JP2009295093A - Gas leak alarm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce install time of a gas leak alarm while preventing misalarming due to variation of an air base caused when a gas sensor 1' of the gas leak alarm is energized and heated. <P>SOLUTION: The gas sensor 1' is used, such that a sensor output from start of energization of the gas sensor 1'until when the air base enters a stationary state has the same polarity with a stationary alarm determination value (Vo) determined for the air base in the stationary state. The stationary alarm determination value (Vo) determined for the air base in the stationary state, an increase value (ΔV) being an increment of an alarm determination value, and an initial time Ti up to when the air base of the gas sensor 1' enters the stationary state are stored in a storage unit 4. A power circuit 2 starts energization and heating of the gas sensor 1. A value obtained by adding the increase value (ΔV) to a peak value of the sensor output of the gas sensor 1 right after energization for heating is set as an alarm determination value. The alarm determination value is varied up to the stationary alarm determination value (Vo) within the initial time Ti. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas leak alarm device for energizing and heating a gas sensor element and performing a gas leak alarm when a sensor output of the gas sensor element reaches an alarm judgment value.

  Conventionally, in a gas leak alarm that detects a gas leak such as LP gas, a catalytic combustion type gas sensor element or a semiconductor type gas sensor element is used. FIG. 8 is a circuit diagram of a main part of a gas leak alarm using a conventional catalytic combustion type gas sensor element. The gas leak detection target gas of the gas leak alarm 100 is LPG and butane gas, and the gas sensor 1 has a catalytic combustion type gas sensor element 1a and a comparison element 1b.

  The catalytic combustion type sensor element 1a has a carrier layer made of an oxide of aluminum or silicon carrying palladium, platinum, rhodium or the like as an oxidation catalyst around a platinum wire. The platinum wire functions as a heater wire that maintains a temperature suitable for the contact reaction of the support layer. When a contact reaction occurs in the support layer, the electric resistance of the platinum wire changes due to the heat. Normally, such a catalytic combustion type sensor element 1a constitutes a bridge circuit together with a comparison element 1b and resistors r1, r2 having the same structure as the catalytic combustion type sensor element 1a except that it does not have an oxidation catalyst.

  The bridge circuit is energized from the power supply circuit 2 under the control of the CPU 10, and the bridge circuit detects a change in the electric resistance of the platinum wire as a sensor signal V. Then, the CPU 10 compares the sensor signal V with a preset alarm determination value Vth, and when the voltage signal V exceeds the alarm determination value Vth, the alarm generation circuit 3 sounds an alarm buzzer or the like.

  Here, the gas sensor 1 is used by heating up to about 300 to 500 ° C. by energizing the catalytic combustion type sensor element 1a and the comparison element 1b. The resistance values of the catalytic combustion type sensor element 1a and the comparison element 1b when there is no target gas also fluctuate.

  FIG. 7 is a diagram showing an example of the response characteristic at the initial stage of energization of the catalytic combustion type gas sensor, and FIG. 7A shows the case where the gas sensor is DC driven. The sensor A, the sensor B, and the sensor C have the air base resistance value changed immediately after energization, and the sensor output (mV) is changing in the positive direction. In about 10 seconds, the sensor output becomes 0 mV and stabilizes. The sensor D slightly varies in the positive direction and gradually becomes 0 mV and becomes stable. In addition, the sensor output (mV) fluctuates in the negative direction immediately after energization, and the sensor output becomes stable at 0 mV in about 10 seconds. On the other hand, the alarm determination value Vth is set to 30 mV, for example. In the case of the sensor A, sensor B, and sensor C, the sensor output exceeds the alarm determination value Vth immediately after energization, and a false alarm is generated. When these sensors are AC driven, sensors A to D have the same characteristics as in FIG. 7A, but in the case of sensor E, when DC driving is performed as shown in FIG. 7B. The characteristic of the negative direction of is determined and fluctuates in the positive direction.

As described above, the contact combustion type gas sensor 1 may generate a false alarm because the air base resistance value fluctuates at the start of energization heating regardless of direct current drive or alternating current drive. Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 2004-102652 (paragraph [0028], etc.), an initial ringing prevention time is provided immediately after the power is turned on, or an energization initial ringing prevention circuit is provided to deal with a false alarm. .
JP 2004-102652 A

  If an initial ringing element time is provided or a current-carrying initial ringing prevention circuit is provided as in conventional gas leak alarms, for example, it takes time to check the operation by blowing inspection gas. There is a problem that it takes time.

  An object of the present invention is to prevent a false alarm immediately after energization in a gas leak alarm using a gas sensor element and to shorten the time when the alarm is installed.

  The gas leak alarm device according to claim 1, wherein the gas sensor element is heated by energizing the gas sensor element, and performs a gas leak alarm when the sensor output of the gas sensor element reaches an alarm judgment value. Immediately after the start of energization to the gas sensor element, the sensor output after the start of energization to the gas sensor element has the same polarity as the steady alarm determination value determined in advance for the air base in the steady state. The alarm determination value is set to a value whose absolute value is larger than the peak value of the sensor output immediately after the energization is opened, and the alarm is set for a predetermined time from the start of energization until the air base is in a steady state. The determination value is changed to the steady alarm determination value.

  In the gas leakage alarm device according to claim 1, the peak value of the sensor output immediately after the start of energization of the gas sensor element may be detected immediately after the start of energization or may be a known peak value set in advance. Then, the alarm determination value serving as the alarm determination standard is set to a value having an absolute value larger than the peak value. Further, the set alarm determination value is changed to the steady alarm determination value during a predetermined time (for example, 10 seconds) from the start of energization until the air base is in a steady state. Therefore, after a predetermined time when the air base is in a steady state, a normal gas leak alarm can be determined, and the alarm determination value is set so that the absolute value is larger than the sensor output within the predetermined time. Therefore, it is possible to suppress false alarms in the initial stage immediately after the start of energization. Note that the alarm determination value may be changed gradually with time, or may be changed in stages.

  According to the gas leak alarm device of the first aspect, the alarm determination value in the initial stage after the start of energization is set to a value whose absolute value is larger than the peak value immediately after energization. The sensor output does not reach the alarm judgment value and can suppress false alarms. Moreover, it is only possible to control misreporting at the initial stage, and it is possible to check the operation with the inspection gas after a predetermined time, and it is possible to reduce the time for installing the alarm device while avoiding misreporting.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a main circuit block diagram of a gas leak alarm of the present invention, and this gas leak alarm uses LP gas as a detection target gas. The configuration of the gas sensor 1 'is the same as that of FIG. 8 described above, and a detailed description of the structure thereof is omitted, but this gas sensor 1' is used in the manufacture of the gas leak alarm as described later. It was selected by measuring the characteristics of

  The control unit 11 is composed of, for example, a microcomputer including a CPU 11a (central processing unit), a ROM 11b (read-only memory), and a RAM 11c (optional read / write memory). The CPU 11a executes various processes including control according to the present embodiment in accordance with a control program stored in the ROM 11b. The RAM 11c is used as a working area for the CPU 11a to execute various processes, and stores programs and the like as appropriate.

  The alarm output circuit 2 includes an audio output circuit and a buzzer for generating an alarm sound and an alarm audio message for outputting a gas leak alarm in response to an alarm signal output from the control unit 11.

  The memory | storage part 4 is comprised by EEPROM (Electrically Erasable and Programmable ROM) etc., for example, and has memorize | stored the preset steady warning determination value Vo. This steady alarm determination value Vo is a value set by measuring the characteristics of the gas sensor 1 ′ at the time of manufacturing the gas leak alarm, and the gas sensor 1 ′ reaches a predetermined temperature in the absence of the detection target gas. The air base resistance is a value set higher by a predetermined voltage than the sensor output (0 mV) in a stable steady state. The storage unit 14 stores data of an increment value ΔV (for example, 15 mV) for increasing the alarm determination value and an initial time Ti (for example, 10 seconds) that is a predetermined time from the start of energization.

  Here, the gas sensor 1 'is selected in accordance with the fluctuation characteristics of the sensor output immediately after the start of energization, and the polarity of the sensor output is the same as the steady alarm judgment value of the gas sensor 1'. .

  With the above configuration, the gas leak alarm operates as follows. The control unit 11 drives the power supply circuit 2 by turning on the power and starts energization heating to the gas sensor 1 ′. In this embodiment, the gas sensor 1 'is DC driven. Further, the output voltage of the gas sensor 1 ′ is taken in as a sensor signal (V). Further, the sensor signal (V) is A / D converted by a circuit (not shown) and internally processed as a sensor output (Vn). Then, immediately after the energization heating, the alarm determination value is set by the peak value of the sensor output, and the alarm determination value is changed to the steady alarm determination value Vo as time elapses within the initial time Ti. Moreover, the control part 11 performs the monitoring operation | movement of a gas leak determination with a sensor output (Vn) and an alarm determination value by the interruption process of predetermined intervals (for example, 2 seconds).

  Next, the operation of the main part of the gas leak alarm according to the embodiment will be described based on the flowcharts of FIGS. 5 and 6. FIG. 5 is a flowchart of an initial process started immediately after the gas leak alarm device is turned on, and FIG. 6 is a flowchart of an interrupt process started at a predetermined interval for performing a monitoring operation. First, in the initial process, the power supply circuit 2 is controlled in step S1 to start energization of the gas sensor 1 ', and a 10-second timer is started based on the data of the initial time Ti in the storage unit 4 in step S2.

  Next, an initial peak (Vp) of the sensor output is detected in step S3. For detection of this peak, the maximum value of the sensor output of a predetermined number of samples is obtained. Next, in step S4, the increment value ΔV (15 mV) is added to the peak (Vp), and the calculation result is set in the alarm determination value register Vth. Next, in step S5, the difference between the value of the register Vth and the steady warning determination value Vo is divided by the initial time Ti (10 seconds), and the calculation result is set in the decrease value register δv. The decrease value δv is data for decreasing the alarm determination value. In this example, the alarm determination value is updated every second.

  Next, in step S6, it is determined whether it is the update time of the alarm determination value. If the determination is NO, the process proceeds to step S8. If the determination is YES, in step S7, the current alarm determination value (Vth) is decreased. δv is subtracted and the calculation result is set in the alarm determination value register Vth, and the process proceeds to step S8. In step S8, the elapse of 10 seconds from the start of energization is monitored, and when 10 seconds elapses, in step S9, the current alarm determination value (Vth) is set to the steady alarm determination value Vo, and the process returns to the main routine.

  In the interrupt process of FIG. 6, the sensor output (Vn) is acquired in step S11, and it is determined in step S12 whether the sensor output (Vn) is greater than or equal to the alarm determination value (Vth). If the sensor output (Vn) is greater than or equal to the alarm determination value (Vth), an alarm is output in step S13 and the process returns to the original routine. If the sensor output (Vn) is not equal to or greater than the alarm determination value (Vth), it is determined in step S14 whether the alarm is currently being output. If the alarm is not being output, the process returns to the original routine and the alarm is being output. If so, the alarm is canceled in step S15 and the process returns to the original routine.

  Drawing 2 is a figure showing Example 1 of a setting state of a sensor output and a warning judgment value in a gas leak alarm of an embodiment. In the gas sensor 1 'of Example 1, the air base greatly fluctuates to the positive side immediately after energization, and the initial peak (Vp) detected in Step S3 is +110 mV. Then, the increment value ΔV (15 mV in this example) is added to this peak (Vp), and an initial value of the alarm judgment value (Vth) indicated by a broken line is set. The alarm determination value (Vth) gradually decreases until 10 seconds have elapsed from the start of energization, and is set to the steady alarm determination value Vo when 10 seconds have elapsed. Therefore, no error is reported in 10 seconds in the monitoring process of the interrupt process. After 10 seconds, the air base is in a steady state.

  FIG. 3 is a diagram illustrating an example in which inspection gas is sprayed in the first embodiment. The sensor output for the inspection gas is masked by the alarm judgment value (Vth) for the first 9 seconds. However, the inspection gas remains even after 10 seconds have elapsed, and the sensor output for this inspection gas becomes higher than the steady alarm determination value Vo, and an alarm is issued. Thereby, an inspection can be performed.

  FIG. 4 is a diagram illustrating a second example of the setting state of the sensor output and the alarm determination value in the gas leak alarm according to the embodiment. In the second embodiment, the gas sensor 1 ′ is the same as the first embodiment, but the alarm judgment value until 10 seconds elapses from the start of energization is reduced stepwise (for example, every 2 seconds). Also in this case, the sensor output for the inspection gas is masked by the alarm determination value (Vth) for the first 9 seconds, but the sensor output becomes higher than the steady alarm determination value Vo due to the remaining inspection gas, and an alarm is issued. . Thereby, an inspection can be performed.

  In the above embodiment, the case where the gas sensor 1 'is driven by a direct current has been described. That is, Examples 1 and 2 are the same in AC driving. On the other hand, the present invention can also be applied to a gas sensor as shown in FIG.

  Further, in the embodiment, the gas sensor 1 ′ is selected from the characteristics of the gas sensor. However, the characteristics such as the gas sensor 1 ′ in this embodiment depend on the adjustment of the platinum coil resistance value of the gas sensor, the element size, the material, and the like. It is possible to make adjustments, and those adjusted in this way may be used.

  In the above embodiment, an example of a catalytic combustion type gas sensor has been described, but a semiconductor type gas sensor or a hot wire semiconductor type gas sensor can also be applied.

It is a principal part circuit block diagram of the gas leak alarm of this invention. It is a figure which shows Example 1 of the setting state of the sensor output and alarm determination value in the gas leak alarm of embodiment. It is a figure which shows the example of the sensor output with respect to the inspection gas in Example 1. FIG. It is a figure which shows Example 2 of the setting state of the sensor output and alarm determination value in the gas leak alarm of embodiment. It is a flowchart of the initial process started immediately after power-on of the gas leak alarm device in embodiment. It is a flowchart of the interruption process for performing the monitoring operation | movement of the gas leak alarm device in embodiment. It is a figure which shows an example of the response characteristic of the electricity supply initial stage of a contact combustion type gas sensor. It is a principal part circuit diagram of the gas leak alarm using the conventional catalytic combustion type gas sensor element.

Explanation of symbols

1 'gas sensor 2 power supply circuit 3 alarm generation circuit 4 storage unit 11 control unit

Claims (1)

In the gas leak alarm device that conducts a gas leak alarm when the gas sensor element is energized and heated, and the sensor output of the gas sensor element reaches an alarm judgment value,
As the gas sensor element, the sensor output after the start of energization to the gas sensor element is a gas sensor element having the same polarity as a steady alarm judgment value predetermined for a steady-state air base,
Immediately after the start of energization of the gas sensor element, the alarm determination value is set to a value whose absolute value is larger than the peak value of the sensor output immediately after the energization is opened and until the air base is in a steady state from the start of energization. A gas leak alarm device characterized by changing the set alarm judgment value to the steady alarm judgment value for a predetermined time.

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