AU2014299396B2

AU2014299396B2 - Cooking hob with integrated gas sensor

Info

Publication number: AU2014299396B2
Application number: AU2014299396A
Authority: AU
Inventors: Bernard Gerhardus Colenbrander; Jeroen VAN EERTSEN; Sjoerd Michiel VAN HAASTER; Antonius Cornelis Maria WOUTERS
Original assignee: Intell Properties BV
Current assignee: Intell Properties BV
Priority date: 2013-06-27
Filing date: 2014-06-25
Publication date: 2017-12-07
Anticipated expiration: 2034-06-25
Also published as: EP3014180A1; WO2014209118A1; AU2014299396A1; NL2011051C2

Abstract

Cooking hob (1) with a surface plate (2), a conduit (5) for a gas-air mixture and at least one gas burner (3) having a burner body. The burner body comprises a base portion (4) and a planar burner head (6), and provides at least one aperture from which the gas-air mixture is exhausted and from which a flame may emerge. An impermeable tube (9) is provided of which the proximal end (9p) opens into a gap (b) between burner head (6) and a pan. A gas intake device (10) is provided to generate a suction force at the proximal end (9p) to draw exhaust gas there-through. A sensor (11) is disposed within the impermeable tube (9) which is adapted to measure the content of at least one target molecule in any exhaust gas drawn through the tube (9).

Description

Cooking Hob with Integrated Gas Sensor Field of the Invention

The present invention is directed to a gas cooking hob which is responsive to changes in the composition of the combustion gas delivered to its constituent gas burner(s).

Background of the invention

The Netherlands became a significant producer and exporter of natural gas following the discovery, in 1959, of a gas field near the village of Slochteren in the northern province of Groningen. Offshore production in the Dutch sector of the North Sea began in the 1970s.

At the present time, the Netherlands produces two types of natural gas which are transported on separate networks. The first type of gas, which originates mainly from the Groningen region, has a low-range calorific value of below 10.5 kWh/m3 (L-gas), and is consumed by residential and commercial users in the Netherlands. The second gas type, which originates from smaller gas fields, has a higher calorific value of from 10.5 to 12.8 kWh/m3 (H-gas) and is consumed predominantly by industry and for power generation.

The domestic production of both gas types is however declining, indeed, the Netherlands is expected to become a net importer of gas sometime in the period from 2020 to 2025. Thereby at a national scale, it is clear that there must be: well-timed investments in storage capacities and LNG installations in order to maintain supply flexibility; robust accounting for changes to the alkane composition and reservoir impurity levels of domestic gas supplies as they are depleted; and, effective regulation of imported natural gas which might, for instance, diverge from the present standards in place in the Netherlands (i.e. European Standards CE G25 and G31). At the residential and commercial scale, appliances will have to adapt for and tolerate temporal changes in the composition, quality and calorific value of the (L-) gas which they consume.

The present invention responds to this need in the art as it applies to cooking hobs which have at least one burner which is fed with natural gas.

The complete combustion of methane in the presence of oxygen would yield only water and carbon dioxide as products. In practice, the combustion of natural gas in the presence of air is normally incomplete and yields, amongst other by-products, un-reacted hydrocarbons, carbon monoxide (CO), nitrogen dioxide (N02), sulphur oxides (SOx) and, particulate matter such as soot. Temporal fluctuations in the composition of the natural gas combusted in the burner of a cooking hob will change the levels of these by-products in the exhaust gases.

The present application is concerned with the detection of target molecules in these exhaust gases and to the subsequent use of the detected level of the target molecules, e.g. as a means of feedback control of the combustion at the burner. In particular, it is concerned with the detection of at least the carbon monoxide content of the exhaust gases.

European Patent EP-B 1 331 444 (Vaillant GmbH) describes a method of controlling a gas burner in which a sensor monitors the carbon monoxide concentration in the exhaust gas, and generates a signal to represent its reading. A calibration process is triggered after a given burning time or at periodic intervals, wherein the gas/air mixture delivered to the burner is enriched until either the exhaust sensor signal alone or a combined signal matches a given threshold value; in this condition, the fuel gas and air volume signals are registered, and the gas/air mixture is reduced to a leaner level in a given ratio to establish the new nominal value for the mixture.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a cooking hob as defined in the appended claims, the cooking hob comprising: a surface plate; a conduit for a gas-air mixture for which an opening is provided in the surface plate; at least one gas burner having a burner body, wherein the burner body comprises a base portion disposed around the opening of the conduit and a planar burner head, the burner head and the base portion being disposed so as to provide at least one aperture from which the gas-air mixture is exhausted and from which a flame may emerge when the burner is activated; and, a pan support disposed above the burner head and defining a horizontal plane substantially parallel to the plane of the burner head but spaced there from by a gap; the cooking hob being characterized in that it further comprises: an impermeable tube of which the proximal end opens into the gap; a gas intake device adapted to generate a suction force at the proximal end of the impermeable tube to draw exhaust gas there-through; and, a sensor disposed within the impermeable tube which is adapted to measure the content of at least one target molecule in any exhaust gas drawn through the tube.

In a further embodiment, the burner head and the base portion are disposed so as to provide at least one aperture through which an annular flame may emerge when the burner is activated and further wherein the proximal end of the impermeable tube would be disposed within the annulus.

The cooking hob in an even further embodiment further comprises a control valve which regulates the supply of the combustible, gas-air mixture to the conduit, wherein the control valve is optionally electronically continuously controllable. In turn, the sensor of the cooking hob may be operatively connected to the control valve; in other words, any output signal from that sensor will be operative in controlling that valve. Such a cooking hob is thereby provided with a means of feedback control, such that the detection of a target molecule or of a specific concentration of a target molecule at the sensor may be used to regulate the gas-air input to the burner of the cooking hob.

In accordance with a second aspect of the invention, there is provided a method of measuring the content of at least one target molecule in the exhaust gas of a burner using the cooking hob as defined above in which the gas burner has been activated, the method comprising the steps of: a) disposing a pan on the pan support; and, b) drawing a fraction of the exhaust gas from the activated burner into and through the impermeable tube and thereby passed the sensor disposed in the tube.

Without being bound by theory, the placement of a pan on the pan support and the ignition of the burner effectively create a closed system. In this circumstance, the gas intake device withdraws exhaust gases from a volume defined by the burner head, the bottom of the pan and the burner flame, itself usually in the form of an annulus.

From these exhaust gases, the "target molecule" is intended to mean a molecule which can be indicative of the complete combustion, incomplete combustion and non-combustion of the gas delivered to the cooking hob, or which can be indicative of impurities within that delivered gas.

The target molecule may be selected from the group consisting of: carbon monoxide (CO); oxygen (02); nitrogen oxides (NOx); sulphur oxides (SOx); methane (CH4); and combinations thereof. The target molecules e.g. comprise carbon monoxide and, optionally methane.

In an embodiment, the method of the present invention further comprises the step of establishing at least one threshold condition for the measured concentration of the target molecule usually in parts per million (ppm) by volume, parts per billion (ppb) by volume or micrograms per cubic meter of air (pg/m 3) - at which the sensor of the cooking hob emits an output signal,

The "threshold condition(s)" will be determined by the target molecule and may also be determined by the regulations governing cooking hobs and appliances. The primary and secondary standards of the National Ambient Air Quality Standards (NAAQS) set by the Environmental Protection Agency (EPA, IIS) might be mentioned as providing exemplary threshold conditions for inter alia CO, NOx and SOx. Similarly, the disclosure of http://ec.europaeu/environment/air/quality/standards.htm might be sourced for guideline threshold conditions.

At its simplest, a threshold condition may be the attainment of a detectable and/or specific concentration of the target molecule, typically measured in parts per million. Alternatively, the threshold condition may require the attainment of a specific concentration and the retention of that condition for a duration of time before a control signal is issued from the sensor. And in a preferred embodiment, the at least one threshold condition is constituted by the maintenance of the measured target molecule concentration at, below or above a predetermined concentration limit for a duration of from 0.1 to 60 seconds, e.g. from 0.1 to 10 seconds before a control signal is issued from the sensor.

Aside from the mechanism of feedback control which will allow a cooking hob to mitigate changes in the composition and calorific value of its combustible gas, it is also considered that the apparatus of the present invention can incorporate a number of additional safety features into the operation of the cooking hob. If, after emplacement of the pan on an activated burner, that pan is partially or wholly removed from its support, there will be a marked change in the level of the carbon monoxide (CO) as a consequence of the fact that the exhaust gases will then be drawn from an open combustion system: this change can be detected at the sensor and result in a signal there from which can be operative to either cut off or reduce the supply of combustible gas to the burner. Further, the detection of methane (CH4) by a sensor can be used as a flame detection system, instead of or in association with a thermocouple or other flame sensor.

Definitions

The words "comprises" and "comprising" when used in this specification are to specify the presence of the stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The term "substantially parallel" is understood to mean that the horizontal plane defined by the pan support and the planar burner head may depart from being precisely parallel where, for instance, the planar burner head might have local deformations such as concavities, hollow regions, bosses, reliefs or ridges,

Short description of drawings

Further objects, features and advantages of the present invention will become apparent from the following detailed description of the annexed drawings, wherein;

Figure 1 is a sectional view of a cooking hob in accordance with an embodiment of the present invention.

Figure 2 is schematic of a control circuit for a cooking hob having four constituent burners which are each operatively connected to a carbon-monoxide sensor, and which is provided in accordance with an embodiment of the present invention.

Figure 3 is a sectional view of a cooking hob in accordance with a further embodiment of the present invention.

Detailed Description of the invention

As stated above, the cooking hobs of the present invention have at least one burner which is fed with natural gas. The hobs may have a plurality of the burners, for instance from 4 to 6 burners, wherein each burner is e.g. of a different size and calorific power and is thereby suitable for use with pans having different dimensions. However, it is not precluded that the cooking hob may be a so-called "mixed hob" in which one or more gas burners are employed with one or more different heat sources, such as: electrical heating elements; radiant elements and halogen lamps; and, inductors or induction sources.

In those cooking hobs which comprise more than one gas burner, it is preferred that each gas burner be associated with a separate sensor disposed within an independent, impermeable tube for detecting target molecules in its exhaust gases. Each burner need not however have its own intake device; a single fan may for instance be used to draw exhaust air through a plethora of tubes.

Whilst it is not presently preferred, cooking hobs having more than one gas burner could be provided with only one gas burner meeting the requirements of this invention, and thereby only a singular sensor. Any signals indicative of a target molecule having reached a threshold condition at that singular burner may be transmitted to the control valves of the other constituent burners of the cooking hob, with appropriate translation of that signal to account for differences in burner configuration. This embodiment has the advantage that it simplifies the components of the cooking hob but has the disadvantage that its effectiveness relies on the user selecting that burner which is operatively connected to a sensor as his primary burner.

As is known in the art, the cooking hob may be provided with a safety valve which disables or enables the gas flow to all of the constituent gas burners of that hob. The or each sensor of the cooking hob of the present invention may be connected to such a safety valve, to open or close that safety valve.

Within the structural constraints described above, the term "burner" is not intended to be limited. It is intended that known commercial burners and, for example, those burners described in US Patent Application Publication No. 2010/089384 (Inzaghi) and W02007 /036772 (Indesit CO SPA) might have utility in the present invention. That aside, it is however preferred that the burner also be structured to ensure even flame distribution: the burner may, for instance, be provided with insert baffles, an internal gauze and / or be tapered in such a way that both the velocity - and pressure of the air/gas mixture are constant throughout the entire length of the burner.

Whilst the burner should provide flames of such size and shape that they transfer the maximum amount of heat to the pan, no specific limitation is placed on the structure of the burner aperture(s) in this invention. A person of ordinary skill will recognize that the size and position of the burner apertures will control, to a great extent, the way in which the flames obtain their secondary air and the capability of a burner to "cross-light" at their normal gas operating rates; he will therefore be abide to assess the advantages and disadvantages of multiple rows of apertures and of the selection of particular aperture diameters.

The term "pan" used herein is intended to include saucepans, frying pans, casserole dishes and other cooking utensils conventionally heated upon gas, electric or mixed hobs.

As used herein, the term "pan support" is intended to include a latticed pattern or other configuration of one or more elements which, in combination, define a horizontal plane on which a pan may be stably positioned and centered above a gas burner. Whilst the, pan support may be formed of a heat-durable, glass-ceramic top plate under which the gas burner is installed, this is not preferred; the presently known gas hobs which include such glass-ceramic top plates are not considered to be sufficiently efficient particularly under cold start conditions because the burners heat the pans indirectly through those plates.

Typically, therefore, the pan support should be comprised of a plurality of ribs (or fingers) disposed in an arrangement to each other and which may optionally be distributed evenly and symmetrically above the gas burner. A person of ordinary skill in the art will of course be aware of a plethora of different configurations of the ribs and of different shapes and materials for the ribs. And suitable configurations of pan supports include those described in US Patent Application Publications No. 2012/012098 (Berr et al.) and 2010/051012 (Martins et al.), the disclosures of which are herein incorporated by reference. Moreover, the provision of coupling means which serve to position the pan support(s) on the surface plate of the cooking hob is not precluded by the present invention.

As used herein, the term "sensor" is a device which transforms chemical information into an analytically useful signal (IUPAC 1991); the chemical information may originate from a chemical reaction of the analyte or from a physical property of the system investigated. Generally, the sensor employed in the present invention will be a solid state gas sensor in which the input signal is the concentration of one or more gaseous species in a carrier namely the exhaust gas drawn through the impermeable tube - and the sensor is solid. The solid state gas sensor may be a metal oxide semiconductor (MOX) gas sensor comprising a high-gap ionic semiconductor. The metal oxide (MOX) body will usually be mounted within housing and the surrounding test gases are introduced into that housing through a meshed entrance. MOX sensors have a high compatibility with microelectronic processing and can be of small dimension, low cost and low power consumption. The background to such MOX devices may be found in: V.E. Henrich and P.A. Cox, The surface science of Metal Oxides, Cambridge University Press; M. Batzill and U. Diebold, The Surface and Materials Science of Tin Oxide, Progress in Surface Science 79:47-154 (2005); M. J. Madou and S. R. Morrison, Chemical Sensing with Solid State Devices, Academic Press (1989), p. 67; and, U. Diebold, The Surface Science of Titanium Dioxide,

Surface 10 Science Reports 48:53 (2003).

The cooking hob may comprise more than one sensor and, in particular, more than solid state gas sensor; the employment of a gas sensor array wherein a plurality of gas sensors can selectively respond to different gases, is certainly not precluded.

In accordance with a valuable aspect of the present invention, one sensor of the apparatus is adapted to measure at least the carbon monoxide (CO) level of the exhaust gases. Moreover, it is preferred that this carbon monoxide sensor be based on tin dioxide (Sn02) which may optionally be doped with noble metals or other metal oxides to create (nano-)composite materials. Importantly, Sn02 has considerable cross-sensitivity to carbon monoxide and methane (CH4).

Important variables in the selection of an appropriate Sn02 sensor both for stability and for selectivity and sensitivity to carbon monoxide may be derived from T.A. Miller et al. Nanostructured Tin Dioxide Materials for Gas Sensor Applications, Department of Mechanical Engineering. University of Michigan Ann Arbor (2006) as published online at http://wwwpersonl.umich.edu/~mswool/publications/Gas_Sensors_preprints.pd.pdf. Without intention to limit the present invention, the use of a CO-sensor which is a Sn02 film sensor of which the Sn02 layer has a film height of from 30 nm to 10 pm, and e.g. from 50 nm to 2 pm, has been found to be suitable.

More particularly, and from the standpoint the temperature stability of the sensor, good results have been obtained when that thin film of Sn02 is disposed around a heating wire through which a variable current may be passed. That heating wire should be formed of a Ni/Cr alloy or a like material which is capable of heating the film of Sn02 to a temperature of from 400°C to 700°C, for example from 575°C to 625°C, in the operation of the cooking hob to ensure the sensitivity of the sensor to CO.

Suitable commercial Sn02 sensors for inclusion in the present invention include: Taguchi Gas Sensor ("TGS") manufactured by Figaro Engineering Inc.

The cooking hob may be provided with one or more covers which can be placed over the respective gas burner and, optionally the pan support whilst such covers may provide an aesthetic effect they may also provide some measure of protection for the burner and for the impermeable tube, particularly the proximal end thereof.

Additionally or alternatively, the proximal end of the tube might also be covered by a suitable cap when not in use. Independent of the presence of a cover or cap as mentioned above, the sensor and the gas intake device may be protected from particulates in the exhaust gas flow through the disposal of a filter element within the impermeable tube; exhaust gas drawn through the tube will be directed through the filter element prior to reaching the sensor.

As shown in Figure 1, a cooking hob is provided with a surface plate 2, usually made of glass ceramic or metal, of which the upper side will generally be metalized or coated to prevent any spillage onto the cooking hob 1 from penetrating to the underside of the plate.

The gas burner 3 is here mounted above the surface plate 2. The base portion 4 of the burner - which would typically be sealed to that surface plate 2 - is disposed around the conduit 5. This base portion may be provided with an igniter, such as an ignition spark plug and, optionally a flame sensor, such as a thermocouple, to determine if the gas burner 3 is on. Neither the igniter nor the flame sensor are shown in the drawings. A burner head 6 is disposed above the base portion 4 of the burner and defines a substantially planar surface 6a. As is known in the art the burner head 6 may be distanced from the base portion 4 of the burner by spacer element (not shown). The plane of the burner head 6a may suitably be sized to provide protection from spillage for an igniter or thermocouple disposed on the burner and may also be provided by an enameled cap, as is known in the art. A supply of gas, regulated by a control valve 7, will issue from an injector nozzle 8, which may have one or more orifices of appropriate dimensions, in accordance with standard practice in this art A separating space a is provided for the entrainment of primary air into the issuing gas stream, with the resultant gas-air mixture passing into the conduit 5 which is substantially aligned with the injector nozzle 8.

The gas-primary air mixture formed moves upwards within the vertical conduit. Depending on the construction of the gas burner 3, the conduction and diffusion of this mixture towards the aperture( s) of the burner may proceed by a plurality of ducts - for instance horizontal Venturi ducts - which extend in a radial direction from an outlet mouth - of the vertical conduit central duct and terminate in an annular chamber.

Whilst this embodiment has not been shown in Figure 1, it is intended that fully pre-mixed burners be within the scope of the present invention. In this embodiment the amount of gas required to provide a heat input is mixed with slightly more air typically 10 to 15 mol.% more - than would be required for complete combustion. When burned on a suitable burner head 6 a short, very hot flame is often produced with almost no visible outer mantle. And moreover, no secondary air is required as all the air for combustion is supplied as primary air. For this embodiment, there may be provided in place of the injection nozzle 8 and the separation a thereof from the conduit 5 as shown in Figure 1 a conduit in which a centrifugal fan is provided. Gas may be mixed with air either before or after the centrifugal fan which then forces the mixture into the burner head.

This pre-mixed air embodiment may enable the use of an oxygen sensor in the apparatus either alone or in combination with a carbon monoxide sensor - given that the content of oxygen in the pre-mixed air can be determined. It may also enable the pan support to be disposed a shorter distance above the planar burner head 6a than might be required for an atmospheric burner.

The width of the gap b between the planar burner head 6 and the plane of the pan support c will typically be of the order of 5 to 50mm, as measured vertically. It is critical to the present invention that the proximal end 9p of the impermeable tube 9 opens into the gap b. This can be achieved by rendering that proximal end 9p flush with the planar burner head. Alternatively, and as depicted in Figure 1, the impermeable tube 9 may penetrate that gap b a vertical distance, which vertical distance is a fraction of the gap’s total width, typically less than 50% of that width and e.g. less than 30% thereof.

In the configuration depicted in Figure 1, the impermeable tube 9 passes directly through the burner body: indeed the tube may be constituted, at least in part, by a bore through that burner body. An alternative configuration may be to provide an impermeable tube 9 which is external to the burner but which is inclined, curved or angled to dispose its proximal end 9p within the gap b, in either configuration, the proximal end 9p of the tube need not be positioned in the centre of the annulus formed by the flames. For instance, the tube 9 may be disposed concentrically or eccentrically within a burner through which it passes, the latter embodiment being that shown in Figure 1. A further alternative embodiment is shown in Figure 3. In this embodiment, the impermeable tube 9 extends through the surface plate 2, and into a spacing provided in a part of pan support 12. The pan support 12 is provided with an extension conduit 12a, which ends in a proximal end 12p within the gap b (instead of the proximal end 9p of the impermeable tube 9). In other words, the pan support 12 is provided with an extension conduit 12a, which effectively shifts the proximal end 9p of the impermeable tube 9 to proximal end 12p of the extension conduit 12a of the pan support 12. In other 15 words, also in this embodiment, the proximal end 9p of the impermeable tube 9 opens into the gap b between plane 6a of the burner head 6 and the plane c of the pan support 12.

The gas intake device of the present invention is here illustrated as a fan 10; such an intake device may be operable so that it generates a suction force only when the :gas burner 3 is activated, but this is not a strict requirement The fan 10 generates a flow within the tube 9 which draws either the gas air mixture or the combustion products from the separation gap b. Disposed prior to the fan 10 in the impermeable tube 9 is the sensor 11 adapted to measure the content of the target molecule in the exhaust gases drawn from that tube. After passing the sensor 11, the so-drawn gases may then be safely vented from the appliance. Should the sensor 11 indicate a condition at the gas burner 3 whereby either combustion is not occurring at all or is incomplete, it is envisaged that either a portion or all of the so-drawn gases may also be recycled to the conduit 5 for feeding into the gas burner 3.

As shown in Figure 2, each of four constituent burners 21a-d is independently associated with an individual CO-sensor 23a-d which measures the carbon monoxide level and optionally the methane level, as mentioned above within the exhaust gases drawn from that individual burner by a common fan 25. Each CO-sensor 23a-d is in turn independently connected to the control valve 22a-d of its associated burner via a printed circuit board PCB, 24. Upon attainment of a threshold condition of carbon monoxide, a signal is transmitted from a sensor 23a-d to the corresponding control valve 22a-d via the printed circuit board 24; that signal is operative to modify the gas flow to the burner 21a-d. A level of carbon monoxide which is retained or attained above a threshold condition of a sensor 23a-d may be indicative of unacceptable, incomplete combustion at the burner; the sensor signal may therefore be operative to modify the gas flow and directly or indirectly increase the amount of primary air. A level of methane above a threshold condition may be processed analogously as an independent means of control of the burner; alliteratively, the threshold level of methane might be employed as a secondary condition for the transmission of a signal - an AND gate, for instance -when the carbon monoxide level has also met or surpassed its threshold condition(s).

To provide a supplementary safety feature, each sensor 23a-d of Figure 2 is further connected to a safety valve 26, to open or close that valve and thereby disable or enable the gas flow to all of the constituent gas burners of that hob.

It is envisaged that each sensor 23a-d may also be operative to send a signal to the user interface 27 of the cooking hob. That user may therefore be made aware of certain conditions prevalent in the cooking hob; a given manufacturer will of course be free to determine what information is displayed to the user and the audio and/ or visual means of that display.

The disclosed user interface 27 may be disposed together with or separately from the standard control knobs or buttons which the user may actuate by finger contact to turn on and I or off each of the burners 21 a-d and to adjust the gas flow and therefore the heat generated by combustion at the burners.

It will be understood that embodiments of the present invention are described herein by way of example only, and that various changes and modifications may be made without departing from the scope of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. Cooking hob comprising: a surface plate; a conduit for a gas-air mixture for which an opening is provided in the surface plate; at least one gas burner having a burner body, wherein the burner body comprises a base portion disposed around the opening of the conduit and a planar burner head, the burner head and the base portion being disposed so as to provide at least one aperture from which the gas-air mixture is exhausted and from which a flame may emerge when the burner is activated; and, a pan support disposed above the burner head and defining a horizontal plane substantially parallel to the plane of the burner head but spaced there from by a gap; the cooking hob further comprising: an impermeable tube of which the proximal end opens into the gap; a gas intake device adapted to generate a suction force at the proximal end of the impermeable tube to draw exhaust gas there-through; and, a sensor disposed within the impermeable tube which is adapted to measure the content of at least one target molecule in any exhaust gas drawn through the tube.
2. Cooking hob according to claim 1, wherein the burner head and the base portion are disposed so as to provide at least one aperture through which an annular flame may emerge when the burner is activated and further wherein the proximal end of the impermeable tube would be disposed within the annular flame in operation.
3. Cooking hob according to claim 2, wherein the proximal end of the impermeable tube is disposed so as to be positioned eccentrically or concentrically in the burner head.
4. Cooking hob according to any one of claims 1 - 3, wherein the gas intake device is operable to generate a suction force only when the gas burner is activated.
5. Cooking hob according to any one of claims 1-4, wherein the sensor is adapted to measure at least the carbon monoxide level of any gas drawn through the tube.
6. Cooking hob according to any one of claims 1-5, wherein the sensor comprises a body of tin(IV)oxide (Sn02) which is heatable by means of a wire.
7. Cooking hob according to any one of claims 1-6, further comprising a control valve which regulates the supply of the combustible gas-air mixture to the conduit, wherein the control valve is optionally electronically continuously controllable.
8. Cooking hob according to claim 7, wherein the sensor is operatively connected to the control valve.
9. Cooking hob according to any one of claims 1 - 8, comprising a electronically continuously controllable valve which is operable to regulate the ratio of gas to air in the gas-air mixture provided to the conduit.
10. Method of measuring the content of at least one target molecule in the exhaust gas of a burner using the cooking hob as defined in any one of claims 1 - 9, in which the gas burner has been activated, the method comprising the steps of: a) disposing a pan on the pan support; and, b) drawing a fraction of the exhaust gas from the activated burner into and through the impermeable tube and thereby passing the sensor disposed in the tube.
11. Method according to claim 10, further comprising the step of establishing at least one threshold condition for the measured concentration (ppm) of the target molecule at which the sensor of the cooking hob emits an output signal.
12. Method according to claim 11, wherein the at least one threshold condition is constituted by the maintenance of the measured target molecule concentration, at, below or above a predetermined concentration limit for a duration of from 0.1 to 60 seconds, e.g. from 0.1 to10 seconds.
13. Method according to claim 11 or claim 12, wherein the sensor is connected to a control valve provided in the cooking hob and wherein the output signal is active during controlling of the valve.
14. Method according to any one of claims 10 -13, for measuring the carbon monoxide level of the gas drawn through the tube, wherein the sensor of the cooking hob comprises a body of tin(IV)oxide (Sn02).
15. Method according to claim 14, wherein the body of tin(IV)oxide (Sn02) is heated by a wire to a temperature of from 400°C to 700°C.
16. Method according to claim 14 wherein the body of tin(IV)oxide (Sn02) is heated to a temperature of from 575°C to 625°C.