JP5239707B2 - Alarm - Google Patents

Description

  The present invention relates to an alarm device, and more particularly to a gas alarm device in which a gas sensor detects a detection target gas and issues an alarm.

Conventionally, semiconductor gas sensors are generally used for gas alarms. In addition, the current gas alarm is mainly one that detects gas leakage and incomplete combustion with one semiconductor gas sensor. As a method of detecting gas leakage and incomplete combustion with one semiconductor gas sensor, for example, a method of driving the gas sensor in two predetermined temperature ranges is employed.
To detect city gas leaks, methane gas, the main component of city gas, can be detected. To detect incomplete combustion, carbon monoxide gas generated during incomplete combustion is detected. do it. In order to detect methane gas (city gas) with a semiconductor gas sensor, the gas sensor temperature is raised to about 400 ° C., while in order to detect carbon monoxide, the gas sensor temperature may be lowered to around 100 ° C.

  Therefore, the gas alarm device having one semiconductor gas sensor repeats the high temperature driving for maintaining the gas sensor at a high temperature and the low temperature driving for maintaining the gas sensor at a predetermined cycle. Then, methane gas is detected at the timing of shifting from high temperature driving to low temperature driving, and carbon monoxide gas is detected at the timing of shifting from low temperature driving to high temperature driving. By doing so, it is possible to detect both gas leakage (methane gas) and incomplete combustion (CO gas) by one semiconductor gas sensor.

A gas alarm that operates in such a cycle needs to detect a gas leak within 60 seconds and issue an alarm as described later. That is, as described above, when the temperature of the gas sensor is changed with a period of 20 seconds, it is necessary to reliably detect methane gas within 2 to 3 periods.
By the way, in recent years, silicone has been frequently used for sealing materials, floor waxes, hair sprays, and the like. This is because silicone is said to be harmless to the human body. However, this silicone has a problem of reducing the sensitivity of the gas sensor (poisoning problem). Also, since sprays such as insecticides contain LP gas, a false alarm may be output when the gas sensor of the alarm device reacts to the LP gas. In order to prevent these problems, a method of improving the airtightness in the gas sensor by attaching an activated carbon filter or the like to the gas sensor has been adopted. However, this type of filter can improve the airtightness, but causes a new problem of deteriorating the responsiveness of the gas sensor to the detection target gas.

In order to solve such a problem, a system that extends the detection time when a predetermined level of gas is detected is known (see, for example, Patent Documents 1 and 2).
When the gas sensor detects a low-concentration detection gas at a gas detection timing that operates at a fixed period, the system continues the drive temperature and determines the presence or absence of gas from the detection level detected again after a predetermined time has elapsed. Is.

Incidentally, the detection delay time from when the gas leak alarm device comes into contact with the gas to be detected until the alarm is issued is set to 60 seconds in the inspection regulations of the Japan Gas Appliances Inspection Association (hereinafter JIA). An example of the response characteristics of the sensor output when this test is performed is shown in FIG. For example, when the gas sensor is driven at a constant period of 20 seconds, referring to this figure, even if the detection delay test is started at the worst timing for driving the gas sensor, in order to satisfy the inspection regulations of the JIA detection delay test, What is necessary is just to make it become the alarm point of 3300 ppm or less of the detection delay test 40 seconds.
Japanese Patent Laid-Open No. 10-283583 JP 2007-65716 A

  However, even if the high temperature driving period after detecting the low-concentration gas using the technique described in the above-mentioned patent document is extended from 5 seconds to 10 seconds, the detection delay test starts 45 seconds or less at 3500 ppm or less. Must be designed to be a warning point. In addition, the sensitivity of the semiconductor gas sensor varies depending on the season because it is greatly affected by the humidity of the surrounding environment. For example, if the gas sensitivity of the alarm is adjusted to the best (center value) in spring or autumn, the gas sensitivity tends to be more sensitive during the dry season in winter, while the gas sensitivity is higher in the summer when the humidity is high. Changes in the direction of desensitization. In other words, if the alarm concentration at the center value is set to 1 for a gas sensor that is greatly affected by seasonal changes, the alarm concentration changes at least 1/2 times in winter and twice at maximum in summer.

  Therefore, the adjustment value (center value) must be set to 1,750 ppm in order to use the above-described gas sensor and further adjust the alarm concentration not to exceed 3,500 ppm which is an alarm concentration for satisfying the JIA detection delay test. For this reason, the alarm concentration at the time of desensitization in summer is 3,500 ppm, and the alarm concentration at the time of sensitization in winter is 875 ppm.

  Further, according to JIA inspection regulations, there is a standard that “no alarm is issued at 1,000 ppm”. Therefore, this standard is not satisfied in the winter season described above. In addition, when the alarm point of the alarm device is at a low concentration, there is a problem that false alarms are easily generated for miscellaneous gas generated in a general household. There is a concern that the user may have distrust in the alarm if the alarm issues a false alarm even though no gas is leaking. If the user has such distrust, even when gas is actually leaking, the procedure may be delayed and a serious accident may be caused.

  The present invention has been made to solve such a situation, and its purpose is to provide a highly reliable alarm device that can suppress and prevent false alarms while maintaining a high concentration of alarm points. Is to provide.

Alarm of the present invention in order to achieve the above object, the heater driving a semiconductor gas sensor that converts the level of the electrical signal corresponding to the concentration of the detection target gas, the the semiconductor gas sensor 20 seconds as one cycle a sensor heater control unit that, there in alarm equipped and determining gas detecting means that detects the detection target gas when the level of the electric signal which the semiconductor gas sensor has output exceeds a predetermined first threshold value And an output change amount calculating means for obtaining a level change amount of the electric signal output from the semiconductor gas sensor per predetermined time, wherein the gas detecting means has a predetermined level of the electric signal output from the semiconductor gas sensor. The gas to be detected when the second threshold value or more and when the level change amount obtained by the output change amount calculation means is a predetermined third threshold value or more Determines that it has detected, the first threshold value exceeds a 2,000ppm set within the following ranges 6,250Ppm, a said second threshold said first threshold value lower numerical, and 3,300ppm below The third threshold is set to 1.35 or less, and the second threshold is set in accordance with the energization time measuring unit that measures the energization time of the alarm device, and the energization time measured by the energization time measurement unit. And a second threshold value correcting means for correcting .

The above alarm device detects the amount of change in gas concentration by calculating the sensor resistance change rate in the immediately preceding cycle when the gas concentration to be detected exceeds a predetermined concentration. It is possible to detect a gas leak that rapidly increases in gas concentration .

  The above-mentioned alarm device corrects the second threshold value for judging that the gas concentration has become a predetermined concentration or more with the energization time of the alarm device, so that the slow sensitization phenomenon due to long-term energization of the semiconductor gas sensor is prevented. Since the second threshold value is corrected so as to be kept constant, a false alarm can be prevented.

  Thus, even if the alarm device of the present invention is a gas sensor with poor responsiveness, if the gas concentration to be detected exceeds a predetermined concentration, the sensor resistance change rate in the immediately preceding cycle is calculated to change the gas concentration. Since the amount is detected, it is possible to detect a gas leak in which the gas leak concentration suddenly increases in a low concentration gas region. In addition, since the alarm device of the present invention corrects the operating point of the detection logic according to the energization time of the alarm device, it can suppress and prevent false alarms and false alarms in the detection logic at the conventional alarm points, and is highly reliable. The gas alarm can be provided to the user.

Hereinafter, an alarm device according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 and 2 show an embodiment of the present invention, and the present invention is not limited by these drawings.
FIG. 1 is a block diagram showing a schematic configuration of a gas alarm device having a fire alarm function according to an embodiment of the present invention. This gas alarm displays power supply unit 2 that converts AC 100V commercial power supply 1 into a DC voltage suitable for the operation of the alarm, the current status of the alarm, and the presence / absence of detection of gas, etc. by lighting, flashing or extinguishing A plurality of LEDs 3, a heat detection unit 4 that detects heat during a fire with a temperature sensor such as a thermistor, a sensor heater control unit 5 that generates two types of heater voltages for maintaining the gas sensor detection unit at a high temperature or a low temperature, a gas sensor This is a circuit mainly composed of a gas detector 6 that detects methane gas (gas leak) and CO gas (incomplete combustion), and outputs a voltage according to the detection state when a gas leak, incomplete combustion, and alarm unit failure is detected. When the detected voltage output unit 7, gas leakage, incomplete combustion, fire, alarm device failure, etc. is detected, the content detected for the user is output as sound (alarm sound, voice, etc.) from the speaker 8. The alarm sound output unit 9 that outputs power, the presence / absence of a fire alarm is output as a contact output, for example, the contact is normally turned off, and the non-voltage output unit 10 that outputs the contact ON when a fire alarm is activated, control that controls these various operations Unit 20 and an external storage unit 11 for storing history data such as adjustment data for each alarm device, setting values for switching operation modes, and status data when the alarm device issues an alarm, such as a threshold value for alarming ing.

  The control unit 20 includes a CPU such as a microcomputer, processes a detection signal from the heat detection unit 4 and the gas detection unit 6, and determines a fire and a gas leak, a fire detection unit 21, and a city gas detection unit 22. And CO gas detection unit 23, LED 3, alarm sound output unit 9, display control unit 24 and output control unit 25 for commanding / controlling various user interface functions of voltage / non-voltage output units 7, 10 and gas detection unit The sensor control part 26 which controls the heater etc. of the gas sensor which the 6 comprises is not shown is provided.

Further, the control unit 20 measures the energized time measuring unit 27 that measures the energized time, and the threshold correction that corrects the threshold for detecting gas leakage and incomplete combustion held in the external storage unit 11 as will be described in detail later. The unit 28 includes an output change amount calculation means 29 for obtaining a level change amount of the electric signal output from the gas sensor per predetermined time.
Specifically, the control unit 20 is a CPU with built-in A / D conversion (analog / digital conversion), and receives an analog signal output from the heat detection unit 4 or the gas detection unit 6, and converts the analog signal into the analog signal. It is configured to read with a corresponding digital value.

  Next, details of the sensor heater controller 5 and the gas detector 6 will be described with reference to FIG. The present embodiment uses a gas sensor that detects gas leakage and incomplete combustion. In order to detect two kinds of gases with high accuracy, the heater of the gas sensor is driven with two kinds of voltages, and gas leakage (methane gas) is detected on the high temperature side and incomplete combustion (CO gas) is detected on the low temperature side. In this embodiment, the heater of the gas sensor is driven and controlled for a total period of 20 seconds, with the high temperature side for 5 seconds and the low temperature side for 15 seconds.

Next, the responsiveness of the gas sensor when the detection delay test of the JIA inspection regulations of the gas alarm is performed will be described with reference to FIG. In this figure, the solid line is obtained by converting the gas concentration from the gas sensor output, and the dotted line indicates the rate of change in sensor resistance. From this figure, it can be seen that the gas concentration of the sensor is 3,300 ppm at the start of the detection delay test 40 seconds.
Therefore, if the second threshold value is set to 3,300 ppm or less, the first threshold value satisfies the standard of the alarm concentration test in which an alarm is issued when the first threshold value exceeds 1,000 ppm and is not more than 1,500 ppm. In addition, the center value may be adjusted to a value in excess of 2,000 ppm and not more than 6,250 ppm, taking into account the fact that the above-mentioned seasonal change is 1/2 to 2 times.

Regarding the change in sensor resistivity, a threshold value for detecting the presence or absence of gas leakage may be provided at a rate equal to or less than the change rate of 60 seconds from the start of the detection delay test. Therefore, the threshold value for determining the change rate may be set to 1.35 or less.
Next, the gas leak determination logic of the gas sensor will be described with reference to FIG. The gas sensor has a characteristic that the sensor resistance value decreases as the gas concentration increases. This figure, the sensor resistance value obtained from the sensor output in the current detection cycle in the gas leak detection point and R _n, is set to R _n-1 of the sensor resistance value obtained from the sensor output in the previous detection cycle. Incidentally, since the sensor resistance value can be obtained from the sensor output by a well-known method, the description thereof is omitted.

Now, city gas detector 22 compares the sensor resistance R _n and a first threshold value which is stored in the external storage unit 11 (sensor resistance in methane concentration which emits gas leak alarm) (S1). As a result, when it determines with it being smaller than a 1st threshold value, the control part 20 issues a gas leak warning by the warning sound by the warning sound output part 9 and the display of LED3 via the speaker 8 (S2). Then city gas detection unit 22, the sensor resistance when it is determined that R _n is larger than the first threshold value, comparing the sensor resistance R _n and a second threshold value (S3). If the sensor resistance R _n is determined to be greater than the second threshold value, the control unit 20 to maintain the monitoring state judges no gas leak (S4).

On the other hand, when the city gas detection unit 22 determines that the sensor resistance value R _n is smaller than the second threshold value, the control unit 20 obtains the change amount [R _n−1 / R _n ] by the output change amount calculation 29. If this is equal to or greater than a predetermined third threshold value that is a gas leak judgment criterion, it is determined that there is a gas leak (S5), and a gas leak alarm is issued (S4). Thereafter, the above-described procedure is repeated every time the reading of the gas sensor is updated.

  Thus, the alarm device of the present invention obtains the sensor resistance change rate in the immediately preceding cycle by the output change amount calculation 29 when the gas concentration to be detected becomes equal to or higher than a predetermined concentration even if, for example, a slow response sensor is used. Since the amount of change in gas concentration is detected, it is possible to detect a gas leak that suddenly increases the gas leak concentration in the low-concentration gas region, and to perform alarm concentration tests and detection delay tests that are JIA inspection regulations. Can be satisfied.

  In addition, the gas sensor has a tendency to be sensitized gently by long-term energization (for example, 75% alarm concentration becomes sensitized in 5 years). For this reason, the alarm device of the present invention adds an aging correction of 5% / year in the direction of desensitization of the sensor sensitivity as shown in FIG. 5 according to the energization time measured by the energization time measurement unit 27, The correction value correction unit 21 corrects the second threshold so as to be constant with respect to the gas concentration.

Therefore, since the alarm device of the present invention corrects the operating point of the gas detection logic according to the energization time of the alarm device, it can suppress and prevent false alarms and false alarms in the gas detection logic at the conventional alarm points, and has high reliability. It is possible to provide the user with a gas alarm device.
In addition, although the Example mentioned above described the detection logic of gas leak, if it replaces with the city gas detection part 22 and replaces it with the CO gas detection part 23, incomplete combustion can be detected reliably similarly. Is possible. Therefore, the same effect as the gas leak detection described above can be obtained for the CO gas detection.

  In the present embodiment, the gas sensor for detecting methane gas (city gas leak) and CO gas has been described. However, the alarm device of the present invention can of course be applied to a gas alarm device for detecting isobutane, LP gas, or the like. It has a great effect on practical use.

The block diagram which shows schematic structure of the gas alarm device provided with the fire alarm function which concerns on one Embodiment of this invention. The figure explaining the drive timing of the gas sensor driven with two types of voltages. The figure which shows an example of the gas sensor response at the time of a methane 12,500ppm detection delay test. The flowchart which shows the algorithm of the city gas detection in the gas alarm device of FIG. The figure which shows an example of an age correction | amendment of the 2nd threshold value with respect to alarm device energization time.

Explanation of symbols

1 Commercial power supply 2 Power supply unit 3 LED
4 Heat detection unit 5 Sensor heater control unit 6 Gas detection unit 7 Voltage output unit 8 Speaker 9 Alarm sound output unit 10 No-voltage output unit 11 External storage unit 20 Control unit 21 Fire detection unit 22 City gas detection unit 23 CO gas detection Unit 24 display control unit 25 output control unit 26 sensor control unit 27 energization time measurement unit 28 threshold correction unit 29 change amount calculation unit

Claims (1)

A semiconductor gas sensor that converts and outputs an electric signal level according to the concentration of the gas to be detected;
A sensor heater controller that drives the semiconductor gas sensor with a period of 20 seconds;
An alarm device comprising: gas detection means for determining that the detection target gas has been detected when the level of an electrical signal output by the semiconductor gas sensor is equal to or higher than a predetermined first threshold;
Furthermore, it comprises an output change amount calculating means for obtaining a level change amount of the electric signal output from the semiconductor gas sensor per predetermined time,
The gas detecting means has a level change amount obtained by the output change amount calculating means equal to or greater than a predetermined third threshold value when the level of the electrical signal output from the semiconductor gas sensor becomes equal to or greater than a predetermined second threshold value. It determines that it has detected the detection target gas when it is,
The first threshold is set within a range of more than 2,000 ppm and not more than 6,250 ppm,
The second threshold is a numerical value lower than the first threshold and set to 3,300 ppm or less,
Setting the third threshold to 1.35 or less;
Furthermore, an energization time measuring unit for measuring the energization time of the alarm device,
Second threshold value correcting means for correcting the second threshold value according to the energization time measured by the energization time measuring unit;
An alarm device comprising:

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