JPH0587761A - Gas detector - Google Patents

Abstract

PURPOSE:To obtain a gas alarm device operated over one year by a dry battery. CONSTITUTION:A standby mode is provided to a control integrated circuit and, after the completion of a control job, a clock is stopped to allow the circuit to stand by and the circuit is started at every sec by the signal of a multivibrator. The LED 8 for the display of a power supply is subjected to pulse driving at a cycle of 10msec/sec to suppress the power consumption of the LED 8. Further, a buzzer BUZ is driven at cycle of 100msec/sec and the frequency of a buzzer driving signal is swept around resonance frequency to be resonated at any point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector used for detecting gas leakage, incomplete combustion, early fire and the like.

[0002]

2. Description of the Related Art The inventor has proposed to drive a metal oxide semiconductor gas sensor in a pulsed manner with an operating cycle of 10 msec / sec or the like (Japanese Patent Laid-Open No. 316/652). The inventor has also proposed a structure of a pulse drive type gas sensor in which a heat insulating glass layer is provided on an insulating substrate and a heater and a metal oxide semiconductor film are laminated on the heat insulating glass layer (Japanese Patent Laid-Open No. 1-1999). 206, 252). Furthermore, in addition to this,
The gas sensor using undercut etching of silicon described in No. 2-2438 and the like is also suitable for pulse driving.

The inventor is developing a battery-powered gas leak alarm using pulse driving of a gas sensor. When the gas sensor is pulse-driven, the power consumption can be reduced to, for example, about 1 mW. For example, when operating a gas leak alarm with four AA batteries, the effective power consumption is 2
If it is set to about mW, the gas leak alarm can be operated for one year or more. However, the power consumption of the microcomputer (4 bit one-chip microcomputer) used for controlling the gas sensor is about 20 mW. The power consumption of the LED (light emitting diode) used for power supply display is about 10 mW. Therefore, even if the power consumption of the gas sensor is about 1 mW, a battery-powered gas leak alarm cannot be realized unless the power consumption of the microcomputer and the LED is reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to realize a battery-powered gas detection device by suppressing the power consumption of a control integrated circuit of a gas sensor and a power supply display LED.

[0005]

According to the present invention, an integrated circuit for pulse-driving a gas sensor and processing a signal of the gas sensor is provided. The integrated circuit stores a control program for a gas detection device and is integrated in the integrated circuit. A standby mode in which the clock inside the circuit is stopped and a normal operation mode in which the clock normally operates are provided, and the integrated circuit is shifted to the standby mode after the control program of the gas detection device is completed. Is provided to shift the integrated circuit from the standby mode to the normal operation mode by the signal of the oscillation circuit, and further, a power supply display LED is provided and the LED is turned on in a pulsed manner at the LED drive duty ratio. Is characterized by.

As the integrated circuit, an ASIC such as a gate array or the like may be used in addition to the microcomputer. In the case of a microcomputer, for example, the standby mode may be one that stops the CPU clock. Some microcomputers have a HALT that stops only the CPU clock in standby mode.
Two modes are provided, a mode and a STOP mode in which the clock is stopped in the entire microcomputer, but either mode may be used.

[0007]

When the gas sensor is pulse-driven, the processing time of the integrated circuit is short and most of the time the integrated circuit is idle. Some integrated circuits have a standby mode, and the power consumption in the standby mode is extremely small. Therefore, the power consumption of the integrated circuit can be reduced by waking up the integrated circuit for a necessary time and sleeping the integrated circuit in the standby mode at other times. For example, if an integrated circuit with a power consumption of 20 mW in the normal operation mode is woken up at an operation cycle of 20 msec / sec, the power consumption will be 0.4
It becomes mW.

Although the power consumption of the LED is about 10 mW, the inventor has confirmed that it can be seen even when the LED is momentarily turned on with a pulse width of about 10 msec. Therefore, if the LED is driven at a cycle of about 10 msec / 10 sec, the power consumption becomes a little over 10 μW.

Therefore, if this is done, the integrated circuit and LE are
The power consumption at D can be reduced to, for example, 0.5 mW or less, and the power consumption of the entire gas detection device can be reduced to a value suitable for battery driving.

[0010]

EXAMPLE An example will be described by taking a gas leak alarm for LPG as an example. In FIG. 1, reference numeral 2 is a microcomputer, here a 4-bit one-chip microcomputer (TMP47C440, TMP47C44 manufactured by Toshiba Corporation).
0 is the product name, OTP version (write once R
(Equipped with OM) was used. The OTP version was used
This is because the ROM mask is unnecessary and the cost is reduced. Reference numeral 4 is a metal oxide semiconductor gas sensor, 6 is an AA dry battery × 4 6V power source, and 8 is, for example, a red power source display LE.
D and 10 are oscillation circuits composed of a multi-vibrator for WAKE / UP of the microcomputer 2, and here, 1
The multi-vibrator of Hz was used. T1 and T2 are transistors, Z1 is a 4.5V Zener diode, 1
2 is a 4 MHz ceramic oscillator. BUZ is a piezo buzzer for alarm of gas leak, and here an inexpensive two-terminal separately excited buzzer was used. The resistance in the figure shows the resistance value in Ω unit, and the capacity is entered in the capacitor. R1 is the load resistance of the gas sensor 4, R2 is the resistance for detecting the power supply voltage, and R3 is L
A current limiting resistor for ED8, R4 is a control resistor for buzzer BUZ. 14 is, for example, a booster coil of 10 mH, and the voltage applied to the buzzer BUZ is several V when the coil 14 is not provided.
The voltage is increased from about 10 to several tens of volts to increase the volume. The terminals K00 to R43 of the microcomputer 2 are input ports for mode determination, K00 to K02 are ports for determining margins N and P of alarm levels with respect to reference values S and A defined in learning, and K03 to R81 are sensors. Ports for determining signal sampling points, R82 and R83 are ports for determining the drive pulse width of the gas sensor. Also R4
2 and R43 are ports for determining the learning cycle of the reference values S and A. The operating conditions of the embodiment differ depending on the input to these ports, but the conditions are shown here using the case of standard input as an example. FIG. 2 shows a block diagram of the microcomputer 2. A control program for the gas detection device is stored in the program memory (ROM) portion of the figure.

FIG. 3 shows a cross section of the gas sensor 4, and FIG. 4 shows a plane of the gas sensor 4. In the figure, 20 is an insulating substrate made of alumina or the like, 21 is a heat insulating glass layer, and here a film thickness of 100
μm, 22 is an iridium oxide film (film thickness 0.5 μm,
0.2 × 0.2 mm square), a heater film 23 is a tin oxide film (0.2 × 0.2 mm square) having a thickness of 10 μm,
24 is an insulating alumina film (film thickness 1 μm). Two
Reference numerals 5 and 25 are gas sensor electrodes, and 26 and 26 are heater electrodes. The type of gas sensor is not limited to this, and, for example, a Japanese Patent Publication No. 62-2438 may be used.

The operation of the embodiment will be described with reference to FIGS. The gas sensor 4 is driven, for example, once every second for 8 ms (the driving duty ratio of the gas sensor is 8/1000).
Then, the sensor temperature changes as shown by the solid line in FIG.
The sensor output with respect to has a waveform similar to the sensor temperature, and changes like the chain line in FIG. The sampling point of the sensor output is the port K03 of the microcomputer 2,
Determined by the 3-bit signal input to R80 and R81, LPG
In the case of or methane, sampling is performed at the last 1 msec of 8 msec, for example. The response waveform of the sensor 4 to gas differs depending on the type of gas. For example, when CO is detected for detecting incomplete combustion or initial fire, the output of the first 1-2 msec of 8 msec is sampled. The power consumption of the sensor 4 in the pulse drive of 8 msec / sec is about 1 mW. The pulse width is, for example, about 0.5 ms to 1 second, and the pulse period is, for example, about 0.1 seconds to 20 seconds. The drive duty ratio of the gas sensor 4 is, for example, 1/20 to 1/2000. These conditions are determined by the power consumption and the allowable range of waiting time until detection. From the characteristic of the gas sensor, in the case of methane detection, the pulse width is set to be long, for example, about 1 second, and the LP
When detecting G, CO, alcohol, etc., a short pulse width of about 8 ms is sufficient.

The sensor 4 responds to the voltage drop of the battery power source 6.
The drive pulse width of is variable. Therefore, the voltage fluctuation is detected from the current flowing through the resistor R2 connected in series with the 4.5V Zener diode Z1, and the pulse width from the output port P10 of the microcomputer 2 is changed accordingly to control the transistor T1. .. That is, the fluctuation of the power supply voltage is detected from the current of the resistor R2, the driving pulse width of the sensor 4 is changed by the transistor T1, and the sensor temperature at the time of sampling the sensor output is made constant.

The output voltage of the transistor T1 is set to the port VA.
It is input from REF and used as the reference voltage (full scale) for A / D conversion in addition to the resistance ladder circuit. The sampled sensor output is input from the AIN0 terminal of the microcomputer 2 and A / D converted into 8 bits. Since the full scale of the A / D conversion is determined by the output voltage of the transistor T1, the change in the sensor resistance can be A / D converted regardless of the fluctuation of the power supply voltage. VARE to the resistance ladder circuit
The input current from the F terminal is large, but this input is 8
Only msec / sec occurs. This is because the input voltage to VAREF also becomes 0 when the gas sensor 4 is not driven.

FIG. 10 shows the drive waveform of the LED 8. LE
The power consumption of D8 is about 10 mW in continuous lighting including the resistance R3. The LED 8 can be seen to be illuminated even if it is momentarily illuminated with a pulse width of, for example, about 10 msec. Therefore, the LED 8 is pulse-driven to save power. A preferable driving condition is a pulse width of 5 to 100 m.
Second, the pulse cycle is about 1 second to 1 minute, and here, it is driven at 10 msec / 10 sec (LED driving duty ratio 1/10).
00). Since the power consumption during driving is increased to increase the brightness of the LED 8, the LED 8 and the resistor R of the power display unit
The power consumption in 3 was a little over 10 μW.

11 to 13 show drive waveforms of the piezo buzzer BUZ. The power consumption of the buzzer BUZ and its peripheral circuits is about 15 mW in the case of continuous driving. Therefore, when a gas leak alarm is issued, it is driven at a cycle of, for example, 100 msec / sec as shown in FIG. 12, and when the power supply voltage drops, it is driven at a period of, for example, 10 msec / sec as shown in FIG. By changing the width of the driving pulse, it is possible to distinguish between gas leakage and decrease in the power supply voltage, and pulse driving saves power consumption. Here, a large duty ratio is assigned to the gas leak signal, which is a more important signal, and a small duty ratio is assigned to a power supply voltage drop signal that is of low importance and must be notified for a long time until the battery is replaced. The notification of the gas leak signal may be performed by continuously ringing the buzzer BUZ at a duty ratio of 1.

Since an inexpensive separately excited piezo buzzer was used for the buzzer BUZ, the resonance frequency (here, about 4 KHz) was used.
Drive pulse must be sent. This resonance frequency changes with temperature and the like. Therefore, as shown in FIG. 11, the drive frequency f from the output port P12 of the microcomputer 2 is swept in the range of 4 KHz ± 0.2 KHz to pass the resonance frequency, for example, at a cycle of 10 msec. The sound pressure at a point 1 m in front of the buzzer BUZ is 85 dB at resonance.
Therefore, it increased by about 20 dB as compared with the non-resonance state.

The operation algorithm of the embodiment will be described with reference to FIGS. The embodiment works with the algorithm of FIG. Here, the time required to process the job shown on the right side of FIG. 5 is usually about 20 msec. Therefore, after the job is finished, the program activates a standby instruction (sleep instruction), and the microcomputer 2
To the standby state. In this state, the power consumption is reduced from 20 mW in the normal operation mode to about 3 μW. Since the clock of the microcomputer 2 is stopped in the standby mode and the static RAM is used as the RAM, no data is lost even if the clock is stopped. In the embodiment, since the gas sensor 4 is pulse-driven at 8 msec / sec, the microcomputer 2 is activated every second. For this purpose, the multivibrator 10 is used to trigger the microcomputer 2 by the edge of a pulse having a cycle of 1 second. As a result, the effective power consumption of the microcomputer 2 is about 0.4 mW. The power consumption of the oscillator circuit 10 is about 80 μW. For these reasons, the effective power consumption of the gas detection device is about 1.5 mW.

As shown in FIG. 5, in the embodiment, the alarm level of gas leak is determined from the reference value determined by learning, and the relative value is detected. Of course, the alarm level may be set by an external resistor or the like. As the reference value, two kinds of a steady value of the gas sensor output and an average value of the gas sensor output are used, and this is subjected to statistical processing over a period of about one month to obtain the reference value. When the steady value of the sensor output is S and the average value is A,
An alarm level is obtained by multiplying this by a constant N or P, and an alarm is issued when the sensor output exceeds any one of N · S and P · A.

The sampling program of the steady value S operates, for example, in a 5-minute cycle, and the sampling program of the average value A operates in a 5-hour cycle, for example. FIG. 6 shows a sampling program for the steady value S, and FIG. 7 shows a sampling program for the average value A. The steady value S is used as a reference value when the sensor output is stable, for example, at night without using gas, and the rate of change of the sensor output in 5 minutes is 5 as shown in FIG. The steady state value S1 is sampled under the condition that the state of less than% continues for 6 hours and the change of the sensor output within 5 hours is within ± 30%. The sampled steady value S1 is statisticized to be a steady value S. An initial learning mode is provided in order to speed up the statistic at the beginning of use, and the integration speed from S1 to S is increased for one week from the start of use. In the sampling program of the average value A (Fig. 7), the gas sensor output is randomly read every 5 hours, and this is statistically analyzed to obtain the average value A.
To calculate.

FIG. 8 shows a program for reducing the power supply voltage. This program is inserted into the job shown in FIG. 5 and executed once per second. The decrease in the power supply voltage is detected from the current flowing through the resistor R2, and the pulse width used for pulse driving of the gas sensor 4 is changed accordingly. For this purpose, the output port P10 is used. When the power supply voltage further drops to, for example, 4.5 V or less, the buzzer BUZ is driven at a cycle of 10 msec / sec to request battery replacement. The operating lower limit voltage of the microcomputer 2 here is 4V. The processing when the power supply voltage drops may be changed as follows, for example. When the voltage of the Zener diode Z1 is set to 4 V and the power supply voltage approaches the operation lower limit of the microcomputer 2, the buzzer BUZ is driven at a cycle of 10 msec / sec to request battery replacement. At this time, the power supply voltage has dropped to near the lower limit of operation, so the transistor T1 is stopped and the gas sensor 4
To stop. Further, the power supply display LED 8 is also stopped. That is, only a signal for lowering the power supply voltage is generated by the buzzer BUZ, gas detection and power supply display are terminated, and battery replacement is requested. This intends to use the battery power source 6 to the limit. On the other hand, the above-mentioned processing is to seek replacement of the battery 6 with a margin and normally try to drive the gas leak alarm until the battery 6 is replaced.

Although a specific program and a specific numerical value are shown here, the present invention is not limited to this.

[0023]

According to the present invention, an integrated circuit and a power source display LE are provided.
The power consumption of D is suppressed, and the gas detection device can be driven by the battery.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a gas detection device according to an embodiment.

FIG. 2 is a block diagram of a microcomputer used in an embodiment.

FIG. 3 is a cross-sectional view of a gas sensor used in an example.

FIG. 4 is a plan view of a gas sensor used in an example.

FIG. 5 is an operation flowchart of the embodiment.

FIG. 6 is a flow chart showing detection of a steady value of a gas sensor signal and statistic processing in the embodiment.

FIG. 7 is a flowchart showing detection and statistic processing of an average value of a gas sensor signal in the embodiment.

FIG. 8 is a flowchart showing a process for a power supply voltage change in the embodiment.

FIG. 9 is a waveform diagram showing a pulse drive waveform of the gas sensor in the example.

FIG. 10 is a waveform diagram showing a lighting waveform of an LED in the example.

FIG. 11 is a waveform diagram showing a drive waveform of the buzzer in the example.

FIG. 12 is a waveform diagram showing a drive waveform of a buzzer when gas leaks in the example.

FIG. 13 is a waveform diagram showing a drive waveform of a buzzer when a power supply voltage drop warning is issued in the example.

[Explanation of symbols]

 2 Microcomputer 4 Gas sensor 6 Battery power 8 Power indicator LED 10 Multivibrator

Claims (1)

[Claims] 1. A gas detection device in which a metal oxide semiconductor gas sensor equipped with a heater is pulse-driven by a battery power source at a gas sensor drive duty ratio to detect gas, and the gas sensor is pulse-driven and the gas sensor is also used. An integrated circuit for processing the signal of is provided, the control program of the gas detection device is stored in this integrated circuit, and the integrated circuit operates normally by the standby mode in which the clock inside the integrated circuit is stopped. A normal operation mode is provided, and after the control program of the gas detection device is completed, the integrated circuit is shifted to the standby mode.An oscillation circuit is provided and the integrated circuit is set to the standby mode by the signal of the oscillation circuit. To the normal operation mode, and a power supply display LED is further provided. , The LED driving duty ratio, characterized in that so as to pulsed manner lighting, gas detection device.