MXPA01007510A - Oven exhaust gas oxygen sensing arrangement and related control circuit and method. - Google Patents

Abstract

An oven exhaust gas oxygen sensing arrangement includes a gas sensor for sensing gases along an oven exhaust trajectory, the oxygen sensor including a heater and a measuring cell. A sensor control circuit includes a sensor initialisation portion connected to a by-pass portion. The by-pass portion is operatively connected so as to energize the heater. The sensor initialisation portion generates a starting signal, which unbalances the by-pass circuit for a starting period of time, therebu causing the by-pass circuit to supply a heating current/voltage to the heater during the starting period of time. After the starting period of time, the sensor initialisation portion does no longer produce the starting signal and the by-pass circuit is balanced in order to deliver an operating current/voltage to the heater. A voltage of the heating current/voltage is smaller than a voltage of the operating current/voltage. The present arrangement allows the oxygen sensor to be heated at the operating temperature thereof at a respective heating voltage and speed which does not harm the sensor, and is particularly useful when the oxygen sensor is of the aperometric type. The sensor may be positioned in a sensing chamber which is located along the exhaust so as to be spaced apart from the primary flow of exhaust gases, the opening of the chamber being useful for receiving gases from the exhaust. Both the sensing chamber and the oxygen sensor located therein are sealed away from the externas gases of the exhaust.

Description

GAS OXYGEN PERCEPTION ARRANGEMENT OF EXHAUST OVEN AND CIRCUIT AND RELATED CONTROL METHOD BACKGROUND OF THE INVENTION The present invention relates in general to combustion control of furnaces, and more particularly, to an arrangement of oxygen perception of exhaust gas from furnaces and related circuit and control method.

BACKGROUND OF THE INVENTION Commercial large ovens, such as support ovens, are commonly of the type that are fired with gas and include one or more burners. For environmental and efficiency reasons, it continues to be desirable to improve the burning conditions by controlling an air / fuel ratio in said furnaces. One technique to do this involves checking the oxygen content of burned gases. However, common oxygen sensors such as those used in automobiles are not very suitable for perceiving higher concentrations of oxygen seen in exhaust gases from furnaces and are very expensive when adapted for that purpose. In addition, maintaining the proper sensor temperature can be a problem. Therefore, it t be desirable to provide an arrangement and,,. ^. ^. ^. J ^. ^ - * Ét. of oxygen perception for ovens, which includes an adequate control mechanism and which is advantageously placed.

COMPENDIUM OF THE INVENTION In one aspect of the present invention, an oxygen perception array for a gas fired oven includes an oxygen sensor positioned to sense gases along an exhaust path of the furnace, the oxygen sensor including a heater and a cell measurement. A sensor control circuit includes a sensor initialization portion connected to a bridge portion. The bridge portion is operatively connected to energize the heater. The initialization portion of the sensor produces a start signal that unbalances the bridge circuit during a start period, causing the bridge circuit to energize the heater to a start level during the start period. After the start period, the initialization portion of the sensor no longer produces the start signal and the bridge circuit is balanced in order to energize the heater at one level of operation. A voltage during start energization is less than a voltage during operation energization. The arrangement allows the oxygen sensor to be heated to its operating temperature at a corresponding heating voltage and rate, which will not damage the sensor, and is particularly useful when the oxygen sensor is an amperometric type sensor.

Another aspect of the invention provides a method for controlling a gas fired oven, which involves providing an oven start mode during which the following W steps are performed: (i) energizing an element of heating a 5 oxygen sensor to a start level; (ii) energize an exhaust fan to remove gases from a combustion area of the furnace; and (iii) maintaining a non-burned condition within the combustion area. An oven mode of operation is provided, following the oven start mode, and during which oven 10 the following steps: (i) energize the heating element of the oxygen sensor at an operation level; and (ii) establish a burning condition within the combustion area. The method allows the oxygen sensor to be heated to its operating temperature at the same time that residual gases are removed from the 15 combustion area before the start of combustion. Since the exhaust of the gases results in a flow of cooling air along the exhaust path, the method preferably also involves placing the oxygen sensor in a chamber adjacent to an exhaust exhaust path away from the furnace. 20 primary flow of exhaust gases but in gaseous communication with the exhaust path. Another aspect of the invention provides an oxygen perception arrangement that includes a combustion area and an exhaust path to receive gases from the combustion area. A 25 sensor chamber is placed along the exhaust duct with in order to be separated from a primary flow of the exhaust gases, but the chamber is open to receive gases in the exhaust duct. An oxygen sensor is placed inside the sensor chamber, and both the sensor chamber and the oxygen sensor there are gas sealed outside the exhaust duct.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front elevational view of a prior art support oven; Figure 2 is a side view of the support oven of Figure 1; Figure 3 is a schematic diagram of an oven including a contemplated embodiment of an oxygen perception arrangement; Figure 4 shows an amperometric oxygen sensor; Figure 5 is a schematic diagram of a sensor control circuit according to an embodiment of the invention; Figure 6 illustrates a contemplated embodiment of a sensor chamber 20; Figure 7 is an exploded view of the sensor chamber of Figure 6, Figure 8 is a front elevation of a support furnace including an amperometric sensor inside the baking chamber for sensing moisture; and Figure 9 is a graph showing the output current of the sensor against the applied voltage.

DETAILED DESCRIPTION OF THE MODALITIES Referring to Figures 1 and 2, there is shown an illustrative prior art support furnace array as described in U.S. Patent No. 5,617,839. As described in that patent, the oven 10 includes two main sections. The 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 burners, a heat exchanger 32 and one or more blowers. 28 to extract air containing moisture from the generator 15 of steam 26 and force air containing moisture through the heat exchanger 32 and into the baking chamber 12. A typical oven 10, as shown in Figure 1, has a baking chamber 12, which includes a wall upstream with openings 14 and a downstream wall 16 partially with openings. Arranged within the chamber 12 is a removable wheel support 18 connected at its upper end to a vertical shaft 22 rotatably driven. The products 24 to be baked, such as bread, are placed in trays or in baking sheets held by the support 18, which rotates for 25 uniformly expose the products 24 to air containing steam, ~ - - - • - - - - - - - ^^ * hot as it flows through the baking chamber 12. The products 24 that are going to be baked are loaded onto • a support with wheels 18 and placed in the baking chamber 12 and 5 the door (not shown) closes, causing the support 18 containing the products 24 to be lifted off the floor through a lifting mechanism 20 as the door is closed and then rotated by the motor 21 attached to the vertical arrow 22. The steam produced by the steam generator 26 is made to infiltrate 10 throughout the oven 10 through the fan 28, where the moisture condenses on the cold surface of the unbaked products 24. After a period of approximately 10 to 30 seconds, the steam is interrupted or continued in defined cycles , depending on the food product being baked, and the cycle of 15 baked started. During the baking cycle, the hot air is continuously circulated in a closed path through the entire oven 10. The air leaving the baking chamber 12 through the opening 17 in a downward wall 16 partially with openings , where it enters the steam generator 26 by heating 20 to the steam generator 26 and collecting additional moisture, if desired. While the steam generator 26 can be selected from any of the steam generators employed in the prior art for supplying steam to a support furnace, it has been found that a particularly effective steam generator is 25 that described in the patent of E. U. A. No. 5,394,791 of Vallee. He Air containing moisture is extracted through the steam generator 26 where the warm, 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 furnace 10. From the plenum section 34, air enters one or more air distribution ducts 36, where it is distributed towards the baking chamber 12 through the openings 15 in the wall 14. The hot air then circulates through the baking chamber 12 putting in contact the 10 baked goods 24 and exits through the openings in the wall W 16. In cycle it is repeated continuously for a period determined by the baking conditions and the product to be baked. Figure 2 is a cross-sectional schematic illustration of the second section of the furnace 10, containing a steam generator 26, a combustion area 30 and a heat exchanger 32. The air in the baking chamber 12 (Figure 1) passes over the steam generator 26, where it collects moisture (if necessary) and then withdraws through the heat exchanger 32 containing a series of 20 elongated heat exchanger tubes 38, which heat the air containing moisture. In a first section of the heat exchanger 32, the elongated heat exchanger tubes 38 are heated by a corresponding number of burners "in draft", which directly ignite the exchanger tubes 25 thermal 38. The hot combustion gases of the burners 40 .. ... ^. * ^^ - ^ Then they are circulated through a second section of the heat exchanger tubes by heating these tubes to a high temperature in order to transfer sufficient heat to the air passing over the heat exchanger tubes 38. The Combustion gases passing through the heat exchanger tubes 38 are vented to the atmosphere through the exhaust outlet 48, which is attached to an appropriate exhaust duct as described in more detail below. The exhaust fan 50 is provided to assist in the removal of the combustion gases, and is also used at the start or ignition of the furnace, before igniting the burner, to remove gases from the combustion area to ensure a safe ignition of the combustion chamber. burner. Although the oxygen perception arrangement described herein is primarily intended for use in a support oven 10 of the type described above, it is recognized and anticipated that the arrangement may be used in relation to other types of gas-fired kilns. As used in the present, the term "gas fired oven" broadly encompasses any device that burns gaseous fuel, either alone or in combination with another type of heating, in order to produce heat for cooking, baking, boiling, and / fry The term "combustion area" broadly encompasses any site where the gaseous fuel is burned inside a gas fired oven. With reference to Figure 3, a gas fired oven 100 includes at least one burner 102 and an associated igniter 104, a valve 106 for controlling the supply of gaseous fuel to the burner 102, an exhaust path 108 for burned gases, the trajectory including an exhaust stack 110 extending from the furnace, an exhaust fan 112 placed 5 to assist the exhaust of the furnace 100 inducing a suction in combination with a controllable firing register 113, and a furnace controller 114 connected to the valve 106, the fan 112 and the firing register 113 for controlling combustion. Placed along the exhaust path 108 is an oxygen sensor 10 116 to perceive the oxygen content of the gases that travel to • along the escape path. The controller 114 is also connected to receive signals from the oxygen sensor 116. In a preferred embodiment, the oxygen sensor 116 is an amperometric type sensor in which a voltage of 15 control to the sensor and the sensor produces a current that varies with an oxygen content of the gases in contact with it. A suitable amperometric sensor having a zirconia electrolyte cell is available from ELECTROVAC GES.M.B.H. from Klosterneuberg, Austria, and is shown in Figure 4, where a The electrochemical oxygen pumping cell 120 made of zirconia is shown having a cathode 122 and an anode 124. When voltage is applied to the cell 120, the oxygen ions are pumped through the cell from the cathode 122 to the anode 124. By attaching a cover 126 with a hole 128 on the cathode side of the cell 120, the 25 current 120 shows saturation due to the limiting step of ^^ - ^^ Mf Muifffa speed in the transfer to the cathode. This limiting current 130 is absolutely proportional to the concentration of oxygen. Oxygen sensors of this type typically operate at a • high temperature and, therefore, include a heating element to which a voltage is supplied for the purpose of heating the sensor to its operating temperature. An advantageous sensor control circuit 140 for achieving the desired operating temperature is illustrated in Figure 5. The sensor control circuit 140 includes a sensor initialization portion 142, the 10 which includes inverted actuators U2F, U2A and a 555 timer • U4 with associated resistive and capacitive components. A positive pulse applied to the input line 144 drives the 555 U4 timer and the timer provides a high production on the line 146 for a predetermined period of time, such as 60. 15 seconds The high output of the chronometer results in a low output of the actuator U2A which, through line 148, unbalances a bridge circuit 150 during a minute of low production so that Q1 is maintained. the bridge circuit 150 is connected to supply a current / voltage to the resistor 20 of heating 152 of sensor 116 through line 154 When bridge circuit 150 is unbalanced, bridge circuit 150 energizes sensor 116, heating resistor 152 to approximately half of its rated voltage. When the 555 U4 timer ends after one minute, the voltage in the Line 146 goes down and the voltage output of the actuator U2A becomes high and is blocked by the diode D1 in order to have no further effect on the bridge circuit 150. The bridge circuit 150 then energizes the resistor of heating to its rated total voltage, the heating resistor 152 of the sensor 116 completing the bridge. During the manufacturing or installation of the system, the bridge is initially balanced to the rated sensor voltage (4.0 volts) by adjusting the variable resistance R3 to satisfy the sensor specification (to achieve a specific output level at a certain voltage, temperature and oxygen level known). The balance is then maintained across the bridge during the operation mode, then allowing the sensor heater 152 to reach the operating temperature. The bridge circuit 150 maintains a constant resistance in order to keep the sensor 116 at a constant temperature. The transistor Q1 is controlled by the output of the amplifier U3D to pass a variable current to activate the bridge 150 and thus the heater resistor 152 of the sensor 116. A sensor cell drive circuit 156 provides a bypass to the cell of measurement 120 of sensor 116 through the output of amplifier U3A. A voltage divider set by resistors R3 and R4, in combination with switching circuit 158, allows the deviation voltage to be set at 0.9 volts to measure free oxygen and at 1.6 volts to measure both free and combined oxygen, how I know described in detail later. The output of the measuring cell 120 of the sensor 116 is a current 130 that follows a logarithmic curve and that varies as the oxygen concentration Wß varies. This sensor output current 130 is converted to a voltage by the converter 158 and the voltage output by the amplifier U1 is regulated by the amplifier 160 (gain of -1) to provide an output voltage at 162 to trace the oxygen measured The above sensor control circuit can be part of a 10 oven controller 114 or can be separated from the controller, ^ but connected to it so that the controller 114 can use the perceived oxygen level information. Since it is desirable to limit the speed of temperature changes of the sensor 116, the initiation portion of the sensor 112 is important for 15 provide an improved life for the sensor by establishing a supply of a measured average voltage to the heating element 152 when the sensor 116 is used for the first time. In this regard, the positive start pulse can be supplied to line 144 when the oven ignition operation is initiated, 20 the sensor 116 is heated at the same time as the oven fan 112 is turned on for the preparation for the ignition of the burner (s) 102. Preferably, the energization of the sensor heater resistor 152 at the lowest voltage level overlaps with the fan in operation for at least 20 seconds 25 before the start of combustion.

Regardless of the duration of the overlap, when the fan is running during the firing of the furnace, and before the initiation of combustion, the relatively cold gases will flow at • length of the exhaust path where the sensor 5 is located 116 These relatively cold gases can interfere with the heating of the sensor 116 if the sensor is placed directly in the primary flow of the exhaust path. Similarly, during operation, the effect of combustion gases that are substantially colder than the temperature 10 sensor operation, which pass through a sensor placed in the • primary flow of the exhaust path, it may also be more difficult to properly maintain the operating temperature of the sensor. Accordingly, a preferred mounting arrangement involves placing the sensor 116 in a sensor chamber 170 positioned on 15 the length of the stack 110, or another portion of the exhaust path 108, as shown in Figure 3. An opening 171 is provided between the exhaust stack 110 and the sensor chamber 170 to allow the exhaust gases arrive at the sensor 116. In a contemplated embodiment illustrated in greater detail in 20 Figures 6 and 7, the sensor chamber 170 is formed by a tube 172, such as a metal pipe. The tube 170 is threadably 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 by suitable fasteners 178. A member of Sensor placement 180 is received within tube 172 and can be moved along the axial length of tube 172, and includes a sensor receiving connector 182 at one of its ends. The sensor 116 is fixed by jump in the connector 182 and the member of • positioning 180 is placed at the desired location along the axial length of tube 172. Positioning member 180 is then fixed at the desired location through a set screw 184, which passes through the opening threaded 186 on the side of the tube 172. This arrangement advantageously allows a separation between the sensor and the exhaust path to be controlled. The cables 10 188 which extend from the connector 182 through the member • 180 towards a sealed connector 190 located near the outer end 192 of the tube 172. An end cap 194 with an opening therein is threaded into the tube end 192 and a portion of the sealed connector 190 outwardly beyond the cap 194 And it is 15 held in place through a notch 196, which is threaded around the protruding portion of the plug 190. The exposed end 198 of the plug 190 includes connector receiving openings to make a cable connection suitable for the # sensor control circuit 140. 20 Unlike traditional potentiometric oxygen sensors that require one side of the sensor to be exposed to the gas being monitored and the opposite side of the sensor exposed to ambient air as a reference, the sensor of amperometric type 116, which is preferred, only 25 must be exposed to the gases that are being measured. By Accordingly, seals, joint compound or other suitable sealing techniques are used to construct the sensor chamber 170 in order to seal the chamber 170 and the sensor 116 placed therein of the external gases of the chamber. the escape path. As previously noted, the use of the sensor chamber 170 positioned adjacent to the exhaust stack 110 allows the sensor 116 to be positioned outside the primary exhaust gas flow designated 198 in Figure 6. The presence of the opening 171 allows an auxiliary or secondary flow 200 of exhaust gases towards 10 the camera 170, and in this way keeps the sensor in communication • with the exhaust gases to perceive the oxygen content of the same. The secondary flow 200, which reaches the chamber 170, however, is substantially lower than the primary flow 198, and thus has a much smaller effect on the temperature of the 15 sensor, allowing the sensor 116 to be heated more quickly during the firing of the furnace, and facilitating proper maintenance of the temperature of the sensor during the operation of the furnace. ^ The oxygen perception arrangement provided here 20 advantageously provides the ability to use the perceived oxygen content of the exhaust gases to control combustion in the furnace. In particular, based on the oxygen content sensed by the sensor 116, the controller can control the speed of the exhaust fan 112 or the registration position. 25 of draft 113 to vary the air / fuel ratio burned in the combustion area of the furnace. Similarly, the controller can control the gas valve 106 to vary the air / fuel ratio, or a combined control of the fan 112, record • Rite 113 and valve 106, can be provided. Instead of controlling the air / fuel ratio, the controller simply checks the oxygen content as indicated by the sensor 116 and establishes an indication or alarm (such as an indicator light, horn or horn) and / or interrupts the oven if the oxygen content falls outside of an acceptable, established window. Although useful for sensing the oxygen content of burned gases, the amperometric type sensor preferred herein is also useful for determining the moisture content of gases as well. This aspect of the sensor is particularly useful in support ovens or other types of ovens, where the generation 15 controlled steam is desirable. In this regard, reference is made to Figure 8, where a support oven 210 is shown, including combustion area 212, heat exchanger 214 and steam generator 216. A baking chamber 218 includes a rotating support 220 placed in the same, with a portion of Support 220 cut to expose a sensor 222 positioned along a side wall of the chamber 220 and a powered or non-driven ventilation 224 positioned on the side wall. The sensor is preferably the amperometric sensor described above, and can be used to sense the moisture content of the air 25 inside the baking chamber 218. in particular, referring to the graph shown in Figure 9, the output response of the sensor for dry air 230 and humid air 232 at a given oxygen content are shown, respectively. Notably, depending on the sensor voltage applied to the sensor cell, the current varies between levels A and B when the air is humid. Level A represents the oxygen-free content of the air, while level B represents the total oxygen content. (free oxygen and oxygen present as moisture in the air). The measurement of level B results from the electrochemical deposition of water vapor in the presence of the highest voltage. When making a measurement of both voltages applied, the humidity or moisture content of the air can be defined as a function of the difference between the two measurements, since the water content of the air is directly proportional to the differential oxygen content. The oven can use the perceived humidity level inside the baking chamber 218 to control the water supply (via a controllable valve) to the steam generator 216. Likewise, the oven controller can use the perceived humidity level within of the oven chamber 218 to control the operation of the oven 224 in order to remove the high humidity air from the oven chamber 218. Although the invention has been described and illustrated in detail to be clearly understood, it is intended for way of illustration and example only and does not intend to be taken as a form of limitation. For example, although the preferred mounting position of the sensor chamber is along the exhaust stack as illustrated, it is recognized that the sensor chamber may be located along other portions of the exhaust path.

• Accordingly, the spirit and scope of the invention will be limited only by the terms of the appended claims.

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Claims (9)

1. - An oxygen perception arrangement for a gas fired oven, comprising: an oxygen sensor positioned to sense gases along an exhaust path of the furnace, the oxygen sensor including a heater and a measured cell; a sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected to energize the heater, wherein the sensor initialization portion produces an ignition signal that unbalances the bridge circuit during an ignition period, causing the bridge circuit to energize the heater to an ignition level during the ignition period, 15 where, after the ignition period, the sensor initiation portion no longer produces the start signal and the bridge circuit is balanced in order to energize the heater at an operation level that is higher than the start level.

2. The arrangement according to claim 1, wherein the bridge portion of the sensor control circuit varies the operating current supplied to the heater in order to maintain a constant heater temperature.

3. The arrangement according to claim 1, further comprising: an exhaust fan located along the path . ^ -á ^ Oh escape; at least one burner lit with gas; a controller connected to control the exhaust fan and the gas-fired burner; 5 an operable controller, after the firing of the furnace, to rotate the exhaust fan for a predetermined period of time before igniting the burner lit with gas.

4. The arrangement according to claim 3, wherein, after the firing of the furnace, the predetermined time period and the start time period run at least partially and concurrently.

5. The arrangement according to claim 3, wherein the exhaust path includes an exhaust stack and a sensor chamber positioned over the length of the stack, in order to be separated from an exhaust gas flow. primary, the sensor chamber opens to gases in the exhaust stack, the oxygen sensor placed inside the sensor chamber.

6. The arrangement according to claim 5, wherein the sensor chamber and the oxygen sensor there are sealed from the external gases of the exhaust stack. The arrangement according to claim 6, wherein the oxygen sensor comprises an amperometric sensor. 8. An oxygen perception arrangement comprising: an oxygen sensor; a sensor control circuit associated with the oxygen sensor, the sensor control circuit including a sensor initialization portion connected to a bridge portion, the bridge portion connected to energize the heater, wherein the initialization portion sensor produces a start signal that unbalances the bridge circuit during an ignition period, causing the bridge circuit to energize the heater to an ignition voltage for a period of ignition timing, where, after the period of time of On, the sensor initialization portion no longer produces the start signal and the bridge circuit is balanced, so that the heater is at an operating voltage that is greater than the ignition voltage. 9. A gas fired oven comprising: at least one burner ignited with gas having an associated exhaust gas path; an exhaust fan located along the exhaust path; a controller connected to control the exhaust fan 20 and the gas-fired burner, the operable controller, after the firing of the furnace, rotates the exhaust fan for a predetermined period of time before lighting the burner with gas; an oxygen sensor placed to perceive gases along the escape path, the sensor including a heater and a gj ^ j measurement cell; a sensor control circuit including a sensor initialization portion connected to a bridge portion, the • bridge portion connected to energize the heater, where, after the firing of the furnace, the initialization portion of the sensor produces a start signal that unbalances the bridge circuit for a period of ignition time, causing the circuit to bridge energizes the heater at an ignition voltage during the ignition timing period, wherein, after the ignition period 10, the initialization portion of the ignition • sensor no longer produces the start signal and the bridge circuit is balanced in order to energize the heater of an operating voltage that is greater than the ignition voltage. 10. The gas-fired oven according to claim 9, wherein the exhaust path includes an exhaust stack and a sensor chamber placed along the length of the stack, in order to be separated from a primary exhaust gas flow, the chamber opens to the gases in the exhaust stack, the oxygen sensor W placed inside the sensor chamber, where the sensor chamber, and the oxygen sensor in it, they are sealed from the external gases of the exhaust stack. 11. The gas-fired oven according to claim 10, wherein the oxygen sensor comprises an amperometric sensor. 12. The gas-fired oven according to claim 9, wherein the sensor control circuit comprises a portion of the controller. 13.- A method to control a gas fired oven, the The method comprises the steps of: providing an oven ignition mode during which the following steps are performed: applying an ignition current to a heating element of an oxygen sensor; energizing an exhaust fan to remove gases from a combustion area of the furnace; • maintain a non-burned condition within the combustion area; providing an oven operation mode, after the oven ignition mode, and during which the following 15 steps are performed: applying an operating current to the heating element of the oxygen sensor; establish a burning condition within the area of • combustion. 14. The method according to claim 13, comprising the additional step of: placing the oxygen sensor in a chamber adjacent to an exhaust path of the furnace, the chamber in gaseous communication with the exhaust path; and 25 sealing the chamber to prevent gases from the exterior of the exhaust path from reaching the oxygen sensor. 15. The method according to claim 13, wherein the oxygen sensor comprises an amperometric sensor, and the # method includes: 5 at least the mode of operation of the furnace, producing a sensor output having a current that varies according to the oxygen content of the exhaust gases of the furnace. 16. The method according to claim 15, comprising the additional step of: 10 at least in one oven operation mode, controlling one • exhaust fan speed based at least partly on the sensor output produced. 1

7. The method according to claim 15, comprising the additional step of: at least in one oven operation mode, controlling a draft registration position based on at least part of the output produced from the sensor. 1

8. The method according to claim 15, which • comprises the additional step of: 20 at least in one oven operation mode, setting an indication if the sensor output produced indicates an unacceptable level of oxygen. 1

9. An oxygen perception arrangement for a gas fired oven, comprising: a combustion area; and ^, ^ J ^ e ^^ m ^ ^^ _ an escape path to receive gases from the combustion area; a sensor camera placed along the path • exhaust, in order to be separated from a primary flow of 5 exhaust gases, the chamber opens to gases in the exhaust path, and an oxygen sensor placed inside the sensor chamber, where both the sensor chamber like the oxygen sensor there are sealed from the external gases of the exhaust path. 20. The arrangement according to claim 19, wherein • the chamber comprises a tube having a first end attached to an opening in the side wall of the exhaust path, and an end cap connected to a second end of the tube. 21 - The arrangement according to claim 19, wherein the oxygen sensor comprises an amperometric sensor, which produces a sensor output signal having a current that varies according to an oxygen content of exhaust gases from the furnace . • The arrangement according to 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 to energize the sensor. heater, wherein the initialization portion of the sensor produces a start signal, which unbalances the bridge circuit for a period of ignition time, causing the bridge circuit to energize the heater at an ignition voltage during the period of ignition time, where, after the ignition time period, the initialization portion of the sensor no longer produces the start signal and the bridge circuit is balanced in order to energize the heater at an operating voltage that is greater than the ignition voltage. 23. A method for mounting an oxygen sensor for sensing an oxygen content of gases traveling along the exhaust path of a gas fired oven, the method comprising: mounting a sensor housing adjacent to a gas duct escape; providing gaseous communication between an interior of the exhaust duct and an interior of the sensor housing; place an oxygen sensor inside the sensor housing; and sealing an interior of the sensor housing of the external gases to the exhaust duct. SUMMARY An oxygen perception arrangement for a furnace on With gas includes an oxygen sensor positioned to sense gases along an exhaust path of the furnace, the oxygen sensor including a heater and a measuring cell. A control sensor circuit includes a sensor initialization portion connected to a bridge portion. The bridge portion is operatively connected to energize the heater. Serving 10 sensor initialization produces an ignition signal, which • unbalances the bridge circuit for a period of ignition time, causing the bridge circuit to supply a heating current / voltage to the heater during the ignition time period. After the time period of On ignition, the sensor initialization portion no longer produces the start signal and the bridge circuit is balanced, in order to supply an operating current / voltage to the heater. A voltage of the heating current / voltage is less than a voltage of the current / operating voltage. The arrangement allows the The oxygen sensor is heated to its operating temperature at a corresponding heating voltage and rate which will not damage the sensor, and is particularly useful when the oxygen sensor is an amperometric type sensor. The sensor can be located in a sensor chamber that is placed along the entire length of the In order to escape from a primary flow of exhaust gases, the opening of the chamber is to receive gases in the exhaust duct. Both the sensor chamber and the oxygen sensor in it are sealed from the external gases of the exhaust duct. •