JPH05325083A - Fire alarm - Google Patents

Abstract

PURPOSE:To provide the fire alarm which changes the sensitivity to a fire in accordance with the ambient brightness. CONSTITUTION:The fire alarm consists of a smoke sensing circuit 1 which always senses the density of smoke and converts it to a voltage value VS to output it, a threshold setting means 2 outputs the terminal voltage of a resistance R1 changed in accordance with the resistance change of a photodetector R2 changing the resistance value in accordance with the luminance of detection light as a threshold voltage VL, a comparing circuit 3 which compares the voltage value VS with the threshold voltage VL and outputs an output signal only in the case of the voltage value VS higher than the threshold voltage VL, and an alarm circuit 4 which receives the output signal from the comparing circuit to raise an alarm by sounding a bell or a buzzer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fire alarm that detects a physical quantity that changes with a fire such as smoke density, heat change amount, and flame, compares the physical quantity with a threshold value, and issues an alarm based on the comparison result. It is related to vessels.

[0002]

2. Description of the Related Art FIG. 5 is a block circuit diagram showing a conventional fire alarm device.

As a conventional fire alarm device, there is one as shown in FIG. 5, for example. However, in FIG. 5, a fire alarm device (hereinafter referred to as “smoke alarm device”) that compares the detected smoke density with a preset threshold value and issues an alarm according to the comparison result.
I said).

In FIG. 5, reference numeral 1 denotes a smoke detection circuit 1, which constantly detects the smoke density, converts the smoke density into a voltage value Vs, and outputs the voltage value Vs. Reference numeral 12 is a threshold value setting means, which gives the comparison circuit 3 a threshold voltage VL to be compared with the voltage value Vs. The threshold value setting means 12 is composed of a series connection circuit of a resistor R4 and a resistor R1.
A constant voltage is applied by the constant voltage source 5 so that the side has a high potential. The threshold value setting means 12 divides the constant voltage of the constant voltage source 5 by the resistors R4 and R1,
The terminal voltage of the resistor R1 is output to the next stage as the threshold voltage VL. The resistance ratio of the resistor R4 and the resistor R1 determines the sensitivity of the fire alarm.

The voltage value Vs from the smoke sensing circuit 1 and the threshold voltage VL from the threshold value setting means 12 are input to the comparison circuit 3 at the next stage. The comparison circuit 3 compares the voltage value Vs with the threshold voltage VL, and outputs an output signal only when the voltage value Vs exceeds the threshold voltage VL. An alarm circuit 4 receives an output signal from the comparison circuit and issues an alarm by ringing a bell or a buzzer.

A constant voltage from a constant voltage source 5 is applied to the smoke detection circuit 1, the threshold value setting means 12, the comparison circuit 3 and the alarm circuit 4, respectively.

In the smoke alarm having the above construction, the smoke density exceeds a certain value (for example, 10% / m when the degree of light extinction due to smoke per 1 m of light is defined as smoke density). In this case, a warning is given by judging that it is a fire and ringing a bell or buzzer.

If the smoke sensing circuit 1 is replaced with a heat sensing circuit that constantly senses the amount of heat change or the amount of heat and outputs an analog voltage value Vs corresponding to it, the amount of heat change or the amount of heat can be sensed. It is possible to configure a fire alarm (hereinafter referred to as “heat alarm”) that detects a fire when the amount of change in heat or the amount of heat exceeds a certain fixed value (for example, 60 ° C.). If the smoke detection circuit 1 is replaced with a flame detection circuit configured to constantly detect a weak amount of ultraviolet rays emitted from a flame and output an analog voltage value Vs corresponding thereto, a fire that detects a flame and detects a fire. Alarm (hereinafter "flame alarm")
Can be configured.

[0009]

However, in the conventional configuration, since the threshold voltage VL given by the terminal voltage of the resistor R1 is always constant, the threshold voltage VL is detected in order to detect a fire early. If VL is set low and sensitivity to smoke or heat is increased, heat or smoke during cooking,
The fire alarm may also react to so-called non-fire factors such as heat from heating or flames from a lighter, which may cause false alarms. In view of this, if the threshold voltage VL is set to be high and sensitivity to smoke or heat is made insensitive, it does not react to the initial fire, and when a fire is found, the fire spreads and it is too late. Was also occurring. In particular, when a person is sleeping, unless a fire is detected at an early stage, it causes a personal injury, which is a very serious problem.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fire alarm which can change the sensitivity to fire depending on the situation. ..

[0011]

In order to achieve the above object, the present invention provides a fire alarm device which senses a physical quantity that changes with a fire, compares the physical quantity with a threshold value, and issues an alarm based on the comparison result. It is characterized in that it has a threshold value setting means for changing the threshold value according to ambient brightness.

[0012]

According to the present invention, the sensitivity to fire is changed according to the brightness of the surroundings by changing the threshold according to the brightness of the surroundings.

[0013]

The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a block circuit diagram showing a smoke alarm device according to a first embodiment of the present invention, and FIG. 2 is a diagram showing its operating state. The same parts as those in the conventional example are designated by the same reference numerals.

In FIG. 1, reference numeral 1 denotes a smoke sensing circuit 1 similar to the conventional example, which constantly senses the smoke density, converts the smoke density into a voltage value Vs, and outputs it.

Reference numeral 2 is a threshold value setting means. The threshold value setting means 2 is composed of a series connection circuit of a photodetecting element R2 that changes a resistance value according to the brightness of the detection light and a resistance R1 whose resistance value does not change. In FIG. 1, the photo-detecting element R2 is an element that reduces its resistance value by increasing the brightness of the detection light, and is represented by a CdS element or the like. A constant voltage from a constant voltage source 5 is applied to the series connection circuit so that the photodetector R2 side has a high potential. Therefore, the threshold value setting means 2 divides the constant voltage of the constant voltage source 5 by the photo-detecting element R2 and the resistor R1, and changes the resistance of the resistor R1 which changes with the resistance change of the photo-detecting element R2. The terminal voltage is output as the threshold voltage VL.

The voltage value Vs from the smoke sensing circuit 1 and the threshold voltage VL from the threshold value setting means 2 are input to a comparison circuit 3 similar to the above-mentioned conventional example. Then, the comparison circuit 3 issues an output signal only when the voltage value Vs exceeds the threshold voltage VL. The alarm circuit 4 similar to the above-mentioned conventional example issues an alarm by receiving an output signal from the comparison circuit and ringing a bell or a buzzer.

The smoke alarm having the above construction operates as shown in FIG. That is, as the ambient brightness becomes brighter as shown in FIG. 2A, the resistance value of the photodetector R2 becomes smaller as shown in FIG. 2B. Accordingly, the terminal voltage of the resistor R1, that is, the threshold voltage VL increases.
When the surrounding brightness becomes dark as shown in FIG. 2 (a), the resistance value of the photodetector element R2 increases as shown in FIG. 2 (b), and the threshold voltage VL decreases accordingly. To do. In parallel with the change of the threshold voltage VL, the smoke sensing circuit 1 always detects the smoke density, and as shown in FIG. 2 (d), the voltage value Vs of the level corresponding to the smoke density is obtained. When the voltage value Vs is being output and the voltage value Vs is lower than the threshold voltage VL, as shown in FIG.
Does not give an alarm and is in a "warning" state, but the voltage value V
If s exceeds the above threshold voltage VL, as shown in FIG.
As shown in (e), the alarm circuit 4 issues an alarm, and "issues".
It becomes the state of.

Therefore, when the surroundings are bright, it responds only to a relatively high level of smoke density, and when the surroundings are dark, it also responds to a relatively low level of smoke density.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block circuit diagram showing a heat alarm device according to a second embodiment of the present invention, and FIG. 2 is a diagram showing its operating state. The same parts as those in the conventional example are designated by the same reference numerals.

The thermal alarm device according to the second embodiment of the present invention comprises a constant voltage source 5, threshold setting means 2, a comparison circuit 3 and an alarm circuit 4 similar to those of the first embodiment of the present invention. However, the heat sensing circuit 6 is further included.
The heat sensing circuit 6 is composed of a series connection circuit of a temperature detecting element RT that changes its resistance value according to the detected temperature and a resistance R3 whose resistance value does not change. In FIG. 3, the temperature detecting element RT is an element that decreases its resistance value as the detected temperature increases, and is represented by a thermistor or the like. A constant voltage from a constant voltage source 5 is applied to the series connection circuit so that the temperature detecting element RT side has a high potential.
Therefore, the heat sensing circuit 6 divides the constant voltage of the constant voltage source 5 by the temperature detecting element RT and the resistor R3, and outputs the terminal voltage of the resistor R3 to the comparison circuit 3 as the voltage value VT.

The voltage value VT from the heat sensing circuit 6 and the threshold voltage VL from the threshold value setting means 2 are input to the comparison circuit 3 similar to the above-mentioned conventional example. Then, the comparison circuit 3 issues an output signal only when the voltage value VT exceeds the threshold voltage VL. Reference numeral 4 as in the above-mentioned conventional example is an alarm circuit, which receives an output signal from the comparison circuit and issues an alarm.

The heat alarm device having the above construction operates as shown in FIG. That is, as the ambient brightness becomes brighter as shown in FIG. 4A, the resistance value of the photodetector R2 becomes smaller as shown in FIG. 4B. Accordingly, the terminal voltage of the resistor R1, that is, the threshold voltage VL increases.
When the surrounding brightness becomes dark as shown in FIG. 4A, the resistance value of the photo-detecting element R2 rises as shown in FIG. 4B, and the terminal voltage of the resistor R1, The threshold voltage VL decreases. In parallel with the change of the threshold voltage VL, the heat sensing circuit 6 always detects the temperature and outputs a voltage value VT of a level corresponding to the detected temperature as shown in FIG. 4 (d). Therefore, when the voltage value VT is lower than the threshold voltage VL, the alarm circuit 4 does not issue an alarm as shown in FIG. When the value VT exceeds the threshold voltage VL, the alarm circuit 4 issues an alarm as shown in FIG.

Therefore, when the surroundings are bright, it responds only to a relatively high level of heat quantity and heat change amount, and when the surroundings are dark, it also reacts to a relatively low level heat quantity and heat change amount. ing.

[0025]

As described above, the fire alarm device of the present invention detects a physical quantity that changes with a fire, compares the physical quantity with a threshold value, and issues an alarm according to the comparison result. It is characterized by having a threshold setting means for changing the threshold according to the brightness of, such as heat and smoke during cooking, heat from heating or flame from a lighter. When a so-called non-fire factor occurs actively, that is, when the surroundings are bright, the sensitivity to heat and smoke becomes insensitive, and when the above non-fire factors do not occur often, that is, when the surroundings are dark such as during sleep, the sensitivity to heat and smoke is sensitive. Therefore, it is possible to detect a fire early in any situation and suppress false alarms due to non-fire factors.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an operating state of the first embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing an operating state of the second embodiment of the present invention.

FIG. 5 is a block circuit diagram showing a conventional example.

[Explanation of symbols]

 1 smoke detection circuit 2 threshold setting means 3 comparison circuit 4 alarm circuit 5 constant voltage source R2 photodetector

Claims (1)

[Claims] 1. A fire alarm that senses a physical quantity that changes with a fire, compares the physical quantity with a threshold value, and issues an alarm according to the comparison result. The threshold value is changed according to the brightness of the surroundings. A fire alarm device having a threshold setting means for controlling the fire alarm.