CA2352648A1 - Oven exhaust gas oxygen sensing arrangement and related control circuit and method - Google Patents
Oven exhaust gas oxygen sensing arrangement and related control circuit and method Download PDFInfo
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Abstract
An oxygen sensing arrangement for a gas-fired oven includes an oxygen sensor positioned for sensing gases along an exhaust path of the oven, the oxygen sensor including a heater and a measurement cell. A sensor control circuit includes a sensor initialization portion connected to a bridge portion. The bridge portion is operatively connected for energizing the heater. The sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to deliver a heating current/voltage to the heater for the start-up time period.
After the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to deliver an operating current/voltage to the heater.
A voltage of the heating current/voltage is less than a voltage of the operating current/voltage. The arrangement enables the oxygen sensor to be heated to its operating temperature at a voltage and corresponding heating rate which will not damage the sensor, and is particularly useful where the oxygen sensor is an amperometric type sensor. The sensor may be located in a sensor chamber is positioned alongside the exhaust duct so as to be spaced from a primary flow of exhaust gases, with the chamber open to receive gases in the exhaust duct. Both the sensor chamber and oxygen sensor therein are sealed off from gases outside of the exhaust duct.
After the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to deliver an operating current/voltage to the heater.
A voltage of the heating current/voltage is less than a voltage of the operating current/voltage. The arrangement enables the oxygen sensor to be heated to its operating temperature at a voltage and corresponding heating rate which will not damage the sensor, and is particularly useful where the oxygen sensor is an amperometric type sensor. The sensor may be located in a sensor chamber is positioned alongside the exhaust duct so as to be spaced from a primary flow of exhaust gases, with the chamber open to receive gases in the exhaust duct. Both the sensor chamber and oxygen sensor therein are sealed off from gases outside of the exhaust duct.
Description
Docket No. 005593-3 890 OVEN EXHAUST GAS OXYGEN SENSING ARRANGEMENT AND RELATED
CONTROL CIRCUIT ANT' METHOD
FIEhD OF THE IIVVEt'~iTION
The present invention relates generally to oven combustion control, and more particularly, to an oven exhaust gas oxygen sensing arrangement and related control circuit and method.
BACKGROUND OF THE II~IVENTION
Large commercial ovens, such as rack ovens, are commonly of the gas-fired type and include one or more burners. For environmental and efficiency reasons, it continues to be desirable to improve burn conditions by controlli~:~g an air/fuel ratio in such ovens. One technique for doing so involves monitoring the oxygen content of combusted gases.
However, common oxygen sensors such as those used in automobiles are not well suited for sensing the larger oxygen concentrations seen in exhaust gases of ovens and become very expensive when adapted for such purpose. Additionali.y, the maintenance of proper sensor temperature can be a problem.
Accordingly, it would be desirable to provide an oxygen sensing arrangement for ovens which includes a suitable control mechanism. and ~nhich is advantageously positioned.
SUMMARY OF THE TN'dBNT ION
In one aspect of the present invention, ~w oxygen sensing arrangement for a gas-fired oven includes an oxygen sensor positioned for sensing gases along an exhaust path of the oven, the oxygen sensor including a heater and a measurement cell. A
sensor control circuit includes a sensor initialization portion connected to a bridge portion. The bridge portion is operatively connected for energizing the heater. The sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing Docket No. 006593-1890 the bridge circuit to energize the heater at a start-up level. for the start-up time period. After the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating level. A voltage during start-up energization is less than a voltage during operating energization. The arrangement enables the oxygen sensor to be heated to ita operating temperature at a voltage and corresponding heating rate ~.vhich will not damage the sensor, and is particularly useful where the oxygen sensor is an amperometric type sensor.
Another aspect of the invention provides a method of controlling a gas-fired oven which involves providing an oven start-up mode during wluch the fol'.owmg steps are performed: (i) energizing a heating element of an oxygen sensor at a sta~-~-up level; (ii) energizing an exhaust fan to exhaust gases from a combustion area of the oven;
and (iii) maintaining a non-burn condition within the combustion area. An oven operating mode is provided, following the oven start-up mode, and during which the following steps are performed: (i) energizing the heating element of the oxygen sensor at an operating level; and (ii) establishing a burn condition within the combustion area. The method enables the oxygen sensor to be heated toward its operating temperature at the same time that residual gases are removed from the combustion area prior to start of combustion.
Because the exhausting of gases results in a cooling air flow along the exhaust path, the method preferably also involves positioning the oxygen sensor in a chamber adjacent an exhaust path of the oven away from the primary flow of exhaust gases but in gaseous communication with the exhaust path.
Still a further aspect of the invention provides an oxygen sensing arrangement including a combustion area and an exhaust path far receiving gases from the combustion area. A sensor chamber is positioned alongside the exlhaust duct so as to be spaced from a primary flow of exhaust gases, but the chamber is open to receive gases in the exhaust duct.
An oxygen sensor is positioned within the sensor chamber, and both the sensor chamber and oxygen sensor therein are sealed off frorr~ gases outside of the exhaust duct.
CONTROL CIRCUIT ANT' METHOD
FIEhD OF THE IIVVEt'~iTION
The present invention relates generally to oven combustion control, and more particularly, to an oven exhaust gas oxygen sensing arrangement and related control circuit and method.
BACKGROUND OF THE II~IVENTION
Large commercial ovens, such as rack ovens, are commonly of the gas-fired type and include one or more burners. For environmental and efficiency reasons, it continues to be desirable to improve burn conditions by controlli~:~g an air/fuel ratio in such ovens. One technique for doing so involves monitoring the oxygen content of combusted gases.
However, common oxygen sensors such as those used in automobiles are not well suited for sensing the larger oxygen concentrations seen in exhaust gases of ovens and become very expensive when adapted for such purpose. Additionali.y, the maintenance of proper sensor temperature can be a problem.
Accordingly, it would be desirable to provide an oxygen sensing arrangement for ovens which includes a suitable control mechanism. and ~nhich is advantageously positioned.
SUMMARY OF THE TN'dBNT ION
In one aspect of the present invention, ~w oxygen sensing arrangement for a gas-fired oven includes an oxygen sensor positioned for sensing gases along an exhaust path of the oven, the oxygen sensor including a heater and a measurement cell. A
sensor control circuit includes a sensor initialization portion connected to a bridge portion. The bridge portion is operatively connected for energizing the heater. The sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing Docket No. 006593-1890 the bridge circuit to energize the heater at a start-up level. for the start-up time period. After the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating level. A voltage during start-up energization is less than a voltage during operating energization. The arrangement enables the oxygen sensor to be heated to ita operating temperature at a voltage and corresponding heating rate ~.vhich will not damage the sensor, and is particularly useful where the oxygen sensor is an amperometric type sensor.
Another aspect of the invention provides a method of controlling a gas-fired oven which involves providing an oven start-up mode during wluch the fol'.owmg steps are performed: (i) energizing a heating element of an oxygen sensor at a sta~-~-up level; (ii) energizing an exhaust fan to exhaust gases from a combustion area of the oven;
and (iii) maintaining a non-burn condition within the combustion area. An oven operating mode is provided, following the oven start-up mode, and during which the following steps are performed: (i) energizing the heating element of the oxygen sensor at an operating level; and (ii) establishing a burn condition within the combustion area. The method enables the oxygen sensor to be heated toward its operating temperature at the same time that residual gases are removed from the combustion area prior to start of combustion.
Because the exhausting of gases results in a cooling air flow along the exhaust path, the method preferably also involves positioning the oxygen sensor in a chamber adjacent an exhaust path of the oven away from the primary flow of exhaust gases but in gaseous communication with the exhaust path.
Still a further aspect of the invention provides an oxygen sensing arrangement including a combustion area and an exhaust path far receiving gases from the combustion area. A sensor chamber is positioned alongside the exlhaust duct so as to be spaced from a primary flow of exhaust gases, but the chamber is open to receive gases in the exhaust duct.
An oxygen sensor is positioned within the sensor chamber, and both the sensor chamber and oxygen sensor therein are sealed off frorr~ gases outside of the exhaust duct.
Docket No. 006593-189If BRIEF DESCRIPTION OF TH'~ DRAWINGS
Fig. 1 is a front elevation of a prior art rack oven;
Fig. 2 is a side elevation of the rack oven of Fig. 2;
Fig. 3'is a schematic diagram of an oven including one contemplated embodiment of an oxygen sensing arrangement;
Fig. 4 shows an arnperometric oxygen sensor;
Fig. 5 is a schematic diagram of a sensor control circuit according to one embodiment of the invention;
Fig. 6 illustrates one contemplated embodiment of a sensor chamber;
Fig. 7 is an exploded view of the sensor chamber of Fig. 6;
Fig. 8 is a front elevation of a rack oven. including an amperometric sensor within the baking chamber for humidity sensing; and Fig. 9 is a graph showing sensor output cuxrent verses applied voltage.
DETAILED DESCRIPTION OF ThIE EMBODIMENTS
Deferring to drawing Figs. 1 and 2 an e;Kemplary prior art rack oven an:angement as described in U.S. Patent No. 5,617,839 is shown. As described in such patent, the oven 10 includes two main sections. The first section 62 houses the baking chamber 12 and the second section 64 contains a steam generator 26, a combustion area 30 which contains a plurality of gas fired in-shot burners, a heat exchanger 32 and one or more blowers 28 for drawing moisture-containing air from the steam generator 26 and forcing the moisture-containing air through the heat exchanger 32 and into the baking chamber 12. A
fiypical oven 10, as shown in FIG. 1, has a baking eharr~ber 12 which includes an apertured upstream wall 14 and a partially apertured downstream wall 16. Disposed within the chamber 12 is a removable wheeled rack 18 connected at its upper end to a rotatably power driv en vertical shaft 22. The products 24 to be baked such as bread are placed in pans or on baking sheets held by rack 18 which rotates to uniformly expose the products 24 to heated, steam-containing air as it flows through the ba.yking chamber 12.
_3_ Docket Na. 006593-~ 890 The products 24 to be baked are loaded ozzta a wheeled rack 18 and placed in the baking chamber 12 and the door (not show~z~ is closed causizzg the rack 18 containing the products 24 to be lifted off the floor by a lift mechanism 20 as the door closes and then made to rotate by motor 21 'attached to vertical shaft 22. ~teaxn produced by the steam generator 26 is made to infiltrate the entire oven 10 by the fan 28 where the moisture condenses on the pool surface of the unbaked products 24. After a period of about 10 to 30 seconds, the steam is discontinued or continued in defined cycles, dependv:zg on the food product being baked, and the baking cycle started. During the baking cycle, heated air is continually circulated in a closed path throughout the entire oven 10. The air exits the baking chamber 12 through aperture 17 irr a partially apertured downside wall 16 where it enters the steam generator 26 heating the steam generator 26 and picking up addition,~l moisture if desired.
While the steam generator 26 can be selected from any of the steam generators employed in the prior art to supply steam to a rack oven, it has been found that a particularly effective steam generator is that described in U.S. Pat. No. 5,394,791 to Vallee. Th:e moisture-containing air is drawn through the steam generator 26 where the heated, moisture-containing air picks up speed as it is pulled through the heat exchanger 32 by one or more: blower fans 28 located in the plenum section 34 at the top of the oven 10. From the plentun section 34, the air enters one or more air distribution ducts 36 where it is distributed to the baking chamber I2 through the apertures 1 S in wall 14. The heated air then circulates through the baking chamber 12 contacting the baking products 24 and exits through thf; ap~rtur~s in wall 1.6. Th.e cycle is repeated continuously for a period of time determined by the baking conditions and the product being baked.
hIfa. 2 is a cross sectional schematic illustration of the second section of the oven 10 which contains a steam generator 26, combustion area 30, and a heat exchanger 32.
The air from the baking chamber 12 (FICi. 1) passes over the steam ger~~rator 26 where it picks up moisture (if necessary) and is then drawn through heat exchanger 32 containing a series of elongated heat exchaxige tubes 38 which heat, tl;e moisture-containing air. In a first _4_ Docket f~lo. 006533-1890 section of the heat exchanger 32, the elongated heat exchange ti~bes 38 are heated by a corresponding number of "in-shot" burners which fire du-ectly into the heat exchanger tubes 38. The hot combustion gases from the burners 40 are th;~n circulated through a second section of heat exchanger tubes heating these tubs to a high temperature in order to transfer sufficient heat to the air passing over the heat exchange tubes 38. The combustion gases passing through the heat exchange tubes 38 are vented into the atmosphere through exhaust outlet 48, which is attached to an appropriate exhaust duct as described in more detail below.
Exhaust fan 50 is provided for assisting in the removal of the combustion gases, and is also utilized at oven start-up, prior to burner ignition, to remove gases from the combustion area I0 to assure safe burner ignition.
While the oxygen sensing arrangement described herein is contemplated primarily for use v~~ith a rack oven 10 of the type dESCrib~~d above, it is recognized and anticipated that the arrangement could be utilized in connection with other types of gas-fired ovens. As used herein the term "gas-fired oven" is intended to broadly encompass any device which bums gaseous fael, either alone or in combination with any other type of heating element, in order to produce heat for cooking, baking, boiling, steaming and/or flying. The term "combustion area" is intended to broadly encompass any location where gaseous fuel is burned within a gas-fired oven.
Referring now to Fig. 3, a gas-fired oven 100 includes at least one burner 102 and associated igniter I04, a valve 105 for controlling g~~seous fuel delivery to the burner 102, an exhaust path I08 for combusted gases, the path including an exhaust stack 110 extending from the oven, an exhaust fa~i 1 I2 positioned to aid in exhausting gases from the oven 100 by inducing a draft in combination ~~ith a controllable dair~per 113, and an oven controller I 14 connected to the valve 105, fan 112, and clatrper I 13 fox controlling combustion. Positioned along the exhaust path 108 is an oxygen sensor 116 for sensing the oxygen content of gases traveling along the exhaust path. The controller 114 is also connected to receive signals from the oxygen sensor 11 fi.
Docket No. OOG593-1890 In a preferred embodiment the oxygen sensor 116 is an amperometric type sensor in which a control voltage is applied to the sensor and the sensor outputs a current which varies with an oxygen content of gases in contact therewith. A suitable amperometric sensor having a zirconia electrolyte cell is available from ELECTRO~IAC
GES.I~~.B.H. of Klosterneuberg, Austria and is shown in Fig. 4 where an. electrochemical oxygen pumping cell 120 made of zirconia is shown having a cathode I22 and anode 124. V~~hen voltage is applied to the cell 120, oxygen ions are pumped through. the cell from the cathode 122 to the anode 124. By at+taching a cap 126 with a pinhole 128 on the cathode side of the Bell 120, the current 130 shoves saturation due to the rate limiting step in the transfer to the cathode. This limiting current 130 is nearly proportional to the oxygen concentration.
Oxygen sensors of this type typically operate at a high temperature and therefore include a heating element to which a voltage is delivered for purposes of heating the sensor to its operating temperature. An advantageous sensor control circuit 140 for achieving the desired operating temperature is depicted in Fig. 5. Sensor control circuit 140 includes a sensor initialization portion 142 which includes inverting triggers U2F, U2A
and 555 timer U4 with associated resistive and capacitive component:.. A positive pulse applied at input Line 144 triggers the 555 timer U4 and the timer provides high output at line 146 for a predetermined time period such as sixty seconds. The high timer output results in a low output from trigger U2A which, via line 148 unbalances a bridge circuit 150 during the one minute low output such that Q 1 is held off. The br. idge: circuit 150 is connected to deliver a current/voltage to heater resistor 152 of sensor 116 via. line 154. When the bridge circuit 150 is unbalanced the bridge circuit 150 energizes the censor 116 heater resistor 152 at about one half its rated voltage. When the 555 timer IJ4 times out after one minute, the voltage at line 146 goes low and the voltage output from trigger U2A goes high and is blocked by diode D 1 so as to have no further affect on the bridge circuit 150. The bridge circuit 150 then energizes the heater resistor at its full rated voltage, with the heater resistor 152 of the sensor I 16 completing the bridge.
Docket No. 006593-1890 During manufacture or system installation, the bridge is initially balanced to the rated sensor voltage (4.0 volts) by adjusting variable resistance R3 to meet the sensor specification (to achieve a specified output level at a certain voltage, temperature and known oxygen level). The balance is thereafter maint~~ined by the bridge during the operating mode, after allowing the sensor heater 152 to come up to operating temperature.
The bridge circuit 150 maintains a constant resistance in order to keep the sensor 116 at a constant temperature. Transistor Q1 is controlled by the output of amplifier U3D to pass a varying current to power the bridge 150 and thus the heater resistor 152 of sensor 116.
A sensor cell powering circuit 156 proviides a bias to the measurement cell 120 of sensor 116 via the output of the amplifier U3A. A voltage divider set up by resistors R3 and R4, in combination with switching circuit 158, enables the bias voltage to be set to 0.9 volts to measure free oxygen and to 1.6 volts to measure both free and combined oxygen, as will be described in further detain below. The output of the measurement cell 120 of sensor I 16 is a current I30 which follows a logarithmic curve and which varies as the oxygen concentration varies. This sensor output current 130 is converted to a voltage by converter 158 and the voltage output by amplifier U1 is buffered by amplifier 160 (gain of -1) to provide an output volW ge at 162 for tracking the measured oxygen.
The above sensor control circuit may be. a part of the oven controller 114 or may be separate from the controller, but connected thereto such that the controller 114 can utilize the sensed oxygen level information. Because it is desirable to limit the speed of .
temperature changes of the sensor 116, the sensor initialization portion 112 is important to providing improved sensor life by establishing delivery of a half rated voltage to the heater element 152 when th.e sensor 1 I6 is first being used. In this regard, the positive start pulse can be delivered to line 144 when an oven start-up operation is initiated, so that the sensor 1 I6 is heated up at the same time that the oven fan 112 is turned on in preparation for ignition of the burners) 102. Preferably, the energization of the sensor heater resistor 152 at _7_ Docket No. 006593-1890 the lower voltage Ieve1 overlaps with the fan on operation by at least twenty seconds prior to the start of combustion.
Regardless of the overlap duration, when the fan is running during oven start-up, and prior to initiation of combustion, relatively cool 3;ases will flow along the exhaust path where the sensor 116 is located. These relatively cool gases could interfere with heating up of the sensor I 16 if the sensor were placed directly in the primary flow of the exhaust path. Similarly, during oven operation the effect of corribustion gases which are substantially cooler than the sensor operating temperature, passing by a sensor positioned in the primary flow of the exhaust path could also make it more difficult to properly maintain the sensor IO operating temperature. Accordingly, a preferable mounting arrangement involves positioning the sensor 116 in a sensor chamber 170 positioned alongside the stack 110, or other portion of the exhaust path 108, as shown in Fig. 3. An opening 171 is provided between the exhaust stack 110 and sensor chamber 170 to permit exhaust gases to reach the sensor 116.
In one contemplated embodiment illustraited in more detail in Figs. 6 and 7, the sensor chamber 170 is formed by a tube 172, such as a metal pipe. The tube 170 is threadedly connected to a mounting bracket 174 at one end 176, and the mounting bracket 174 is connected to the side of the exhaust stack 110 via suitable fasteners 178. A sensor positioning member 180 is received within the tube I72 and movable along the axial length of the tube 172 and includes a sensor receiving connector 382 at one end thereof. The sensor 116 snaps into the connector 182 and the positioning member 180 is placed at the desired location along the axial length of the tube 172. The positioning member 180 is then fixed in the desired location by a set screw 184 which passes through a threaded opening 186 in the side of the tube 172. This arrangement advantageously enables the spacing between the sensor and exhaust path to be controlled. Wires 188 extend from the connector 182 back through member 180 toward a sealed connector 190 located near the outer end 192 of the tube 172. An end cap 194 with an opening there througlh is threaded onto tube end 192 and a portion of the sealed connector 190 extends outward beyond the cap 194 and is held in place _g_ Docket No. 006593-1890 by a nut 196 which is threaded around the protruding portion of the plug 190.
The exposed end 198 of plug 190 includes connector receiving openings for making a suitable wiring connection to the sensor control circuit 140.
Unlike traditional potentiometric type oxygen sensors which require that one side of the sensor be exposed to the gas being monitored and the opposite side of the sensor be exposed to ambient air as a reference, the aniperome~ric type sensor 116, which is preferred, should only be exposed to the gases which are; being measured.
Accordingly, suitable gaskets, joint compound and other sealing techniques are utilized in constructing the sensor chamber 170 in order to seal off the chamber 170 and the sensor I I6 positioned therein from gases outside of the exhaust path.
As previously noted, the use of the sensor chamber 170 positioned adjacent the exhaust stack 110 allows the sensor 116 to be positioned outside the primary exhaust gas flow designated as 198 in Fig. 6. The presence of opening 171 permits an auxiliary or secondary flow 200 of exhaust gases into the charrlber 1'70, and thus maintains the sensor in 1 S communication with the exhaust gases for sensing the o:~ygen content of the same. The secondary flow 200 which reaches the chamber 170, however, is substantially less than the primary flow 198, and therefore has much less of an effect on sensor temperature, enabling the sensor 116 to be heated up more readily during oven start-up, and facilitating proper maintenance of sensor temperature during oven operation.
'The oxygen sensing arrangement provided herein advantageously provides the ability to utilize the sensed oxygen content of the exhaust gases to control the combustion in the oven. In particular, based upon the oxygen content sensed by the sensor 116, the controller can control the speed of the exhaust fan 112 or the position of the damper 113 to vary the air/fuel ratio burned in the combustion area of the oven. Similarly, the controller could control the gas valve 106 to vary the air/fuel ratio, or a combined control of the fan 112, damper 113 and valve 106 could be provided. Rather than controlling the air/fuel ratio, R
the controller could simply monitor the oxygen content as indicated by the sensor 1 I6 and set Docket No. 006593-1890 a flag or alarm (such as and indicator light, horn or buzzer) and/or shut down the oven if the oxygen content falls outside an established, acceptable window.
While useful in sensing oxygen content oiP combusted gases, the amperometric type sensor preferred herein is also useful in determining the moisture content of gases as well. This feature of the sensor is particularly usefiil in rack ovens or other types of ovens in which the controlled generation of steam is desirable. In this regard, reference is made to Fig.
8 where a rack oven 210 is shown, including combustion area 212, heat exchanger 214 and steam generator 216. A baking chamber 218 includes rotatable rack 220 positioned therein, with a portion of the rack 220 cut away to expose a sensor 222 positioned along a side wall of the chamber 220 and a powered or unpowered vent 224 positioned in the side wall. The sensor is preferably the amperometric sensor described above, and can be utilized to sense the moisture content of the hot air within the baking chamber 218. In particular, referring to the graph shown in Fig. 9, the sensor output response for dr~r air 230 and wet air 232 at a given oxygen content are shown respectively. Notably, depending upon the sensor voltage applied to the sensor cell, the current varies between levels A and B when the air is wet. Level A
represents the free oxygen content of the air, while level B represents the total oxygen content (free oxygen and oxygen present as moisture in the air). The Level B
measurement results from the electrochemical deposition of water vapor in the presence of the higher voltage. By making a measurement at both applied voltages, the humidity or moisture content of the air can be defined as function of the difference between the two measurements because the water content of the air is directly proportional to the differential oxygen content. The oven controller can use the sensed humidity level within the oven chamber 218 to control the delivery of water (via a controllable valve) to the steam generator 216.
Likewise, the oven controller can use the sensed humidity level within the oven chamber 218 to control the operation of fan 224 in order to remove high humidity air from the oven chamber 2 i 8.
Although the invention has been described and illustrated in detail it is to be clearly understood that the same is intended by way of illustration and example only and is Docket No. 006593-1890 not intended to be taken by way of limitation. For example, while the preferred mounting position of the sensor chamber is along the exhaust stack as illustrated, it is recognized that the sensor chamber could be located along other portions of the exhaust path.
Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.
Fig. 1 is a front elevation of a prior art rack oven;
Fig. 2 is a side elevation of the rack oven of Fig. 2;
Fig. 3'is a schematic diagram of an oven including one contemplated embodiment of an oxygen sensing arrangement;
Fig. 4 shows an arnperometric oxygen sensor;
Fig. 5 is a schematic diagram of a sensor control circuit according to one embodiment of the invention;
Fig. 6 illustrates one contemplated embodiment of a sensor chamber;
Fig. 7 is an exploded view of the sensor chamber of Fig. 6;
Fig. 8 is a front elevation of a rack oven. including an amperometric sensor within the baking chamber for humidity sensing; and Fig. 9 is a graph showing sensor output cuxrent verses applied voltage.
DETAILED DESCRIPTION OF ThIE EMBODIMENTS
Deferring to drawing Figs. 1 and 2 an e;Kemplary prior art rack oven an:angement as described in U.S. Patent No. 5,617,839 is shown. As described in such patent, the oven 10 includes two main sections. The first section 62 houses the baking chamber 12 and the second section 64 contains a steam generator 26, a combustion area 30 which contains a plurality of gas fired in-shot burners, a heat exchanger 32 and one or more blowers 28 for drawing moisture-containing air from the steam generator 26 and forcing the moisture-containing air through the heat exchanger 32 and into the baking chamber 12. A
fiypical oven 10, as shown in FIG. 1, has a baking eharr~ber 12 which includes an apertured upstream wall 14 and a partially apertured downstream wall 16. Disposed within the chamber 12 is a removable wheeled rack 18 connected at its upper end to a rotatably power driv en vertical shaft 22. The products 24 to be baked such as bread are placed in pans or on baking sheets held by rack 18 which rotates to uniformly expose the products 24 to heated, steam-containing air as it flows through the ba.yking chamber 12.
_3_ Docket Na. 006593-~ 890 The products 24 to be baked are loaded ozzta a wheeled rack 18 and placed in the baking chamber 12 and the door (not show~z~ is closed causizzg the rack 18 containing the products 24 to be lifted off the floor by a lift mechanism 20 as the door closes and then made to rotate by motor 21 'attached to vertical shaft 22. ~teaxn produced by the steam generator 26 is made to infiltrate the entire oven 10 by the fan 28 where the moisture condenses on the pool surface of the unbaked products 24. After a period of about 10 to 30 seconds, the steam is discontinued or continued in defined cycles, dependv:zg on the food product being baked, and the baking cycle started. During the baking cycle, heated air is continually circulated in a closed path throughout the entire oven 10. The air exits the baking chamber 12 through aperture 17 irr a partially apertured downside wall 16 where it enters the steam generator 26 heating the steam generator 26 and picking up addition,~l moisture if desired.
While the steam generator 26 can be selected from any of the steam generators employed in the prior art to supply steam to a rack oven, it has been found that a particularly effective steam generator is that described in U.S. Pat. No. 5,394,791 to Vallee. Th:e moisture-containing air is drawn through the steam generator 26 where the heated, moisture-containing air picks up speed as it is pulled through the heat exchanger 32 by one or more: blower fans 28 located in the plenum section 34 at the top of the oven 10. From the plentun section 34, the air enters one or more air distribution ducts 36 where it is distributed to the baking chamber I2 through the apertures 1 S in wall 14. The heated air then circulates through the baking chamber 12 contacting the baking products 24 and exits through thf; ap~rtur~s in wall 1.6. Th.e cycle is repeated continuously for a period of time determined by the baking conditions and the product being baked.
hIfa. 2 is a cross sectional schematic illustration of the second section of the oven 10 which contains a steam generator 26, combustion area 30, and a heat exchanger 32.
The air from the baking chamber 12 (FICi. 1) passes over the steam ger~~rator 26 where it picks up moisture (if necessary) and is then drawn through heat exchanger 32 containing a series of elongated heat exchaxige tubes 38 which heat, tl;e moisture-containing air. In a first _4_ Docket f~lo. 006533-1890 section of the heat exchanger 32, the elongated heat exchange ti~bes 38 are heated by a corresponding number of "in-shot" burners which fire du-ectly into the heat exchanger tubes 38. The hot combustion gases from the burners 40 are th;~n circulated through a second section of heat exchanger tubes heating these tubs to a high temperature in order to transfer sufficient heat to the air passing over the heat exchange tubes 38. The combustion gases passing through the heat exchange tubes 38 are vented into the atmosphere through exhaust outlet 48, which is attached to an appropriate exhaust duct as described in more detail below.
Exhaust fan 50 is provided for assisting in the removal of the combustion gases, and is also utilized at oven start-up, prior to burner ignition, to remove gases from the combustion area I0 to assure safe burner ignition.
While the oxygen sensing arrangement described herein is contemplated primarily for use v~~ith a rack oven 10 of the type dESCrib~~d above, it is recognized and anticipated that the arrangement could be utilized in connection with other types of gas-fired ovens. As used herein the term "gas-fired oven" is intended to broadly encompass any device which bums gaseous fael, either alone or in combination with any other type of heating element, in order to produce heat for cooking, baking, boiling, steaming and/or flying. The term "combustion area" is intended to broadly encompass any location where gaseous fuel is burned within a gas-fired oven.
Referring now to Fig. 3, a gas-fired oven 100 includes at least one burner 102 and associated igniter I04, a valve 105 for controlling g~~seous fuel delivery to the burner 102, an exhaust path I08 for combusted gases, the path including an exhaust stack 110 extending from the oven, an exhaust fa~i 1 I2 positioned to aid in exhausting gases from the oven 100 by inducing a draft in combination ~~ith a controllable dair~per 113, and an oven controller I 14 connected to the valve 105, fan 112, and clatrper I 13 fox controlling combustion. Positioned along the exhaust path 108 is an oxygen sensor 116 for sensing the oxygen content of gases traveling along the exhaust path. The controller 114 is also connected to receive signals from the oxygen sensor 11 fi.
Docket No. OOG593-1890 In a preferred embodiment the oxygen sensor 116 is an amperometric type sensor in which a control voltage is applied to the sensor and the sensor outputs a current which varies with an oxygen content of gases in contact therewith. A suitable amperometric sensor having a zirconia electrolyte cell is available from ELECTRO~IAC
GES.I~~.B.H. of Klosterneuberg, Austria and is shown in Fig. 4 where an. electrochemical oxygen pumping cell 120 made of zirconia is shown having a cathode I22 and anode 124. V~~hen voltage is applied to the cell 120, oxygen ions are pumped through. the cell from the cathode 122 to the anode 124. By at+taching a cap 126 with a pinhole 128 on the cathode side of the Bell 120, the current 130 shoves saturation due to the rate limiting step in the transfer to the cathode. This limiting current 130 is nearly proportional to the oxygen concentration.
Oxygen sensors of this type typically operate at a high temperature and therefore include a heating element to which a voltage is delivered for purposes of heating the sensor to its operating temperature. An advantageous sensor control circuit 140 for achieving the desired operating temperature is depicted in Fig. 5. Sensor control circuit 140 includes a sensor initialization portion 142 which includes inverting triggers U2F, U2A
and 555 timer U4 with associated resistive and capacitive component:.. A positive pulse applied at input Line 144 triggers the 555 timer U4 and the timer provides high output at line 146 for a predetermined time period such as sixty seconds. The high timer output results in a low output from trigger U2A which, via line 148 unbalances a bridge circuit 150 during the one minute low output such that Q 1 is held off. The br. idge: circuit 150 is connected to deliver a current/voltage to heater resistor 152 of sensor 116 via. line 154. When the bridge circuit 150 is unbalanced the bridge circuit 150 energizes the censor 116 heater resistor 152 at about one half its rated voltage. When the 555 timer IJ4 times out after one minute, the voltage at line 146 goes low and the voltage output from trigger U2A goes high and is blocked by diode D 1 so as to have no further affect on the bridge circuit 150. The bridge circuit 150 then energizes the heater resistor at its full rated voltage, with the heater resistor 152 of the sensor I 16 completing the bridge.
Docket No. 006593-1890 During manufacture or system installation, the bridge is initially balanced to the rated sensor voltage (4.0 volts) by adjusting variable resistance R3 to meet the sensor specification (to achieve a specified output level at a certain voltage, temperature and known oxygen level). The balance is thereafter maint~~ined by the bridge during the operating mode, after allowing the sensor heater 152 to come up to operating temperature.
The bridge circuit 150 maintains a constant resistance in order to keep the sensor 116 at a constant temperature. Transistor Q1 is controlled by the output of amplifier U3D to pass a varying current to power the bridge 150 and thus the heater resistor 152 of sensor 116.
A sensor cell powering circuit 156 proviides a bias to the measurement cell 120 of sensor 116 via the output of the amplifier U3A. A voltage divider set up by resistors R3 and R4, in combination with switching circuit 158, enables the bias voltage to be set to 0.9 volts to measure free oxygen and to 1.6 volts to measure both free and combined oxygen, as will be described in further detain below. The output of the measurement cell 120 of sensor I 16 is a current I30 which follows a logarithmic curve and which varies as the oxygen concentration varies. This sensor output current 130 is converted to a voltage by converter 158 and the voltage output by amplifier U1 is buffered by amplifier 160 (gain of -1) to provide an output volW ge at 162 for tracking the measured oxygen.
The above sensor control circuit may be. a part of the oven controller 114 or may be separate from the controller, but connected thereto such that the controller 114 can utilize the sensed oxygen level information. Because it is desirable to limit the speed of .
temperature changes of the sensor 116, the sensor initialization portion 112 is important to providing improved sensor life by establishing delivery of a half rated voltage to the heater element 152 when th.e sensor 1 I6 is first being used. In this regard, the positive start pulse can be delivered to line 144 when an oven start-up operation is initiated, so that the sensor 1 I6 is heated up at the same time that the oven fan 112 is turned on in preparation for ignition of the burners) 102. Preferably, the energization of the sensor heater resistor 152 at _7_ Docket No. 006593-1890 the lower voltage Ieve1 overlaps with the fan on operation by at least twenty seconds prior to the start of combustion.
Regardless of the overlap duration, when the fan is running during oven start-up, and prior to initiation of combustion, relatively cool 3;ases will flow along the exhaust path where the sensor 116 is located. These relatively cool gases could interfere with heating up of the sensor I 16 if the sensor were placed directly in the primary flow of the exhaust path. Similarly, during oven operation the effect of corribustion gases which are substantially cooler than the sensor operating temperature, passing by a sensor positioned in the primary flow of the exhaust path could also make it more difficult to properly maintain the sensor IO operating temperature. Accordingly, a preferable mounting arrangement involves positioning the sensor 116 in a sensor chamber 170 positioned alongside the stack 110, or other portion of the exhaust path 108, as shown in Fig. 3. An opening 171 is provided between the exhaust stack 110 and sensor chamber 170 to permit exhaust gases to reach the sensor 116.
In one contemplated embodiment illustraited in more detail in Figs. 6 and 7, the sensor chamber 170 is formed by a tube 172, such as a metal pipe. The tube 170 is threadedly connected to a mounting bracket 174 at one end 176, and the mounting bracket 174 is connected to the side of the exhaust stack 110 via suitable fasteners 178. A sensor positioning member 180 is received within the tube I72 and movable along the axial length of the tube 172 and includes a sensor receiving connector 382 at one end thereof. The sensor 116 snaps into the connector 182 and the positioning member 180 is placed at the desired location along the axial length of the tube 172. The positioning member 180 is then fixed in the desired location by a set screw 184 which passes through a threaded opening 186 in the side of the tube 172. This arrangement advantageously enables the spacing between the sensor and exhaust path to be controlled. Wires 188 extend from the connector 182 back through member 180 toward a sealed connector 190 located near the outer end 192 of the tube 172. An end cap 194 with an opening there througlh is threaded onto tube end 192 and a portion of the sealed connector 190 extends outward beyond the cap 194 and is held in place _g_ Docket No. 006593-1890 by a nut 196 which is threaded around the protruding portion of the plug 190.
The exposed end 198 of plug 190 includes connector receiving openings for making a suitable wiring connection to the sensor control circuit 140.
Unlike traditional potentiometric type oxygen sensors which require that one side of the sensor be exposed to the gas being monitored and the opposite side of the sensor be exposed to ambient air as a reference, the aniperome~ric type sensor 116, which is preferred, should only be exposed to the gases which are; being measured.
Accordingly, suitable gaskets, joint compound and other sealing techniques are utilized in constructing the sensor chamber 170 in order to seal off the chamber 170 and the sensor I I6 positioned therein from gases outside of the exhaust path.
As previously noted, the use of the sensor chamber 170 positioned adjacent the exhaust stack 110 allows the sensor 116 to be positioned outside the primary exhaust gas flow designated as 198 in Fig. 6. The presence of opening 171 permits an auxiliary or secondary flow 200 of exhaust gases into the charrlber 1'70, and thus maintains the sensor in 1 S communication with the exhaust gases for sensing the o:~ygen content of the same. The secondary flow 200 which reaches the chamber 170, however, is substantially less than the primary flow 198, and therefore has much less of an effect on sensor temperature, enabling the sensor 116 to be heated up more readily during oven start-up, and facilitating proper maintenance of sensor temperature during oven operation.
'The oxygen sensing arrangement provided herein advantageously provides the ability to utilize the sensed oxygen content of the exhaust gases to control the combustion in the oven. In particular, based upon the oxygen content sensed by the sensor 116, the controller can control the speed of the exhaust fan 112 or the position of the damper 113 to vary the air/fuel ratio burned in the combustion area of the oven. Similarly, the controller could control the gas valve 106 to vary the air/fuel ratio, or a combined control of the fan 112, damper 113 and valve 106 could be provided. Rather than controlling the air/fuel ratio, R
the controller could simply monitor the oxygen content as indicated by the sensor 1 I6 and set Docket No. 006593-1890 a flag or alarm (such as and indicator light, horn or buzzer) and/or shut down the oven if the oxygen content falls outside an established, acceptable window.
While useful in sensing oxygen content oiP combusted gases, the amperometric type sensor preferred herein is also useful in determining the moisture content of gases as well. This feature of the sensor is particularly usefiil in rack ovens or other types of ovens in which the controlled generation of steam is desirable. In this regard, reference is made to Fig.
8 where a rack oven 210 is shown, including combustion area 212, heat exchanger 214 and steam generator 216. A baking chamber 218 includes rotatable rack 220 positioned therein, with a portion of the rack 220 cut away to expose a sensor 222 positioned along a side wall of the chamber 220 and a powered or unpowered vent 224 positioned in the side wall. The sensor is preferably the amperometric sensor described above, and can be utilized to sense the moisture content of the hot air within the baking chamber 218. In particular, referring to the graph shown in Fig. 9, the sensor output response for dr~r air 230 and wet air 232 at a given oxygen content are shown respectively. Notably, depending upon the sensor voltage applied to the sensor cell, the current varies between levels A and B when the air is wet. Level A
represents the free oxygen content of the air, while level B represents the total oxygen content (free oxygen and oxygen present as moisture in the air). The Level B
measurement results from the electrochemical deposition of water vapor in the presence of the higher voltage. By making a measurement at both applied voltages, the humidity or moisture content of the air can be defined as function of the difference between the two measurements because the water content of the air is directly proportional to the differential oxygen content. The oven controller can use the sensed humidity level within the oven chamber 218 to control the delivery of water (via a controllable valve) to the steam generator 216.
Likewise, the oven controller can use the sensed humidity level within the oven chamber 218 to control the operation of fan 224 in order to remove high humidity air from the oven chamber 2 i 8.
Although the invention has been described and illustrated in detail it is to be clearly understood that the same is intended by way of illustration and example only and is Docket No. 006593-1890 not intended to be taken by way of limitation. For example, while the preferred mounting position of the sensor chamber is along the exhaust stack as illustrated, it is recognized that the sensor chamber could be located along other portions of the exhaust path.
Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.
Claims (23)
1. An oxygen sensing arrangement for a gas-fired oven, comprising:
an oxygen sensor positioned for sensing gases along an exhaust path of the oven, the oxygen sensor including a heater and a measurement cell;
a sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up level for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating level which is greater than the start-up level.
an oxygen sensor positioned for sensing gases along an exhaust path of the oven, the oxygen sensor including a heater and a measurement cell;
a sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up level for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating level which is greater than the start-up level.
2. The arrangement of claim 1 wherein the bridge portion of the sensor control circuit varies the operating current delivered to the heater in order to maintain a substantially constant heater temperature.
3. The arrangement of claim 1, further comprising:
an exhaust fan located along the exhaust path;
at least one gas-fired burner;
a controller connected for controlling the exhaust fan and the gas-fired burner;
the controller operable, upon oven start-up, to turn the exhaust fan on for a predetermined time period prior to igniting the gas-fired burner.
an exhaust fan located along the exhaust path;
at least one gas-fired burner;
a controller connected for controlling the exhaust fan and the gas-fired burner;
the controller operable, upon oven start-up, to turn the exhaust fan on for a predetermined time period prior to igniting the gas-fired burner.
4. The arrangement of claim 3 wherein, upon oven start-up, the predetermined time period and the start-up time period run at least partially concurrently.
5. The arrangement of claim 3 wherein the exhaust bath includes an exhaust stack and a sensor chamber positioned alongside the stack so as to beg spaced from a primary exhaust gas flow, the sensor chamber open to gases in the exhaust stack, the oxygen sensor positioned within the sensor chamber.
6. The arrangement of claim 5 wherein the sensor chamber and oxygen sensor therein are sealed off from gases outside of the exhaust stack.
7. The arrangement of claim 6 wherein the oxygen sensor comprises an amperometric sensor.
8. An oxygen sensing arrangement, comprising:
an oxygen sensor;
a sensor control circuit associated with said oxygen sensor, the sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up voltage for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to the heater at an operating voltage which is greater than the start-up voltage.
an oxygen sensor;
a sensor control circuit associated with said oxygen sensor, the sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up voltage for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to the heater at an operating voltage which is greater than the start-up voltage.
9. A gas-fired oven, comprising:
at least one gas-fired burner having an associated exhaust gas path;
an exhaust fan located along the exhaust path;
a controller connected for controlling the exhaust fan and the gas-fired burner, the controller operable, upon oven start-up, to turn the exhaust fan on for a predetermined time period prior to igniting the gas-fired burner;
an oxygen sensor positioned for sensing gases along the exhaust path, the sensor including a heater and a measurement cell;
a sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein, upon oven start-up, the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up voltage for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating voltage which is greater than the start-up voltage.
at least one gas-fired burner having an associated exhaust gas path;
an exhaust fan located along the exhaust path;
a controller connected for controlling the exhaust fan and the gas-fired burner, the controller operable, upon oven start-up, to turn the exhaust fan on for a predetermined time period prior to igniting the gas-fired burner;
an oxygen sensor positioned for sensing gases along the exhaust path, the sensor including a heater and a measurement cell;
a sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein, upon oven start-up, the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize the heater at a start-up voltage for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating voltage which is greater than the start-up voltage.
10. The gas-fired oven of claim 9 wherein the exhaust path includes an exhaust stack and a sensor chamber positioned alongside the stack so as to be spaced from a primary exhaust gas flow, the chamber open to gases in the exhaust stack, the oxygen sensor positioned within the sensor chamber, wherein the sensor chamber, and oxygen sensor therein, are sealed off from gases outside of the exhaust stack.
11. The gas-fired oven of claim 10 wherein the oxygen sensor comprises an amperometric sensor.
12. The gas-fired oven of claim 9 wherein the sensor control circuit comprises a portion of the controller.
13. A method of controlling a gas-fired oven, the method comprising the steps of:
providing an oven start-up mode during which the following steps are performed;
applying a start-up current to a heating element of an oxygen sensor;
energizing an exhaust fan to exhaust gases from a combustion area of the oven;
maintaining a non-bum condition within the combustion area;
providing an oven operating mode, following the oven start-up mode, and during which the following steps are performed:
applying an operating current to the heating element of the oxygen sensor;
establishing a burn condition within the combustion area.
providing an oven start-up mode during which the following steps are performed;
applying a start-up current to a heating element of an oxygen sensor;
energizing an exhaust fan to exhaust gases from a combustion area of the oven;
maintaining a non-bum condition within the combustion area;
providing an oven operating mode, following the oven start-up mode, and during which the following steps are performed:
applying an operating current to the heating element of the oxygen sensor;
establishing a burn condition within the combustion area.
14. The method of claim 13, comprising the further step of:
positioning the oxygen sensor in a chamber adjacent an exhaust path of the oven, the chamber in gaseous communication with the exhaust path; and sealing the chamber to prevent gases from outside the exhaust path from reaching the oxygen sensor.
positioning the oxygen sensor in a chamber adjacent an exhaust path of the oven, the chamber in gaseous communication with the exhaust path; and sealing the chamber to prevent gases from outside the exhaust path from reaching the oxygen sensor.
15. The method of claim 13 wherein the oxygen sensor comprises an amperometric sensor, and the method includes:
in at least the oven operating mode, producing a sensor output having a current which varies according to an oxygen content of oven exhaust gases.
in at least the oven operating mode, producing a sensor output having a current which varies according to an oxygen content of oven exhaust gases.
16. The method of claim 15 comprising the further step of:
in at least the oven operating mode, controlling a speed of the exhaust fan based at least in part upon the produced sensor output.
in at least the oven operating mode, controlling a speed of the exhaust fan based at least in part upon the produced sensor output.
17. The method of claim 15, comprising the further step of:
in at least the oven operating mode, controlling a damper position based at least in part upon the produced sensor output.
in at least the oven operating mode, controlling a damper position based at least in part upon the produced sensor output.
18. The method of claim 15, comprising the further step of:
in at least the oven operating mode, setting a flag if the produced sensor output indicates an unacceptable oxygen level.
in at least the oven operating mode, setting a flag if the produced sensor output indicates an unacceptable oxygen level.
19. An oxygen sensing arrangement for a gas-fired oven, comprising:
a combustion area;
an exhaust path for receiving gases from the combustion area;
a sensor chamber positioned alongside the exhaust path so as to be spaced from a primary flow of exhaust gases, the chamber open to gases in the exhaust path, an oxygen sensor positioned within the sensor chamber, wherein both the sensor chamber and oxygen sensor therein are sealed off from gases outside of the exhaust path.
a combustion area;
an exhaust path for receiving gases from the combustion area;
a sensor chamber positioned alongside the exhaust path so as to be spaced from a primary flow of exhaust gases, the chamber open to gases in the exhaust path, an oxygen sensor positioned within the sensor chamber, wherein both the sensor chamber and oxygen sensor therein are sealed off from gases outside of the exhaust path.
20. The arrangement of claim 19, wherein the chamber comprises a tube having a first end attached to an opening in a sidewall of the exhaust path, and an end cap connected to a second end of the tube.
21. The arrangement of claim 19 wherein the oxygen sensor comprises an amperometric sensor which produces a sensor output signal having a current which varies with according to an oxygen content of oven exhaust gases.
22. The arrangement of claim 19, wherein the oxygen sensor is connected to a sensor control circuit having a sensor initialization portion connected to a bridge portion, the bridge portion connected for energizing the heater, wherein the sensor initialization portion produces a start signal which unbalances the bridge circuit for a start-up time period, causing the bridge circuit to energize to the heater at a start-up voltage for the start-up time period, wherein, after the start-up time period the sensor initialization portion no longer produces the start signal and the bridge circuit balances so as to energize the heater at an operating voltage which is greater than the start-up voltage.
23. A method of mounting an oxygen sensor for sensing an oxygen content of gases traveling along an exhaust path of a gas-fired oven, the method comprising:
mounting a sensor housing adjacent an exhaust duct;
providing gaseous communication between an interior of the exhaust duct and an interior of the sensor housing;
positioning an oxygen sensor within the interior of the sensor housing; and sealing off an interior of the sensor housing from gases external to the exhaust duct.
mounting a sensor housing adjacent an exhaust duct;
providing gaseous communication between an interior of the exhaust duct and an interior of the sensor housing;
positioning an oxygen sensor within the interior of the sensor housing; and sealing off an interior of the sensor housing from gases external to the exhaust duct.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66493600A | 2000-09-19 | 2000-09-19 | |
| US09/664,936 | 2000-09-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2352648A1 true CA2352648A1 (en) | 2002-03-19 |
Family
ID=24668054
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2352648 Abandoned CA2352648A1 (en) | 2000-09-19 | 2001-07-06 | Oven exhaust gas oxygen sensing arrangement and related control circuit and method |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2352648A1 (en) |
| MX (1) | MXPA01007510A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2480862B (en) * | 2010-06-03 | 2013-02-13 | Kidde Tech Inc | Smoke detection system |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112180037B (en) * | 2020-09-15 | 2022-09-09 | 华帝股份有限公司 | Oxygen sensor and household appliance |
-
2001
- 2001-07-06 CA CA 2352648 patent/CA2352648A1/en not_active Abandoned
- 2001-07-25 MX MXPA01007510 patent/MXPA01007510A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2480862B (en) * | 2010-06-03 | 2013-02-13 | Kidde Tech Inc | Smoke detection system |
Also Published As
| Publication number | Publication date |
|---|---|
| MXPA01007510A (en) | 2002-05-24 |
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