Gas heater

Abstract: In a gas heater, a ceramic heater(40) is used to ignite gas supplied to a gas burner(14). The ceramic heater(40) is disposed in flame while the gas is burnt such that a change in the resistance value of the ceramic heater(40) is sensed by a resistance value sensor(54) to detect a flame extinction. Since the resistance value is varied between ceramic heaters(40), the deviation of the resistance value is compensated for depending on a reference value at a reference temperature of the ceramic heater so as to detect the flame extinction.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a gas heater, and in particular, to a gas heater of which ignition of gas is accomplished by a ceramic heater. Description of the Prior Art A gas heater has a high heating efficiency and a low requirement of fuel and hence has been applied to various kinds of heating applications. For example, in a heating operation in a field of the stock raising and agriculture such as the hog raising, since hogsties are required to be heated for a long period of time, the gas heater has been effectively used. In a gas heater of this type, a heater is ordinarily disposed to ignite gas supplied to a burner of the gas heater, thereby achieving ignition of the gas. However, in a case where flame of the gas is extinguished for some reasons after the ignition, it is needed to detect the condition of the flame extinction as soon as possible to interrupt the gas supply for safety. Conventionally, a flame sensor has been adopted as means for detecting the flame extinction. The flame sensor is disposed in the flame so as to sense a change in the resistance value thereof at the flame extinction, thereby detecting the condition. In the gas heater of the prior art, the igniting means and the extinction sensing means are separately disposed, which leads to a problem of an increased number of members disposed in the flame. Moreover, when detecting the flame extinction according to the change in the resistance value, since the resistance value varies between the sensors, there arises a problem that it is impossible to set a fixed temperature for the detection of the flame extinction. A gas heater of the kind defined by the precharacterizing clause of claim 1 is known from the JP-A-01244215. The ceramic heater of this known gas heater also is used for detecting a flame extinction. The flame extinction is detected by means of the resistance value of the ceramic heater's resistance. Ceramic heaters, however, are produced with an error of about 10% concerning the resistance value of the resistor thereof. That means, that, depending on the resistance value inherent to the resistor of the ceramic heater the flame extinction can not be correctly detected. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a gas heater of the kind defined by the precharacterizing clause of claim 1 allowing for a correctly detected flame extinction independently of the deviation of the resistance value of the ceramic heater. This object is attained by the features of the characterizing clause of claim 1. Advantageous developments of the invention are given in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic block diagram showing the configuration of an embodiment of a gas heater for use in the stock raising and agriculture in accordance with the present invention; Fig. 2 is a side view showing the mechanical construction of the gas heater of Fig. 1 Fig. 3 is a front view showing a ceramic heater employed in the gas heater of Fig. 1 Fig. 4 is a perspective view showing a process of manufacturing the ceramic heater of Fig. 3, Fig. 5 is a perspective view showing a process of manufacturing the ceramic heater of Fig. 3, Fig. 6 is a schematic diagram showing the constitution of the ceramic heater of Fig. 3, and Fig. 7 is a perspective view showing attaching and detaching of an air cap of the gas heater of Fig. 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, a description will be given in detail of a gas heater in accordance with the present invention. Fig. 2 shows a portion of the structure of an embodiment in which the present invention is applied to a gas heater for use in a field of the stock raising and agriculture. As shown in this diagram, the gas heater includes a gas burner 14 at a position inside a reflecting cap or hood 12 in the form of a lamp shade or a dome. The reflecting hood 12 has a reflecting surface of a curved plane represented by a parabola. The reflecting hood 12 is hanged from, for example, the ceiling of a hogsty by use of a hook 18; whereas the gas burner 14 is suspended or attached by a suspending or attaching member 16 from or to a central portion of the reflecting hood 12. The gas burner 14 includes a burner head 14a having substantially a cylindrical shape with a large number of flame holes 14b disposed in the periphery of the burner head 14a. A ceramic heater 40 is disposed in the proximity of the flame holes 14b. The ceramic heater 40 has a contour of Fig. 3 and is produced through a manufacturing process as shown in Fig. 4. Namely, a resistor 44 is printed on a ceramic base 42 formed with a silicon nitride Si 3 N 4 so as to be sintered together with another ceramic plate 46 as shown in Fig. 5. After metalizing the sintered items, power supply wires 50 are connected via metal members 48 to the resistor 44. As well known, the temperature of the ceramic heater 40 is increased when powered. This heater 40 is hence used as an igniting device thanks to its strength against heat and shock. In this gas heater, the ceramic heater 40 functions as an igniting device powered; moreover, the heater 40 is used as a sensor for sensing extinction of the gas flame. As will be described later, when a predetermined period of time is elapsed after the ceramic heater 40 is powered, the body thereof is heated to a high temperature. Thereafter, fuel gas is supplied to the gas burner 14 to be ignited by the ceramic heater 40. Since the resistance value of the ceramic heater 40 varies with a change in the temperature thereof, the ceramic heater 40 is also adopted as a sensor for detecting a flame extinction. The ceramic heater 40 disposed in the flame from the flame holes and is kept remained at a high temperature while the gas heater is in a heating operation. However, at an occurrence of an extinction of flame, the temperature and accordingly the resistance value thereof are reduced, thereby sensing the flame extinction. Fig. 1 shows in a block diagram a circuit configuration for igniting gas and for sensing a flame extinction by the ceramic heater 40. As can be seen from this diagram, the ceramic heater 40 is connected to a resistance value detecting circuit 54, which is in turn connected to an extinction detecting circuit 52. The resistance value detecting circuit 54 is disposed to sense the resistance value of the ceramic heater 40, the resistance value altering depending on the temperature thereof as described above. The circuit 54 is also connected to an additional variable resistor circuit 56. Since the ceramic heater 40 develops a resistance value different from a reference resistance value at a reference temperature, this circuit 56 is adopted to correct the deviation of the resistance value. Namely, for the resistance correction, the correcting resistance value of this circuit 56 can take various values. The resistance value established by the additional variable resistor circuit 56 is added to that of the ceramic heater 40 such that the resultant resistance value is sensed by the resistance detecting circuit 54. Based on the obtained resistance value, a flame extinction is detected by the extinction detecting circuit 52. In the ceramic heater 40, the reference resistance is 90 ohms at a reference temperature 25°C. However, for the reference resistance value of the ceramic heater 40, an error of about 10% is allowed in general. Consequently, ceramic heaters having the resistance value, for example, ranging from 81 to 99 ohms at 25 °C have been put to the market. In the heater of this embodiment, when the temperature of the ceramic heater 40 is lowered to 110°C after ignition of the gas, it is assumed by the extinction detecting circuit 52 that a flame extinction is detected. In a case where the ceramic heater 40 has the reference resistance value above, the resistance value at 110°C is 105.5 ohms. Consequently, the flame extinction is assumed when the resistance value is decreased to 105.5 ohms. However, when the ceramic heater 40 has a reference resistance value different from that described above, the resistance value at 110 °C is also different from the value above. For example, when the ceramic heater 40 has a reference resistance value of 81 ohms at 25 °C, the resistance value at 110 °C is 94.9 ohms; moreover, when the resistance value at 25 °C is 99 ohms, the resistance value at 110°C is 116.0 ohms. To correct the deviation of the resistance value, various resistance values are set by the additional variable resistor circuit 56. The additional variable resistor circuit 56 is supplied as an input thereto with a resistance value of the ceramic heater 40 at 25°C from input means not shown. Based on the value, the resistance value is determined by the resistor circuit 56 for the correction. For example, when the resistance value of the ceramic heater 40 employed in the gas heater is 81 ohms at 25°C, this value is inputted from the input means to the resistor circuit 56, which then accordingly sets a difference between the resistance values i.e. 90-81=9 ohms, thereby sending this difference (9 ohms at 25 °C) to the resistance value detecting circuit 54. In the circuit 54, the received value is added to the resistance value of the ceramic heater 40 at 25°C to detect the resultant resistance value. The extinction detecting circuit 52 is disposed to detect a flame extinction depending on the corrected resistance value of the ceramic heater 40 sent from the resistance value detecting circuit 54. Namely, in this embodiment, when a condition that the corrected resistance value of the ceramic heater 40 is decreased to 105.5 ohms is detected, it is assumed that the temperature of the ceramic heater 40 is lowered to 110°C, thereby determined that the flame is extinguished. Moreover, there may be installed, in place of the resistance value detecting circuit 54 and the extinction detecting circuit 52, a circuit which directly detects the flame extinction based on signals supplied from the ceramic heater 40 and the additional variable resistor circuit 56. The extinction detecting circuit 52 is connected to a control circuit 60, which is connected to a timer circuit 62, an electromagnetic valve 64, a power source 66, and a switch 68. The control circuit 60 controls various sections of the system in response to such signals to be used for decision of the flame extinction as an input from the switch 68 and an output from the extinction detecting circuit 52. The control circuit 60 is advantageously configured with a microprocessor. The timer circuit 62 includes a timer for measuring a predetermined period of time. In this ceramic heater 40, particularly, the circuit 62 measures a lapse of time for a control operation to supply power from the power supply to the ceramic heater 40 and to open/close the electromagnetic valve 64. The electromagnetic value 64 is disposed on a nozzle pipe 20 shown in Fig. 1 to control the volume of gas supplied to the gas burner 14, which will be described later. The power supply 66 is connected via the power line 50 to the ceramic heater 40 to supply power to the ceramic heater 40. The switch 68 is disposed for the user to input various instructions to the gas heater, for example, an ignition instruction. Returning to Fig. 2, a nozzle 14c is disposed to face upward at an inner lower position of the gas burner 14. The nozzle 14c is coupled with the nozzle pipe 20. On a bottom surface of the gas burner 14, an air cap 22 (Fig. 7) having a predetermined number of air holes 22a is engaged. When propane gas delivered via the nozzle pipe 20 is ejected from the nozzle 14c into the gas burner 14, the ejected gas is mixed by the gas ejecting force therein with air fed through the air holes 22a in the lower portion of the burner 14. The mixed gas is then ejected from the flame holes 14b disposed in the periphery of the burner head 14a to be ignited and to be burned by the ceramic heater 40. In the upper portion of the gas burner 14, there is disposed a radiant heat plate 24 having a hollow sphere enclosing the burner head 14a. The plate 24 absorbs the heat energy from the gas flame to irradiate far infrared rays, which are easily absorbed by young pigs or hoglings. The nozzle pipe 20 is bent upward at a position outside the reflecting hood 12 such that an end portion thereof is coupled with a pipe 32 via the electromagnetic valve 64 and a valve 26 for regulating the flow rate of gas. The electromagnetic valve 64 is opened or closed in response to signals from the control circuit 60 to supply gas to the nozzle pipe 20 or to interrupt the gas supply thereto, respectively. The valve 26 includes a pipe section 26a and a dial 26b to open/close the valve 26 installed in the pipe section 26a, which is detachably attached in an end portion of the nozzle pipe 20. When the dial 26b is turned by the operator of the valve 26, the volume of gas fed to the nozzle pipe 20 is changed so that the combustion amount thereof is set to a predetermined value in a range, for example, 200 to 1800 Kcal/hour. As a result, the operator can set the gas heater to either one of the heating positions for the high, middle, and low heating calorific power levels. In operation of the gas heater, when the operator inputs an ignition instruction from the switch 68, the instruction is sent to the control circuit 60, which then outputs a control signal to the power supply 66. The power supply 66 delivers power via the power line 50 to the ceramic heater 40. The temperature of the ceramic heater 40 is thereby increased. When the operation to power the ceramic heater 40 is started, a control signal is delivered from the control circuit 60 to the timer circuit 62. The timer 62 initiates measuring a predetermined period of time. When the predetermined period of time, for example, a period of ten seconds is elapsed, the ceramic heater 40 is heated to a gas ignition temperature, for example, 1000°C. As a result of the measurement, when the timer circuit 62 notifies that the condition of the elapse of ten seconds, the control circuit 60 opens the electromagnetic valve 64 depending on the output from the timer circuit 62 to feed gas to the burner 14. Accordingly, gas ejected from the flame holes 14b is ignited so as to start the combustion thereof. After the electromagnetic valve 64 is opened to start burning the supplied gas, a control signal is outputted from the control circuit 60 to the timer circuit 62, which starts measuring a predetermined time in response thereto. When the predetermined period of time e.g. a period of ten seconds is elapsed i. e. when the timer 62 notifies the condition, a control signal is responsively fed from the control circuit 60 to the power supply 66, thereby stopping power supplied to the ceramic heater 40. The power supplied to the ceramic heater 40 is thus interrupted when the predetermined period of time is elapsed after the ignition, which prevents the ceramic heater 40 from being deteriorated. After the ignition, while an ordinary fuel combustion is taking place, the flame directly heats the ceramic heater 40. Consequently, the ceramic heater 40 is kept retained at a high temperature. However, when the flame is extinguished for some reasons, for example. by an air blow or wind, the ceramic heater 40 is not heated and hence the temperature thereof is gradually lowered. As already described above, the resistance value detecting circuit 54 detects a resistance value of the ceramic heater 40, the resistance value being corrected by a resistance value received from the additional variable resistor circuit 56. The detected resistance value is fed to the extinction detecting circuit 52. In the extinction detecting circuit 52, when it is detected that the corrected resistance value of the ceramic heater 40 is reduced to, for example, 105.5 ohms, it is assumed that the temperature of the ceramic heater 40 is lowered to 110°C, thereby assuming the flame extinction. When the flame extinction is detected by the extinction detecting circuit 52, the control circuit 60 output a control signal to the electromagnetic valve 64 and the power supply 66 depending on a signal from the extinction detecting circuit 52. Resultantly, the electromagnetic valve 64 is closed to immediately stop the gas supplied to the gas burner 14. Thereafter, the power supply 66 starts again supplying power to the ceramic heater 40, thereby heating the ceramic heater 40. As above, when a period of time, for example, a period of ten seconds is elapsed after the power is started to be supplied to the ceramic heater 40, the temperature of the ceramic herater 40 reaches the ignition temperature, for example, 1000°C. Consequently, the electromagnetic valve 64 is opened to supply again gas to the gas burner 14. According to the gas heater of the embodiment above, the ceramic heater 40 is employed as igniting means and as flame extinction detecting means. Consequently, in this gas heater, unlike in the conventional apparatus including igniting means and flame extinction detecting means, the number of members disposed in the flame can be minimized and hence the constitution of the gas heater can be simplified. Moreover, a resistance value is additionally used in consideration of the deviation of the resistance value of the ceramic heater 40 from the reference resistance value such that the additional resistance value is added to the resistance value inherent to the ceramic heater 40 to dectect the flame extinction depending on the measurement of the resultant resistance value. In consequence, the temperature is detected independently of the resistance value of the ceramic heater 40 used in the gas heater so as to correctly detect the flame extinction. Furthermore, at the ignition of gas, the electromagnetic valve 64 is opened when a predetermined period of time is elapsed after the ceramic heater 40 is powered; whereas, at a detection of the flame extinction, the electromagnetic valve is immediately closed and power is supplied to the ceramic heater 40. Resultantly, the ignition in the initial state and the ignition after the flame extinction can be appropriately conducted with safety. In the embodiment above, there is disposed the additional variable resistor circuit 56 for an addition of a resistance value in consideration of the deviation of the resistance value of the ceramic heater 40 such that the resistance value of the additional variable resistor circuit 56 is altered to compensate for the deviation of the resistance value of the ceramic heater 40. However, A resistor having a correction resistance value associated with the resistance value at the reference temperature of the ceramic heater 40 used in the gas heater may be installed in the gas heater together with the ceramic heater 40 such that when the ceramic heater 40 employed is replaced, the correction resistance value is also replaced together therewith. In addition, it may also be possible that a resistance value at the reference temperture of the ceramic heater 40 used is inputted in advance to set a threshold value of a resistor for detecting a flame extinction such that the resistance value detecting circuit 54 detects the resistance value of the ceramic heater 40 and then the extinction detecting circuit 52 compares the detected value with the threshold value, thereby detecting the flame extinction. In accordance with the present invention, the ceramic heater is adopted as igniting means for igniting gas and a resistance value of the ceramic heater disposed in the flame is sensed to detect the flame extinction, which simplifies the constitution of the gas heater. Moreover, since the flame extinction is detected in consideration of the resistance value of the ceramic heater at the reference temperature, the flame extinction can be correctly detected independently of the deviation of the resistance value of the ceramic heater.

Claims: A gas heater comprising a ceramic heater (40) including a support body (42) made of a ceramic material and a heater formed thereon, a temperature of said ceramic heater (40) being increased when said resistor (44) is powered, thereby igniting gas supplied, resistance value detecting means (54) for detecting a resistance value of said ceramic heater (40) disposed in flame formed by burning the gas, extinction detecting means (52) for detecting a flame extinction according to the resistance value of said ceramic heater (40), the resistance value being outputted from said resistance value detecting means (54), and control means (60) for controlling said respective means (52,54), said control means (60) controlling said extinction detecting means (52) to detect the flame extinction according to the resistance value of said ceramic heater (40) detected by said resistance value detecting means (54), characterized in that the resistance value of said ceramic heater (40) detected by said resistance value detecting means (54) is corrected for the deviation of this resistance value from a reference resistance value at a reference temperature by means of a variable resistor circuit (56). The gas heater in accordance with claim 1, characterized in that said gas heater further comprises: power supply means (66) for supplying power to said ceramic heater (40), gas supply control means (64) for controlling supply of the gas; and timer means (62), said control means (60) controlling, at an ignition of the gas, said power supply means (66) to power said ceramic heater (40), controlling, when a lapse of a predetermined period of time is detected by said timer means (62) after the ignition, said gas supply control means (64) to supply the gas, and controlling, when a lapse of another predetermined period of time is detected by said timer means (62) thereafter, said power supply means (66) to stop supplying power to said ceramic heater (40). The gas heater in accordance with claim 2, characterized in that said control means (60) controls said gas supply control means (64) to stop supplying the gas when the flame extinction is detected by said extinction detecting means (52). The gas heater in accordance with claim 3, characterized in that said control means (60) achieves an operation to be conducted at the ignition. A gas heater in accordance with anyone of claims 1 to 4, characterized in that said gas heater further comprises a resistor connected to said ceramic heater (40), said resistor having a value computed depending on the resistance value at the reference value of said ceramic heater (40), wherein said extinction detecting means detects the flame extinction according to the resistance value of said ceramic heater and the resistance value of said resistor. The gas heater in accordance with one of the claims 1 to 6, characterized in that said resistor (44) connected to said ceramic heater (40) is replaceable together with said ceramic heater (40).

Inventors: KANESAKA ICHIRO, KANESAKA, ICHIRO
Applicants: KANESAKA ICHIRO, KANESAKA, ICHIRO
Application year: 1991
Main classification: F23Q7
IPC codes: F23Q7, F24C1, F23N5