JP5155027B2 - Gas leak alarm - Google Patents

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. 7 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. 6 is a diagram showing an example of a response characteristic of the catalytic combustion type gas sensor at the initial stage of energization, and FIG. 6A shows a 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) fluctuated 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. 6A, but in the case of sensor E, when DC driving is performed as shown in FIG. 6B. 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 is directed to the gas sensor element with respect to a gas sensor circuit having a circuit configuration that forms a bridge circuit together with a gas sensor element, a comparison element having a structure equivalent to the gas sensor element, and two resistors. In the gas leak alarm that conducts a gas leak alarm when the sensor output that is the output of the gas sensor circuit reaches an alarm judgment value when energized and heated, the gas sensor element as the gas sensor element after the start of energization to the gas sensor element The sensor output, which is the output of the gas sensor circuit, uses a gas sensor element having the same polarity as the steady alarm determination value determined in advance for the air base in the steady state, and the air base is in the steady state from the start of energization to the gas sensor element. the predetermined time until set as the determination value release time, the output of the gas sensor circuit when the gas concentration increases The direction in which the sensor output varies as the direction of the gas detection sensitivity, the sensor output is the output of the gas sensor circuit generates an alarm when the change in the direction of the gas detection sensitivity in the determination value release time, the determination The steady alarm determination value is set as a reference for alarm determination after the value release time has elapsed.

  In the gas leak alarm device according to claim 1, a predetermined time (for example, 20 seconds) until the air base is in a steady state after the start of energization to the gas sensor element is set as the determination value release time. During this determination cancellation time, an alarm is generated when the sensor output fluctuates in the direction of gas detection sensitivity, and after the determination value cancellation time elapses, the steady alarm determination value is set as a reference for alarm determination. Therefore, the normal gas leak alarm can be determined after the determination value cancellation time has passed, and the inspection gas can be detected by the fluctuation of the sensor output in the gas detection sensitivity direction within the determination value cancellation time.

  According to the gas leak alarm device of the first aspect, since the alarm determination based on the alarm determination value is not performed during the determination value release time after the start of energization, it is possible to suppress the false alarm due to the fluctuation of the air base of the gas sensor element. In addition, it only controls false alarms during the judgment value release time, and it is possible to check the operation with the inspection gas during the judgment value release time, reducing the time for installing the alarm device while avoiding false alarms. Can do.

  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 shown in FIG. 7 described above, and a detailed description of the structure thereof is omitted. However, the 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. Further, the storage unit 14 stores each data of a determination value release time Ti (for example, 20 seconds), which is a predetermined time for prohibiting alarm judgment by a steady alarm determination value 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 to start energization heating to the gas sensor 1 ′, and sets the determination value release time by setting the release flag. 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). During the judgment value release time, the sensor output is monitored for fluctuation, and an alarm is issued when the fluctuation is in the direction of gas detection sensitivity. In addition, when the determination value release time has elapsed, the control unit 11 performs a gas leak determination monitoring operation based on the sensor output (Vn) and the alarm determination value by interruption processing at a predetermined interval (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. 4 and 5. FIG. 4 is a flowchart of an initial process started immediately after the gas leak alarm device is turned on, and FIG. 5 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 '. In step S2, a 20-second timer is started based on the data of the determination value release time Ti in the storage unit 4. Next, the release flag is set to “1” in step S3, and the process proceeds to step S4.

  Next, the sensor output (Vn) is acquired in step S4, and it is determined in step S5 whether the sensor output has changed in the direction of gas detection sensitivity (in this example, the plus direction). If it does not change in the direction of the gas detection sensitivity, the process proceeds to step S7 as it is, and if it changes in the direction of the gas detection sensitivity, an alarm is output in step S6 and the process proceeds to step S7. In step S7, it is determined whether 20 seconds (determination value release time) has elapsed since the start of energization. If 20 seconds have not elapsed, the process returns to step S4. If 20 seconds have elapsed, the release flag is set to “0” in step S8. In step S9, the steady alarm determination value Vo is set in the alarm determination value register Vth as a reference for alarm determination, and the process returns to the main routine.

  In the interrupt process of FIG. 5, it is determined in step S11 whether the release flag is “1”. If it is “1”, the determination value release time is in effect, and the process returns to the original routine. If the release flag is not “1”, the determination value release time has elapsed, so the sensor output (Vn) is acquired in step S12, and the sensor output (Vn) is greater than or equal to the alarm determination value (Vth) in step S13. Determine whether. If the sensor output (Vn) is greater than or equal to the alarm determination value (Vth), an alarm is output in step S14 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 S15 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 S16 and the process returns to the original routine.

  FIG. 2 is a diagram showing an example of sensor output and alarm determination value setting states in the gas leak alarm of the embodiment. In the gas sensor 1 'of this embodiment, the air base greatly fluctuates to the positive side immediately after energization. That is, the sensor output fluctuates in the direction of gas detection sensitivity. Then, 20 seconds from the start of energization is set as a judgment value release time Ti, and within this judgment value release time Ti, alarm judgment is not performed by comparing the sensor output level and the alarm judgment value. No false alarms occur. After the determination value release time Ti elapses, the steady alarm determination value Vo is set as the alarm determination value (Vth) indicated by a broken line. The air base is in a steady state after 10 seconds, but is further in a steady state after 20 seconds.

  FIG. 3 is a diagram illustrating an example in which inspection gas is blown in the embodiment. The sensor output for the inspection gas changes in the air base in a direction different from the normal steady state (direction of gas detection sensitivity), and an alarm is generated by the change in the sensor output. Thereby, an inspection can be performed.

  In the embodiment, the gas detection sensitivity direction of the gas sensor 1 ′ is positive, and the steady alarm determination value Vo is also a positive value. However, depending on the circuit configuration, the sensor output and the steady alarm determination value Vo The polarity may be opposite to that of the embodiment.

  In the above embodiment, the case where the gas sensor 1 'is driven by direct current has been described. However, the same applies to the case where the gas sensor 1' is driven by alternating current. That is, in the case of the above-described embodiment and the above-described sensor A to sensor D in FIG. On the other hand, the gas sensor as shown in FIG. 6B by AC driving is not applied.

  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 the Example 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 an Example. 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)

Against the gas sensor circuit of the circuit arrangement constitute a bridge circuit together with comparative element and two resistors having a gas sensor element equivalent structure as the gas sensor element is heated by supplying an electric current to the gas sensor element, of the gas sensor circuit In the gas leak alarm that performs gas leak alarm when the sensor output that is output reaches the alarm judgment value,
As the gas sensor element, a gas sensor element in which the sensor output, which is the output of the gas sensor circuit after the start of energization to the gas sensor element, has the same polarity as the steady alarm determination value predetermined for the steady-state air base is used. ,
A predetermined time from the start of energization to the gas sensor element until the air base is in a steady state is set as a determination value release time,
The direction in which the sensor output, which is the output of the gas sensor circuit, fluctuates when the gas concentration increases is defined as the direction of gas detection sensitivity, and the sensor output, which is the output of the gas sensor circuit, during the determination value release time is the gas detection sensitivity. A gas leak alarm device, wherein an alarm is generated when the direction fluctuates, and the steady alarm determination value is set as a reference for alarm determination after the determination value release time elapses.

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