flame height; the correct setting is indicated by a coloured marker and an intermittent acoustic signal for a duration of approx. 3 seconds. With the burner adjusted to this wick setting, to operate e.g. for another 4 as to prevent the emission of smell-forming This period allows the heating pipe and the the burner will continue minutes so components, burner head to cool down sufficiently.

Thereafter, a solenoid in the shut-down means is energized to deactivate the burner to minimum of smell being developed. The cooling period may be terminated at any time by turning the wick up by means of the control knob of the burner wick adjustor device.

The inventive safety apparatus includes a replaceable set of batteries to supply power to all electric power consuming elements inside the kerosene heater, such as the ignition coil, the electronic control circuitry including the microprocessor, the heater element associated with the CO sensor.

Turning the wick adjusting device in a clockwise direction causes the main switch to be activated to close the electronic control circuit. Initially, the battery is tested. If battery voltage Uh is lower than 2.3 V, ignition will not be possible and the buzzer will sound a continuous signal for about 30 seconds to indicate that the battery should be replaced. After 30 seconds, the alarm signal is discontinued and the process of warming up or heating the kerosene heater discontinued by a solenoid acting to reset the wick.

With the battery voltage in its normal range, ignition will be possible and must take place within e.g. 15 seconds. If it does not, an intermittent buzzer signal will be sounded for e.g. 90 seconds; during the period, it is still possible to ignite the heater. If ignition has not been effected after 90 seconds, the solenoid resets the heater to its deactivated condition.

After ignition has been effected, a periodic monitoring cycle is started wherein the battery voltage is checked in the aforesaid manner; also, both flame height and CO2 concentration in the off-gas are checked 4 min. after the initial warm-up of the kerosene heater In the inventive safety apparatus, it has turned out to be advantageous that the frequency of the microprocessor can be selected to reduce the power consumption of the electronic control circuitry. The microprocessor operates satisfactorily between 0.5 and 5 MHz. At a frequency f= 0.5 MHz, current I as selected is 2.5 mA and increases to I = 30 mA at f = 5 MHz. 0.5 MHz, the At microprocessor operates much more slowly that at MHz; in the present application totally inconsequential, however. :his difference is nventive safety apparatus inside the housing of the the burner igniting means from operating in case the improperly placed into the It should be noted that the i includes a mechanism mounted kerosene heater which prevents and the wick adjusting means battery is missing or has been battery case.

The fuel level is monitored in a continuous manner at the bottom of the fuel tank by means of conventional circuitry. If the level is too low, an intermittent buzzer signal will be emitted together with a flashing bottom light for a time of e.g. 3 minutes. The amount of fuel available at the tank bottom in this condition is sufficient to keep the burner operating for another 30 minutes or so.

The inventive process and the inventive safety apparatus for practicing said process will now be explained under reference to the drawing.

Fig. 1 shows a schematic view in section of a kerosene heater equipped with the inventive safety apparatus; Fig. 2 shows a view in perspective of the kerosene heater in Fig. 1; Fig. 3 is a plot showing the manner of determining sensor operating voltage Uo; Fig. 4 plots the oxygen in the indoor air versus time and CO-CO? concentration; Fig. 5 is a block diagram showing the process of monitoring the operation of the kerosene heater and ensuring the safety thereof; Fig. 6a, 6b show views in perspective of two embodiment examples of a mechanism included in the inventive safety apparatus to prevent burner ignition or operation of the wick setting means if the battery is missing or has been placed improperly in the battery case.

As shown in Figs. 1 and 2, kerosene heater 1 has a housing 2 wherein is centrally mounted a burner 4 having wick adjusting means 3 associated therewith; the burner may be a one or two-stage design. Further, the heater has a burner housing 6 which is perforated and open at the top and defines a combustion chamber. Between burner housing 6 and rear wall 7 of housing 2 of kerosene heater 1 (on the left in Fig. 1), there is mounted a vertically downwardly extending reflecting screen 8 which has adjacent top wall 9 of housing 2 of kerosene heater 1 an opening 10 through which may flow a portion of the off-gases emitted by burner 4 and escaping upwardly therefrom (arrow A). A vertical holder 12 secured to the bottom of housing 2 supports in the lower regions of that housing an 0£ sensor 13 in the form of a galvanic cell coupled to a microprocessor included in an electronic control circuit 14. Behind heat reflecting screen 8, there is mounted in the upper left corner (in Fig. 1) of housing 2 a CO sensor 11 on a CO monitoring circuit board 15 in such a manner that it will be contacted by the off-gases escaping through opening 10 in heat reflecting screen 9. Circuit board 15 is connected electrically to electronic control circuit 14 of the safety apparatus, which in turn is coupled to warning signal means (not shown) and automatic shut-down means 16 for burner 4. A light sensor 19 associated with the top limit 17 of a predetermined range of the height of the flame 18 produced by burner 4 is mounted behind heat reflecting screen 8 in a manner to detect flames higher than top limit 17 of the aforesaid predetermined flame height range. Light sensor 19 is coupled to electronic control circuit 14» When light sensor 19 detects flames 18 higher than top limit 17 of the aforesaid flame height range, it provides a measuring signal which is supplied to electronic control circuit 14 to trigger an acoustic warning signal. The user of the kerosene heater has 90 seconds now to actuate wick adjusting means 3 so as to return flames 18 of burner 4 to the predetermined flame height range in accordance with the normal operating condition of burner 4. Failure to effect such a return within the aforesaid 90 seconds causes shut-down means 16 to be activated by electronic control circuit 14 and burner 4 to be automatically deactivated.

If kerosene heater 1 is turned on in a properly ventilated indoor space, the influence of the ambient temperature will cause output Usensor from 02 sensor 13 in the safety apparatus to increase to approx. 2 mV within 90 minutes. While kerosene heater 1 is operating, 02 sensor 13 continuously detects the O2 concentration of the air inside housing 2 and converts that concentration to a corresponding voltage signal. Since a decrease in 02 relates directly to an increase in C02, the voltage signal indicating the 02 concentration is a measure of the instantaneous amount of C02 in the indoor air. As shown in Fig. 3, the microprocessor in the electronic control circuit 14 proceeds after an activation of burner 4 to determine operating voltage Uo to 02 sensor 13 as a maximum before poor ventilation of the indoor space causes sensor voltage Usensor to decrease. As shown in Fig. 3 sensor voltage uSensor -^s detected every 4 min. and compared with the preceding value. In Fig. 3, U^ is the maximum voltage level existing before poor ventilation of the indoor space causes Usensor to decrease (see U5 < U4) . For this reason, U4 = Uo. After the operating voltage has been determined, alarm voltage Ua of 02 sensor 13 follows to be Ua = Uo -AUa. If the oxygen concentration detected by 02 sensor 13 corresponds to the voltage level of alarm voltage Ua, an alarm signal will be generated. If the ventilation in the indoor space does not improve within 90 seconds, the 02 concentration will continue to decrease and the kerosene heater will be shut down by automatic shut-down means 16, which comprises a solenoid, at an output Usensor from 02 sensor 13 which is lower than alarm voltage Ua.

While kerosene heater 1 operates, CO sensor 11 is capable of continuously detecting the CO concentration in the off-gas (arrow A) from burner 4 in housing 2, with the measured CO concentration continuously converted to a by the electronic same time, the measure for the The diagram of Fig.

CO CO C02 corresponding electrical voltage monitoring circuitry. At the concentration can be used as a concentration in the indoor air. shows the CO and CO2 concentration relative to the oxygen percentage in the indoor air versus the operating time of the direct kerosene heater 1 . As may be seen, inter-relationship between a decrease of 02 and increase of CO2 establishes a corresponding between the O2 decrease and a CO decrease relationship between the increase of C02 and CO. 3.Π relationship through the The block diagram of Fig. 5 shows the various process steps for monitoring and maintaining the safety of the operation of a kerosene heater within an indoor space both in the normal heating mode and outside such mode, with the blocks referred to showing the functional interrelationship that exists between the various process measures .

Figs. 6a and 6b show two embodiments of a mechanism - 19 included in the safety apparatus to block the ignition means for burner 4 and the wick adjusting means 3 - and thus the ignition of the wicks by means of a match - in case battery 20 is missing or improperly seated in battery case 21.

The aforesaid mechanism comprises a functional spring 22 which assumes a compressed condition when the battery is properly seated, i.e. when it contacts a sensor plate 23 inside battery case 21, with a trigger wire 24 (Fig. 6a) having its two ends connected to trigger plate 25 of a safety device 26 responsive to vibrations (including earthquake tremors) and to sensor plate 23, respectively, being slack so that burner 4 may be ignited. If battery 20 is removed from battery case 21 or does not properly contact sensor plate 23, the latter is urged forwardly by the compressed functional spring 22, causing trigger wire 24 to be stretched taut and moving trigger plate 25 so that safety device 26 will be activated to prevent ignition or to block the wick adjusting mechanism or to shut down burner 4. In the embodiment of Fig. 6b, trigger place 25 of safety device 26 is replaced by a latch 27 having one end of trigger wire 24 connected thereto to actuate latch 27 when functional spring 22 is moved, so as to trigger safety device 26.

Claims (17)

CLAIMS:

1. A process of monitoring and ensuring the safe operation of an unvented oven and particularly of a kerosene heater in an indoorspace in the normal heating condition in which the height of the flames produced by the burner is within a predetermined range which is monitored by radiation-response means to detect flame heights outside said range, as well as in operation outside said normal heating condition, wherein flame heights higher and lower than said predetermined range causing corresponding control signals to be generated and to be coupled to an electronic control circuit so as to enable the normal heating condition to be restored or, if the burner consistently operates outside said predetermined flame height range for more than a predetermined period of time, to generate a warning signal and to automatically shut down the burner after a corresponding timeout delay, characterised in that the 0 2 percentage in the burner off-gases inside the kerosene heater is detected sensitively and used as a measure for monitoring the amount of CO? in the burner off-gases and converted to a voltage signal forming said control signal, that in burner operation outside th® predetermined flame height range the sensitive O 2 detection is effected under program control both for restoring the normal heating condition and for monitoring burner operation at minimum flame height, and that the electronic control circuit is used to generate the alarm signal and to automatically shut down the burner after a delay at predetermined first and second 0? concentrations in the burner off-gases each corresponding to a predetermined. CO 2 concentration in the indoor air, said second concentration being lower than said first concentration. - 21

2. A process as in claim 1, characterised by the alarm signal being generated and the burner shut down automatically when the O2 concentration in the burner off-gas has reached a level corresponding to the maximum CO? concentration of 0.8% permissible in indoor air.

3. A process as in claim 1 and 2, characterised in that the automatic shut down of the burner is effected 90 seconds after the triggering of the warn signal indicating too low a level of O2 or too high a level of CO/CO? in the burner off-gas.

4. A process as in claim 1 to 3, characterised in that each time the burner is switched on a maximum value of the voltage characterising a sufficient ventilation condition and again allowing the burner operation only after shut down the burner is determined as operating voltage U o and being fixed for a predetermined length of time by a microprocessor of the electronic control circuit, when the burner has been shut down.

5. A process as in claim 4, characterised by the operating voltage being fixed for 45 minutes when the burner has shut down because of an excessive CO? level in the indoor air.

6. A process as in claim 1„ characterised in that the voltage from O? sensor is detected cyclically and compared with the preceding sensor voltage value.

7. A process as in claim 6, characterised in that the voltage from the Oj sensor is detected every four minutes , - 22

8. A process as in claim 1, characterised in that the electronic control circuit is powered by a battery which is connected through a mechanism with the electronic control circuit and the voltage is checked automatically for the stability of a prescribed value, with a battery voltage lower than said prescribed value causing an ignition of the burner to be prevented and an alarm signal indicating the necessity of a battery replacement being generated and the warm-up or heating operating of the kerosene heater being terminated automatically.

9. A process as in claim 1 and 8, characterised in that an incorrect working position of the battery or its removal from the working position the mechanism connected with the control circuit cause ignition of the burner to be prevented automatically.

10. A process as in claim 9, characterised in that burner ignition is prevented by mechanical means.

11. A process as in claim 1, characterised in that the electronic control circuit is used to continuously check the fuel level and to generate an intermittent signal in response to the fuel dropping below a predetermined level.

12. Safety apparatus for monitoring and ensuring the safe operation of an unvented oven and particularly of a kerosene heater in an indoor space in the normal heating condition in which the height of the flames produced by the burner is within a predetermined range which is monitored to detect flame heights outside the range by a light sensor of a sensor means mounted in the housing of the kerosene heater in 23 association with the top limit of a predetermined range of flame heights, defining the normal heating condition of the kerosene heater, as well in operation outside said normal heating condition, wherein flame heights higher and lower than said predetermined range causing a corresponding control signal to be generated and to be coupled to an electronic control circuit which is connected to the battery and through which wick adjusting means of the burner may be adjusted according with a measuring signal from the light sensor in response to the flame height being outside said predetermined flame height range, said wick adjusting means also being adjustable by hand, and comprising timing means being coupled to warning means and means for automatically shutting the burner down and actuatable with delay when the burner is operated above said predetermined flame height range to a time longer than predetermined, for practising the process of claim 1 to 11, characterised by the sensor means additionally comprising an O2 sensor (13) coupled to a microprocessor, said sensor (13) being mounted within housing (2) of kerosene heater (1) in the bottom housing position, detecting the O 2 percentage in the burner off-gases inside the kerosene heater (1), said O 2 percentage is used as a measure for monitoring the amount of C0 2 in the burner off-gases and converted to a voltage signal forming said control signal in the electronic control circuit (14) coupling said control signal to the wick adjusting means (3), the warning means and shut down means (16) for the burner (4), each of them are connected with the electronic circuit (14), wherein, when the burner (4) is operating outside said predetermined flame height range, the voltage signal of the O 2 sensor is causing the wick adjusting means (3) to re-establish the normal heating - 24 condition of the kerosene heater (1) and is serving to monitor the operation of the burner (4) at the lowest flame height in a manner, that with predetermined first and second O 2 concentration in the off-gases of burner (4) warning means and the automatic shut down means (16) of burner (4) are operated by the electronic control circuit (14) with said second concentration being lower than said first concentration, and that a vibration protection means (26) is provided.

13. Apparatus as in claim 12, characterised by a mechanism ( 22, 24) coupled with vibration-responsive protecting means (26) to prevent the igniting means of burner (4) from being activated or to cause wick adjusting means (3) to be latched in its basic position in which the wick cannot be ignited by hand if the battery is missing or improperly placed in battery case (21).

14. Apparatus as in claim 13, characterised by mechanism (22, 24) comprising a functional spring (22) engaging a sensor plate (23) of battery case (21) and compressed in the rest condition of mechanism (22, 24) as well as a triggering wire (24) having its ends connected to sensor plate (23) and to a triggering plate (25) of protection means (26), respectively, said triggering wire being slack in the rest position of mechanism (22, 24), wherein the absence or an improper placement of battery (20) causes sensor plate (23) to be displaced in the battery case (21) by functional spring (22) of the activated mechanism (22, 24), triggering wire (24) to be stretched taut and triggering plate (25) of protection device (26) to be activated. I - 25

15. Apparatus as in claim 14, characterised by triggering plate (25) of protection device (26) being replaced by a pivotable latch (27).

16. A process of monitoring and ensuring the safe operation of unvented ovens as claimed in claim 1, substantially as herein described with reference to the accompanying drawings.

17. Safety apparatus according to claim 12, substantially as herein described with reference to and as shown in the accompanying drawings.