JPH0282396A - Smoke detector for air cleaner - Google Patents

Abstract

PURPOSE:To highly accurately detect the concentration of a gas with the title detector even when the concentration of contaminants is high without stopping the oscillation of an astable multivibrator circuit by changing the junction of the transistor used for the circuit from NPN to PNP. CONSTITUTION:When the internal air resistance value of a gas sensor 14 drops due to the concentration of contaminant in air becomes higher, the voltage across both ends of a resistance 15 connected with the sensor 14 in series becomes higher and, when the potential at a prescribed one point becomes lower than that at another prescribed point, a transistor 11 is turned off. However, an astable multivibrator circuit 3 does not stop oscillation, since the circuit 3 uses a PNP junction transistor 3a. Therefore, the detecting range of this sensor 14 is widened and the operation of an apparatus 19 can be controlled in accordance with the contaminated state of air by the operation of a microcomputer 18, because the transistor 17 makes outputs corresponding to the gas concentration until the moment just before the transistor 17 is turned off. Accordingly, the concentration of a gas can be detected with high accuracy without stopping the oscillation of the multivibrator circuit even when the air is highly contaminated.

Description

[Detailed description of the invention] Industrial application field The present invention detects the degree of air pollution using a gas sensor,
This invention relates to a smoke detection device for an air purifier that controls the device according to its state.

2. Description of the Related Art In recent years, air purifiers have become popular as indoor airtightness and smoke-free awareness have increased, but gas sensors have been primarily used to detect indoor air contamination.

Conventionally, this type of smoke detection device has had a configuration as shown in FIG. That is, the power supply voltage is stepped down by the transformer 11 and made into a constant voltage through the stabilization circuit 1, and power is supplied to the RV conversion circuit 4, astable multivib break circuit 5, and microcomputer 18, which are connected later. On the other hand, the gas sensor 14 is supplied with voltage-stepped power by the transformer 12 and is connected to a resistor 15 in the RV conversion circuit 4 . Then, the internal electrical resistance of the gas sensor 14 changes depending on the pollution state of the indoor air, and the change is caused by the resistance 1
5, and this fluctuating voltage is corrected and input to an astable multivibrator circuit 5 using an NPN junction transistor for A/D conversion. Then, the A/D converted data is transferred to the microcomputer 1.
8 calculates, and if the contamination concentration is higher than the standard value, device 1
The configuration was to operate 9.

Problems to be Solved by the Invention In such a conventional configuration, when the air contamination concentration is extremely high, the current flowing through the gas sensor 14 increases, and as a result, the voltage across the resistor 16 directly connected to the gas sensor 14 increases. Then, the potential at point A shown in the figure decreases and may become lower than the potential at point B. In that case, transistor 1 is turned off and the oscillation of astable multivibrator circuit 5 eventually stops. There is a phenomenon, but to prevent it, the light emitting diode 26 with a forward voltage of several ■
is inserted so that the pace potential of the transistor 17 is always higher than the potential at point B.

Therefore, when the contamination concentration is low, the gas sensor 14
has a large internal electrical resistance, and the voltage across the resistor 15 decreases, but since the voltage of the light emitting diode 26 is constantly present, the voltage does not drop below a certain value, and the output of the multi-vibration circuit 4 is equal to the resistance value of the gas sensor 14. The problem was that it did not follow changes accurately.

The present invention solves the above-mentioned conventional problems, and is an air purifier that can detect gas concentration with high precision even in a clean state without stopping the oscillation of the astable multivib break circuit 5 even when the concentration of contaminants is high. The purpose of this invention is to provide a detection device.

Means for Solving Issue jJ In order to achieve this objective, the air purifier detection device of the present invention includes a gas sensor for detecting a change in gas concentration, an RV conversion circuit connected to the gas sensor, and an R-V conversion circuit connected to the gas sensor. - an astable multivibrator circuit that A/D converts the output of the astable multivibrator circuit; and a microcomputer that processes the output of the astable multivibrator circuit;
The conversion circuit includes a detection resistor directly connected to the gas sensor, a transistor for correcting and converting changes in the voltage across the detection resistor, and a general-purpose diode connected to the base terminal of the transistor. The vibrator circuit has a structure including a PNP junction transistor.

Effect: With this configuration, when the concentration of reverse contamination is high and the change in the resistance value of the gas sensor is extremely small, the voltage across the detection resistor becomes high, and the base voltage of the transistor in the R-V conversion circuit becomes lower than the emitter voltage. ,!゛The transistor is turned off, but the transistor of the astable multivibrator circuit is PNP.
Because it is a bonded device, it does not stop oscillating and adapts to changes in the resistance value of the gas sensor due to air pollution with reliable precision, allowing the device to operate according to the air pollution state. .

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. Components having the same configuration as those of the conventional example are given the same numbers and detailed explanations will be omitted. As shown in the figure, the I-disk 3a of the multi-bye break circuit 3 is of a PNP junction, and the general-purpose diode 16 connected to the base of the transistor 170 has a forward voltage of several hundred mV.

6,-7 To explain the operation of the above configuration, when the air pollution concentration is high and the internal air resistance value of the gas sensor 14 becomes extremely small, the voltage across the resistor 150 connected in series with the gas sensor 14 increases, and A When the potential at the point becomes lower than the potential at point B, the transistor 11 is turned off. However, since the astable multivibrator circuit 3 uses the PNP junction 1-lung nut 3a, the oscillation does not stop. Therefore, the first transistor 17 outputs an output corresponding to the gas concentration until just before it is turned off, which has a wide detection range, and the microcomputer 18 stops the operation of the device 19 in accordance with the air contamination state. be able to.

Effects of the Invention As described above, the air purifier smoke detection device of the present invention has a transistor used in the astable multivibrator circuit.
By changing from a PN junction to a PNP junction, the astable multivibrator circuit will not stop oscillating even when the air pollution concentration is high, and will operate stably, reducing the forward voltage of a general-purpose diode even in extremely clean conditions. Since the output of the multivibrator circuit can be changed in accordance with the voltage change of the gas sensor, it is possible to accurately detect the concentration in a wide range of air pollution conditions, even at low concentrations. This makes it possible to realize a smoke detection device for a purifier.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a smoke detection device for an air cleaner according to this embodiment, and FIG. 2 is a circuit diagram of a conventional smoke detection device for an air cleaner. 2...R-V conversion circuit, 3...Astable multi-vibration circuit, 3a...PNP junction l-lung nut, 14...Gas sensor, 15.
...Detection resistor, 16...General-purpose diode, 1-transistor, 18...
microcomputer.

Claims (1)

[Claims] a gas sensor that detects a change in gas concentration; an RV conversion circuit connected to the gas sensor; an astable multivibrator circuit that A/D converts the output of the RV conversion circuit; The R-V conversion circuit includes a detection resistor directly connected to the gas sensor, a transistor for correcting and converting changes in voltage across the detection resistor, and a base of the transistor. A smoke detection device for an air purifier, comprising a general-purpose diode connected to a terminal, and the astable multivibrator circuit comprising a PNP junction transistor.