JP7524834B2 - Gas Measuring Devices - Google Patents

Description

This disclosure relates to a gas measurement device.

JP 09-49797 A (Patent Document 1) discloses an infrared gas analyzer that measures the concentration of gas components by switching between a sample gas and a reference gas. In this infrared gas analyzer, a three-way valve is switched, and the sample gas and the reference gas are alternately supplied to the cell at a predetermined cycle. In parallel with this, a sector is rotated by a motor, and infrared light from a light source is intermittently irradiated into the cell. This allows the detector to alternately detect infrared light that has passed through the sample gas or the reference gas, making it possible to analyze the gas components based on the output ratio of the detection output of the reference gas and the detection output of the sample gas.

Japanese Patent Application Publication No. 9-49797

The infrared gas analyzer disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 9-49797 detects the concentration of _SO2 in a sample gas, but environmental standards have been established for CO, _CO2 , NOx, etc. in addition to _SO2 , and there is a need to monitor their concentrations. Therefore, multi-component measuring instruments capable of measuring multiple gas components have also been developed.

To measure a plurality of gas components, such as SO ₂ , CO, CO ₂ , and NO, four detectors and a central processing unit (CPU) having at least four ports for receiving output signals from these detectors are required.

In recent years, in order to further improve detection accuracy, there has been a demand to detect components that interfere with the gas being detected, in addition to the gas components being detected, and correct the detection results. However, when improving and using existing devices, there are often cases where the CPU input ports are insufficient. However, changing the CPU and designing and manufacturing a new device requires a large amount of development costs.

The present disclosure aims to provide a gas measurement device that can improve accuracy while keeping development costs down.

The gas measurement device of the present disclosure includes a sample cell filled with a sample gas, a light source that irradiates the sample cell with light, a detection unit that detects the light intensity of the light irradiated from the light source onto the sample cell and transmitted through the sample cell, a central processing unit that repeatedly analyzes the gas components in the sample gas based on the detection results of the detection unit, and an interface circuit that transmits the detection signal detected by the detection unit to the central processing unit. The detection unit includes a first detector that detects the gas component to be analyzed in the sample gas, and a plurality of second detectors that detect a plurality of components for interference correction of the gas component to be analyzed. The interface circuit includes a first signal processing unit that preprocesses the detection signal of the first detector so that it can be input to the central processing unit and transmits it to the central processing unit, and a second signal processing unit that preprocesses the detection signals of the plurality of second detectors so that they can be input to the central processing unit and transmits them sequentially in a time-division manner to the central processing unit.

The gas measurement device disclosed herein requires only modifying a portion of the signal processing section of an existing configuration, so there is no need to change the central processing unit, and development efforts are reduced. In addition, it is easy to improve the accuracy of existing devices.

1 is a diagram illustrating an overall configuration of a gas measurement device according to an embodiment of the present invention. 2 is a block diagram showing a configuration of a control device 30 in FIG. 1 . 4 is a diagram for explaining signals input to each port of a CPU; FIG.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated.

Figure 1 is a diagram showing the overall configuration of the gas measurement device of this embodiment. The gas measurement device 1 shown in Figure 1 includes a sample gas line ML, a reference gas line RL, a switching valve 5, and a sample cell 9.

Sample gas M is introduced into the sample gas line ML. The sample gas line ML includes a filter 2 through which the sample gas M passes, a pump 3 that delivers the sample gas M, and a needle valve 4 that adjusts the flow rate of the sample gas M.

A reference gas R is introduced into the reference gas line RL. The reference gas line RL includes a filter 12 through which the reference gas R passes, a pump 13 that delivers the reference gas R, and a needle valve 14 that adjusts the flow rate of the reference gas R.

The switching valve 5 includes a three-way valve 5M arranged on the sample gas line ML and a three-way valve 5R arranged on the reference gas line RL. The three-way valves 5M and 5R configure a flow path so that, in response to a selection signal SEL, gas that has passed through either the reference gas line RL or the sample gas line ML is sent to the sample cell 9, and gas that has passed through the other line is exhausted. By switching the selection signal SEL, the sample cell is alternately filled with the reference gas and the sample gas.

The gas measurement device 1 further includes a motor 6, a sector 8, a light source 7, a detection unit 20, and a control device 30.

The sample cell 9 has a gas inlet 9a and a gas outlet 9b. A sample gas or a reference gas is supplied into the sample cell 9 from the gas inlet 9a via the switching valve 5 and is exhausted from the gas outlet 9b. A light source 7 that emits infrared light is provided at one end of the sample cell 9, and a detection unit 20 for detecting the infrared light that has passed through the sample cell 9 is provided at the other end of the sample cell 9.

A sector 8 for turning on and off infrared light is provided between the light source 7 and the end of the sample cell 9. This sector 8 has a light-shielding portion and a light-transmitting portion. The sector 8 is configured to rotate around a sector rotation axis 8e . When the light-transmitting portion is above the sample cell 9, infrared light is irradiated into the sample cell 9, and when the light-shielding portion is above the sample cell 9, irradiation of infrared light into the sample cell 9 is blocked. A control device 30 controls the rotational position of the sector 8 via the motor 6, and also controls the drive of the switching valve 5 by a selection signal SEL so as to be synchronized with the rotation of the motor 6.

The detection unit 20 includes a first detector 21 for detecting the measurement target gas and a second detector for detecting the correction gas. The first detector 21 includes an _SO2 detector 22, an NO detector 23, and a CO detector 24 for detecting SO2, NO, and CO, respectively. The second detector includes a CO2 detector 25 and a CH4 detector 26 for detecting _CO2 and _CH4 , respectively.

_SO2 , NO, and CO each absorb light at a specific wavelength in the infrared region ( _SO2 : 7.4 μm, NO: 5.3 μm, CO: 4.6 μm). Therefore, by measuring the absorption of infrared light after passing through the measurement gas using a detector sensitive only to each of these wavelengths, the concentration of each component can be measured.

Each detector contains the target gas contained in the sample gas, and detects the infrared light intensity of a frequency specific to the target gas by changes in internal pressure. The control device 30 receives the detection output from the detection unit 20, performs a predetermined signal processing, and calculates a concentration value that indicates the concentration of the measured gas in the sample gas.

Figure 2 is a block diagram showing the configuration of the control device 30 in Figure 1. The configuration of the gas measurement device 1, including the internal configuration of the control device 30, will be described with reference to Figures 1 and 2.

The gas measurement device 1 includes a sample cell 9, a switching valve 5 that selectively supplies a reference gas and a sample gas to the sample cell, a light source 7 that irradiates light onto the sample cell, and a detection unit 20 that detects the light intensity of the light irradiated from the light source 7 onto the sample cell 9 and transmitted through the sample cell 9.

The gas measuring device 1 further includes a control device 30. The control device 30 includes an interface circuit 36, a calculation unit (CPU) 31, a storage unit (memory) 32, a concentration display unit 33, an input unit 34, and an output unit 35. A user inputs data for calibration, settings, etc. via the input unit 34. The CPU 31 also outputs concentration values, etc. from the output unit 35.

The interface circuit 36 transmits the detection signal detected by the detection unit 20 to the CPU 31. The CPU 31 repeatedly analyzes the gas components in the sample gas based on the detection results of the detection unit 20.

The detection unit 20 includes a first detector 21 that detects the gas components to be analyzed ( _SO2 , NO, CO), and a CO2 detector 25 and a CH4 detector 26 that detect multiple components ( _CO2 , _CH4 ) for interference correction of the gas components to be analyzed. The interface circuit 36 includes a first signal processing unit (41, 42, 43) that preprocesses the detection signal of the first detector 21 so that it can be input to the CPU 31 and transmits it to the CPU 31, and a second signal processing unit (44) that preprocesses the detection signals of the CO2 detector 25 and the CH4 detector 26 so that they can be input to the CPU 31 and transmits them alternately to the CPU 31 in a time-division manner.

The light that the light source 7 irradiates onto the sample cell is infrared light. Even in a gas measurement device that uses ultraviolet light, the correction components can be transmitted alternately in a time-division manner, as in this embodiment.

The gas components to be analyzed include _SO2 gas, NO gas, and CO gas. The first detector 21 includes an SO2 detector 22, an NO detector 23, and a CO detector 24. The components for interference correction include _CH4 gas and _CO2 gas. The CPU 31 has a first port P1, a second port P2, a third port P3, and a fourth port P4.

The first signal processing unit (41, 42, 43) has a first preprocessing circuit 41 that preprocesses the output signal of the SO2 detector 22 and outputs it to the first port P1, a second preprocessing circuit 42 that preprocesses the output signal of the NO detector 23 and outputs it to the second port P2, and a third preprocessing circuit 43 that preprocesses the output signal of the CO detector 24 and outputs it to the third port P3.

The second signal processing unit 44 is configured to alternately output a signal obtained by preprocessing the output signal of the CH4 detector 26 and a signal obtained by preprocessing the output signal of the CO2 detector 25 to the fourth port P4.

The first pre-processing circuit 41 includes an analog circuit 51 that adjusts the gain of the output signal from the SO2 detector 22, and a conversion circuit 52 that converts the output of the analog circuit 51 so that it can be input to the first port P1.

The second pre-processing circuit 42 includes an analog circuit 53 that adjusts the gain of the output signal of the NO detector 23, and a conversion circuit 54 that converts the output of the analog circuit 53 so that it can be input to the second port P2.

The third pre-processing circuit 43 includes an analog circuit 55 that adjusts the gain of the output signal from the CO detector 24, and a conversion circuit 56 that converts the output of the analog circuit 55 so that it can be input to the third port P3.

The second signal processing unit 44 includes a second analog circuit 58 that adjusts the gain of the output signal of the CH4 detector 26 , a third analog circuit 57 that adjusts the gain of the output signal of the CO2 detector 25, a multiplexer 59 that alternately selects the output of the second analog circuit 58 and the output of the third analog circuit 57, and a second conversion circuit 60 that converts the output of the multiplexer 59 so that it can be input to the fourth port P4.

In the present embodiment, configured as described above, the signal from the CO2 detector 25 and the signal from the CH4 detector are alternately switched over time and taken into one port P4, and the _CO2 concentration and the _CH4 concentration are calculated, respectively.

Both CO2 and _CH4 are measurement targets for interference correction, and are not the main measurement targets of air pollutant components _SO2 and NO, or CO, which is _{the measurement target for incomplete combustion monitoring as a dioxin countermeasure. Therefore, for CO2 and CH4} , even if the minimum detection limit becomes slightly higher (about 1.4 times) by thinning out the signal from the detector and calculating the concentration, gas measurement is not affected.

Figure 3 is a diagram for explaining the signals input to each port of the CPU. Ports P1 to P3 of the CPU 31 continuously receive signals from the corresponding detectors without switching. The control device 30 switches the switching valve 5 twice in one 20-second cycle using the selection signal SEL. In the first half of the 20-second cycle, a detection signal is input when the reference gas R from the reference gas line RL is filled into the sample cell 9, and in the second half, a detection signal is input when the sample gas M from the sample gas line ML is filled into the sample cell 9.

In FIG. 3, R indicates the detection signal (reference signal) when the reference gas is filled into the sample cell 9, and M indicates the detection signal (measurement signal) when the sample gas is filled into the sample cell 9. The CPU 31 calculates the concentration of the gas to be measured in the sample gas by applying the reference signal and the measurement signal to a predetermined calculation formula.

Port P4 receives a signal from the CO2 detector 25 and a signal from the CH4 detector 26, switching them every 20 seconds. Using the selection signal SEL2, the CPU 31 selects between the A input and the B input of the multiplexer 59 as shown in FIG. 3. The selection signal SEL2 has a period twice as long as that of the selection signal SEL of the switching valve 5. The CPU 31 also calculates the concentration of the measurement target gas in the sample gas for _CO2 and _CH4 for interference correction by applying the reference signal and the measurement signal to a predetermined calculation formula. The frequency at which this concentration is updated is half that of the main analysis targets _SO2 , NO, and CO. In this embodiment, the selection signal SEL2 is output from the CPU 31, but by providing a frequency divider circuit in the second signal processing unit 44, it is also possible to generate SEL2 in the second signal processing unit 44 using the selection signal SEL.

The CPU 31 corrects the concentrations of SO ₂ , NO, and CO, which are updated every 20 seconds of one cycle, by the concentrations of CO ₂ and CH ₄ , which are updated every 40 seconds of two cycles.

The gas measurement device of this embodiment can be easily realized by improving an existing gas measurement device. For example, even in a device that only corrects the interference component CO by using a configuration similar to that of pre-processing circuits 41 to 43 instead of second signal processing unit 44 and does not correct the interference component CH ₄ , if each pre-processing circuit 41 is configured as a single replaceable board, it is possible to introduce correction of the interference component CH ₄ simply by replacing one of the existing boards with the board of second signal processing unit 44 and changing the calculation processing of CPU 31 by software modification.

In this case, modifications can be easily made to already delivered equipment, and the time required to modify the equipment is only about half a day, shortening the time that data is lost and thereby reducing the man-hours required by service personnel.

In the above-described embodiment, the case has been described where there are three types of gas components to be detected and two types of gas components for interference correction, but these numbers may be changed. There may be one to two types of gas components to be detected, or four or more types. There may also be three or more types of gas components for interference correction. Even in such a case, the number of ports used can be reduced by using one port per gas component to be detected, and inputting the gas components for interference correction sequentially to one port of the CPU in a time-division manner.

In addition, in this embodiment, an infrared gas analyzer that uses a reference gas has been described, but the same concept can also be applied to an infrared gas analyzer that does not use a reference gas and calculates the concentration only from the measurement signal of the sample gas, and to an infrared gas analyzer that uses a reference cell in which the reference gas is filled and sealed rather than circulating.

[Aspects]
It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

(1) The gas measurement device of the present disclosure includes a sample cell filled with a sample gas, a light source that irradiates the sample cell with light, a detection unit that detects the light intensity of the light irradiated from the light source to the sample cell that passes through the sample cell, a central processing unit that repeatedly analyzes the gas components in the sample gas based on the detection results of the detection unit, and an interface circuit that transmits the detection signal detected by the detection unit to the central processing unit 31. The detection unit includes a first detector that detects the gas component to be analyzed in the sample gas, and a plurality of second detectors that detect a plurality of components for interference correction of the gas component to be analyzed. The interface circuit includes a first signal processing unit that performs preprocessing so that the detection signal of the first detector can be input to the central processing unit and transmits it to the central processing unit, and a second signal processing unit that performs preprocessing so that the detection signals of the plurality of second detectors can be input to the central processing unit and transmits them sequentially in a time-division manner to the central processing unit. With this configuration, even if the central processing unit has a small number of input ports, the detection results of the plurality of components for interference correction can be handled by the central processing unit.

(2) Preferably, the light that the light source irradiates onto the sample cell is infrared light.

(Term 3) More preferably, the gas components to be analyzed include _SO2 gas, NO gas, and CO gas. The first detector includes an SO2 detector, an NO detector, and a CO detector. The multiple components for interference correction include CH4 gas and CO2 gas. The multiple second detectors include a CH4 detector and a CO2 detector. The central processing unit has a first port, a second port, a third port, and a fourth port. The first signal processing unit has a first preprocessing circuit that preprocesses the output signal of the SO2 detector and outputs it to the first port, a second preprocessing circuit that preprocesses the output signal of the NO detector and outputs it to the second port, and a third preprocessing circuit that preprocesses the output signal of the CO detector and outputs it to the third port. The second signal processing unit is configured to alternately output a signal obtained by preprocessing the output signal of the CH4 detector and a signal obtained by preprocessing the output signal of the CO2 detector to the fourth port.

(4th paragraph) More preferably, each of the first to third pre-processing circuits includes a first analog circuit that adjusts the gain of the output signal of the corresponding detector, and a first conversion circuit that converts the output of the first analog circuit so that it can be input to a corresponding one of the first to third ports. The second signal processing unit includes a second analog circuit that adjusts the gain of the output signal of the CH4 detector, a third analog circuit that adjusts the gain of the output signal of the CO2 detector, a multiplexer that alternately selects the output of the second analog circuit and the output of the third analog circuit, and a second conversion circuit that converts the output of the multiplexer so that it can be input to the fourth port.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and is intended to include all modifications within the meaning and scope of the claims.

1 Gas measuring device, 2, 12 Filter, 3, 13 Pump, 4, 14 Needle valve, 5 Switching valve, 5M, 5R Three-way valve, 6 Motor, 7 Light source, 8 Sector, 8c Sector rotating shaft, 9 Sample cell, 9a Gas inlet, 9b Gas outlet, 20 Detection section, 21-26 Detector, 30 Control device, 31 Central processing unit, 33 Concentration display section, 34 Input section, 35 Output section, 36 Interface circuit, 41-43 Pre-processing circuit, 44 Second signal processing section, 51, 53, 55, 57, 58 Analog circuit, 52, 54, 56, 60 Conversion circuit, 59 Multiplexer, ML Sample gas line, P1-P4 Port, RL Reference gas line.

Claims (4)

a sample cell for filling with a sample gas;
a light source that irradiates the sample cell with light;
a detection unit that detects the intensity of light irradiated from the light source onto the sample cell and transmitted through the sample cell;
a central processing unit that repeatedly analyzes the gas components in the sample gas based on the detection results of the detection unit;
an interface circuit that transmits a detection signal detected by the detection unit to the central processing unit;
The detection unit is
a first detector for detecting a gas component to be analyzed in the sample gas;
a second detector for detecting a plurality of components for interference correction of the gas component to be analyzed;
The interface circuit includes:
a first signal processing unit that performs preprocessing on a detection signal of the first detector so that the detection signal can be input to the central processing unit and transmits the preprocessed signal to the central processing unit;
a second signal processing unit that performs preprocessing on the detection signals of the plurality of second detectors so that the detection signals can be input to the central processing unit, and sequentially transmits the detection signals to one port of the central processing unit in a time-division manner ;
The gas measurement device , wherein the central processing unit calculates the concentrations of the plurality of components for use in interference correction based on the signal acquired from the one port. The gas measurement device according to claim 1, wherein the light emitted by the light source to the sample cell is infrared light. The gas components to be analyzed include _SO2 gas, NO gas, and CO gas;
the first detector includes a _SO2 gas detector, a NO gas detector, and a CO gas detector;
The plurality of components for interference correction include _CH4 gas and _CO2 gas;
the plurality of second detectors include a _CH4 gas detector and a _CO2 gas detector;
the central processing unit has a first port, a second port, a third port, and a fourth port;
the one port is the fourth port,
The first signal processing unit is
a first pre-processing circuit that pre-processes an output signal of the _SO2 gas detector and outputs the pre-processed signal to the first port;
a second pre-processing circuit that pre-processes the output signal of the NO gas detector and outputs the pre-processed signal to the second port;
a third pre-processing circuit that pre-processes the output signal of the CO gas detector and outputs the pre-processed signal to the third port;
3. The gas measurement device according to claim 2, wherein the second signal processing unit is configured to alternately output a signal obtained by preprocessing an output signal of the _CH4 gas detector and a signal obtained by preprocessing an output signal of the _CO2 gas detector to the fourth port. Each of the first to third pre-processing circuits includes:
a first analog circuit for adjusting the gain of an output signal of a corresponding detector;
a first conversion circuit that converts an output of the first analog circuit so that the output can be input to a corresponding one of the first to third ports;
The second signal processing unit is
a second analog circuit for adjusting the gain of the output signal of the _CH4 gas detector;
a third analog circuit for adjusting the gain of an output signal of the _CO2 gas detector;
a multiplexer that alternately selects the output of the second analog circuit and the output of the third analog circuit;
4. The gas measurement device of claim 3, further comprising a second conversion circuit for converting the output of said multiplexer so that it can be input to said fourth port.

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