JP4540992B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device that detects incomplete combustion of a combustor, gas leakage, and the like using a semiconductor gas sensor.

  Gas detection is normal if the contact combustion type gas sensor or semiconductor type gas sensor used in the gas detection device that detects incomplete combustion of the combustor, gas leakage, etc., and the heater that heats these gas sensors are disconnected. It is very important to recognize whether or not they are disconnected, and even if the catalytic combustion gas sensor or semiconductor gas sensor element itself is destroyed, the gas It is also very important to recognize failures due to the destruction of these sensor elements, since detection cannot be performed normally.

  As for the disconnection state of the heater, there has already been proposed what detects the state of low internal resistance of the catalytic combustion gas sensor associated therewith by using an operational amplifier (for example, Patent Document 1). Even when the sensor element of the gas sensor is broken (disconnected due to disconnection), if the catalyst that covers the sensor element of the catalytic combustion type gas sensor falls off due to a crack or the like and the disconnection state of the catalytic combustion type gas sensor occurs, the heat dissipation function of the heater through the catalyst Is damaged, the heater is heated, and the equilibrium state of the bridge circuit including the heater and the catalytic combustion type gas sensor is lost. Therefore, the phenomenon can be easily determined using this phenomenon.

  However, in the case of a sensor element of a semiconductor type gas sensor, since there is no bridge circuit configured with a heater like a contact combustion type gas sensor, if no CO gas is present when CO gas having a low heating temperature is detected by the heater, the semiconductor The internal resistance value of the sensor element of the gas type gas sensor becomes so high that it is not much different from the disconnection state. After all, even if the output of the semiconductor type gas sensor is low, it is due to the presence of CO gas. Cannot be determined.

Therefore, the detection of the disconnection state of the sensor element in the conventional semiconductor gas sensor is performed by detecting the output (air base) of the semiconductor gas sensor when there is no hydrocarbon gas (for example, methane gas) in which the heating temperature by the heater is high and the internal resistance value is low. However, it has been inevitably performed by determining that the output is higher than the output of the semiconductor gas sensor that appears in the disconnection state (for example, Patent Document 2).
JP-A-5-312749 JP 2002-230661 A

  As described above, the disconnection state of the sensor element of the conventional semiconductor gas sensor is a method that cannot be detected unless the situation of the presence of the gas to be inspected is prepared in advance. There were many constraints in terms of conditions to perform detection, leaving room for consideration.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas detection capable of reliably detecting a disconnection state of a sensor element of a semiconductor gas sensor regardless of the presence / absence of a gas to be inspected. To provide an apparatus.

The gas detection device of the present invention for achieving the object, as shown in the basic configuration diagram in FIG. 1, the sensor element is heated by intermittently turning on / off the driving or high / low driven heater R _H R _In the gas detection device that detects the concentration of a single type or a plurality of types of gases using the semiconductor gas sensor 21 having _S , when the driving of the heater _RH is switched from one of on and off to the other, or The output change measuring means 3A for measuring the amount of change in output of the semiconductor gas sensor 21 and the output change amount measuring means 3A at the time of shifting from one of high and low driving of the heater _RH to the other were measured. the semiconductor gas sensor the amount of change in the output of the semiconductor gas sensor 21 at the time of transition of the driving of the heater R _H is generated during the transition in the normal conducting state of the sensor element R _S The determination means 3B for determining whether or not the output change amount of the semiconductor gas sensor 21 measured by the output change amount measurement means 3A exceeds the minimum amount. A basic technique is to include a disconnection recognition unit 3C that recognizes that the sensor element _RS is in a disconnected state when the determination unit 3B determines.

In the gas detection device according to the first aspect of the present invention, in the basic technique , the first resistor _RL and the switching element Q1 connected in series to the first resistor _RL are connected to the first resistor _RL . A voltage dividing resistor string in which a second resistor R _F having a resistance value higher than R _L is connected in parallel is connected in series to the sensor element R _S , and the switching element Q 1 is switched when the heater R _H is driven. The resistance value of the voltage dividing resistor string is turned off to be the resistance value of the second resistor R _F , and the switching element Q1 is turned on at the time of detecting the concentration of the single kind or plural kinds of gases to turn on the voltage dividing resistor string Is further provided with switching means 3D for setting the resistance value of the first resistance R _L and the second resistance R _F to be a combined resistance value, and the output change amount measuring means 3A sets the resistance value to the switching means. and the resistance value of the second resistor R _F by 3D And the amount of change potential difference appearing across the voltage-dividing resistor string, and shall be measured as the amount of change in the output of the semiconductor gas sensor 21 at the time of transition of the driving of the heater R _H.

Further, the gas detection device of the present invention described in claim 2 is the gas detection device of the present invention described in claim 1 according to a difference between an ambient temperature of the semiconductor gas sensor 21 and a predetermined reference temperature. Temperature compensation means A for correcting the output of the semiconductor gas sensor 21 measured by the output change amount measurement means 3A, and the determination means 3B after the correction by the temperature compensation means A is performed. It is determined whether or not the output change amount of the semiconductor gas sensor 21 measured by the output change amount measuring means 3A exceeds the minimum amount.

The gas detection device of the present invention described in claim 3 is the gas detection device of the present invention described in claim 2 , when the disconnection recognition means 3C recognizes that the sensor element _RS is in a disconnection state. In addition, it is further provided with failure alarm means 5 for informing the outside that the semiconductor gas sensor 21 is in failure.

According to the basic technique of the present invention, the output change amount measurement is performed when the heater _RH drive is switched from one of on and off to the other, or when the heater _RH drive is switched from one of high and low to the other. The amount of change in the output of the semiconductor gas sensor 21 measured by the means 3A includes the influence of the presence / absence of the inspected gas before and after the change in the same way. , The effect of the presence / absence of the gas to be inspected is offset.

Therefore, whether the sensor element R _S is in a disconnected state based on the determination result by the determination unit 3B in the situation where the inspection target gas exists or, conversely, in the situation where the inspection target gas does not exist. It can be accurately recognized by means 3C.

In order to adjust the output of the semiconductor gas sensor 21 to a range that is preferable in terms of operation of the means for determining the concentration of the gas when detecting the concentration of a single type or a plurality of types of gas based on the output of the semiconductor type gas sensor 21, the semiconductor The direct output of the gas sensor 21 is often divided, but conversely, the output change amount measuring means 3A measures in order to detect the disconnection state of the sensor element _RS in which the internal resistance is in an infinite state. Since the absolute value of the output change amount of the semiconductor gas sensor 21 when the heater _RH is shifted to the drive is reduced, the accuracy of the disconnection state detection may be adversely affected as it is.

However, as in the gas detection device of the present invention described in claim 1 , when detecting the disconnection state of the sensor element R _S , the switching element Q1 is turned on by the switching means 3D and the resistance value of the voltage dividing resistor string is set. If the resistance value of the second resistor R _F is used, the resistance value of the voltage dividing resistor array is the first resistance when the switching means 3D detects the concentration of a single kind or plural kinds of gases that turn on the switching element Q1. The resistance value is higher than the resistance value of the voltage dividing resistor string, which is a combined resistance value of R _L and the second resistor R _F.

Therefore, the change amount of the potential difference appearing between both ends of the voltage dividing resistor array, which is measured by the output change amount measuring means 3A as the amount of change in the output of the semiconductor gas sensor 21 at the time of driving the heater _RH , is single or plural. The determination means 3B uses the measured value of the output variation measuring means 3A as a value larger than the potential difference appearing at both ends of the voltage dividing resistor array measured by the output variation measuring means 3A when detecting the concentration of the seed gas. The semiconductor gas sensor 21 is set within a range that is preferable in terms of the operation of the means for calculating the gas concentration when the determination resolution is increased, thereby detecting the concentration of a single type or a plurality of types of gas based on the output of the semiconductor type gas sensor 21. while ensuring that match the output, it is possible to maintain high recognition accuracy breakage recognition means at the time of detecting the disconnection state of the sensor element R _S.

On the other hand, if the ambient temperature of the semiconductor gas sensor 21 is lower than the reference temperature, the internal resistance value of the sensor element _RS when the gas to be detected is absent increases, and conversely the ambient temperature of the semiconductor gas sensor 21. However, if the temperature is higher than the reference temperature, the internal resistance value of the sensor element _RS when the gas to be detected is absent becomes low, so that the output of the semiconductor gas sensor 21 changes due to the influence of fluctuations in the ambient temperature. .

However, as in the gas detection device of the present invention as set forth in claim 2 , the temperature compensation means A outputs the output change amount measurement means 3A according to the difference between the ambient temperature of the semiconductor gas sensor 21 and a predetermined reference temperature. By correcting the measured output change amount of the semiconductor gas sensor 21, it is possible to suppress a decrease in the accuracy of detection of the disconnection state of the sensor element _RS due to a change in the ambient temperature of the semiconductor gas sensor 21.

Further, according to the gas detection device of the present invention described in claim 3 , in the gas detection device of the present invention described in claim 1, 2 or 3, the sensor element _RS is in a disconnected state by the notification of the failure alarm means 5. Thus, it can be recognized from the outside of the gas detection device that the semiconductor gas sensor 21 is in failure.

  Hereinafter, a gas detection apparatus of the present invention will be described with reference to the drawings.

  FIG. 2 is a block diagram showing a block diagram of an embodiment of a gas leak alarm device in which the gas detection device of the present invention is implemented. As shown in FIG. The circuit part 2, the control part 3, the memory | storage part 4, and the alarm output part 5 are comprised. The power supply circuit unit 1 receives power supply from, for example, a battery or a commercial power supply, converts it into a voltage suitable for the operation of each part of the gas leak alarm, and outputs it. The power supply circuit unit 1 may include a backup battery when receiving power supply from a commercial power supply.

  The detection circuit unit 2 includes, for example, a semiconductor sensor 21 as an incomplete combustion sensor and a gas leak sensor. In the present embodiment, a gas leak alarm device of a combined type of a gas leak sensor and an incomplete combustion sensor is illustrated, but the present invention is a gas leak alarm device that functions as only one of the sensors. Alternatively, it may be a combined type gas leak alarm device including four or more sensors to which other types of sensors are added. However, here, a description will be given using a gas leak alarm of a composite type of three types of sensors.

The semiconductor sensor 21 applies a heating voltage from the power supply circuit unit 1 to the heating element R _H to improve the reaction of the sensor element R _S to combustible gas, and a potential difference corresponding to the internal resistance of the sensor element R _S. Is a known sensor output. In the gas leak alarm of the present embodiment, as shown in the uppermost part of the timing chart of FIG. 3, a high / low voltage is applied to the heating element R _H (corresponding to the heater in the claims), The heating element _RH is heated to about 80 ° C. during detection of CO gas for detecting incomplete combustion, and heated for detection of methane gas for detection of gas leakage during the high period. The element _RH is heated to about 400 ° C.

When detecting either CO gas or methane gas, the internal resistance of the sensor element _RS shown in FIG. 2 is normally high in the atmosphere, and the internal resistance decreases when CO gas or methane gas is present. Shown in the second row from the top in FIG. 3, the detection time and the CO gas arriving late in the low period of the voltage applied to the heating element R _H, shown in the third row from the top in FIG. 3, the heating element R _H When detecting the methane gas that arrives at the end of the high period in the voltage application, the internal resistance of the sensor element R _S , the resistance R _F (corresponding to the second resistance in the claims) and the resistance R _L (claim) The voltage divided by the parallel resistor (corresponding to the first resistor in the section) is supplied to the control unit 3 via the interface circuit 22 as a sensor output for a safety alarm. Therefore, when detecting CO gas or methane gas, the switching transistor Q1 (corresponding to the switching element in the claims) connected in series with the resistor R _L is in the ON state.

On the other hand, the transition period from low to high in the voltage application to the heating element _RH shown in the lowermost stage of FIG. 3 (in the gas leak alarm of this embodiment, the voltage application to the heating element _RH is switched from OFF to ON. Since the high period comes at the beginning of the transition, the switching transistor Q1 is detected at the disconnection detection of the sensor element R _S arriving at the heating element R _H , including the transition period from turning off the voltage application to the heating element R _H. Is turned off, and the voltage divided by the internal resistance of the sensor element R _S and the parallel resistance of the resistance R _F is supplied to the control unit 3 via the interface circuit 22 as a sensor output for disconnection alarm.

Incidentally, in the gas leak alarm of this embodiment, the internal resistance (= air base) of the sensor element R _S when no CO gas or methane gas is present in the vicinity is 200 KΩ at a reference temperature (20 ° C.) and the methane gas concentration is 3000 ppm. The internal resistance of the sensor element R _S is 2 KΩ at the reference temperature (20 ° C.), the resistance value of the resistance R _F is 200 KΩ, and the resistance value of the resistance R _L is much lower than the resistance value of the resistance R _F 2 KΩ. Therefore, when the switching transistor Q1 is turned on, the combined resistance value of the parallel resistances of the resistor R _F and the resistor R _L is about 1.98 KΩ (≈2 KΩ).

The interface circuit 22 is configured to include an amplifier circuit or the like for converting the sensor voltage output to the control unit 3 into a voltage suitable for processing in the control unit 3. Note that the internal resistance (= air base) of the sensor element R _S which is 200 KΩ at the reference temperature (20 ° C.) increases to 400 to 500 KΩ when the ambient temperature decreases to 0 ° C., for example, and the value of the sensor output of the semiconductor sensor 21 The internal resistance when the sensor element R _S is disconnected is greatly affected. Therefore, the interface circuit 22 includes, for example, a thermistor Rc as temperature compensation means A for correcting the temperature of the sensor output.

  The control unit 3 includes a microcomputer in which a CPU, a ROM, a RAM, and the like are integrated into an IC. The CPU controls the entire alarm device using the RAM as a work area in accordance with a program built in the ROM, basic data, and externally input data. For example, the control unit 3 receives the sensor signal for the security alarm from the detection circuit unit 2 acquired at the timing shown in the second or third stage from the top in FIG. The alarm output unit 5 is controlled so as to issue a warning regarding the safety of the gas leakage and the incomplete combustion with reference to the threshold value for the safety alarm regarding the incomplete combustion and the gas leakage. Further, the control unit 3 receives a sensor signal for a disconnection alarm from the detection circuit unit 2 acquired at the timing shown in the lowermost stage of FIG. 3 and stores a sensor signal for a fault alarm stored in the storage unit 4 The alarm output unit 5 is controlled so as to issue an alarm regarding the failure of the detection circuit unit 2, in particular, the semiconductor sensor 21, with reference to the amount of change per unit time.

The storage unit 4 stores a threshold value for a safety alarm related to gas leakage and incomplete combustion, and a threshold value of a change amount per unit time of a fault alarm used as a reference for determining a failure of the semiconductor sensor 21. Has been. Each threshold value is obtained in advance based on the performance of the semiconductor sensor 21 used, the circuit characteristics of the interface circuit 22, and the like. In particular, the threshold value of the change amount per unit time of the failure alarm is The sensor output of the semiconductor gas sensor 21 generated when the voltage applied to the heating element _RH is turned off or shifts from a low level to a high level in a normal conduction state where the sensor element _RS of the semiconductor gas sensor 21 is not disconnected. The minimum amount of change is set.

  The alarm output unit 5 (corresponding to the failure alarm means in the claims) includes an audio output unit 51 and a display output unit 52. The audio output unit 51 is, for example, a buzzer or a speech processor, and the display output unit 52 is, for example, an LED or an LCD. In addition to normal security warnings, when a failure is detected, contents such as “the sensor is disconnected” are output as voice or displayed. Alternatively, a failure alarm may be issued by a combination of sound and display.

  Next, in the gas leak alarm device having the hardware configuration as described above, a processing procedure performed by the control unit 3 will be described using the flowcharts of FIGS. 4 and 5.

When power is supplied to the control unit 3, first, as shown in FIG. 4, the switching transistor Q1 is turned off (step S1), and then a high-level voltage is applied to the heating element _{RH in the} off state. (Step S3), and after the transition period required for the voltage applied to the heating element _RH to reach a high level has elapsed (Y in step S5), it is acquired via the interface circuit 22 during the transition period. amount of change ΔV in the sensor output for break alarm, i.e., obtains the amount of change in voltage divided by the parallel resistance of the internal resistance and the resistance R _F of the sensor element R _S sensor (step S7), and was obtained variation [Delta] V of the output is stored in the storage unit 4, the threshold value [Delta] V _th (e.g. 0.1 changes per fault unit alarm time used as a criteria for determining a failure of the semiconductor sensor 21 V) If it is not equal to or higher (N in step S9), the alarm output unit 5 outputs an alarm indicating that the semiconductor sensor 21 is faulty due to disconnection, such as “sensor is disconnected”. Audio output or display output is performed from the unit 51 or the display output unit 52 (step S11).

If the obtained change amount ΔV of the sensor output for the disconnection alarm is equal to or larger than the threshold value ΔV _th of the change amount per unit time of the failure alarm (Y in step S9), the switching transistor Q1 is turned on (step S9). S13) Next, after the standby period required for the applied voltage to the heating element _RH having reached the high level to elapse (Y in step S15), the sensor output V for the safety alarm, that is, the sensor A voltage _{divided by} the internal resistance of the element R _S and the parallel resistance of the resistance R _F and the resistance R _L is acquired via the interface circuit 22 (step S17), and the acquired sensor output V is stored in the storage unit 4. If it exceeds the threshold value V _thH for the safety alarm relating to the gas leak stored in (Y in step S19), an alarm _indicating that a gas leak has occurred is output to the voice of the alarm output unit 5. Voice output or display output is performed from the output unit 51 or the display output unit 52 (step S21).

On the other hand, if the acquired sensor output V does not exceed the threshold value V _thH for the safety alarm regarding gas leakage (N in step S19), as shown in FIG. 5, the heating element _RH is in the high level state. switching the voltage applied to the low level (step S23), the transition period in which the voltage applied to the heating element R _H is required until switches from the high level to the low level, the voltage applied to the heating element R _H has reached the low level After a period including a waiting period required for stabilization of the sensor has elapsed (Y in step S25), the sensor output V for the safety alarm, that is, the internal resistance of the sensor element R _S , the resistance R _F and the resistance R _L The voltage divided by the parallel resistance is acquired via the interface circuit 22 (step S27), and the acquired sensor output V is stored in the storage unit 4 and is a security related to incomplete combustion. If the alarm threshold value V _thL is exceeded (Y in step S29), an alarm indicating that incomplete combustion has occurred is output from the audio output unit 51 or the display output unit 52 of the alarm output unit 5. Audio output or display output is performed (step S31).

If the acquired sensor output V does not exceed the threshold value V _thL for the safety alarm relating to gas leakage (N in step S29), the switching transistor Q1 is turned off (step S33), and then the low level state is _reached. After the voltage application to the heating element R _H is switched to the high level (step S35), after the transition period required until the voltage applied to the heating element R _H reaches the high level again (in step S5). Y) A change amount ΔV of the sensor output for the disconnection alarm during the transition period is acquired (step S7), and the acquired change amount ΔV of the sensor output is a threshold value ΔV of the change amount per unit time of the failure alarm. unless _th (e.g. 0.15V) above (in step S9 N), to the effect that the semiconductor sensor 21 is located in failure due to breakage, "sensor is not broken The alarm of the contents of the void ", etc., and displays the output or audio output from the audio output unit 51 and the display output unit 52 of the alarm output unit 5 (step S11). That is, after step S35 in FIG. 5, the processing after step S5 in FIG. 4 is repeated.

An alarm indicating that the semiconductor sensor 21 is a failure due to disconnection, an alarm indicating that gas leakage has occurred, or an alarm indicating that incomplete combustion has occurred. After the voice output or the display output from the voice output unit 51 or the display output unit 52 of the alarm output unit 5 (steps S11, 21, 31), as shown in FIG. 5, voltage application to the heating element _RH is performed. After turning off (step S37), a series of processing is terminated.

  As is clear from the above description, in the gas leak alarm of this embodiment, the output change amount measuring means 3A, the determining means 3B, the disconnection recognizing means 3C, and the switching means 3D in the claims are included in the control unit 3. It is constituted by.

  In the series of operations described above, the sensor output V acquired by the control unit 3 via the interface circuit 22 and the amount of change ΔV are both the reference temperature (for example, 20 ° C.) and the actual semiconductor type. The fluctuation caused by the difference with the temperature around the sensor 21 is temperature compensated by, for example, the thermistor Rc as the temperature compensation means A in the interface circuit 22, that is, the temperature compensated for the output at the reference temperature. It is. This temperature compensation may be performed by a circuit like the temperature compensation means A in the interface circuit 22, or the temperature around the semiconductor sensor 21 is measured by the temperature sensor and taken into the control unit 3. It may be realized by processing logic performed in the control unit 3 based on the value. In this case, the control unit 3 corresponds to the temperature compensation means A in the claims.

According to the gas leak alarm of the present embodiment configured as described above, the failure of the semiconductor sensor 21 is determined until the voltage applied to the heating element _RH reaches the high level from the off state or the low level. Since the change amount ΔV of the sensor output during the required transition period is used, even if CO gas or methane gas exists in the vicinity of the semiconductor sensor 21, the fluctuation of the sensor output V due to the influence is the sensor output before and after the change. Since it acts on V in the same manner, it is canceled when the change amount ΔV of the sensor output is acquired. For this reason, regardless of whether CO gas or methane gas is present around the semiconductor sensor 21, the obtained sensor output change ΔV is the threshold of change per unit time of the failure alarm. Whether or not the sensor element R _S of the semiconductor gas sensor 21 is in a disconnected state can be accurately determined by the control unit 3 based on whether or not the value ΔV _th or more.

Moreover, according to the gas leak alarm of this embodiment, when detecting CO gas and methane gas, the switching transistor Q1 is turned on and the parallel resistance of the resistance R _F and the resistance R _L is about 1.98 KΩ (≈2 KΩ). Since the voltage corresponding to the voltage dividing ratio between the combined resistance of the sensor element R _{S and} the internal resistance of the sensor element R _S becomes the sensor output V, the sensor output V can be used in the operation of the control unit 3 even if the internal resistance of the sensor element R _S is low. On the other hand, when the disconnection state of the sensor element R _S of the semiconductor gas sensor 21 is detected, the switching transistor Q1 is turned off and the resistance R _{F of} 200 KΩ and the internal resistance of the sensor element R _S can be suppressed. Since the voltage corresponding to the voltage division ratio becomes the sensor output V, even if the internal resistance of the sensor element R _S is in an infinite state, the sensor output V is discriminated by the control unit 3. It is possible to maintain a preferable voltage and to detect the disconnection state of the sensor element R _S with high resolution and high accuracy.

Incidentally, for the sensor output V of the semiconductor gas sensor 21, for example, temperature compensation by a thermistor Rc as the temperature compensation means A in the interface circuit 22, or in the control unit 3 based on the temperature around the semiconductor sensor 21. Although temperature compensation by processing logic is not indispensable, if a temperature compensation configuration is provided, the internal resistance (= air base) of the sensor element R _S is increased around the semiconductor sensor 21 as described above. Even if it fluctuates greatly depending on the temperature, the disconnection state of the sensor element R _S is detected with the influence removed, so that the disconnection state of the sensor element R _S can be detected with high accuracy.

Further, when the disconnection state of the sensor element R _S is detected, the alarm output by the alarm output unit 5 is not indispensable as in the gas leak alarm of the present embodiment, and the external device is notified by the external output of the alarm signal. The configuration may be such that an alarm is given by an external device or the like and appropriate processing is performed in conjunction.

Furthermore, in the gas leak alarm of this embodiment, the change amount ΔV of the sensor output for the disconnection alarm during the period in which the voltage application to the heating element _RH is in the off state or shifts from the low level to the high level is Whether or not the sensor element R _S of the semiconductor sensor 21 is in a disconnected state is determined based on whether or not the change amount per unit time is greater than or equal to a threshold value ΔV _th (for example, 0.15 V). However, or alternatively, the change amount ΔV of the sensor output for the disconnection alarm during the period in which the voltage application to the heating element _RH shifts from the high level to the low level is the unit of the failure alarm. Whether or not the sensor element _RS is in a disconnected state may be determined based on whether or not the change amount is equal to or greater than a threshold value ΔV _th (for example, 0.15 V).

Further, in the gas leak alarm of the present embodiment, when detecting CO gas and methane gas, the switching transistor Q1 is turned on, and the combined resistance of the parallel resistance of the resistance R _F and the resistance R _L and the internal resistance of the sensor element R _S When the disconnection state of the sensor element R _S of the semiconductor gas sensor 21 is detected by setting the voltage corresponding to the voltage division ratio to the sensor output V, the switching transistor Q1 is turned off, and the resistance R _F and the inside of the sensor element R _S A voltage corresponding to the voltage dividing ratio with the resistor is set as the sensor output V.

However, the value of the internal resistance of the sensor element R _S in the value of internal resistance, the detection of CO gas and methane gas sensor elements R _S at the time of detecting a disconnection state of the sensor elements R _S semiconductor gas sensor 21, less If it does not change, the following configuration may be adopted.

That is, instead of the parallel resistance of the resistor R _L and the switching transistor Q1 connected in series with the resistor R _F , a single voltage dividing resistor R _F0 having the same resistance value as the combined resistance of the parallel resistor is provided. In both cases of detecting the disconnection state of the sensor element R _S of the semiconductor gas sensor 21 connected in series to the sensor element R _S of the semiconductor sensor 21 and detecting CO gas and methane gas, A voltage corresponding to the voltage division ratio between the sensor element R _S and the voltage dividing resistor R _F0 may be used as the sensor output V.

Furthermore, in this embodiment, when detecting CO gas that arrives at the end of the low period in the voltage application to the heating element _RH , or when detecting methane gas that arrives at the end of the high period in the voltage application to the heating element _RH . In either case, the resistor used in series with the sensor element R _S in order to obtain the sensor output V is configured as a parallel resistance of the resistor R _F and the resistor R _L.

However, the sensor element R _S of the semiconductor sensor 21 has a characteristic that even if the gas concentration per unit volume is the same, the value of the internal resistance generated at that time is different between CO gas and methane gas. In some cases, the following configuration may be adopted accordingly.

That is, with respect to the resistor R _L and the switching transistor Q1 connected in series with this, the resistance R _F1 for detecting CO gas having a resistance value according to the characteristic of the internal resistance value when detecting CO gas, and the resistance R _F1 for detecting methane gas. A methane gas detection resistor R _F2 having a resistance value corresponding to the characteristic of the internal resistance value is connected in parallel so that it can be switched. When CO gas is detected, the parallel resistance of the CO gas detection resistor R _F1 and the resistor R _L The voltage corresponding to the voltage dividing ratio with the sensor element R _S is set as the sensor output V, and when detecting methane gas, the voltage according to the voltage dividing ratio between the resistance of the methane gas detecting resistor R _F2 and the parallel resistance of the resistor R _L and the sensor element R _S is set. The sensor output V may be used.

Further, as described above, the sensor element R _S and the voltage dividing resistor R _F0 are both detected when the disconnection state of the sensor element R _S of the semiconductor gas sensor 21 is detected and when the CO gas and the methane gas are detected. In addition, the sensor output V is set to a voltage corresponding to the voltage division ratio, and further, the difference in the internal resistance value generated in the sensor element R _S of the semiconductor sensor 21 with respect to the gas concentration per unit volume. In the case of corresponding, the following configuration can be adopted.

That is, instead of the voltage dividing resistor R _F0 , a single CO gas detecting _{voltage dividing} resistor R _F01 having the same resistance value as the combined resistance of the resistor R _L and the CO gas detecting resistor R _F1 in parallel, In order to obtain a sensor output V, a single methane gas detection voltage _dividing resistor R _F22 having the same resistance value as the combined resistance of the resistance R _L and the parallel resistance of the methane gas detection resistance R _F2 is provided to the sensor element R _S. A resistor connected in series is connected in parallel so that it can be switched. When CO gas is detected, the sensor output V is a voltage corresponding to the voltage dividing ratio between the CO gas detecting voltage dividing resistor R _F01 and the sensor element R _S. When detecting methane gas, the sensor output V can be a voltage corresponding to the voltage dividing ratio between the methane gas detecting voltage dividing resistor R _F22 and the sensor element R _S.

It is a basic lineblock diagram showing basic technology of a gas leak alarm of the present invention. It is a block diagram which shows partially one Embodiment of the gas leak alarm which implemented the gas detection apparatus of this invention. 3 is a timing chart showing a relationship between a voltage application pattern to a heating element of the semiconductor sensor of FIG. 2 and detection timings of incomplete combustion, gas leakage, and sensor element disconnection. It is a flowchart which shows the process sequence implemented in the control part of FIG. It is a flowchart which shows the process sequence implemented in the control part of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Control part 3A Output variation | change_quantity measurement means 3B Judgment means 3C Disconnection recognition means 3D Switching means 5 Fault alarm means 21 Semiconductor type gas sensor A Temperature compensation means Q1 Switching element R _F 2nd resistance R _H heater R _L 1st resistance R _S sensor element

Claims (3)

In a gas detection device that detects a concentration of a single type or a plurality of types of gas using a semiconductor gas sensor having a sensor element heated by a heater that is intermittently turned on / off or high / low driven,
An output for measuring the amount of change in output of the semiconductor gas sensor at the time of transition from one of the heater driving on and off to the other, or from one of the heater driving high and low to the other. Change measuring means;
The amount of change in output of the semiconductor gas sensor measured during the transition of the heater drive measured by the output change amount measuring means is the minimum of the output change of the semiconductor gas sensor that occurs during the transition in the normal conduction state of the sensor element. Determining means for determining whether or not the amount is exceeded;
Disconnection recognition means for recognizing that the sensor element is in a disconnected state when the determination means determines that the amount of output change of the semiconductor gas sensor measured by the output change amount measurement means does not exceed the minimum amount. And
A voltage dividing resistor string in which a first resistor and a switching element connected in series to the first resistor are connected in parallel to a second resistor having a resistance value higher than that of the first resistor is connected in series to the sensor element. The switching element is turned off when the heater is shifted to make the resistance value of the voltage dividing resistor array the resistance value of the second resistor, and when the concentration of the single kind or plural kinds of gases is detected. And further comprising switching means for turning on the switching element and setting the resistance value of the voltage dividing resistor string to a combined resistance value of the first resistor and the second resistor,
The output change amount measuring unit is configured to calculate a change amount of a potential difference appearing between both ends of the voltage dividing resistor row, the resistance value of which is the resistance value of the second resistor by the switching unit, at the time of transition of driving of the heater. A gas detection device that measures the amount of change in output of the semiconductor gas sensor . A temperature compensating means for correcting the output of the semiconductor gas sensor measured by the output change amount measuring means according to a difference between an ambient temperature of the semiconductor gas sensor and a predetermined reference temperature; means for the variation of the output of the measured the semiconductor gas sensor of the output change amount measuring means after being corrected by the temperature compensating means, as claimed in claim 1, wherein determining whether exceeds said minimum amount Gas detection device. 3. The gas according to claim 1 , further comprising a failure alarm unit that notifies the outside that the semiconductor gas sensor is in failure when the disconnection recognition unit recognizes that the sensor element is in a disconnected state. Detection device.

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