JPH0273143A - Smell detector - Google Patents

Abstract

PURPOSE:To allow rate detection without the influence of a drift by a change in temp. and humidity by providing two pieces of semiconductor gas sensors, a means of taking the output difference therebetween and a means of deciding that an smell is detected when the output difference changes. CONSTITUTION:A bridge circuit which obtains the output difference of the semiconductor gas sensors 2, 3 is formed of the sensors 2, 3 and variable resistors 4, 5 disposed apart from each other. The resistors are first so adjusted and set as to satisfy the equil. conditions of high sensitivity. The potential difference V0 between A and B is zero when a burning smell is not detected. The potential difference is generated between A and B when the smell is detected. This potential difference V0 is amplified by a buffer amplifier 6 and the output value thereof is compared with a prescribed reference value by a decision circuit 7. The output difference change if the potential difference is above the reference value. An alarm is then emitted by an alarm device 8 to inform that the burning smell is detected. Since the sensor outputs both drift, the output difference is surely detected without being affected by the drift even if the drift exists in this case.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an odor detection device that detects odor using a semiconductor gas sensor.

(Prior Art) A semiconductor gas sensor changes its resistance value when gas is adsorbed and desorbed onto the semiconductor surface. For example, when an oxidizing gas comes into contact with an n-type semiconductor sensor, anions are adsorbed, electrons are transferred from the sensor to the adsorbed gas, a space charge layer is formed on the sensor surface, and the resistance value of the sensor increases. On the other hand, when a reducing gas comes into contact with it, it adsorbs cations and releases electrons into the sensor, so the resistance value of the sensor decreases.

This type of sensor is generally used in gas leak alarms, etc., and can be used to detect abnormal odors such as burning smell that occur in the early stages of a fire. can be alerted.

When detecting odors using this gas sensor, the sensor output is small, and therefore, when used as an odor sensor, a resolution of about 10 mV is required at room temperature. However, since semiconductor gas sensors perform detection based on gas adsorption phenomena, they are affected by temperature, and furthermore, because water vapor is a type of gas that changes the resistance value of the sensor, they are also affected by humidity. In other words, the output of the sensor drifts depending on external temperature and humidity. For example, when the temperature changes from 15"C to 30°C, the sensor output will drift from 300mV to 450mV.The sensor's resolution needs to be about 10mV, so this is not enough to detect odors such as burnt smell during a fire. cannot be detected reliably.

(Objective and Structure of the Invention) The present invention has been made in view of the above points, and an object thereof is to enable a semiconductor gas sensor to reliably detect odors without being influenced by drift caused by changes in temperature or humidity. In order to achieve this purpose, two semiconductor gas sensors are installed apart from each other, a means for measuring the output difference between these two semiconductor gas sensors, and a means for detecting an odor when the output difference changes. The odor detection device was constituted by the judgment means for making the judgment.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 is a schematic configuration diagram of a fire alarm using the odor detection device according to the present invention, where l is a power source battery, 2.3 is a semiconductor gas sensor, 4 and 5 are variable resistors, and gas sensor 2.
, 3 and variable resistors 4 and 5 form a bridge circuit that takes the difference in the outputs of the gas sensors 2 and 3.

As shown in FIG. 2, the gas sensors 2 and 3 are installed separately in a room R that is the object of fire detection.

Therefore, for example, if a burnt odor occurs from an odor source F such as a fire source, the distance from the odor source F to each sensor is different, so the burnt odor will be transmitted to the closer of sensors 2 and 3, that is, sensor 2. reach. sensor 2
Since the resistance value of sensor 2.3 changes and its output changes, the output difference of sensor 2.3, which has remained unchanged until now, changes. After that, when the burnt smell reaches the sensor 3, the resistance value of the sensor 3 changes and its output also changes, and the output difference between the two sensors returns to the original value again.

Therefore, it can be determined that a burnt odor has been detected when the difference in output between the two gas sensors 2 and 3 changes.

Now, returning to Figure 1, gas sensors 2 and 3 and variable resistor 4
, 5 and the potential difference V between A-8 of the bridge circuit formed by
, it is possible to detect the difference in output between both sensors. The resistance values of gas sensors 2 and 3 are R2゜R3, variable resistors 4 and 5.
Assuming that the resistance values of R4 and R5 are R4 and R5, the equilibrium condition of the bridge is Ra/R2=Rs/R3. Therefore, the variation in individual parts can be reduced by using a variable resistor of 4.5
If we adjust it to satisfy this equilibrium condition,
When no burnt odor is detected, the potential difference between A-8 V8 = 0
When a burnt odor is detected, a potential difference is generated between A-8. In addition, in the above equilibrium condition equation, Ra/R2
(or R5/R3)=, then ■(=1 when V
Since the change in ll is the largest, k=1, that is, R4
It is preferable to set each resistance value so that =R2, R5=R3.

Now, the potential difference V8 between A-8 is amplified by the buffer amplifier 6, and its output value is compared with a predetermined reference value by the determination circuit 7. If it is greater than or equal to the reference value, the output difference between the gas sensors 2 and 3 is has changed, and therefore a burnt odor is detected by the alarm 8! Issue an F-alarm.

FIG. 3 is a diagram showing this situation, where the output value C of the buffer amplifier 6 is the reference value V. , the alarm device 8 issues an alarm.

With the above method, detection is based on the change in the output difference between the two sensors, so even if the output value of the sensor drifts due to changes in temperature or humidity, the output of the two sensors will both drift, so the output of the sensor will change. The difference does not change and no alarm is issued. On the other hand, when an odor occurs, the routes of the odor reaching the two sensors are different, so the difference in output between the sensors changes, and by detecting this change, the odor can be reliably detected. Furthermore, the configuration of the device is extremely simple, there is no need to use calculation means such as a computer, and installation and operation are easy.

The use of the odor detection device of the present invention is not limited to fire alarms, but if the present invention is applied to fire alarms in particular, it is possible to reliably detect burnt odors and abnormal odors that occur in the early stages of a fire. can be detected early, which has a great effect on disaster prevention.

In the above embodiment, a bridge circuit was used as a means to measure the output difference of the gas sensor, but it is not limited to this.
In short, other circuits or devices may be used as long as they can measure the difference in output between the two semiconductor gas sensors.

(Effects of the Invention) As explained above, in the present invention, two semiconductor gas sensors installed apart from each other, a means for determining the output difference between these two semiconductor gas sensors, and a means for determining the output difference between the two semiconductor gas sensors, and when the output difference changes, Since the odor detection device is configured with the determination means that determines that an odor has been detected, the odor can be reliably detected without being affected by the drift of the semiconductor gas sensor due to changes in temperature or humidity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example in which the odor detection device according to the present invention is applied to a fire alarm, FIG. 2 is a diagram showing the installation state of a gas sensor, and FIG. 3 is an output waveform diagram of a buffer amplifier. 2.3... Semiconductor gas sensor, 6... Buffer amplifier Patent applicant: Nisshin Seifun Co., Ltd. Representative Patent attorney: Hiroshi Suzuki Male 1st Figure 2

Claims (1)

[Claims] two semiconductor gas sensors installed apart from each other;
means for determining the output difference between these two semiconductor gas sensors;
An odor detection device characterized by comprising: determination means for determining that an odor has been detected when the output difference changes.