JP2007198940A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector for detecting troubles in the semiconductor type gas sensor and another constituent element in the gas detector that have been difficult to detect heretofore for discriminating the content of the trouble. <P>SOLUTION: A first detection resistor R1 and a second detection resistor R2, which are respectively different resistance values between a plate power supply Vcc and a plate electrode 3b, are changed-over and connected by a detection resistor change-over means 12, during the supply of predetermined heater voltage from a heater power supply 11. Furthermore, the difference between the sensor output voltage of the semiconductor-type gas sensor 3, when the first detection resistor R1 is connected to the plate electrode 3b and the sensor output voltage of the semiconductor-type sensor 3, when the second detection resistor R2 is connected to the plate electrode 3b is measured by a sensor output difference measuring means 10b. It is determined that there is trouble on the semiconductor type gas sensor 3 by a first trouble-determining means 10d, when the difference, measured by the sensor output difference measuring means 10b, does not lie within a preset normal range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas detection device that detects gas leakage or incomplete combustion in a combustor using a semiconductor gas sensor.

  If a gas sensor used in a gas detection device that detects a gas leak or incomplete combustion of a combustor, or other components such as a resistor and a transistor are in a fault state such as short-circuited or open (disconnected), It is very important to recognize whether or not these are in a fault state, since detection cannot be performed normally.

  In order to accurately measure the resistance value of a gas sensor whose resistance value varies greatly depending on the type of gas to be detected, such as a semiconductor gas sensor used in a gas detection device that detects a plurality of gases, for example, FIG. In the gas detection apparatus having the configuration shown in (2), it is common to perform measurement by switching the detection resistance for each gas type to be detected.

  When detecting a sensor failure in a gas detection apparatus using such a semiconductor gas sensor, as shown in FIG. 3, the normal range of sensor output obtained by driving one detection resistor (for example, resistor R1) is set. If it deviates from this normal range, it is determined as a failure.

  Specifically, in the gas detection apparatus having the configuration of FIG. 2, for example, by turning on the transistors Tr1 and Tr2 by the control signals from the output ports P1 and P2 of the CPU 10 for each gas type of methane and CO, methane The detection resistors R1 and R2 are switched in accordance with the respective gases of CO and CO, and measurement is performed at the optimum timing for each gas type.

  That is, as shown in FIG. 4, in the case of methane, the sensor output is measured immediately before the heater voltage from the heater voltage supply circuit 11 switches from high (Hi) to low (Lo), and in the case of CO, The sensor output is measured at a timing immediately before the heater voltage is switched from low (Lo) to high (Hi).

  In the case of sensor output at the time of methane measurement, the sensor resistance value range to be measured (based on failure determination) is about 100Ω to several hundred kΩ, and the sensor resistance value range at the time of CO measurement is about 100Ω to several MΩ. Is common. When it is necessary to measure a wide resistance value range as in failure determination, failure determination is performed for a relatively narrow resistance value range to be measured, such as during methane measurement, rather than during CO measurement.

  As described above, when one detection resistor is used for one gas detection, a failure that can be discriminated in the other components of the semiconductor gas sensor and the gas detection device is caused by the connection of the semiconductor gas sensor plate electrode to GND (ground). It is about short-circuited, and other failure states cannot be distinguished from alarm states and standby states (normal air state) (see Table 1 described later).

  In particular, conditions B (short between plate electrode and heater), D (short of detection resistor R1), E (short of detection resistor R2), F (short of transistor Tr1), G (short of transistor Tr2) in Table 1 ) Is in a fail-out state, it is necessary for the user to be able to detect these failures.

  Therefore, in view of the above-described problems, the present invention has an object to provide a gas detection device that can detect a failure of a semiconductor gas sensor and other components in a gas detection device that has been difficult to detect in the past and determine the content of the failure. It is said.

  As shown in the basic configuration diagram of FIG. 1, the invention according to claim 1, which has been made to solve the above-described problem, is a heater 3 a to which a predetermined heater voltage is supplied from the heater power supply 11 and a predetermined voltage from the plate power supply Vcc. A gas detection device that detects a gas concentration by using a semiconductor gas sensor 3 having a plate electrode 3b to which a plate voltage is supplied, and the plate while the heater power supply 11 is supplying a predetermined heater voltage. Detection resistor switching means 12 for switching and connecting the first detection resistor R1 or the second detection resistor R2 having different resistance values between the power source Vcc and the plate electrode 3b, and the first detection resistor connected to the plate electrode 3b Sensor output voltage of the semiconductor gas sensor 3 when R1 is connected, and the second detection on the plate electrode 3b Sensor output difference measuring means 10b for measuring the difference in sensor output voltage of the semiconductor gas sensor 3 when the anti-R2 is connected, and the difference measured by the sensor output difference measuring means 10b being set to normal The gas detection apparatus includes a first failure determination unit 10d that determines that the semiconductor gas sensor 3 has failed when it is not within the range.

  According to the first aspect of the present invention, the gas detection device includes a heater 3a to which a predetermined heater voltage is supplied from the heater power supply 11, and a plate electrode 3b to which a predetermined plate voltage is supplied from the plate power supply Vcc. 3 is used to detect the gas concentration. Further, while a predetermined heater voltage is supplied from the heater power source 11 by the detection resistance switching means 12, the first detection resistor R1 or the second detection resistor R1 having a different resistance value between the plate power source Vcc and the plate electrode 3b. The detection resistor R2 is switched and connected. The sensor output difference measuring means 10b connects the sensor output voltage of the semiconductor gas sensor 3 when the first detection resistor R1 is connected to the plate electrode 3b and the second detection resistor R2 to the plate electrode 3b. The difference of the sensor output voltage of the semiconductor gas sensor 3 is measured. Then, when the difference measured by the sensor output difference measuring unit 10b is not within a preset normal range by the first failure determining unit 10d, it is determined that the semiconductor gas sensor 3 has failed.

  According to a second aspect of the present invention, there is provided the gas detection device according to the first aspect, wherein the detection resistance switching means 12 is connected between the plate power source Vcc and the first detection resistance R1. The first switching element Tr1, the second switching element Tr2 connected between the plate power source Vcc and the second detection resistor R2, and the first or second switching element Tr1 or Tr2. Control means 10a for supplying a control signal to perform the first failure determination means 10d, when the difference measured by the sensor output difference measurement means 10b is not within a preset normal range, The semiconductor gas sensor 3, the first detection resistor R1, the second detection resistor R2, the first switching element Tr1, or the second switch It consists in gas detection apparatus characterized by determining a failure of any of the quenching element Tr2.

  According to the second aspect of the present invention, the detection resistor switching means 12 includes the first switching element Tr1 connected between the plate power source Vcc and the first detection resistor R1, and between the plate power source Vcc and the second detection resistor R2. And a control means 10a for supplying a control signal for turning on the first or second switching element Tr1 or Tr2. When the difference measured by the sensor output difference measuring unit 10b is not within a preset normal range, the first failure determination unit 10d performs the semiconductor gas sensor 3, the first detection resistor R1, and the second detection resistor. R2 is determined as a failure of either the first switching element Tr1 or the second switching element Tr2.

  According to a third aspect of the present invention, there is provided the gas detector according to the first or second aspect, wherein a predetermined heater voltage is being supplied from the heater power source 11 and the plate is the plate. When no predetermined plate voltage is supplied from the power source Vcc to the plate electrode 3b, the sensor output measuring means 10c when no plate is applied to measure the sensor output voltage of the semiconductor gas sensor 3, and the sensor output measurement when the plate is not applied A second failure determination means 10e for determining that the first or second detection resistor R1 or R2 has failed when the sensor output voltage when no plate is applied measured by the means 10c is not within a preset normal range; Further, the present invention resides in a gas detection device.

  The invention according to claim 3 further includes a sensor output measuring means 10c when no plate is applied and a second failure determining means 10e. The sensor output measuring means 10c when no plate is applied is a semiconductor type when the predetermined heater voltage is supplied from the heater power supply 11 and when the predetermined plate voltage is not supplied from the plate power supply Vcc to the plate electrode 3b. The sensor output voltage of the gas sensor 3 is measured. The second failure determination means 10e is the first or second detection resistor R1 when the sensor output voltage when no plate is applied measured by the sensor output measuring means 10c when no plate is applied is not within a preset normal range. Or, it is determined that the failure is R2.

  In order to solve the above-mentioned problem, the invention according to claim 4 is the gas detection device according to any one of claims 1 to 3, wherein the failure is detected by the first or second failure determination means 10d or 10e. When the determination is made, the sensor output voltage of the semiconductor gas sensor 3 when the first detection resistor R1 is connected to the plate electrode 3b and the second detection resistor R2 is connected to the plate electrode 3b. When the sensor output voltage of the semiconductor gas sensor 3 at the same time is almost the same, it is determined that the semiconductor gas sensor 3 is out of order, and when the sensor output voltage is not the same, the first detection resistor R1, Further, the third failure determination means 10f for determining the failure of the second detection resistor R2, any of the first switching element Tr1 or the second switching element Tr2 is further provided. It consists in gas detection apparatus characterized by comprising.

  The fourth aspect of the present invention further includes third determination means 10f. The third determination means 10f is a sensor of the semiconductor gas sensor when the first detection resistor R1 is connected to the plate electrode 3b when the failure determination is made by the first or second failure determination means 10d or 10e. When the output voltage and the sensor output voltage of the semiconductor type gas sensor when the second detection resistor R2 is connected to the plate electrode 3b are substantially the same, it is determined that the semiconductor type gas sensor 3 has failed and is in agreement. If not, it is determined that one of the first detection resistor R1, the second detection resistor R2, the first switching element Tr1, or the second switching element Tr2 has failed.

  In order to solve the above-mentioned problem, the invention according to claim 5 is the gas detection device according to any one of claims 1 to 4, wherein the gas detection device includes pulses in which a high level and a low level alternate. A heater voltage is supplied from the heater power supply 11 to the heater 3a. While the high level heater voltage is being supplied, the detection resistance switching means 12 causes the first power supply Vcc and the plate electrode 3b to move between the plate power supply Vcc and the plate electrode 3b. The concentration of the first gas is detected by the sensor output voltage of the semiconductor gas sensor 3 when one detection resistor R1 is connected, and the detection resistor is switched while the low-level heater voltage is supplied. The semiconductor when the second detection resistor R2 is connected between the plate power source Vcc and the plate electrode 3b by means 12 It consists in a gas detection device which is a gas detection apparatus that detects the concentration of the first gas and the gas species different second gas by the sensor output voltage of the formula gas sensor 3.

  In the invention according to claim 5, the gas detection device detects the pulse-shaped heater voltage in which the high level and the low level are alternately supplied from the heater power supply 11 to the heater and is supplied with the high level heater voltage. The resistance switching means 12 detects the concentration of the first gas based on the sensor output voltage of the semiconductor gas sensor 3 when the first detection resistor R1 is connected between the plate power source Vcc and the plate electrode 3b, and at the low level. The first gas is detected by the sensor output voltage of the semiconductor gas sensor 3 when the second detection resistor R2 is connected between the plate power source Vcc and the plate electrode 3b by the detection resistor switching means 12 while the heater voltage is supplied. And a gas detection device for detecting the concentration of the second gas having a different gas type.

  In order to solve the above-described problem, the invention according to claim 6 is the gas detection device according to any one of claims 1 to 5, wherein the first gas is methane, and the second gas. Exists in a gas detection device characterized by being CO.

  In the invention described in claim 6, the first gas is methane and the second gas is CO.

  According to the first aspect of the present invention, the semiconductor gas sensor 3 having the heater 3a to which a predetermined heater voltage is supplied from the heater power supply 11 and the plate electrode 3b to which a predetermined plate voltage is supplied from the plate power supply Vcc is used. A gas detection device for detecting a gas concentration, wherein a first detection resistor R1 having different resistance values between the plate power supply Vcc and the plate electrode 3b while a predetermined heater voltage is supplied from the heater power supply 11. Alternatively, the detection resistor switching means 12 for switching and connecting the second detection resistor R2, the sensor output voltage of the semiconductor gas sensor 3 when the first detection resistor R1 is connected to the plate electrode 3b, and the plate electrode 3b Sensor output for measuring the difference in sensor output voltage of the semiconductor gas sensor 3 when the two detection resistors R2 are connected. A difference measurement unit 10b, and a first failure determination unit 10d that determines that the semiconductor gas sensor 3 has failed when the difference measured by the sensor output difference measurement unit 10b is not within a preset normal range. Therefore, it is possible to determine a failure of a semiconductor gas sensor, such as a disconnection of a plate electrode, a short between a plate electrode and a GND (ground)), a short between a plate electrode and a heater, etc., which is impossible with a conventional apparatus. Thus, the fail-out state does not occur as in the conventional apparatus.

  According to the second aspect of the present invention, the detection resistor switching means 12 includes the first switching element Tr1 connected between the plate power source Vcc and the first detection resistor R1, the plate power source Vcc, and the second detection resistor R2. A second switching element Tr2 connected in between, and a control means 10a for supplying a control signal for turning on the first or second switching element Tr1 or Tr2. The first failure determination means 10d includes a sensor When the difference measured by the output difference measuring means 10b is not within a preset normal range, the semiconductor gas sensor 3, the first detection resistor R1, the second detection resistor R2, the first switching element Tr1, or the first Since it is determined that one of the switching elements Tr2 of the failure is a failure, the semiconductor type gas sensor 3 in the gas detection device or the detection resistor constituting the device 1, failure of R2 and the switching elements Tr1, Tr2 also can determine, it is eliminated as a fail-out state as in the conventional apparatus.

  According to the third aspect of the present invention, when the predetermined heater voltage is supplied from the heater power source 11 and when the predetermined plate voltage is not supplied from the plate power source Vcc to the plate electrode 3b, the semiconductor gas sensor 3 when the sensor output voltage when no plate is applied is measured and the sensor output voltage when no plate is applied measured by the sensor output measurement means when the plate is not applied is not within a preset normal range. Is further provided with a second failure determination means 10e for determining that the first or second detection resistor R1 or R2 has failed, so that it is also possible to determine a short-circuit failure of the first or second detection resistor. As shown in FIG.

  According to the fourth aspect of the present invention, when a failure determination is made by the first or second failure determination means 10d or 10e, the semiconductor gas sensor when the first detection resistor R1 is connected to the plate electrode 3b. 3 and the sensor output voltage of the semiconductor gas sensor 3 when the second detection resistor R2 is connected to the plate electrode 3b substantially match, the failure of the semiconductor gas sensor 3 If it is determined that they do not coincide with each other, a third failure determination that determines that the first detection resistor R1, the second detection resistor R2, the first switching element Tr1, or the second switching element Tr2 has failed. Since the means 10f is further provided, it is possible that the semiconductor gas sensor 3 has a failure or other components such as the detection resistors R1, R2 and the switching element Tr. , It is possible to identify whether Tr2 failure are.

  According to a fifth aspect of the present invention, in the gas detection device according to any one of the first to fourth aspects, the gas detection device has a pulsed heater voltage in which a high level and a low level alternate, and the heater power supply 11 The semiconductor gas sensor when the first detection resistor R1 is connected between the plate power source Vcc and the plate electrode 3b by the detection resistor switching means 12 while being supplied to the heater 3a and the high level heater voltage is being supplied. The first gas concentration is detected by the sensor output voltage 3 and the second detection resistor R2 is connected between the plate power source Vcc and the plate electrode 3b by the detection resistor switching means 12 while the low level heater voltage is supplied. The concentration of the second gas, which is different from the first gas, is detected by the sensor output voltage of the semiconductor gas sensor 3 when the gas is connected. Since the first gas detection device for detecting the first gas and the second gas detection device for detecting the second gas having a different gas type from the first gas, the semiconductor type The failure of the gas sensor and other components can be determined.

  According to the invention described in claim 6, since the first gas is methane and the second gas is CO, the first detection resistor for detecting methane and the second detection for detecting CO. The resistance can be used to determine the failure of the semiconductor gas sensor and other components.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  (First Embodiment) FIG. 2 is a circuit diagram showing a configuration of a gas detection apparatus according to a first embodiment of the present invention. In FIG. 2, the gas detection device 1 includes a semiconductor gas sensor 3, a microcomputer (hereinafter referred to as CPU) 10, a heater voltage supply circuit 11, a detection resistance switching circuit 12, and an alarm circuit 13.

  The CPU 10 has output ports P1, P2, P4 and P5 and an input port P3. The semiconductor gas sensor 3 includes a heater 3 a connected to the heater voltage supply circuit 11 and a plate electrode 3 b connected to the input port P 3 of the CPU 10. The CPU 10 includes a control unit 10a, a sensor output difference measurement unit 10b, a sensor output measurement unit 10c when no plate is applied, a first failure determination unit 10d, a second failure determination unit 10e, and a third failure determination unit 10f. Work as.

  The heater voltage supply circuit 11 supplies a pulsed heater voltage in which a high (Hi) level and a low (Lo) level alternate to the heater 3 a of the semiconductor gas sensor 3. The low (Lo) level of the heater voltage is set to a level for heating the semiconductor gas sensor 3 to a temperature suitable for CO detection, and the high (Hi) level is set to a level for heating to a temperature suitable for methane detection. Yes. The heater voltage supply circuit 11 serves as a heater power supply in the claims.

  The detection resistor switching circuit 12 has a methane detection resistor R1 and a CO detection resistor R2 connected to the plate electrode 3b of the semiconductor gas sensor 3, and a collector and an emitter connected between the detection resistor R1 and the power source Vcc. A pnp transistor Tr1 whose base is connected to the port P1 via the resistor R3, a collector and an emitter are connected between the detection resistor R2 and the power supply Vcc, and a base is connected to the output port P2 of the CPU 10 via the resistor R4 And a pnp transistor Tr2. The detection resistance switching circuit 12 serves as detection resistance switching means in the claims. The detection resistors R1 and R2 function as first and second detection resistors in the claims, respectively. The transistors Tr1 and Tr2 function as first and second switching elements in the claims, respectively.

  The alarm circuit 13 includes an npn transistor Tr3 whose base is connected to the output port P4 of the CPU 10, an LED (light emitting diode) 14 as an alarm display means connected between the collector of the transistor Tr3 and the power supply Vcc, The output port P5 includes an npn transistor Tr4 whose base is connected, and a buzzer (BZ) 15 as an alarm sound output means connected between the collector of the transistor Tr4 and the power supply Vcc. The alarm circuit 13 functions as an alarm means.

  In the gas detection device having the above-described configuration, in order to detect methane gas when the heater voltage supplied from the heater voltage supply circuit 11 is at a high (Hi) level, as shown in FIG. 5, the output ports P1 and P2 of the CPU 10 The transistors Tr1 and Tr2 are driven so as to be sequentially turned on by the control signal from, the two detection resistors R1 and R2 are switched in a time-sharing manner, and a plate voltage is applied to the plate electrode 3b of the semiconductor type gas sensor 3. Sensor outputs Vrs1 and Vrs2 of the semiconductor gas sensor 3 are measured.

  The relationship between the sensor output voltage obtained by this measurement and the gas concentration is shown in FIG. In the present invention, from the relationship between the sensor output voltage Vrs1 when using the detection resistor R1 and the sensor output voltage Vrs2 when using the detection resistor R2 measured by the two detection resistors, the sensor failure of the semiconductor gas sensor 3 and other configurations Determine the hardware failure of the element.

  First, on the simulation, the normal measurement range is obtained from the relationship between the sensor resistance value Rs of the semiconductor gas sensor 3 to be measured and the sensor output voltage Vrs. As a specific example, Vcc = 5 V, the sensor resistance value measurement range at the time of methane measurement is 100Ω to 200 kΩ, the detection resistance R1 = 1 kΩ (when methane 3000 ppm is detected), and R2 = 4.7 kΩ (when CO 50 ppm is detected). In this case, the relationship between the sensor resistance value Rs, the sensor output voltage Vrs1 when switched to the detection resistor R1, and the sensor output voltage Vrs2 when switched to the detection resistor R2 is shown in FIG.

From the relationship of FIG. 7, the upper and lower limit values of the difference ΔVrs between the sensor output voltage Vrs1 and the sensor output voltage Vrs2 are calculated and set as the failure determination threshold value as shown in FIG. 7 and 8, the minimum value V1 of the difference ΔVrs between the sensor outputs (when the detection resistors R1 and R2 are switched) is 0.082V, and the maximum value V2 is 1.765V. Therefore, when the difference ΔVrs between the sensor outputs (when the detection resistors R1 and R2 are switched) deviates from the range of the upper and lower limit values indicated by the normal range in FIG.
(Vrs1-Vrs2) ≦ V1 (0.082V) (1)
Or (Vrs1−Vrs2) ≧ V2 (1.765V) (2)
If any of the ranges is detected, it is determined that a sensor or hardware failure has occurred.

  Using this judgment value, condition A (disconnection of the plate electrode of the semiconductor gas sensor 3), condition B (opening of the detection resistor R1), condition C (opening of the detection resistor R2), condition D (transistor Tr1) shown in FIG. ), Condition E (opening between the emitter and collector of the transistor Tr2), condition F (short circuit between the plate electrode of the semiconductor gas sensor 3 and GND (ground)), condition G (semiconductor gas sensor 3) Plate electrode-heater short), condition H (detection resistor R1 short-circuit), condition I (detection resistor R2 short-circuit), condition J (emitter-collector short-circuit between transistor Tr1) and condition K (transistor Tr2 of The failure of each part of the emitter-collector short circuit is determined.

  Table 1 below shows a comparison between what can be detected by the conventional apparatus and what can be detected by the apparatus of the present invention regarding the failure of the semiconductor gas sensor 3 and other components in the gas detection apparatus. In Table 1, ◯ indicates a detectable failure, and X indicates a non-detectable failure.

In Table 1, * 1 to * 4 are as follows.
* 1) The conventional device is described under the conditions when the detection resistor R1 is used for methane measurement and the detection resistor R2 is used for CO measurement similarly to the device of the present invention.
* 2) In the conventional technology, this component failure is a failure in fail-out mode that cannot be detected and a failure alarm cannot be issued.
* 3) Since the voltage of the power supply Vcc is always applied to the plate electrode, a gas sensor of the type that cannot always apply the plate voltage will lead to sensor failure.
* 4) Even in the present invention, failure detection is not possible in normal air conditions (it can be detected during a gas concentration alarm)), but if the detection resistor R2 is used as a gas concentration detection resistor, it will be prevented from failing. Can do. In addition, when the gas concentration is detected in this state, a failure determination can be made.

  (Operation of Gas Detector) Next, details of the operation of the gas detector having the above-described configuration performed under the control of the microcomputer 10 will be described with reference to the flowchart of FIG.

  First, when the gas alarm is turned on, the output ports P1 and P2 of the microcomputer 10 are at the high (H) level, the output ports P4 and P5 are at the low (L) level, and the transistors Tr1 to Tr4 are all off. It is in a state.

  Next, a pulse-like heater voltage with alternating high (Hi) level and low (Lo) level is applied from the heater voltage supply circuit 11 to the heater 3a of the semiconductor gas sensor 3, and when the heater voltage is high (H) level. Then, the sensor output voltage Vrs0 input to the input port P3 is measured (step S1).

  Next, while the heater voltage is at the next high (H) level, a low (L) level control signal is output from the output port P1 to control the transistor Tr1 to be turned on (step S2). Then, the sensor resistor R1 is driven and the sensor output voltage Vrs1 input to the input port P3 at that time is measured (step S3). Next, while the heater voltage is at the high (H) level, a low (L) level control signal is output from the output port P2 to control the transistor Tr2 to be turned on (step S4). The resistor R2 is driven and the sensor output voltage Vrs2 input to the input port P3 at that time is measured (step S5).

  Next, it is determined whether or not the difference (Vrs1−Vrs2) of the measured sensor output voltage is within the range of the above-described minimum voltage V1 and maximum voltage V2 (V1 <(Vrs1−Vrs2) <V2) (step) S6). If the difference between the sensor output voltages is not within the range between the minimum voltage V1 and the maximum voltage V2 (No in step S6), then a failure alarm process is performed (step S7). In this failure alarm process, a PWM control signal of alternating high (H) level and low (L) level is output from the output port P4 to control the transistor Tr3 to be on, and the output port P5. This is done by outputting a higher (H) level control signal to turn on the transistor Tr4, causing the LED 14 to blink and a buzzer 15 to sound a failure alarm sound. Following step S7, the process returns to step S1.

  On the other hand, if the difference between the sensor output voltages is within the range between the minimum voltage V1 and the maximum voltage V2 (Yes in step S6), then the sensor output voltage Vrs0 is within the range between V3 and V4 (V3 <Vrs0 < V4) is determined (step S8). This determination is made within the range of the lower limit value and the upper limit value of the variation set in consideration of the variation of the semiconductor gas sensor 3 with respect to the sensor output Vrs0 measured when no voltage is applied to the plate electrode 3b in step S1. It asks whether or not there is. For example, when the heater voltage is 0.9 V, the sensor output voltage Vrs0 when no plate electrode is applied is ½ (0.45 V) of the heater voltage according to the specifications of the semiconductor gas sensor 3, and the lower limit value V3 = 0. .1V, upper limit value V4 = 0.8V.

  Next, if the sensor output voltage Vrs0 is not within the range between the lower limit value V3 and the upper limit value V4 (No in step S8), the process proceeds to step S7, and failure alarm processing is performed.

  On the other hand, if the sensor output voltage Vrs0 is within the range between V3 and V4 (Yes in step S8), then the failure alarm is canceled (step S9), and then the alarm determination process is performed (step S10). This alarm determination process is the same as the alarm process for the conventional gas concentration. That is, when the sensor output voltage Vrs1 measured in step S3 exceeds a preset alarm threshold value stored in the internal memory of the microcomputer 10, a high (H) level and a low (L) level are output from the output port P4. ) Outputs PWM control signals with alternating levels to control the transistor Tr3 to be turned on intermittently, and outputs a high (H) level control signal from the output port P5 to turn on the transistor Tr4. This is performed by blinking the LED 14 and generating a gas concentration alarm sound from the buzzer 15. Note that the blinking of the LED 14 at the time of failure detection and the failure alarm sound of the buzzer 15, and the blinking of the LED 14 at the time of gas concentration detection and the gas concentration alarm sound of the buzzer 15 can be in different forms so that they can be identified. Following step S10, the process returns to step S1.

  Thus, according to the first embodiment of the present invention, failure of the semiconductor gas sensor 3 and other components, for example, condition A (disconnection of the plate electrode of the semiconductor gas sensor 3), condition B shown in FIG. (Opening of detection resistor R1), Condition C (Opening of detection resistor R2), Condition D (Opening between emitter and collector of transistor Tr1), Condition E (Opening between emitter and collector of transistor Tr2), Condition F (Semiconductor Of the gas sensor 3 plate electrode to GND (ground)), condition G (short circuit of the semiconductor gas sensor 3 plate electrode to heater), condition H (short of the detection resistor R1), condition I (detection resistor R2 of Short), condition J (short-circuit between the emitter and collector of transistor Tr1) and condition K (transistor Tr2 Jitter - can determine a failure of each part of the short-circuit) between the collector, it is no longer a fail-out state as in the conventional apparatus.

  (Second Embodiment) Next, details of the above-described failure detection operation will be described with reference to the flowchart of FIG. In the first embodiment described above, the failure of the semiconductor gas sensor 3 and other components can be determined. In the second embodiment, the failure of the semiconductor gas sensor 3 and the failure of other components are identified. Is something that can be done. In addition, the structure of the gas detection apparatus in this 2nd Embodiment is the same as the structure of 1st Embodiment of FIG. 2, and only the flowcharts differ.

  First, when the gas alarm is turned on, the output ports P1 and P2 of the microcomputer 10 are at the high (H) level, the output ports P4 and P5 are at the low (L) level, and the transistors Tr1 to Tr4 are all off. It is in a state.

  Next, a pulse-like heater voltage with alternating high (Hi) level and low (Lo) level is applied from the heater voltage supply circuit 11 to the heater 3a of the semiconductor gas sensor 3, and when the heater voltage is high (H) level. Then, the sensor output voltage Vrs0 input to the input port P3 is measured (step S21).

  Next, while the heater voltage is at the next high (H) level, a low (L) level control signal is output from the output port P1 to control the transistor Tr1 to be turned on (step S22). Then, the detection resistor R1 is driven, and the sensor output voltage Vrs1 input to the input port P3 at that time is measured (step S23). Next, while the heater voltage is at the high (H) level, a low (L) level control signal is output from the output port P2, and the transistor Tr2 is controlled to be turned on (step S24). The resistor R2 is driven and the sensor output voltage Vrs2 input to the input port P3 at that time is measured (step S25).

  Next, it is determined whether or not the difference (Vrs1−Vrs2) of the measured sensor output voltage is within the range of the above-described minimum voltage V1 and maximum voltage V2 (V1 <(Vrs1−Vrs2) <V2) (step) S26). If the difference between the sensor output voltages is not within the range between the minimum voltage V1 and the maximum voltage V2 (No in step S26), it is then determined whether or not the measured sensor output voltages Vrs1 and Vrs2 are substantially equal (step). S27). If the measured sensor voltages Vrs1 and Vrs2 are not substantially equal (No in step S27), then it is determined that a circuit failure has occurred (step S28), and then failure alarm processing is performed (step S29). In this failure alarm process, a high-level (H) level and low-level (L) level alternating PWM control signal is output from the output port P4 to control the transistor Tr3 to be turned on intermittently. This is done by outputting a high (H) level control signal from the port P5 and controlling the transistor Tr4 to be turned on, causing the LED 14 to blink and a buzzer 15 to emit a failure alarm sound. Following step S29, the process returns to step S21.

  On the other hand, if the sensor output voltages Vrs1 and Vrs2 are substantially equal (Yes in step S27), then it is determined that the sensor has failed (step S30), and then the same failure alarm processing as in step S29 described above is performed (step S30). S31), and then returns to step S21.

  If the difference between the sensor output voltages is within the range between the minimum voltage V1 and the maximum voltage V2 (Yes in step S26), then whether the sensor output voltage Vrs0 is within the range between V3 and V4 (V3 <Vrs0 <V4) It is determined whether or not (step S32). This determination is made within the range of the lower limit value and the upper limit value of the variation set in consideration of the variation of the semiconductor gas sensor 3 with respect to the sensor output Vrs0 measured when no voltage is applied to the plate electrode 3b in step S21. It is asked whether or not there is, and is performed in the same manner as step S8 in the first embodiment.

  Next, if the sensor output voltage Vrs0 is not within the range between the lower limit value V3 and the upper limit value V4 (No in step S32), the process proceeds to step S27.

  On the other hand, if the sensor output voltage Vrs0 is within the range between V3 and V4 (Yes in step S32), then the failure alarm is canceled (step S33), and then an alarm determination process is performed (step S34). This alarm determination process is the same as the alarm process for the conventional gas concentration. That is, when the sensor output voltage Vrs1 measured in step S23 exceeds an alarm threshold value that is preset and stored in the internal memory of the microcomputer 10, a high (H) level and a low (L) level are output from the output port P4. ) Outputs PWM control signals with alternating levels to control the transistor Tr3, and outputs a high (H) level control signal from the output port P5 to turn on the transistor Tr4. This is performed by blinking the LED 14 and generating a gas concentration alarm sound from the buzzer 15.

  It should be noted that the LED 14 blinks when the circuit failure is detected and the buzzer 15 malfunction alarm sound, the LED 14 blinks and the buzzer 15 malfunction alarm sound when the sensor malfunction is detected, and the LED 14 blinks and the buzzer 15 gas concentration when the gas concentration is detected. The alarm sounds can be in different forms so that each can be identified. Following step S34, the process returns to step S21.

  As described above, according to the first embodiment of the present invention, it is possible to identify whether the failure is caused by the semiconductor gas sensor 3 or other components such as the detection resistors R1, R2 and the switching elements Tr1, Tr2. Can do.

FIG. 12 is a diagram showing waveforms of sensor output voltages Vrs1 and Vrs2 of the semiconductor gas sensor 3 that occur in each condition of failure in the sensor or other components. The dotted line indicates a normal waveform without a failure. In FIG.
(1) In the case of condition A (plate electrode is open): Vrs1 = Vrs2 = Vc, and the failure determination condition is Vrs1-Vrs2 ≦ V1, and it can be determined that a failure has occurred.
(2) Condition B (resistor R1 is open) or condition D (transistor Tr1 is open): Vrs1 = VH (heater voltage) / 2 and the failure determination condition is Vrs1-Vrs2 ≦ V1 It can be determined that a failure has occurred.
(3) Condition C (resistor R2 is open) or condition E (transistor Tr2 is open): Vrs2 = VH / 2, and the failure determination condition is Vrs1-Vrs2 ≧ V2, and a failure occurs Can be determined.
(4) In the case of condition F (the plate electrode is short-circuited to the ground): Vrs1 = Vrs2 = 0V, and the determination condition is Vrs1-Vrs2 ≦ V1, and it can be determined that a failure has occurred. .
(5) In the case of condition G (the plate electrode is short-circuited to the heater): Vrs1 = Vrs2 = VH (0.2 V or 0.9 V), and the judgment condition is Vrs1-Vrs2 ≦ V1, and the failure Can be determined.
(6) In the case of condition H (resistor R1 is short-circuited): Vrs1 = Vcc, and the failure determination condition is Vrs1-Vrs2 ≧ V2, and failure cannot be determined in normal air, but during gas concentration alarm The failure can be identified.
(7) When condition I (resistor R2 is short-circuited): Vrs2 = Vcc, and the failure determination condition is Vrs1-Vrs2 ≦ V1, and it can be determined that a failure has occurred.
(8) In the case of condition J (transistor Tr1 is short-circuited): the detection resistor R1 is always operating, and the failure determination condition is Vrs1-Vrs2 ≦ V1, or a sensor when no voltage is applied to the plate electrode Measure the output voltage.
(9) Condition K (when the transistor Tr2 is in a short state) The detection resistor R2 is always operating, and the determination condition is to measure the sensor output voltage when no voltage is applied to the plate electrode.

  Thus, the actual sensor output state for each failure state in Table 1 is shown in FIG. In conditions other than condition H (R1 short) and conditions J and K (Tr1 or Tr2 short) in Table 1, the failure state can be determined by applying the above range of determination values as they are. Moreover, about the conditions which cannot be discriminate | determined only by the said determination conditions, the state of failure detection or fail-out can be avoided by satisfying the following conditions.

  In the example of the condition D (when R1 is short-circuited) in FIG. 8, unless the sensor resistance value is close to the alarm state, (Vrs1-Vrs2) ≧ 1.765V is not satisfied, and failure detection cannot be performed in the normal state. .

  However, instead of measuring one detection gas with one detection resistor as in the past, if two detection resistors for one gas are optimally selected for the resistance value of the gas sensor, When the detection resistor R1 is short-circuited, the gas concentration can be measured with the detection resistor R2, and fail-out does not occur.

  Further, when the gas is detected and the sensor output voltage decreases and exceeds the maximum value V2, such as during an alarm, it is possible to notify the failure with an LED or the like regardless of whether an alarm is generated.

  Conditions J and K (when Tr1 or Tr2 is short-circuited) always apply a voltage to the plate electrode 3b of the semiconductor gas sensor 3, so the sensor output is measured at the timing when the transistors Tr1 and Tr2 are not turned on. Thus, the normal state and the failure state can be discriminated (FIG. 13).

  FIG. 13 is a diagram illustrating heater voltages, sensor output voltages Vrs0, Vrs1, and Vrs2 and the timing of data measurement points.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various deformation | transformation and application are possible.

  For example, in addition to the first and second embodiments, failure detection can be performed even if, for example, three or more detection resistors are used for measurement for one gas detection point. In that case, the upper and lower limits of the normal range are determined in consideration of the relationship between the detection resistance and the sensor output voltage. Except for the case where there are a plurality of failure locations of the gas detection device at the same time, it is possible to determine from the measured data whether the semiconductor gas sensor 3 is faulty or other circuit components are faulty. The sensor output voltage at the time of failure caused by the semiconductor gas sensor 3 is always constant, whereas when other circuit components fail, the sensor output differs for each detection resistor depending on the conditions. This is used to distinguish between sensor failures and circuit failures.

  Also, if the contents of the failure are stored in a non-volatile memory such as an EEPROM, or if there is a display means such as an LED, the failure is displayed (by changing the display method depending on the content of the failure, etc.) Useful for failure analysis.

1 is a basic configuration diagram of a gas detection device according to a first embodiment of the present invention. It is a circuit diagram which shows the specific structure of a gas detection apparatus. (Conventional example and first embodiment) It is a figure which shows the sensor output characteristic in the conventional gas detection apparatus. (Conventional example) It is a timing chart of the signal of each part in the conventional gas detection apparatus. (Conventional example) It is a timing chart of the signal of each part in the gas detection apparatus of the present invention. ((First Embodiment) It is a figure which shows the sensor output characteristic in the gas detection apparatus of this invention. (First embodiment) It is a figure which shows the sensor resistance value Rs in the gas detection apparatus of this invention, the sensor output voltage Vrs1 when switched to detection resistance R1, and the sensor output voltage Vrs1 when switched to detection resistance R2. (First embodiment) It is a figure which shows the threshold value (upper / lower limit value) applied to the failure determination in the gas detection apparatus of this invention, and a normal range. (First embodiment) It is a figure which shows the conditions of failure in the gas detection apparatus of this invention. (First embodiment) It is a flowchart explaining operation | movement of the gas detection apparatus of this invention. (First embodiment) It is a flowchart explaining operation | movement of the gas detection apparatus which concerns on the 2nd Embodiment of this invention. (Second Embodiment) It is a figure which shows the waveform of sensor output voltage Vrs1 and Vrs2 of the semiconductor type gas sensor 3 which generate | occur | produces in each condition of the failure in a sensor or another component. (First and second embodiments) It is a figure which shows the timing of a heater voltage, sensor output voltage Vrs0, Vrs1, and Vrs2, and a data measurement point. (First and second embodiments)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detection apparatus 3 Semiconductor type gas sensor 3a Heater 3b Plate electrode 10 Microcomputer (CPU)
DESCRIPTION OF SYMBOLS 10a Control means 10b Sensor output difference measurement means 10c No-plate sensor output measurement means 10d 1st failure determination means 10e 2nd failure determination means 10f 3rd failure determination means 11 Heater voltage supply circuit (heater power supply)
12 Detection resistance switching circuit (Detection resistance switching means)
13 Alarm circuit R1 Detection resistor (first detection resistor)
R2 detection resistor (second detection resistor)
Tr1 transistor (first switching element)
Tr2 transistor (second switching element)

Claims (6)

A gas detection device that detects a gas concentration using a semiconductor gas sensor having a heater to which a predetermined heater voltage is supplied from a heater power source and a plate electrode to which a predetermined plate voltage is supplied from a plate power source,
Detection resistor switching means for switching and connecting a first detection resistor or a second detection resistor having different resistance values between the plate power source and the plate electrode while a predetermined heater voltage is supplied from the heater power source. When,
Sensor output voltage of the semiconductor gas sensor when the first detection resistor is connected to the plate electrode and sensor of the semiconductor gas sensor when the second detection resistor is connected to the plate electrode Sensor output difference measuring means for measuring the difference in output voltage;
First failure determination means for determining a failure of the semiconductor gas sensor when the difference measured by the sensor output difference measurement means is not within a preset normal range;
A gas detection device comprising: The gas detection device according to claim 1,
The detection resistance switching means includes: a first switching element connected between the plate power supply and the first detection resistance; a second switching element connected between the plate power supply and the second detection resistance; And control means for supplying a control signal for turning on the first or second switching element,
The first failure determination means, when the difference measured by the sensor output difference measurement means is not within a preset normal range, the semiconductor gas sensor, the first detection resistor, the second detection resistance, It is determined that a failure occurs in any one of a detection resistor and the first switching element or the second switching element. The gas detection device according to claim 1 or 2,
A plate mark for measuring the sensor output voltage of the semiconductor gas sensor while a predetermined heater voltage is being supplied from the heater power source and when the predetermined plate voltage is not supplied to the plate electrode from the plate power source. Measuring sensor output measuring means;
A second failure that is determined as a failure of the first or second detection resistor when the sensor output voltage when the plate is not applied is not within a preset normal range measured by the sensor output measuring means when the plate is not applied A gas detection device further comprising: a determination unit. In the gas detection device according to any one of claims 1 to 3,
When a failure determination is made by the first or second failure determination means, the sensor output voltage of the semiconductor gas sensor when the first detection resistor is connected to the plate electrode, and the plate electrode When the sensor output voltage of the semiconductor type gas sensor when the second detection resistor is connected substantially matches, it is determined that the semiconductor type gas sensor has failed. A gas detection apparatus, further comprising: a detection resistor, a second detection resistor, a third failure determination unit that determines that one of the first switching device and the second switching device is failed. The gas detection device according to any one of claims 1 to 4,
In the gas detection device, a pulse-like heater voltage in which a high level and a low level are alternately supplied to the heater from the heater power source, and the detection resistance switching unit performs the detection resistance switching while the high level heater voltage is being supplied. The concentration of the first gas is detected by the sensor output voltage of the semiconductor gas sensor when the first detection resistor is connected between the plate power source and the plate electrode, and the low level heater voltage is supplied. While the second detection resistor is connected between the plate power source and the plate electrode by the detection resistor switching means, the first gas and the gas type of the semiconductor gas sensor are detected by the sensor output voltage. A gas detection device for detecting a concentration of a different second gas. In the gas detection device according to any one of claims 1 to 5,
The gas detection apparatus, wherein the first gas is methane and the second gas is CO.

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