JP2784404B2 - Gas alarm - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas alarm device which detects an abnormality in gas concentration increase such as gas leakage and gives an alarm, and more particularly to a gas alarm device using a bridge circuit including a contact combustion type gas sensor. It is.

[0002]

2. Description of the Related Art Conventionally, a gas alarm device of this type having a configuration as shown in FIG. 4 is known. In the figure,
Reference numeral 1 denotes a transformer that uses, for example, a commercial AC power supply of 100 V AC as a primary voltage, and 2 denotes an AC bridge that is provided on the secondary side of the transformer 1 and that uses a stepped-down AC as a power supply. There is connected to the contact combustion type gas sensor L _1, L ₂ which varies, in other sides resistors R _1, R ₂ are connected. Further, between the power supply input terminals volume R ₃ for adjusting the balance it is connected.

[0003] Reference numeral 3 denotes a full-wave rectifier circuit using a diode bridge provided on the secondary side of the transformer 1, and reference numeral 4 denotes an operational amplifier. This to the inverting input of the operational amplifier 4 is connected one of the other output terminal of the output terminal is connected to the reference potential (earth) AC bridge 2 via a DC blocking capacitor C ₁ and resistor R ₄ I have. The rectified output of the full-wave rectifier circuit 3 is smoothed by the capacitor C ₂ to the non-inverting input,
Reference voltage the DC voltage stabilized with a Zener diode ZD is divided by series resistors R ₅ and R ₆ is applied.
The stabilized DC voltage is used as an operation power supply for the operational amplifier 4. A period resistor R ₇ between the inverting input and the output of the operational amplifier 4 are connected to constitute an AC amplifier with resistor R _4.

[0004] The output voltage of the operational amplifier 4 is applied to both ends of the resistor R ₈ through the capacitor C ₃ DC blocking, it is smoothed by the capacitor C ₄ and a resistor R ₉ after being rectified by the diode D _1. This smoothed voltage is applied to the discriminator 5
, And the buzzer 6 is driven based on the determination result output from the determiner 5.

In the above configuration, when the AC bridge 2 is set in an equilibrium state when the gas concentration is normal, the output voltage becomes 0 V as shown by a solid line in FIG. Accordingly, the output voltage V ₁ of the operational amplifier 4 is also 0 V as shown by the solid line in FIG. 5B, and the voltage V ₂ rectified by the diode D _{1 and} smoothed by the capacitor C ₄ is also shown by a solid line in FIG. It becomes 0V as shown by.

On the other hand, each passive element L ₁ , L
_{2. When} R _{1 to} R ₃ are in a normal state, in the event of an abnormality such as an increase in gas concentration, the AC bridge 2 shifts to an unbalanced state,
An AC voltage is generated as an output voltage as shown by e in the figure. The peak value of this AC voltage is usually about several tens mV.
Therefore the operational amplifier 4, the more configured AC amplifier resistor R ₄ and R ₇ to the output voltage of the AC bridge 2 as shown by e in FIG. 5 (b) was amplified with a predetermined gain, the capacitor C
₃ through applied across the resistor R _8. The amplified AC voltage is rectified by a diode D ₁ and smoothed to a DC voltage V ₂ by a capacitor C ₄ and a resistor R ₉ , thereby obtaining FIG.
As shown by e, a high level DC voltage is obtained. The DC voltage V ₂ is determined this discriminator 5 and increases above a predetermined level, generating an alarm by driving the buzzer 6.

The broken line in FIG. 5 shows the state of each part when the contact combustion type gas sensors L ₁ , L _2, etc. are disconnected or deteriorated. Even when such a situation occurs, the gas concentration increases. The abnormal state is determined in the same manner as when
Can be driven.

By the way, in the above-mentioned conventional alarm device,
The alarm point in the discriminator 5 is generally set to a gas concentration of 1/4 or less of a lower risk level (LEL) which is a lower concentration at which there is a risk of explosion.
In addition to the following, there is an increasing demand for an alarm device that can set an alarm point at about 1/100 of the LEL and perform a two-step alarm.

[0009]

However, in the above-mentioned conventional alarm device, about 1 LEL of the LEL is simply stored in the discriminator 5.
If an alarm point of / 100 is set, a malfunction may occur. This is the value of the resistor R ₃ for performing balancing of the AC bridge 2 is changed by an external impact, the output of the AC Bushijji 2 by the change of the resistance R _3, a corresponding change to the micro gas concentration occurs This is because

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a gas alarm device capable of detecting a minute gas concentration without malfunctioning in view of the above-mentioned conventional problems.

[0011]

In order to achieve the above object, a gas alarm device according to the present invention, as shown in the basic configuration diagram of FIG. 1, uses an AC power supply as a power supply and detects a contact combustion type gas on at least one side. An AC bridge 2 including an element, amplifying means 4 for amplifying the output of the AC bridge, and comparing the output level of the amplifying means with a first alarm determination level,
First determining means 1 for determining the output level of the amplifying means
0a and a second determination for determining the output level of the amplifying means by comparing the output of the amplifying means with a second warning determination level corresponding to a minute gas concentration sufficiently smaller than the first warning determination level. Means 10b, wherein when the output level of the amplifying means is equal to or higher than each determination level, the first
And a gas alarm device configured to generate an alarm based on the output of the second determination means. The setting means 10c for setting the alarm determination level of

[0012]

In the above construction, the setting means 10c sets the minimum value of the output level of the amplifying means 4 for amplifying the output of the AC bridge 2 including the contact combustion type gas detecting element on at least one side using the AC power supply as a power supply for a certain period. Since the second alarm judgment level corresponding to the minute gas concentration sufficiently smaller than the first alarm judgment level is set based on the detected minimum value, the first alarm judgment is made. Even if the level is extremely small and the output of the AC bridge fluctuates due to the displacement of the adjusting means due to impact or the like, the minute judgment level is updated every fixed time, so the output of the AC bridge is It is possible to prevent erroneous determination at the first alarm determination level due to fluctuation.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of the gas alarm device according to the present invention. In FIG. 2, the same parts as those of the conventional one described above with reference to FIG. 4 are denoted by the same reference numerals, and the detailed description thereof will be omitted.

In the gas alarm device according to the present invention, the discriminator 5 is replaced with, for example, a 4-bit microcomputer (CPU) 10 only. In this configuration, the CPU 10 has a built-in read-only ROM storing a predetermined control program and a RAM storing various data in a readable and writable manner.
It has an input port I ₁ and an output port O ₁ . The input port I ₁ output of the operational amplifier 4 is connected via a diode D and a capacitor C3, the output after being amplified rectified smoothed AC bridge 2 is input. On the other hand, a buzzer is connected to the output port O ₁ and this port O ₁
Is set to the H level, the buzzer 12 is operated.

The CPU 10 reads the DC voltage corresponding to the output of the AC bridge 2 input to the input port I ₁ according to the control program, performs A / D conversion, compares the read DC voltage with the previously read A / D converted value, The smaller data is stored in a predetermined area of the RAM. This operation is, for example, 3
By repeating the process for a predetermined time of 0 minutes, a minimum value V ₂ ′ within the predetermined time is obtained. Using this minimum value V ₂ ′, the first alarm determination level Y ₁ is obtained by the calculation of Y ₁ = V ₂ ′ + α. In addition, when there is no minute gas leakage, the minute gas leakage occurs and the output is about 1 / L of the lower limit dangerous level (LEL).
This is a value corresponding to the gas concentration reaching point 100.

As described above, the value V ₂ obtained by reading the DC voltage corresponding to the output of the AC bridge 2 input to the input port I ₁ and performing A / D conversion is the first sharp value obtained as described above. It is compared with the fist judgment level Y ₁ and the second predetermined alarm judgment level Y _2, and when Y ₁ <V ₂ , the _first alarm judgment level Y ₂ is set.
When Y ₂ <V ₂ , a drive signal is output to the output port O ₁ so that a second-stage alarm is generated by the buzzer 6.

The details of the operation of the device outlined above are given in C
The following describes the processing performed by the PU 10 according to a predetermined control program with reference to the flowchart of FIG.
The CPU 10 starts operation when the power is turned on, and in the first step S1, starts a 30 minute timer configured in the RAM. Then the process proceeds to step S2, where reads the voltage input to the input port I _1, which is converted A / D. Next, the process proceeds to step S3, where the A / D converted value of the voltage read this time and the RA
An A / D conversion value stored in a predetermined area of M is compared, and the smaller value is stored in a predetermined area of the RAM. Subsequently, the process proceeds to step S4, where it is determined whether or not the 30-minute timer started in step S1 has timed out. If the determination is NO, the process proceeds to step S4.
Go to 5.

In step S5, the above step S5
The V ₂ read in 2 compares the second and warning determination level Y ₂ stored predetermined in ROM, V ₂ ≧ Y
It is determined whether it is ₂ . Determination of the determination in step S5 is compared with V ₂ read in the first warning determination level Y ₁ and step S2 to be stored in a predetermined area in the RAM in steps described below proceeds to step S6 when the NO, V determines whether or not the ₂ ≧ Y _1.
If the determination in step S6 is also NO, the process returns to step S2 to repeat steps S2 to S6.

If the determination in step S4 becomes YES while the above steps S2 to S6 are repeated, that is, if the 30-minute timer started in step S1 times out, the process proceeds to step S7. By repeating the process of S4 for 30 minutes, 3
The minimum value V ₂ ′ of V ₂ within a certain period of 0 minutes is the RAM
Is stored in a predetermined area.

In step S7, Y ₁ = V ₂ ′ + α is calculated by using the minimum value V ₂ ′ to obtain a _first alarm determination level Y ₁ , and then the process proceeds to step S8. storing a first warning determination level Y ₁ obtained at the step S7 in a predetermined area in the RAM.
Then, the process proceeds to step S9 to start a 30-minute timer, and then proceeds to step S5 described above.

Thereafter, the level stored in the RAM in step S8 is used as the first alarm determination level used in the determination in step S6.
When 6 is determined in YES, that is, when a V ₂ ≧ Y ₁ returns from it outputs a drive signal to the output port O ₁ so as to generate an alarm first stage proceeds to step S10 to step S2. The determination in step S5 is Y
When ES, i.e., V ₂ ≧ Y ₂ is a step S2 from the output of the drive signal to the output port O ₁ so as to generate a second-stage alarm proceeds to step S11 when
Return to

As is clear from the above description, the CPU 10 performing the processing shown in the flowchart of FIG.
A first determining means for comparing the output level of the amplifying means for amplifying the output of the AC bridge with a first alarm determination level to determine the output level of the amplifying means, and determining the output of the amplifying means as a first alarm determination A second judging means 10b for judging the output level of the amplifying means by comparing with a second alarm judging level corresponding to the minute gas concentration sufficiently smaller than the level, and a minimum value of the output level of the amplifying means during a certain period. It functions as setting means 10c for detecting a value and setting a second alarm determination level based on the detected minimum value.

[0023]

As described above, according to the present invention, the minute judgment level is updated at regular time intervals, so that even if the output of the AC bridge changes due to an impact or the like, the minute judgment level is minutely updated. The determination of the output of the AC bridge with respect to an extremely small alarm determination level for determining gas leakage can be performed without error to enable detection of a minute gas concentration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a gas alarm device according to the present invention.

FIG. 2 is a view showing one embodiment of a gas alarm device according to the present invention.

FIG. 3 is a flowchart illustrating a process performed by a CPU in FIG. 2;

FIG. 4 is a diagram showing an example of a conventional gas alarm device.

FIG. 5 is a waveform chart for explaining the operation of the device of FIG. 4;

[Explanation of symbols]

 2 AC bridge 4 Amplifying means (operational amplifier) 10a First judging means (CPU) 10b Second judging means (CPU) 10c Setting means (CPU)

Continuation of the front page (56) References JP-A-3-180996 (JP, A) JP-A-5-210793 (JP, A) JP-A-59-27395 (JP, A) JP-A-2-22020 (JP, A) , A) Real opening 63-48298 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G08B 21/00 G01N 27/16

Claims (1)

(57) [Claims] An AC bridge including a contact combustion type gas detection element on at least one side using an AC power supply as a power supply, an amplifying means for amplifying an output of the AC bridge, and an output level of the amplifying means being set to a first alarm determination level. And a second alarm corresponding to a minute gas concentration sufficiently smaller than the first alarm determination level. The first alarm determines the output level of the amplifier. A second judging means for judging an output level of the amplifying means in comparison with a judging level, wherein the first and second judging means when the output level of the amplifying means becomes equal to or more than each judgment level. In a gas alarm device that generates an alarm by an output, a minimum value of an output level of the amplifying means during a predetermined period is detected, and the second alarm determination level is determined based on the detected minimum value. Gas alarm device, characterized in that it comprises a setting means for constant for.