JP5562538B2 - Concentration measuring device - Google Patents

Description

  The present invention relates to a concentration measuring apparatus that measures the concentration of a predetermined gas such as carbon dioxide.

  For example, a concentration measuring device that measures the concentration of a predetermined gas such as carbon dioxide receives a light source, a gas sample chamber that guides light from the light source, and light from the light source that is guided from the gas sample chamber. The gas sample based on the intensity of light from the light source received by the sensor, and a light receiving portion provided with a transmission member that transmits only light of a predetermined wavelength between the sensor and the light source. A concentration calculation unit that calculates a predetermined gas concentration in the room.

  The light source emits infrared rays, for example. The light receiver includes an infrared sensor and a filter that is disposed between the infrared sensor and the light source and transmits only infrared rays having a predetermined wavelength. The wavelength of infrared rays that pass through the filter is determined by the concentration of the gas to be measured.

Then, the concentration measuring device supplies the atmosphere into the gas sample chamber by a pump or the like, and measures the intensity of infrared rays from the light source received by the infrared sensor through the filter. The concentration of gas is measured (for example, refer to Patent Document 1).
JP 2007-212315 A

  However, in the conventional concentration measuring apparatus disclosed in Patent Document 1 described above, since the potential on the ground side of the infrared sensor is grounded to 0 potential, the sensor output is caused by the thermal fluctuation of the light source used in the light emitting unit. Waviness occurred, and the waviness became noise, and it was difficult to measure the concentration with high accuracy.

  Then, this invention makes it a subject to provide the density | concentration measuring apparatus which can measure the density | concentration of the gas of the measuring object in atmosphere accurately.

The invention according to claim 1, which has been made to solve the above problems, includes a light source, a gas sample chamber that guides light from the light source, and a thermopile that receives light from the light source guided from the gas sample chamber. A light receiving portion provided with a transmission member that transmits only light of a predetermined wavelength between the mold sensor and the light source and the thermopile sensor; and the intensity of light from the light source received by the thermopile sensor. A concentration calculation unit that calculates a concentration of a predetermined gas in the gas sample chamber based on a constant voltage source that supplies a predetermined constant voltage, and a supply from the constant voltage source bias applying means is provided for dividing a resistor, a constant voltage is, applies a voltage divided by the resistor as a bias voltage to the cold junction of the thermopile sensor Provided, together with the thermopile sensor to the light receiving portion is provided with a plurality, concentration measuring device wavelengths transmitted through the transmission member respectively corresponding to the plurality of the Samopai Le sensor are different from each other, characterized in that It is.

The invention according to claim 2 is a light source, a gas sample chamber that guides light from the light source, a thermopile sensor that receives light from the light source guided from the gas sample chamber, the light source, and the thermopile type. A light receiving portion provided with a transmission member that transmits only light of a predetermined wavelength between the sensor and a predetermined intensity in the gas sample chamber based on the intensity of light from the light source received by the thermopile sensor. in the concentration measuring apparatus and a concentration calculator that calculates the concentration of the gas was measured density which is characterized by comprising a bias applying means for applying a predetermined bias voltage to the cold junction of the thermopile sensor Device.

Invention according to claim 3, in the invention described in claim 2, together with the thermopile sensor to the light receiving portion is provided with a plurality of said Samopai Le sensor transmission for wavelengths of a plurality of said transmission member Are subtracted by subtracting the intensity of light from the light source received by one of the thermopile sensors and the intensity of light from the light source received by the other sensor. And the bias applying means adjusts the light intensity of the one sensor and the bias voltage with the other sensor so that the difference between the subtracting means becomes zero. .

The invention according to claim 4 is the invention according to claim 3 , wherein the concentration calculation unit calculates the concentration of the gas based on a subtraction result of the subtraction means .

Invention according to claim 5, in the invention described in claim 2, together with the thermopile sensor to the light receiving portion is provided with a plurality of said Samopai Le sensor transmission for wavelengths of a plurality of said transmission member The bias applying means adjusts the bias voltages of the one sensor and the other sensor to be equal based on the outputs of the plurality of thermopile sensors when the light source is turned off. It is characterized by doing.

As described above, according to the first aspect of the present invention, the bias applying means can apply a predetermined bias voltage to the cold junction side of the thermopile type sensor , so that the sensor when the light source is pulsed is applied. Since the low-side output value that is the lower end value of the light source can be reliably detected, noise generated due to fluctuations in the sensor output waveform due to thermal fluctuation on the light source side can be eliminated, and accurate and stable measurement can be performed. . Further, the bias applying means includes a constant voltage source, and a constant voltage of the constant voltage source is divided by a resistor and supplied to the thermopile sensor as a bias voltage, so that the sensor output waveform due to thermal fluctuation on the light source side is supplied. Noise generated by fluctuations can be eliminated and accurate and stable measurement can be performed. Moreover, since the several thermopile type sensor is provided in the light-receiving part, and the wavelength of the transmissive member corresponding to each of the several thermopile type sensor is mutually different, the density | concentration of multiple types of gas can be measured.

According to the second aspect of the present invention, since a predetermined bias voltage can be applied to the cold junction side of the thermopile sensor by the bias applying means, the lower limit value of the sensor when the light source is pulsed is obtained. Since the low-side output value can be detected reliably, noise that has been caused by fluctuations in the sensor output waveform due to thermal fluctuations on the light source side can be eliminated, and accurate and stable measurement can be performed.

According to the invention described in claim 3, the subtracting means subtracts the light intensity from the light source received by one of the plurality of sensors and the light intensity from the light source received by the other sensor. Since the bias applying means adjusts the bias voltage between one sensor and the other sensor so that the difference between the subtracting means becomes zero, the individual difference or temperature difference between the sensors can be absorbed with high accuracy. The bias voltages of a plurality of sensors can be made equal.

According to the fourth aspect of the present invention, since the gas concentration is calculated based on the subtraction result of the subtracting means, the resolution of the gas concentration measurement can be increased, so that the concentration is measured with higher accuracy. be able to.

According to the invention of claim 5, since the bias voltage between one sensor and another sensor bias applying means on the basis of the outputs of the plurality of sensors when the light source off is adjusted to be the same By absorbing individual differences and temperature differences between sensors, it is possible to equalize the bias voltages of a plurality of sensors with high accuracy.

[First Embodiment]
Hereinafter, a concentration measuring apparatus according to a first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the concentration measuring device 1 includes a gas sample chamber 2 filled with an atmosphere containing a gas whose concentration is to be measured, a light emitting unit 40, a light receiving unit 41, a control circuit unit 3, and a light receiving unit. A circuit unit 4 and a microcomputer (hereinafter referred to as μcom) 5 as a concentration calculation unit are provided.

  The gas sample chamber 2 includes a measurement cell 6 as shown in FIG. The measurement cell 6 is formed in a cylindrical shape and guides infrared rays from a light source 7 described later to the light receiving unit 8.

  The light emitting unit 40 is provided at one end of the measurement cell 6 and is formed in, for example, a substantially box shape, and the light source 7 is provided therein. The light source 7 emits infrared light as light from one end portion to the other end portion of the measurement cell 6 by applying a voltage. As the light source, for example, a black body furnace or a light bulb is used. A reflector 30 is attached to the light source 7. The reflector 30 reflects the light emitted from the light source 7 and directs it to the light receiving unit 8 as parallel light.

  The light receiving unit 41 is provided at the other end of the measurement cell 6 and is formed, for example, in a substantially box shape, and the light receiving unit 8 is provided therein. As shown in FIGS. 2 and 3, the light receiving unit 8 includes a unit main body 11, a plurality of light receivers 12, and a light collecting member 13. The unit main body 11 is formed in a box shape. In addition, the light emitting unit 40 and the light receiving unit 41 are provided with a supply unit (not shown) for supplying or discharging an external atmosphere. The supply unit is connected to a pump and piping, forcing the atmosphere in the gas sample chamber 2. The gas in the gas sample chamber 2 is forcibly discharged.

  In the illustrated example, two light receivers 12 are provided. Each of the light receivers 12 includes an infrared sensor 14 as a sensor and a transmission member 15. The infrared sensor 14 is attached to the unit main body 11. The infrared sensors 14 of the plurality of light receivers 12 are arranged on the same plane. The infrared sensor 14 receives infrared rays emitted from the light source 7 and transmitted through the transmission member 15 and converts the heat of the infrared rays into electric energy. The infrared sensor 14 converts infrared heat into electrical energy and outputs the converted energy toward the μcom 5 as a sensor output. As the infrared sensor 14, a thermopile type is used, for example.

  The transmission member 15 is attached to the unit body 11 and is disposed between the infrared sensor 14 and the light source 7. The transmission members 15 of the plurality of light receivers 12 are arranged on the same plane. Each of the transmissive members 15 transmits only infrared rays having a predetermined wavelength out of infrared rays from the light source 7 and guides the infrared rays having the transmitted wavelengths to the infrared sensor 14. The transmission members 15 of the plurality of light receivers 12 have different wavelengths of infrared rays that pass through each other.

  The wavelength of infrared rays that pass through the transmissive member 15 is determined according to the gas that the concentration measuring device 1 is to measure the concentration of. The wavelength of the infrared ray transmitted through the transmission member 15 is set to a wavelength of an infrared ray having a small transmittance with respect to the gas whose concentration is to be measured. The light receiver 12 uses carbon dioxide as a gas to be measured. In the illustrated example, one of the light receivers 12 is used as a reference, and the transmitting member 15 transmits only infrared light having a wavelength of about 4.0 μm that does not attenuate at all in the atmosphere. The other light receiver 12 is used to measure the concentration of carbon dioxide, and the transmission member 15 transmits only infrared rays having a wavelength that is likely to be attenuated in the carbon dioxide described above in the vicinity of 4.3 μm.

  The condensing member 13 condenses infrared rays in a predetermined angle range such as 300 degrees and concentrates the infrared rays on the transmitting member 15, that is, the infrared sensor 14. Then, in addition to the infrared rays directly incident from the light source 7, infrared rays reflected by the inner surface of the outer wall of the measurement cell 6 can be collected in the infrared sensor 14, so that the infrared light receiving efficiency can be improved. Note that a Fresnel lens or the like can be used as the light collecting member 13.

  As shown in FIG. 1, the control circuit unit 3 includes an oscillator 16, a clock frequency dividing circuit 17, a constant voltage circuit 18, and the like, and blinks the light source 7 at a predetermined frequency according to a command of μcom5.

  As shown in FIG. 4, the light receiving circuit unit 4 includes a plurality of amplifiers 19, a switching device 20, an A / D converter 21, and a voltage dividing circuit 23. The amplifiers 19 are provided in one-to-one correspondence with the infrared sensor 14. The amplifier 19 amplifies the signal from the corresponding infrared sensor 14 and outputs it to the A / D converter 21 via the switcher 20. The A / D converter 21 converts the signal from the infrared sensor 14 into a digital signal and outputs it to the μcom 5.

  As shown in FIG. 4, the voltage dividing circuit 23 as a bias applying means applies a predetermined constant voltage to the cold junction side of the thermopile. The voltage dividing circuit 23 is a circuit in which a resistor 25 and a resistor 26 are connected in series to a constant voltage source 24 that outputs a predetermined constant voltage, and an intermediate point between the resistor 25 and the resistor 26 is an infrared sensor 14 ( It is connected to the cold junction of the thermopile. As a result, a voltage obtained by dividing the constant voltage source 24 by the ratio of the resistance values of the resistors 25 and 26 is applied to the cold junction as a bias voltage. One voltage dividing circuit 23 may be commonly connected to the plurality of infrared sensors 14 or may be provided individually for each infrared sensor 14.

  Further, as shown in FIG. 5, the voltage dividing circuit of FIG. 4 may not be provided, and the DC power source (constant voltage source) may be directly connected to the cold junction of the infrared sensor 14. Also in this case, the two infrared sensors 14 may be connected in common, or a DC power source may be provided individually.

  The μcom 5 is connected to the control circuit unit 3 and the light receiving circuit unit 4 and controls these operations, thereby controlling the operation of the concentration measuring apparatus 1 as a whole. μcom5 is a computer that operates according to a predetermined program. As is well known, this μcom 5 is a central processing unit (CPU) that performs various processes and controls in accordance with a predetermined program, a ROM that is a read-only memory storing a program for the CPU, and various data. And a RAM that is a readable / writable memory having an area necessary for processing operations of the CPU.

  In addition, the μcom 5 is connected to an electrically erasable / rewritable read-only memory capable of holding stored contents even when the concentration measuring apparatus 1 itself is in an OFF state. The memory stores various information such as an extinction coefficient, a measurement distance, and a concentration conversion coefficient necessary for calculating the concentration, and stores the calculated concentration in a time series so that it can be read from the outside.

  In the concentration measuring apparatus 1 having the above-described configuration, the light source 7 blinks (pulse lighting), and the infrared rays from the light source 7 are received by each infrared sensor 14. The μcom 5 of the concentration measuring apparatus 1 measures the concentration of a predetermined gas (carbon dioxide) in the atmosphere based on the intensity of infrared rays received by the infrared sensor 14 and the like. Specifically, the μcom 5 of the concentration measuring apparatus 1 compares the intensity of infrared light received by the infrared sensor 14 used as a reference with the intensity of infrared light received by the infrared sensor 14 for measuring carbon dioxide, Measure the concentration of carbon dioxide to be measured.

  At this time, the output waveform of the infrared sensor 14 is as shown in FIG. The concentration of carbon dioxide is calculated by calculating the difference between the Hi (mountain) value and lo (valley) value of the output waveforms of the two infrared sensors 14 generated when the light source 7 is pulsed. To measure. In the case of this embodiment, the output of the infrared sensor 14 is raised by the bias voltage by the circuits shown in FIGS. That is, by applying a potential higher than 0 potential (ground potential), the value of the lo portion of the pulse waveform can be reliably measured, so that the influence of noise due to waveform undulation can be eliminated as shown in FIG.

  According to the present embodiment, since the predetermined bias voltage is applied to the cold junction of the infrared sensor 14 provided in the light receiving unit 41 of the concentration measuring device 1 by the voltage dividing circuit 23, the output waveform of the infrared sensor 14 is The lo portion can be reliably measured, and the influence of noise caused by the undulation of the output waveform due to the thermal fluctuation of the light source 7 can be eliminated. Therefore, the gas concentration can be accurately measured.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. Note that the same parts as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, the light receiving circuit unit 4 is different from the first embodiment. The light receiving circuit unit 4 of this embodiment includes a plurality of amplifiers 19, a switcher 20, an A / D converter 21, a subtraction circuit 27, and a plurality of D / A converters 28. The plurality of amplifiers 19, the switcher 20, and the A / D converter 21 are the same as those in the first embodiment. A subtracting circuit 27 as subtracting means is a circuit that subtracts the outputs of the amplifier 19. Specifically, the subtracted value is obtained by subtracting the output through the amplifier 19 of the infrared sensor 14 receiving the infrared light near 4.3 μm from the output through the amplifier 19 of the infrared sensor 14 receiving the infrared light near 4.0 μm. Amplify. The D / A converter 28 is provided in one-to-one correspondence with the infrared sensor 14, converts the bias voltage value calculated by μcom 5 into an analog voltage, and applies the analog voltage to the infrared sensor 14 as a bias voltage.

In the present embodiment, initially, a bias voltage value higher than a predetermined 0 potential (ground potential) preset in μcom 5 is applied to each of the two infrared sensors 14 via the D / A converter 28, and the subtraction circuit The difference between the value (through the amplifier 19) of the infrared sensor 14 that has received the infrared light around 4.0 μm and the value (through the amplifier 19) of the infrared sensor 14 that has received the infrared light around 4.3 μm calculated in 27. In μcom5, the bias voltage values of the two infrared sensors 14 are adjusted to be the same (that is, the difference is zero), and the adjusted bias voltage value is supplied to the D / A converter 28. Output . By this, it is possible to improve the accuracy of concentration calculation of gas (carbon dioxide) it is possible to match the bias voltage of the two infrared sensor 14 more accurately.

  In this embodiment, the value of the infrared sensor 14 that has received the infrared light around 4.0 μm calculated by the subtraction circuit 27 (via the amplifier 19) and the (amplifier) of the infrared sensor 14 that has received the infrared light around 4.3 μm are calculated. The concentration is calculated by μcom5 based on the value obtained by amplifying the difference from the value (via 19). As a result, it is possible to increase the density calculation resolution as compared with the calculation based on the difference between Hi and lo in the waveform of FIG.

  In the present embodiment, in addition to the adjustment of the bias voltage using the subtraction circuit 27 described above, based on the value of lo of the waveform in FIG. 6 among the output values via the amplifiers 19 of the two infrared sensors 14. There is a way to adjust. More specifically, since the period of lo is a period when the light source 7 is turned off when the light source 7 is pulsed, the value measured at this time is not the intensity of light received by the infrared sensor 14. It becomes the bias voltage itself. Therefore, the outputs (bias voltages) of the two infrared sensors 14 in the lo period may be measured and adjusted by μcom 5 so that they are equal. In other words, the bias voltages of one infrared sensor 14 and the other infrared sensor 14 are adjusted to be equal based on the outputs of the plurality of infrared sensors 14 when the light source 7 is turned off.

  In the present embodiment, the light receiving circuit section 4 is configured so that both the method using the subtracting circuit 27 described above and the method using the output of the infrared sensor 14 when the light source 7 is turned off can be used. Any one of the above-described method using the subtraction circuit 27 and the method using the output of the infrared sensor 14 when the light source 7 is turned off may be selected as appropriate. The bias voltage may be adjusted by adjusting the voltage of one infrared sensor 14 to the voltage of the other infrared sensor 14, or between the voltage of one infrared sensor 14 and the voltage of the other infrared sensor 14. A method of matching the voltage may be used.

  According to the present embodiment, the difference between the value of the infrared sensor 14 that has received infrared light in the vicinity of 4.0 μm and the value of the infrared sensor 14 that has received infrared light in the vicinity of 4.3 μm is calculated by the subtraction circuit 27, and Since the adjustment is made with μcom5 so that the bias voltages of the two infrared sensors 14 are equal to each other (so that the difference becomes 0), individual differences and temperature differences between the infrared sensors 14 are absorbed and highly accurate. The bias voltages of the two infrared sensors can be made equal. Therefore, the gas concentration can be measured with higher accuracy.

  In addition, the bias voltage is measured from the outputs of the two infrared sensors 14 during the period when the light source 7 is turned off, and is adjusted by μcom 5 so that they are equal (so that the difference is 0). It is possible to equalize the bias voltages of the two infrared sensors with high accuracy by absorbing individual differences and temperature differences. Therefore, the gas concentration can be measured with higher accuracy.

  In addition, the gas concentration is measured from the difference between the value of the infrared sensor 14 that receives infrared light around 4.0 μm calculated by the subtracting circuit 27 and the value of the infrared sensor 14 that receives infrared light near 4.3 μm. Therefore, the resolution can be increased, and more accurate concentration measurement can be performed.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

It is explanatory drawing which shows the structure of the density | concentration measuring apparatus concerning one Embodiment of this invention. It is explanatory drawing which shows typically the front of the light-receiving unit of the gas sample chamber shown by FIG. It is explanatory drawing which shows typically the cross section of the VI-VI line in FIG. It is explanatory drawing which shows the structure of the light-receiving circuit of the density | concentration measuring apparatus shown by FIG. FIG. 5 is an explanatory diagram showing another configuration of the bias applying circuit of the infrared sensor in the light receiving circuit shown in FIG. 4. FIG. 5 is an output waveform diagram of an infrared sensor of the light receiving circuit shown in FIG. 4. It is explanatory drawing which shows the structure of the light-receiving circuit of the density | concentration measuring apparatus concerning the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Concentration measuring device 2 Gas sample chamber 4 Light receiving circuit part 5 Microcomputer (Concentration calculation part, bias application means)
6 Measurement cell 7 Light source 14 Infrared sensor (sensor)
15 Transmission member 23 Voltage dividing circuit (bias applying means)
24 constant voltage source 27 subtraction circuit (subtraction means)
40 Light emitting part 41 Light receiving part

Claims (5)

A light source, a gas sample chamber for guiding light from the light source, a thermopile sensor for receiving light from the light source guided from the gas sample chamber, and a predetermined wavelength between the light source and the thermopile sensor A light receiving portion provided with a transmission member that transmits only the light of the light, and a concentration for calculating a predetermined gas concentration in the gas sample chamber based on the intensity of light from the light source received by the thermopile sensor In a concentration measuring device comprising a calculation unit,
A predetermined constant voltage source for supplying a constant voltage, the and a for dividing resistor a constant voltage supplied from the constant voltage source, cold junction of the divided voltage by the resistor the thermopile sensor comprising a bias application means for applying a bias voltage to,
Together with the thermopile sensor is provided with a plurality on the light receiving portion, different wavelengths for transmission of the transmission member respectively corresponding to the plurality of the Samopai Le sensor each other,
A concentration measuring apparatus characterized by the above. A light source, a gas sample chamber for guiding light from the light source, a thermopile sensor for receiving light from the light source guided from the gas sample chamber, and a predetermined wavelength between the light source and the thermopile sensor A light receiving portion provided with a transmission member that transmits only the light of the light, and a concentration for calculating a predetermined gas concentration in the gas sample chamber based on the intensity of light from the light source received by the thermopile sensor In a concentration measuring device comprising a calculation unit,
Concentration measuring apparatus characterized by comprising a bias application means for applying a predetermined bias voltage to the cold junction of the thermopile sensor. Together with the the light receiving portion is provided with a plurality the thermopile sensor, a wavelength which passes through the transmitting member is different from each other in correspondence with the plurality of the Samopai Le sensor,
Subtracting means for subtracting the intensity of light from the light source received by one sensor among the plurality of thermopile sensors and the intensity of light from the light source received by the other sensor,
3. The density according to claim 2, wherein the bias applying unit adjusts the light intensity of the one sensor and the bias voltage with the other sensor so that the difference between the subtracting units becomes zero. measuring device.   The concentration measuring apparatus according to claim 3, wherein the concentration calculating unit calculates the concentration of the gas based on a subtraction result of the subtracting unit. Together with the the light receiving portion is provided with a plurality the thermopile sensor, a wavelength which passes through the transmitting member is different from each other in correspondence with the plurality of the Samopai Le sensor,
The bias applying means adjusts the bias voltages of the one sensor and the other sensor to be equal based on outputs of the plurality of thermopile sensors when the light source is turned off. 2. The concentration measuring apparatus according to 2.

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