JPH10332618A - Gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector for detecting the rising of a gas sensor signal quickly while suppressing error in which noise due to variation of temperature or humidity is suppressed and erroneous detection due to drift of gas sensor signal is prevented. SOLUTION: The gas detector comprises a gas sensor 1 and a signal processing section 5 wherein the signal processing section 5 comprises a reference value generating section 8, a calculating section 11, a contamination calculating section 9 and a D/A converter 10. Conditions for updating a reference value are determined depending on the contamination at the calculating section 11 and updated at the reference value generating section 8 in order to prevent erroneous detection due to drift of sensor signal thus obtaining a gas detector in which detection error is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a gas detector.

[0002]

2. Description of the Related Art Conventionally, there has been known a sensor disclosed in Japanese Patent Application Laid-Open No. 6-66750 for detecting atmospheric pollution, particularly generation of carbon dioxide gas due to smoking, using a gas sensor made of a metal oxide semiconductor. I have. In this conventional example, an envelope of a gas sensor signal is obtained and used as a reference value in order to correct a drift due to an ambient temperature of the gas sensor, a change with time, and the like, and the envelope of the gas sensor is used as a reference value. When the gas sensor signal is on the polluted side, that is, when the gas concentration is lower than the reference value, the reference value is changed to the gas sensor signal. , And a comparison is made between the level of the gas sensor signal and the level of the current reference value. If the difference between the two levels exceeds an allowable value, it is determined that gas is generated. FIG. 8 shows the level (a) of the gas sensor signal of this conventional example.
And the transition of the reference value (b).

[0003]

By the way, in the above conventional example, when the level of the gas sensor signal exceeds the reference value as shown in FIGS. Is close to the gas sensor signal level, so that the difference between the reference value and the level of the gas sensor signal does not increase regardless of the gas concentration and the state in which it should be determined that gas is generated. Had a problem that accurate detection was not possible.

[0004] In addition, it is difficult to detect a wide range of gas sensor signals.

SUMMARY OF THE INVENTION The present invention solves such a conventional problem, and can prevent noise due to a change in temperature or humidity, erroneous detection due to a drift of a gas sensor signal, and can quickly detect a rise of a gas sensor signal. It is another object of the present invention to provide a gas detection device that can reduce an error due to calculation of a reference value after gas detection and that can process a wide range of gas sensor signals without lowering calculation accuracy.

[0006]

According to the gas detecting apparatus of the present invention, a reference value updating means for updating a reference value serving as a reference of an output signal of a gas sensor so as to approach an output signal, wherein an updating condition is set in accordance with a degree of contamination. It is provided with an update condition determining means for changing.

According to the present invention, since the reference value is appropriately updated in accordance with the degree of contamination, it is possible to obtain a gas detection device with a small detection error while correcting the drift of the sensor signal.

Another means is that the update condition determining means determines the update condition by changing the amount by which the reference value approaches the output signal.

According to the present invention, the amount of updating of the reference value is changed in accordance with the degree of contamination, so that a gas detection device having an effect of reducing errors due to updating of the reference value can be obtained.

Another means is that the update condition determining means determines the update condition by changing a cycle for bringing the reference value closer to the output signal.

According to the present invention, an opportunity for updating the reference value is determined according to the degree of contamination, so that a gas detection device capable of obtaining an accurate reference value can be obtained.

Another means is that the update condition determining means determines the update condition by changing the period and amount of bringing the reference value closer to the output signal.

According to the present invention, it is possible to obtain a gas detection device that can obtain an accurate reference value with a smaller error caused by updating the reference value.

Further, the other means determines a level of the gas sensor signal, and changes a load resistance value connected in series to the gas sensor in accordance with the level. The reference value,
And a reference value correcting means for correcting such that the relationship with the level of the gas sensor signal does not change.

According to the present invention, it is possible to obtain a gas detection device capable of performing highly accurate detection even when the sensor signal greatly varies due to the variation or drift of the gas sensor.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An output signal of a gas sensor, a reference value serving as a reference for the output signal, and output means for comparing the reference value with the output signal to output a degree of contamination of an atmosphere.
A reference value updating unit that updates the reference value so as to approach the output signal; and an update condition determining unit that changes an update condition of the reference value updating unit in accordance with the contamination level.

Further, the update condition determining means determines the update condition by changing the amount by which the reference value approaches the output signal.

Further, in the update condition determining means, the update condition is determined by changing a cycle of bringing the reference value closer to the output signal.

Further, the update condition determining means determines the update condition by changing the cycle and amount of bringing the reference value closer to the output signal.

Load resistance switching means for determining a level of the gas sensor signal and switching a load resistance value connected in series to the gas sensor in accordance with the level; and a reference value for the gas sensor signal in response to a change in the load resistance value. Reference value correcting means for correcting so as not to change the relationship with the level is provided, and it is possible to prevent an error in the degree of contamination output before and after switching the load resistance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0022]

【Example】

(Embodiment 1) As shown in FIG. 1, a metal oxide semiconductor gas sensor (hereinafter abbreviated as gas sensor) 1 is connected to a DC power source 3 such as a battery via a load resistance circuit.
Reference numeral 4 denotes a heater provided in the gas sensor 1, and this heater 4 is also connected to the DC power supply 3. The load resistance circuit includes the resistance 2.

Reference numeral 5 denotes a one-chip signal processing unit comprising, for example, a 4-bit microcomputer for performing signal processing in the present embodiment. In FIG. Voltage VRL
Via the A / D converter 6, the sensor resistance calculator 7 for calculating the sensor resistance value Rs of the gas sensor 1 from the voltage VRL via the A / D converter 6, and a reference value Rsm for comparison with the sensor resistance value Rs. , A pollution degree calculator 9 for calculating the pollution degree by comparing the reference value Rsm and the sensor resistance value Rs, and converting the pollution degree calculated by the pollution degree calculator 9 into an analog value. It comprises a D / A converter 10 for conversion, a calculation unit 11 for calculating an update amount X and an update period Z of the reference value Rsm from the pollution degree, and the like.

Next, the circuit of FIG. 1 will be described with reference to the flowchart shown in FIG. First, when the apparatus is started, the signal processing unit 5 initializes the load resistance value RL and the reference value Rsm of the reference value generation unit 8.

After setting the initial value, the current load resistance value RL
And the sensor resistance calculator 7 calculates the sensor resistance value Rs from the voltage VRL. This calculation is performed by, for example, the equation of Rs = ((256−VRL) × 64) / VRL.

As described above, the sensor resistance value Rs is compared with the current reference value Rsm generated by the reference value generation unit 8 by the comparators 12 and 13, and the sensor resistance value Rs is compared with the reference value Rsm.
If not, the reference value Rsm is updated by the contamination direction reference value updating unit 8b, and conversely, the sensor resistance value Rs is changed to the reference value Rs.
If m0 or more, the reference value Rsm is updated by the cleaning direction reference value updating unit 8a. The update amount and the update period are calculated by the calculation unit 11 and provided to the update units 8a and 8b.

In this case, in the clean direction, for example, Rsm = Rsm0 + (Rs-Rsm0) / 3 for each sampling.
Will be updated. Note that Rsm0 indicates the current reference value.

In the case of the contamination direction, every reference value update cycle
(For example, when the number of times of sampling from the previous update timing becomes equal to or more than the predetermined value Z), Rsm = Rsm0
Update by (Rsm0-Rs) / X. Here, X indicates a reference value update amount, and X = C1 = (Rsm−Rs) × Vsp
It is determined from an × 8 / Rsm. C1 indicates the calculated output of the gas sensor 1. Vspan is a constant, and X is 1
The range is 0 <X <100, and its initial value is 10.

While the reference value is being updated as described above, the pollution degree calculating section 9 obtains the pollution degree from the difference from the sensor resistance value Rs, and externally obtains the pollution degree via the D / A converter 10. Output to

Based on the pollution degree output, for example, in the case of an air purifier or a ventilation fan, the operation of the fan is controlled in accordance with the pollution degree.

As described above, by changing the update amount of the reference value update according to the output, it is possible to reduce the update amount at high density and increase the update amount at low density.
Since the reference value is actively updated at the time of low density to be set as the reference value, and the update is reduced at the time of high density which should not be set as the reference value, it is possible to detect with little error due to the update of the reference value.

In the calculation of the sensor resistance value Rs,
In this embodiment, the temperature is directly calculated from the voltage VRL. However, correction such as temperature correction or humidity correction by a temperature sensor such as a thermistor or a humidity sensor may be added.

(Embodiment 2) A description will be given with reference to FIG. The description of the same parts as those in the first embodiment of the present invention is omitted.

If the sensor resistance value Rs is in the contamination direction equal to or less than the reference value Rsm0, Rsm = R
Update with sm0- (Rsm0-Rs) / X1. Here, X1 indicates the reference value update amount, and is a constant in the range of 10 <X1 <1000.

The update period Z is obtained from Z = C1 × Vk5. Vk5 is an update cycle coefficient, and Z is 20 <Z <
The range is 1000, and its initial value is 20.

As described above, by changing the reference value update cycle in accordance with the output, the update timing is increased at a low density at which the reference value is to be obtained, and the reference value can be reliably obtained. Detection can be performed.

(Embodiment 3) A description will be given with reference to FIG. The description of the same parts as those in the first and second embodiments of the present invention will be omitted.

If the sensor resistance value Rs is in the contamination direction equal to or less than the reference value Rsm0, Rsm = Rsm0- (Each time when the number of times of sampling from the previous update timing becomes equal to or more than the predetermined value Z). Rsm0-Rs) / X
Update with. Here, X indicates a reference value update amount, and X = C1
= (Rsm-Rs) x Vspan x 8 / Rsm. C1 indicates the calculated output of the gas sensor 1. Vs
pan is a constant, X is in the range of 10 <X <500, and its initial value is 10.

The update period Z is obtained from Z = C1 × Vk5. Vk5 is an update cycle coefficient, and Z is 20 <Z <
The range is 1000, and its initial value is 20.

FIG. 5A shows the state of updating the reference value according to the present invention by converting the sensor resistance value Rs into a voltage VRL and converting the reference value Rsm into voltage levels (a) and (b). When the sensor resistance Rs is lower than the reference value Rsm in the pollution direction, that is, when the voltage VRL which is the gas sensor signal level greatly exceeds the reference value level, the gas sensor signal level is compared with the reference value level. The speed is updated in inverse proportion to the gas sensor signal level so as to approach gently. Conversely, when the sensor resistance Rs is higher than the reference value Rsm in the clean direction, that is, the voltage V
When the RL is below the reference value level, the reference value level is updated so as to approach the voltage VRL quickly. FIG.
(b) shows the pollution degree output at that time. As shown in the figure, it is possible to accurately detect a change in the degree of contamination.

As described above, by changing the update amount of the reference value update and the update cycle according to the output, it is possible to reduce the update error and to reliably obtain the reference value.

(Embodiment 4) A description will be given with reference to FIGS. The description of the same parts as in the first, second, and third embodiments of the present invention will be omitted.

FIG. 6 shows the overall structure of a fourth embodiment of the present invention. In FIG. 6, a metal oxide semiconductor gas sensor (hereinafter abbreviated as gas sensor) 1 is connected to a DC power source 3 such as a battery via a load resistance circuit. Connected. Reference numeral 4 denotes a heater provided in the gas sensor 1, and this heater 4 is also connected to the DC power supply 3. The load resistance circuit is composed of a combined resistance obtained by connecting the resistance 2 and the resistances 15 and 16 in parallel under the conditions described later. Reference numeral 5 denotes a one-chip signal processing unit comprising, for example, a 4-bit microcomputer for performing signal processing in the present embodiment, and its function is shown in a block form in FIG.
RL is taken in through the A / D converter 6, and the voltage VR
A sensor resistance calculation unit 7 for calculating the sensor resistance value Rs of the gas sensor 1 from L is taken in via the A / D converter 6, and the load resistance switching unit 14 for switching the load resistance value RL from the voltage VRL is compared with the sensor resistance value Rs. A reference value generator 8 for generating a reference value Rsm
And a sensor resistance value Rs, the pollution degree calculator 9 for calculating the pollution degree, a D / A converter 10 for converting the pollution degree calculated by the pollution degree calculator 9 into an analog value, and a reference based on the pollution degree. It comprises a calculation unit 11 for calculating an update amount X and an update period Z of the value Rsm.

The resistors 15 and 16 are connected to the load resistance switching unit 14.
Are connected in parallel to the resistor 2 through the switch elements 17 and 18 of FIG. 2. When only the resistor 2 is used, the voltage VRL between both ends of the load resistance circuit becomes the maximum value. The voltage VRL is set to a minimum value in a state where both the resistors 15 and 16 are connected in parallel to the resistor 2.

Next, the circuit of FIG. 6 will be described with reference to the flowchart shown in FIG. First, when the apparatus is started, the signal processing unit 5 initializes the load resistance value RL and the reference value Rsm of the reference value generation unit 8. Here, the control unit 19 of the load resistance switching unit 14 sets the initial resistance value RL of the load resistance circuit to be a combined value of the parallel circuit of the resistance 2 and the resistance 15.
Turns on the switch element 17.

Now, after setting the initial value, the current load resistance value RL
And the load resistance switching unit 14
The lower limit value VRLm is determined by comparators 20 and 21 provided in
in, the lower limit value VRLm compared with the upper limit value VRLmax.
in and the upper limit value VRLmax are determined, and if not, if it is lower than the lower limit value VRLmin, the upper limit value VRLmax is conversely set so that the load resistance value RL becomes the highest. Exceeds the load resistance value R
The control unit 19 of the load resistance switching unit 14 controls the switch elements 17 and 18 so that L becomes the lowest. After switching the load resistance value RL, the voltage VRL is measured,
The reference value correction unit 8c of the reference value generation unit 8 determines the reference value correction amount after the switching of the load resistance value RL based on the measured value and the measurement value before the switching, and determines the reference value R that is currently generated.
sm is corrected according to the load resistance value RL.

On the other hand, the voltage VRL is equal to the lower limit value VRLm.
When the value is in the range from “in” to the upper limit value VRLmax, the sensor resistance calculator 7 calculates the sensor resistance value Rs from the voltage VRL.

At the load resistance switching timing, a reference value update calculation is performed before the switching, and the following calculation is performed, for example, 5 seconds after the switching.

When Rs1 ≧ Rs (Rs1 indicates a value immediately after switching) Rsm = Rs1 + (Rsm−Rs) × (Rs1 / Rs) (when Rs <Rsm) Rsm = Rs1 + (Rs−Rsm) × (Rs1 / Rs) (if Rs> Rsm) Then, Rs = Rs1.

As described above, by switching the load resistance, even when the resistance value of the gas sensor 1 varies greatly during manufacture or during use, highly accurate detection can always be performed. , It is possible to prevent an error caused by switching the load resistance.

[0051]

According to the present invention, in a gas detection apparatus for detecting the cleanliness and contamination of an atmosphere by comparing the level of a gas sensor signal of a gas sensor with a reference value, the level of the gas sensor signal changes in a clean direction. The reference value is updated so as to approach the level of the gas sensor signal early, and when the level of the gas sensor signal is changing in the direction of contamination, the reference value is updated at a speed inversely proportional to the level of the gas sensor signal. Equipped with a reference value updating means that updates to approach the level, preventing noise due to changes in temperature and humidity and erroneous detection due to drift of the gas sensor signal, as well as quickly detecting the rise of the gas sensor signal and accurately detecting the air pollution state This has the effect that it becomes possible to detect

Further, when the update amount of the reference value changes according to the output, the update amount is increased when the output is small, that is, when the concentration is low, and the update amount is small when the output is large, that is, when the gas concentration is high. Therefore, the error due to the reference value update can be reduced, and highly accurate detection can be performed.

Also, by changing the reference value update cycle in accordance with the output, it is possible to increase the update timing at a low density, and it is possible to use the output at the time of cleaning as the reference value, thereby achieving accurate detection. Can be.

Further, by changing the cycle and amount of the reference value update according to the output, the error due to the reference value update is reduced and the reference value can be accurately obtained.

Means for judging the level of the gas sensor signal and switching a load resistance value connected in series to the gas sensor in accordance with the level; and changing the reference value in accordance with the change in the load resistance value to the level of the gas sensor signal. And a means for correcting the relationship so as not to change, so that there is an effect that a wide range of gas sensor signals can be processed without lowering the calculation accuracy.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a first embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation.

FIG. 3 is a flowchart for explaining the operation of the second embodiment.

FIG. 4 is a flowchart for explaining the operation of the third embodiment.

FIG. 5 is an explanatory diagram when the reference value is updated.

FIG. 6 is an overall configuration diagram of the fourth embodiment.

FIG. 7 is a flowchart for explaining the operation.

FIG. 8 is an explanatory diagram of a conventional reference value update.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas sensor 2,15,16 Resistance 7 Sensor resistance calculation part 8 Reference value generation part 9 Pollution degree calculation part 10 D / A converter 11 Calculation part 12,13 Comparator 14 Load resistance switching part 17,18 Switch element 20,21 Comparator

Claims (5)

[Claims] An output means for outputting an output signal of a gas sensor, a reference value serving as a reference for the output signal, and comparing the reference value with the output signal to output a degree of contamination of an atmosphere; A gas detection apparatus comprising: a reference value updating unit that updates an output signal so as to approach the output signal; and an update condition determining unit that changes an update condition of the reference value updating unit in accordance with the pollution degree. 2. The gas detection device according to claim 1, wherein the update condition determining means determines the update condition by changing an amount by which the reference value approaches the output signal. 3. The gas detection device according to claim 1, wherein the updating condition determining means determines the updating condition by changing a cycle of bringing the reference value closer to the output signal. 4. The gas detecting apparatus according to claim 1, wherein said updating condition determining means determines the updating condition by changing a period and an amount of bringing the reference value closer to the output signal. 5. A load resistance switching means for determining a level of a gas sensor signal and switching a load resistance value connected in series to the gas sensor according to the level, and a reference value according to a change in the load resistance value. A gas detection device comprising: a reference value correction unit that corrects the relationship with the level of a gas sensor signal so as not to change.