JP2010048654A - Concentration measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration measuring instrument capable of keeping the pressure in a gas sample chamber constant. <P>SOLUTION: The pressure in the carbon dioxide module 2 of the concentration measuring instrument 1 is measured by an absolute pressure sensor 43, and the measuring result and a preset reference pressure set value are subtracted. In a case that the pressure in the carbon dioxide module 2 is lower than the reference pressure set value, the number of rotations of the motor of a pump 45 is raised to increase the flow velocity of the atmosphere supplied into the carbon dioxide module 2 and, in a case that the pressure in the carbon dioxide module 2 is higher than the reference pressure set value, the number of rotations of the motor of the pump 45 is lowered to decrease the flow velocity of the atmosphere supplied into the carbon dioxide module 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 includes a light source, a gas sample chamber that guides light from the light source, and a sensor that receives light from the light source guided from the gas sample chamber. The gas sample chamber is predetermined based on the intensity of light from the light source received by the sensor, the supply unit for supplying the atmosphere into the gas sample chamber, the discharge unit for discharging the atmosphere in the gas sample chamber, and the sensor. A concentration calculation unit for calculating the concentration of the gas obtained.

  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 from the supply unit with a pump or the like into the gas sample chamber, and measures the intensity of infrared rays from the light source received by the infrared sensor through the filter, thereby the above-described atmosphere in the atmosphere. The concentration of the gas to be measured is measured (see, for example, Patent Document 1).

Further, since the gas concentration varies depending on the pressure, Patent Document 2 discloses a correction method for measuring the pressure in the gas sample chamber and correcting the concentration based on the pressure.
JP 2007-212315 A JP 2003-14632 A

  Since the correction method disclosed in Patent Document 2 described above is performed by applying the Boyle-Charles law, there is a problem that pressure correction cannot be performed accurately at low concentrations (several hundred ppm or less). there were.

  In Patent Document 2, correction is performed on the premise that there is pressure fluctuation, but if the pressure in the gas sample chamber can be kept constant by eliminating fluctuations in atmospheric pressure, there is no need to perform correction by a correction formula. .

  Then, this invention makes it a subject to provide the density | concentration measuring apparatus which can keep the pressure in a gas sample chamber constant.

  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 sensor that receives light from the light source guided from the gas sample chamber. On the basis of the intensity of light from the light source received by the sensor, a supply unit for supplying an atmosphere into the gas sample chamber, a discharge unit for discharging the atmosphere in the gas sample chamber, A concentration measuring device comprising: a concentration calculating unit that calculates a predetermined gas concentration in the gas sample chamber; and a pressure measuring unit that measures the pressure in the gas sample chamber; and the pressure measuring unit Pressure comparison means for comparing the pressure in the gas sample chamber with a predetermined pressure set in advance, and the supply amount of the atmosphere to the supply unit based on the comparison result of the pressure comparison means A supply quantity changing means for further, the concentration measuring apparatus characterized by comprising a.

  According to a second aspect of the present invention, in the first aspect of the present invention, when the pressure in the gas sample chamber is lower than the preset predetermined pressure as a result of comparison by the pressure comparison means, the supply is performed. The amount changing means increases the supply amount of the atmosphere to the supply unit.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein when the pressure in the gas sample chamber is higher than the predetermined pressure set as a result of comparison by the pressure comparison means, The supply amount changing means reduces the supply amount of the atmosphere to the supply unit.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein an orifice is provided in the discharge portion.

  As described above, according to the first aspect of the present invention, the pressure in the gas sample chamber measured by the pressure measuring means is compared with a predetermined pressure set in advance by the pressure comparing means, and the comparison result is obtained. Since the supply amount changing means changes the supply amount of the atmosphere of the supply unit based on this, the pressure in the gas sample chamber can be maintained at a predetermined pressure, and pressure correction or the like becomes unnecessary. Therefore, it is possible to measure the concentration with high accuracy without depending on the pressure.

  According to the second aspect of the present invention, when the pressure in the gas sample chamber is lower than the predetermined pressure set as a result of the comparison by the pressure comparison means, the supply amount change means supplies the supply amount of the atmosphere in the supply section. Therefore, the flow rate of the atmosphere can be increased so as to keep the pressure of the gas sample chamber constant.

  According to the third aspect of the present invention, when the pressure in the gas sample chamber is higher than a predetermined pressure set as a result of the comparison by the pressure comparison means, the supply amount change means supplies the supply amount of the atmosphere in the supply section. Therefore, the flow rate of the atmosphere can be lowered so as to keep the pressure of the gas sample chamber constant.

  According to the invention described in claim 4, since the orifice structure is provided in the discharge part, it is possible to suppress an increase in pressure fluctuation in the gas sample chamber and to easily control the pressure fluctuation.

  Hereinafter, a concentration measuring apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.

  As shown in FIG. 1, the concentration measuring apparatus 1 includes a carbon dioxide module 2 as a gas sample chamber filled with an atmosphere containing a gas whose concentration is to be measured, a control unit 42, and an absolute pressure as pressure measuring means. A sensor 43, a subtractor 44 as pressure comparison means, a pump 45 as supply amount changing means, and a humidity sensor 46 are provided.

  As shown in FIGS. 1 and 2, the carbon dioxide module 2 includes a measurement cell 6, a light emitting unit 40, a light receiving unit 41, an INLET 47 as a supply unit, and an OUTLET 48 as a discharge unit.

  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. 3 and 4, 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 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 electric energy, and outputs it as a sensor output to the μCOM 5 of the control unit 42 described later. 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.

  The INLET 47 is a pipe for supplying an external atmosphere such as the atmosphere into the carbon dioxide module 2 and is formed in a cylindrical shape and connected to the light emitting unit 40 or the light receiving unit 41.

  The OUTLET 48 is a pipe for discharging the atmosphere in the carbon dioxide module 2 to the outside, and is formed in a cylindrical shape and connected to the light receiving unit 41 or the light emitting unit 40. Further, the OUTLET 48 is provided with an orifice 50 inside as shown in FIG. The orifice 50 is provided with a plurality of small holes 51 in a plate formed on the disk, and is provided perpendicular to the direction in which the atmosphere flows.

  As shown in FIG. 2, the control unit 42 includes a control circuit unit 3, a light receiving circuit unit 4, and a microcomputer (hereinafter referred to as μcom) 5 as a concentration calculation unit.

  As shown in FIG. 2, 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 (pulse lighting) according to a command of μcom5. Let

  As shown in FIG. 6, the light receiving circuit unit 4 includes a plurality of amplifiers 19, a switcher 20, and an A / D converter 21. 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.

  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.

  The absolute pressure sensor 43 is configured by, for example, a semiconductor pressure sensor, and is a sensor that measures the absolute pressure (pressure based on complete vacuum) in the carbon dioxide module 2.

  The subtracter 44 subtracts the reference pressure set value as a predetermined pressure set in advance and the absolute pressure in the carbon dioxide module 2 measured by the absolute pressure sensor 43, and outputs the result to the pump 45. The reference pressure set value is desirably set to an absolute pressure of 1 atm (1013 hPa) or more, for example.

  The pump 45 sucks an atmosphere such as the outside air by a built-in motor and outputs it to the humidity sensor 46. Further, the pump 45 changes the flow rate of the atmosphere output to the humidity sensor 46 by changing the number of rotations of the motor based on the result of the subtracter 44.

  The humidity sensor 46 is composed of, for example, a polymer film type sensor, is provided in the INLET 47 of the carbon dioxide module 2, and measures the humidity of the atmosphere supplied into the carbon dioxide module 2.

  In the concentration measuring device of the present embodiment, when the result of subtraction by the subtracter 44 becomes a positive value, the absolute pressure in the carbon dioxide module 2 measured by the absolute pressure sensor 43 is lower than the reference pressure set value. As a result, the pump 45 increases the rotational speed of the motor to increase the amount of the atmosphere to be sucked and increase the flow rate of the atmosphere supplied into the carbon dioxide module 2. That is, the absolute pressure in the carbon dioxide module 2 is increased by increasing the flow rate. That is, when the pressure in the carbon dioxide module 2 is lower than the reference pressure set value, the pump 45 increases the supply amount of the atmosphere to the INLET 47.

  If the result of subtraction by the subtractor 44 is a negative value, it is determined that the absolute pressure in the carbon dioxide module 2 measured by the absolute pressure sensor 43 is higher than the reference pressure set value, and the pump 45 is a motor. The number of atmospheres to be sucked is reduced by lowering the number of rotations, and the flow rate of the atmosphere supplied into the carbon dioxide module 2 is lowered. That is, the absolute pressure in the carbon dioxide module 2 is lowered by lowering the flow rate. That is, when the pressure in the carbon dioxide module 2 is higher than the reference pressure set value, the pump 45 reduces the supply amount of the atmosphere to the INLET 47. When the result of subtraction by the subtracter 44 is 0, the absolute pressure in the carbon dioxide module 2 is the reference pressure set value, so the rotation speed of the motor of the pump 45 is not changed.

  In this embodiment, the subtractor 44 is provided and the output of the absolute pressure sensor 43 is subtracted from the reference pressure set value. However, the output of the absolute pressure sensor 43 is input to μcom 5 of the control unit 42, and The reference pressure set value may be stored in a memory or the like, compared, and the comparison result may be output from the control unit 42 to the pump 45.

  According to the present embodiment, the pressure in the carbon dioxide module 2 of the concentration measuring device 1 is measured by the absolute pressure sensor 43, and the measurement result is subtracted from the preset reference pressure set value to obtain the reference pressure set value. If the absolute pressure in the carbon dioxide module 2 is low, the rotational speed of the motor of the pump 45 is increased to increase the flow rate of the atmosphere supplied into the carbon dioxide module 2, and the carbon dioxide module 2 has a higher flow rate than the reference pressure setting value. When the absolute pressure is high, the rotation speed of the motor of the pump 45 is lowered to lower the flow velocity of the atmosphere supplied into the carbon dioxide module 2, so that the pressure in the carbon dioxide module 2 can be kept at a predetermined pressure. This eliminates the need for pressure correction. Therefore, it is possible to measure the concentration with high accuracy without depending on the pressure.

  In addition, since the orifice 50 is provided in the OUTLET 48, it is possible to suppress an increase in pressure fluctuation in the gas sample chamber and to easily control the pressure fluctuation.

  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 the structure of the carbon dioxide module and control unit which were shown by FIG. It is explanatory drawing which shows typically the front of the light reception unit of the carbon dioxide module shown by FIG. It is explanatory drawing which shows typically the cross section of the VI-VI line in FIG. FIG. 2 is a cross-sectional perspective view showing the inside of OUTLET shown in FIG. 1. It is explanatory drawing which shows the structure of the light-receiving circuit of the density | concentration measuring apparatus shown by FIG.

Explanation of symbols

1 Concentration measuring device 2 Carbon dioxide module (gas sample chamber)
7 Light source 14 Infrared sensor (sensor)
40 Light emitting part 41 Light receiving part 43 Absolute pressure sensor (pressure measuring means)
44 Subtractor (pressure comparison means)
45 Pump (Supply amount changing means)
47 INLET (supply section)
48 OURLET (Discharge Department)
50 orifice

Claims (4)

A light source, a gas sample chamber for guiding light from the light source, a light receiving unit provided with a sensor for receiving light from the light source guided from the gas sample chamber, and a supply for supplying an atmosphere into the gas sample chamber A concentration unit that calculates a predetermined gas concentration in the gas sample chamber based on the intensity of light from the light source received by the sensor, a discharge unit that discharges the atmosphere in the gas sample chamber In a concentration measuring device comprising:
Pressure measuring means for measuring the pressure in the gas sample chamber;
Pressure comparing means for comparing the pressure in the gas sample chamber measured by the pressure measuring means with a predetermined pressure set in advance;
Supply amount changing means for changing the supply amount of the atmosphere to the supply unit based on the comparison result of the pressure comparison means;
A concentration measuring apparatus comprising:   When the pressure in the gas sample chamber is lower than the preset predetermined pressure as a result of comparison by the pressure comparison means, the supply amount changing means increases the supply amount of the atmosphere to the supply section. The concentration measuring apparatus according to claim 1, wherein the apparatus is a concentration measuring apparatus.   When the pressure in the gas sample chamber is higher than the predetermined pressure set as a result of comparison by the pressure comparison means, the supply amount changing means reduces the supply amount of the atmosphere to the supply section. The concentration measuring apparatus according to claim 1 or 2, characterized in that:   The concentration measuring apparatus according to claim 1, wherein an orifice is provided in the discharge unit.

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