JP4294633B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device.

Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 6-66750, a gas sensor made of a metal oxide semiconductor is used to detect atmospheric contamination, particularly the generation of carbon dioxide due to smoking. In this conventional example, in order to correct the drift due to the ambient temperature of the gas sensor, changes with time, etc., the envelope of the gas sensor signal is obtained and the envelope is used as a reference value, and the gas sensor signal level is higher than the reference value. If the gas sensor signal is on the side where the gas concentration is lower than the reference value, the reference value is set to the gas sensor signal. By slowly comparing the level of the gas sensor signal and the level of the current reference value, it is determined that gas has been generated when the difference between the two exceeds an allowable value. FIG. 8 shows the transition of the level (A) of the gas sensor signal and the reference value (B) of this conventional example.
JP-A-6-66750

  By the way, in the conventional example, as shown in FIGS. 8A and 8B, when the level of the gas sensor signal exceeds the reference value, the reference value approaches the gas sensor signal level at regular intervals. Therefore, the difference between the reference value and the level of the gas sensor signal does not increase regardless of the soot state that should be determined as gas generation due to high gas concentration, and the pollution level output cannot be detected accurately. there were.

  In addition, it was difficult to target a wide range of gas sensor signals as a detection target, and a limited range was targeted.

  The present invention solves such a conventional problem, and can prevent noise due to temperature and humidity changes, misdetection due to drift of the gas sensor signal, can quickly detect the rise of the gas sensor signal, and An object of the present invention is to provide a gas detection device that can reduce an error due to calculation of a reference value after detection, and can process a wide range of gas sensor signals without reducing calculation accuracy.

The gas detection device of the present invention is configured to determine a current level of a metal oxide semiconductor gas sensor signal and to change a load resistance switching unit that switches a load resistance value connected in series to the gas sensor according to the current level, and the load A reference for correcting a reference value of the output signal of the gas sensor in accordance with the change of the resistance value so that the relationship with the level of the gas sensor signal does not change before and after the load resistance switching, thereby preventing an error due to the load resistance switching. And a value correcting means.

According to the present invention, it is possible to obtain a gas detection device capable of always performing highly accurate detection even when sensor signals vary greatly due to variations or drifts in metal oxide semiconductor gas sensors .

The present invention, a means for switching to determine the current level of load resistance connected in series to the gas sensor in accordance with the current level of the metal oxide semiconductor gas sensor signal, in response to said change in the load resistance value Since a reference value that serves as a reference for the output signal of the gas sensor is corrected so that the relationship with the level of the gas sensor signal does not change before and after the load resistance switching, a means for preventing errors due to the load resistance switching is provided. There is an effect that the signal can always be processed without reducing the calculation accuracy. Even when the resistance value of the gas sensor varies greatly during manufacturing or during use, highly accurate detection is always possible, and errors due to load resistance switching can be prevented.

To determine the current level of metal oxide semiconductor gas sensor signal, and the load resistance switching means for switching the load resistance connected in series to the gas sensor in accordance with the current level, the gas sensor according to the change of the load resistance And a reference value correcting means for correcting the reference value as a reference of the output signal so that the relationship with the level of the gas sensor signal does not change before and after switching the load resistance and preventing an error caused by switching the load resistance . Further, it is possible to prevent an error in the degree of contamination output before and after switching the load resistance. Even when the resistance value of the gas sensor varies greatly during manufacturing or during use, highly accurate detection is always possible, and errors due to load resistance switching can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

( Reference Example 1)
As shown in FIG. 1, a metal oxide semiconductor gas sensor (hereinafter abbreviated as a 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 source 3. The load resistance circuit includes a resistor 2.

Reference numeral 5 denotes a signal processing unit comprising, for example, a 4-bit microcomputer on a single chip for performing signal processing in this reference example. In the figure, the function is shown in a block form, and the voltage VRL across the load resistance circuit is expressed as a block. A sensor resistance calculation unit 7 that takes in through the A / D converter 6 and calculates the sensor resistance value Rs of the gas sensor 1 from the voltage VRL is taken in through the A / D converter 6 and a reference value Rsm to be compared with the sensor resistance value Rs is obtained. A reference value generation unit 8 to be generated, a contamination degree calculation unit 9 that calculates a contamination degree by comparing the reference value Rsm and the sensor resistance value Rs, and the contamination degree calculated by the contamination degree calculation unit 9 is converted into an analog value. The D / A converter 10 that performs the calculation, the calculation unit 11 that calculates the update amount X and the update cycle Z of the reference value Rsm from the degree of contamination, and the like.

  Next, the circuit of FIG. 1 will be described based on 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 generating unit 8.

  Now, after setting the initial value, the voltage VRL based on the current load resistance value RL is taken in, and the sensor resistance calculation unit 7 calculates the sensor resistance value Rs from the voltage VRL. This calculation is performed by, for example, an equation of Rs = ((256−VRL) × 64) / VRL.

  In this way, the sensor resistance value Rs is compared with the current reference value Rsm generated by the reference value generator 8 by the comparators 12 and 13, and if the sensor resistance value Rs is not equal to or greater than the reference value Rsm, the contamination direction reference value is updated. The reference value Rsm is updated by the unit 8b. Conversely, if the sensor resistance value Rs is equal to or greater than the reference value Rsm0, the reference value Rsm is updated by the cleaning direction reference value update unit 8a. These update amounts and update cycles are calculated by the calculation unit 11 and given to the respective update units 8a and 8b.

  In this case, in the clean direction, for example, Rsm = Rsm0 + (Rs−Rsm0) / 3 is updated every sampling. Rsm0 represents the current reference value.

  In the contamination direction, it is updated at Rsm = Rsm0− (Rsm0−Rs) / X every reference value update cycle (for example, when the number of times of sampling from the previous update timing is equal to or greater than a predetermined value Z). Here, X represents the reference value update amount, and is obtained from X = C1 = (Rsm−Rs) × Vspan × 8 / Rsm. C1 indicates the calculated output of the gas sensor 1. Vspan is a constant, X is in the range of 10 <X <100, and its initial value is 10.

  Now, while the reference value is updated as described above, the contamination degree calculation unit 9 obtains the contamination degree from the difference from the sensor resistance value Rs, and outputs the contamination degree to the outside via the D / A converter 10. .

  For example, in the case of an air cleaner or a ventilation fan, the operation of the fan is controlled according to the degree of contamination.

As described above, by changing the update amount of the reference value according to the output, it is possible to reduce the update amount at a high concentration in the contamination direction and increase the update amount at a low concentration in the clean direction. Since the reference value is actively updated when the density should be low and the update is small when the density should not be the standard value, detection with less error due to the update of the reference value is possible.

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

( Reference Example 2)
This will be described with reference to FIG. Note that the description of the same parts as those in Reference Example 1 is omitted.

  If the sensor resistance value Rs is a contamination direction equal to or less than the reference value Rsm0, the sensor resistance value Rs is updated at Rsm = Rsm0− (Rsm0−Rs) / X1 every reference value update period Z. Here, X1 represents the reference value update amount, and is a constant in the range of 10 <X1 <1000.

  The update cycle Z is obtained by Z = C1 × Vk5. Vk5 is an update cycle coefficient, Z is in the range of 20 <Z <1000, and its initial value is 20.

  As described above, by changing the reference value update period according to the output, the update timing increases at the low concentration when the reference value should be taken, the reference value can be taken reliably, and accurate detection is performed. be able to.

( Reference Example 3)
This will be described with reference to FIG. The description of the same parts as those in Reference Examples 1 and 2 is omitted.

  If the sensor resistance value Rs is a contamination direction equal to or less than the reference value Rsm0, Rsm = Rsm0− (Rsm0−Rs) every reference value update period (when the number of samplings from the previous update timing is equal to or greater than the predetermined value Z). ) / X. Here, X represents the reference value update amount, and is obtained from X = C1 = (Rsm−Rs) × Vspan × 8 / Rsm. C1 indicates the calculated output of the gas sensor 1. Vspan is a constant, X is in the range of 10 <X <500, and its initial value is 10.

  The update cycle Z is obtained by Z = C1 × Vk5. Vk5 is an update cycle coefficient, Z is in the range of 20 <Z <1000, and its initial value is 20.

FIG. 5A shows the state of the reference value update according to this reference example, in which the sensor resistance value Rs is converted into the voltage VRL, and the reference value Rsm is converted into the voltage levels (A) and (B). When the sensor resistance value Rs is lower than the reference value Rsm in the contamination direction, that is, when the gas sensor signal level voltage VRL is in a contamination direction that greatly exceeds the reference value level , that is, when the concentration is high , the gas sensor signal level Thus, the speed is updated in inverse proportion to the gas sensor signal level so that the reference value level approaches gradually. Conversely, when the sensor resistance value Rs is higher than the reference value Rsm in the cleaning direction, that is, when the voltage VRL is lower than the reference value level, the reference value level is updated so as to approach the voltage VRL earlier. FIG. 5B shows the contamination level 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 and update cycle of the reference value update according to the output, it is possible to reduce the update error and reliably take the reference value.

(Example 1 )
This will be described with reference to FIGS. The description of the same parts as those in Reference Examples 1, 2, and 3 is omitted.

FIG. 6 shows the overall configuration of Embodiment 1 of the present invention. In FIGS. 6 and 6, a metal oxide semiconductor gas sensor (hereinafter abbreviated as a gas sensor) 1 is connected to a DC power source 3 such as a battery via a load resistance circuit. It is. Reference numeral 4 denotes a heater provided in the gas sensor 1, and this heater 4 is also connected to the DC power source 3. The load resistance circuit is composed of a combined resistance of resistors 2 and 15 and 16 connected in parallel under the conditions described later. Reference numeral 5 denotes a signal processing unit composed of, for example, a 4-bit microcomputer on a single chip for performing signal processing in this embodiment, and its function is shown in a block form in the figure, and the voltage VRL across the load resistor circuit is expressed as a block. A sensor resistance calculation unit 7 that takes in through the A / D converter 6 and calculates the sensor resistance value Rs of the gas sensor 1 from the voltage VRL is taken in through the A / D converter 6 and loads from the voltage VRL that is the gas sensor signal level. A load resistance switching unit 14 for switching RL, a reference value generating unit 8 for generating a reference value Rsm to be compared with the sensor resistance value Rs, and a pollution degree calculation for calculating a pollution degree by comparing the reference value Rsm and the sensor resistance value Rs. Unit 9, a D / A converter 10 that converts the pollution degree calculated by the pollution degree calculation unit 9 into an analog value, and the pollution degree It consists calculation unit 11 and the like for calculating the update amount X and the update period Z of standard value Rsm.

  The resistors 15 and 16 are connected in parallel to the resistor 2 via the switch elements 17 and 18 of the load resistance switching unit 14. When only the resistor 2 is present, the voltage VRL across the load resistor circuit becomes the maximum value, and the resistor 15 is changed to the resistor 2. The voltage VRL is set to an intermediate value when connected in parallel, and the voltage VRL is set to the minimum value when both resistors 15 and 16 are connected in parallel to the resistor 2.

  Next, the circuit of FIG. 6 will be described based on 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 generating unit 8. Here, the control unit 19 of the load resistance switching unit 14 turns on the switch element 17 so that the initial resistance value RL of the load resistance circuit becomes a composite value of the parallel circuit of the resistors 2 and 15.

  Now, after setting the initial value, the voltage VRL based on the current load resistance value RL is taken, and compared with the lower limit value VRLmin and the upper limit value VRLmax by the comparators 20 and 21 provided in the load resistance switching unit 14, the lower limit value VRLmin and the upper limit value are compared. It is determined whether or not it is in the range of VRLmax. If not, if it is below the lower limit value VRLmin, the load resistance value RL is maximized so that it is above the upper limit value VRLmax. The control unit 19 of the load resistance switching unit 14 controls the switch elements 17 and 18 so that the load resistance value RL becomes the lowest. Then, after switching the load resistance value RL, the voltage VRL is measured, and based on this measured value and the measured value before switching, the reference value correcting unit 8c of the reference value generating unit 8 performs the reference after switching the load resistance value RL. A value correction amount is determined and the currently generated reference value Rsm is corrected according to the load resistance value RL.

  On the other hand, when the voltage VRL is in the range from the lower limit value VRLmin to the upper limit value VRLmax, the sensor resistance calculation unit 7 calculates the sensor resistance value Rs from the voltage VRL.

  At the load resistance switching timing, the reference value update calculation is performed before switching, and the following calculation is performed, for example, 5 seconds after 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)
... (when Rs> Rsm)
Then, Rs = Rs1 is set.

  As described above, by switching the load resistance, even when the resistance value of the gas sensor 1 varies greatly during manufacturing variations or during use, highly accurate detection is always possible, and the reference value is corrected after switching the load resistance. By doing so, errors due to load resistance switching can be prevented.

  The present invention relates to a gas detection device.

Overall configuration diagram of Reference Example 1 Flow chart for explaining the operation Flow chart for explaining operation of Reference Example 2 Flow chart for explaining operation of Reference Example 3 Explanatory drawing when updating the standard value Overall configuration diagram of Embodiment 1 of the present invention Flow chart for explaining the operation Explanatory drawing of conventional reference value update

Explanation of symbols

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

Claims (1)

To determine the current level of metal oxide semiconductor gas sensor signal, and the load resistance switching means for switching the load resistance connected in series to the gas sensor in accordance with the current level, the gas sensor according to the change of the load resistance And a reference value correcting means for correcting the reference value as a reference of the output signal so that the relationship with the level of the gas sensor signal does not change before and after the load resistance switching, and preventing an error due to the load resistance switching. A gas detection device.

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