JP2012026834A - Infrared gas analyzer - Google Patents

Abstract

An infrared gas analyzer that eliminates the drift and calculates an accurate concentration even when the drift changes.
[Solution]
The first difference data is calculated based on the difference between the measurement gas detection data and the detection data before the comparison gas, and the second difference data is calculated based on the difference between the measurement gas detection data and the detection data after the comparison gas. And an infrared gas analyzer that calculates the concentration using averaged data obtained by averaging the second difference data.
[Selection] Figure 2

Description

  The present invention relates to an infrared gas analyzer for measuring the concentration of a specific component contained in a measurement gas.

  An infrared gas analyzer is an apparatus that irradiates measurement gas with infrared rays, detects the amount of light that changes due to absorption of infrared rays, and measures the concentration of the measurement gas. A flow path switching system is known as a measurement system for such an infrared gas analyzer. Further, in this flow path switching method, there are a method using one measurement cell (hereinafter referred to as a single beam method) and a method using two measurement cells (hereinafter referred to as a double beam method).

As a conventional technique related to such a single beam type infrared gas analyzer, for example, one described in Patent Document 1 (Japanese Patent Laid-Open No. 9-49797, title of invention: infrared gas analyzer) is known. It has been.
Further, as a conventional technique related to a double beam type infrared gas analyzer, for example, Patent Document 2 (Japanese Patent Laid-Open No. 5-256778, title of invention: gas concentration measurement method and apparatus using a reference gas concentration adjustment method) What has been described is known.

JP-A-9-49797 (FIG. 6) JP-A-5-256778 (FIG. 1)

In these infrared gas analyzers, accurate detection cannot be performed particularly due to contamination of the measurement cell or deterioration of parts, and drift in which the measurement value changes may occur.
Prior to the creation of the channel switching method, this change appears as a change in the measured value and causes an error in the measured value. Therefore, periodic calibration (an act of correcting the deviation of the measured value) was necessary. It was. However, in the flow path switching method, the measurement gas and the reference gas are periodically exchanged and measured, and by taking the difference between them, it is possible to remove the drift and eliminate the influence of the drift.

The removal of this drift will be described.
For example, an infrared gas analyzer of a double beam system is configured to measure the concentration by exchanging the measurement gas and the reference gas in the measurement cell 1 and the measurement cell 2 at regular intervals, and the behavior based on the obtained detection data is shown in FIG. As shown by 6, it is trapezoidal. The signal at the timing (4) when the measurement gas flows into one measurement cell 1 (that is, the timing when the comparison gas flows into the other measurement cell 2) is C + Δd (C is the gas concentration equivalent amount, Δd is a drift amount). Further, the signal at the timing (3) or (5) in which the reference gas is flowing in the measurement cell 1 (that is, the timing at which the measurement gas is flowing in the other measurement cell 2) is −C + Δd. In this way, the concentration-corresponding component C of the measurement gas is inverted, but the drift amount Δd appears as it is because it is not related to the gas flow.

  Here, signals at the respective timings are detected and stored as measurement data / comparison data, and the difference data is obtained by subtracting the comparison data from the measurement data as in the following equation.

[Equation 1]
(C + Δd) − (− C + Δd) = 2C

  Thus, the drift amount Δd disappears, and only the concentration-corresponding component C of the measurement gas is extracted. In this way, the difference value is used as the concentration value, thereby eliminating the influence of the drift.

  However, since the gas exchange in the measurement cells 1 and 2 takes a certain time, there is a time lag between the measurement timing of the reference gas and the measurement timing of the measurement gas. It is good if the drift amount is a constant value, but when the drift amount changes according to time, the drift amount change is added to the detector output during the measurement time of the two gases, and the drift amount change amount Will appear as a measurement error. Therefore, the above removal method has a problem that the drift cannot be completely removed.

  For example, as shown in FIG. 7, a case is assumed where the drift amount increases. Assume that the measurement data (C + Δd + b) is acquired at the timing (4) and the comparison data (−C + Δd + c) is obtained at the timing (5). Then, when the comparison data is subtracted from the measurement data as in the above removal method, the difference value is expressed by the following equation.

[Equation 2]
(C + Δd + b) − (− C + Δd + c) = 2C + b−c

  Thus, bc remains, and there is a problem that the drift cannot be completely removed.

Furthermore, since the value of bc increases as the change in drift increases, there is a problem that the error increases.
In addition, although the change in the drift amount is small, there is a problem that the influence of the change in the drift amount becomes large even when the change in the drift amount becomes a relatively large change because the concentration to be measured is small.

  In the case where the concentration value is calculated and output at each timing without taking the difference (for example, immediately after the introduction of the reference gas and immediately before switching to the measurement gas or immediately after the introduction of the measurement gas and immediately before switching to the comparison gas), There was a problem that the vertical concentration corresponding to the slope of the drift occurred around the original concentration value, and an accurate concentration could not be obtained.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an infrared gas analyzer that removes the drift component and calculates an accurate concentration even when the drift component changes. It is in.

In order to solve the above-described problem, an infrared gas analyzer according to the first aspect of the present invention provides:
Infrared gas that irradiates infrared rays to the reference gas and measurement gas introduced alternately into the measurement cell, and obtains detection signals according to the concentrations of these comparison gas and measurement gas from the detector to measure the concentration of the measurement gas In the analyzer
Measurement gas detection data detected for the measurement gas, comparison gas pre-detection data detected at a time n times (n is a natural number) times from the measurement gas detection, and gas switching n times from the measurement gas detection Data extraction means for extracting the detection data after the comparison gas detected at the time after the cycle, respectively, from the detection data;
First difference data calculation means for obtaining first difference data based on a difference between the measurement gas detection data and the detection gas pre-detection data;
Second difference data calculation means for obtaining second difference data based on the difference between the measured gas detection data and the detection gas post-detection data;
Averaging means for averaging the first difference data and the second difference data to obtain averaged data;
It was set as the infrared gas analyzer characterized by providing.

The infrared gas analyzer of the invention according to claim 2 of the present invention is
The infrared gas analyzer according to claim 1,
A flow path switching unit for switching the gas flowing into the measurement cell is provided.
The infrared gas analyzer is characterized in that the measurement gas detection data, the detection data before the comparison gas, and the detection data after the comparison gas are acquired at the switching timing of the flow path switching unit.

The infrared gas analyzer of the invention according to claim 3 of the present invention is
In the infrared gas analyzer according to claim 1 or 2,
The infrared gas analyzer is characterized by a single beam system having one measuring cell.

The infrared gas analyzer of the invention according to claim 4 of the present invention is
In the infrared gas analyzer according to claim 1 or 2,
An infrared gas analyzer characterized in that it is a double beam system having two measuring cells.

  According to the present invention as described above, it is possible to provide an infrared gas analyzer that calculates an accurate concentration by removing the drift even when the drift varies.

1 is a system configuration diagram of a single beam infrared gas analyzer according to an embodiment for carrying out the present invention. It is explanatory drawing explaining the detail of a calculation control part. It is explanatory drawing of the behavior of detection data. It is explanatory drawing of the behavior of detection data. It is a system block diagram of the infrared gas analyzer of another form of the double beam system. It is explanatory drawing of the behavior of detection data. It is explanatory drawing of the behavior of detection data.

Then, the form for implementing this invention is demonstrated, referring a figure. First, the entire infrared gas analyzer 1 will be described. The infrared gas analyzer 1 according to this embodiment is a so-called single beam infrared gas analyzer.
As shown in FIGS. 1 and 2, the infrared gas analyzer 1 includes a motor 11, a chopper 12, an infrared light source 13, a measurement cell 14, a detector 15, an amplifier 16, an AD converter 17, an arithmetic control unit 18, an SSR 19, A first flow path switching solenoid valve 20, a second flow path switching solenoid valve 21, and an output unit 22 are provided.

The motor 11 is rotationally driven by a driver (not shown).
The chopper 12 is rotated by the motor 11.
The infrared light source 13 emits infrared light. This infrared ray is an infrared ray that is intermittently modulated by the chopper 12 at a constant period.

The measurement cell 14 transmits infrared light to the measurement gas and the reference gas introduced therein.
The detector 15 detects infrared rays transmitted from the measurement cell 14. In the measurement cell 14, infrared light is absorbed according to the concentration of the internal gas, and the amount of infrared light that has not been absorbed is measured by the detector 15. The detection signal output from the detector 15 has a small amplitude when the absorption in the measurement cell 14 is large, that is, when the concentration of the measurement gas is high, and conversely, when the concentration is low, the amplitude is large. It becomes a detection signal.

The amplifier 16 amplifies the detection signal output from the detector 15 until it reaches a predetermined amplitude.
The AD converter 17 converts the detection signal, which is an analog signal, into detection data, which is digital data, and outputs the detection data.
The arithmetic control unit 18 is, for example, an MPU (microprocessor), and performs data analysis based on detection data. Further, the opening and closing of the first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 is controlled via the SSR 19.

The SSR 19 is a solid state relay, and opens and closes by passing a current to the first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21.
The first flow path switching solenoid valve 20 includes a common terminal (COM), a normally open terminal (NO), and a normally closed terminal (NC), and controls whether to flow the reference gas to the measurement cell 14 or the exhaust path. To do.
The second flow path switching solenoid valve 21 includes a common terminal (COM), a normally open terminal (NO), and a normally closed terminal (NC), and controls whether to flow the measurement gas to the measurement cell 14 or the exhaust path. To do.
The first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 are examples of the flow path switching unit of the present invention, and the first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 are switched. Thus, the reference gas and the measurement gas are alternately introduced into the measurement cell 14 at a constant period.

  The output unit 22 outputs information on density. The output unit 22 is, for example, a display unit that displays a screen, a printer that prints, a communication unit that performs data communication with an external device, or a computer that performs further data processing. It is to use. These various selections are possible.

Subsequently, an analysis process including removal of a drift amount that characterizes the present invention will be described.
First, as shown in FIG. 2, the arithmetic control unit 18 functions as the flow path switching unit 181 so that the measurement gas flows into the measurement cell 14. Specifically, as shown in FIG. 1, the arithmetic control unit 18 sends a switching control signal to the SSR 19, and the SSR 19 opens the normally closed terminal (NC) of the second flow path switching electromagnetic valve 21 to the measuring cell 14. Flow measurement gas. Infrared light emitted from the infrared light source unit 2 is converted into an optically modulated infrared light beam that is intermittent in the open / close cycle of the chopper 13, and this infrared light beam is incident on the measurement cell 14. In the measurement cell 14, infrared rays in the wavelength band specific to each gas component constituting the measurement gas are absorbed according to the concentration of the gas component and reach the detector 15 in the process of transmitting the infrared light beam.

  The detection signal output from the detector 15 is amplified by the amplifier 16, is AD converted by the AD converter 17, becomes detection data, and is sequentially taken into the arithmetic control unit 18. As shown in FIG. 2, the arithmetic control unit 18 functions as the detection data storage unit 182 and registers the detection data in a storage device (not shown). In this case, it is assumed that it is registered as detection data as it is, not in terms of concentration.

  Subsequently, the arithmetic control unit 18 functions again as the flow path switching unit 181 and causes the reference gas to flow into the measurement cell. Specifically, the normally open terminal (NO) of the first flow path switching electromagnetic valve 20 is opened, and the comparison gas is allowed to flow to the measurement cell 14. Infrared light flux is incident on the measurement cell 14 and in the process of passing through the measurement cell 14, infrared light absorbed according to the concentration of the gas component reaches the detector 15. The detection signal output from the detector 15 passes through the amplifier 16 and the AD converter 17 and becomes detection data, which is sequentially taken into the arithmetic control unit 18. The arithmetic control unit 18 functions as the detection data storage unit 182 and registers the detection data in a storage device (not shown).

  Thereafter, the measurement gas analysis / comparison gas analysis is repeated. It is necessary to acquire a plurality of data required for the difference and averaging described later over a predetermined period. At first, in order to accumulate data, the flow path switching means 181 and the detection data storage means 182 are repeated to obtain necessary detection data. obtain.

  The detection data acquired in this way has a trapezoidal waveform as shown in FIG. In order to facilitate understanding, for example, this behavior is illustrated as an analog detection signal output from the amplifier 16, but is described as a behavior of detection data for convenience. The behavior of the detection data is stable at a small value at the time of the comparison gas. When the gas is switched to the measurement gas, the value gradually increases as the gas in the measurement cell 14 is switched. When the gas is completely replaced, the constant value is stably maintained. Then, when the gas is switched to the reference gas, the reference gas increases in the measuring cell 14 and gradually decreases. The same behavior is repeated thereafter.

Next, calculation of concentration including drift removal will be described. Generalized as follows.
As shown in FIG. 2, the control arithmetic unit 18 functions as data extraction means 183 that extracts the measurement gas detection data, the pre-comparison gas detection data, and the post-comparison gas detection data from the behavior of the concentration.

  This pre-comparison gas detection data is obtained before the gas switching period n times (n is an odd number such as 1, 3, 5,...) Than the measurement gas detection data. In this embodiment, n = 1, and the detection data before the comparison gas is data obtained immediately before the measurement gas detection data is acquired.

  The post-comparison gas detection data is obtained after a gas switching period n times (n is an odd number) than the measurement gas detection data. In this embodiment, n = 1 is set, and the post-comparison gas detection data is data obtained immediately after the measurement gas detection data is acquired.

The gas switching cycle is a cycle in which the first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 are switched in order to switch the gas flowing into the measurement cell. At this time, as shown in FIG. 3, the period from the start to the switching from the reference gas to the measurement gas and the end to the switching from the measurement gas to the comparison gas is the gas switching cycle. Similarly, a gas switching cycle is a period in which the period from the measurement gas to the comparison gas is started and the period from the comparison gas to the measurement gas is terminated. Detection data is acquired for each gas switching period.
The timing for obtaining the measurement gas detection data, the detection data before the comparison gas, and the detection data after the comparison gas was set to the same timing as the switching timing of the first flow path switching solenoid valve 20 and the second flow path switching solenoid valve 21.
The arithmetic control unit 18 collectively registers the detection data representing the above behavior in association with the switching timing, and from among these, the measurement gas detection data, the detection data before the comparison gas, and the detection after the comparison gas are detected at the switching timing. Data is extracted by acquiring data.

  The arithmetic control unit 18 functions as a difference unit 184 that obtains a difference value using these data. Specifically, it functions as a first difference data calculation unit that obtains first difference data by taking a difference between certain measurement gas detection data and pre-comparison gas detection data. Similarly, it functions as a second difference data calculation unit that obtains second difference data by taking the difference between the measurement gas detection data and the detection gas post-detection data.

The arithmetic control unit 18 functions as an averaging unit 185 that averages the first difference data and the second difference data to obtain averaged data.
Then, the arithmetic control unit 18 functions as a density conversion unit 186 that performs density conversion processing thereafter to obtain density data.
Finally, the calculation control unit 18 functions as an output unit 187 for outputting the density data to the output unit 22 such as a monitor / printer.

Next, the principle of removing the drift will be described in detail. First, a case where the drift amount is almost constant will be described. In this embodiment, n = 1 and a gas switching cycle of 1 time.
For example, as shown in FIG. 3, the arithmetic control unit 18 detects the measurement gas detection data at the timing (2), the detection data before the comparison gas at the timing (1), and the detection after the comparison gas at the timing (3). Get the data. These data are as follows.

[Equation 3]
Detection data before comparison gas of (1) = Δd
Measurement gas detection data of (2) = C + Δd
Detection data after comparison gas of (3) = Δd

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 4]
First difference data = measured gas detection data of (2) −pre-comparison gas detection data of (1)
= C + Δd−Δd
= C

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 5]
Second difference data = measured gas detection data of (2) −detection data after comparison gas of (3)
= C + Δd−Δd
= C

  Subsequently, the arithmetic control unit 18 performs averaging. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 6]
Averaged data = 2C / 2 = C

  This averaged data matches the density equivalent C, and the density to be obtained can be obtained by converting the density.

  Here, Δd is a drift amount, but this Δd is constant and can be eliminated as described above. Even if Δd is not constant, if it is a fluctuation in a sufficiently long unit with respect to the gas switching period, the change can be ignored, and even in this case, the drift can be eliminated.

Next, as shown in FIG. 4, a case where the drift amount changes quickly with respect to the gas switching period (for example, the drift amount increases for each measurement as shown in FIG. 4) will be described.
As shown in FIG. 4, the drift amount increases every time the solenoid valve is switched. For example, measured gas detection data = C + Δd + b at the timing (4), comparative gas pre-detection data = Δd + a at the timing (3), and It is assumed that the detection data after comparison gas = Δd + c is acquired at the timing of (5).

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 7]
First difference data = measured gas detection data of (4) −pre-comparison gas detection data of (3)
= C + Δd + b− (Δd + a) = C + b−a

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 8]
Second differential data = Measured gas detection data of (4) −Comparative gas post-detection data of (5)
= C + Δd + b− (Δd + c) = C + b−c

  Subsequently, the arithmetic control unit 18 performs averaging. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 9]
Averaged data = (first difference data + second difference data) / 2
= (C + ba-C + bc) / 2 = C + b- (a + c) / 2

  Here, assuming a linear function in which the drift amount is an inclination α and changes in the gas switching period T, when the height of b is regarded as a reference (= 0), a = −αT, b = 0, c = + αT Therefore, when substituting into the above equation 9, b− (a + c) / 2 = 0. Therefore, the averaged data = C, and the drift is removed. The concentration from which the drift is removed is calculated by converting the averaged data into a concentration.

  In addition, when taking the difference, the comparison gas pre-detection data 3 or 5 times before the gas switching cycle is used from the measurement gas detection data, and the comparison after 3 or 5 times the gas switching cycle from the measurement gas detection data. Gas post-detection data may be used. Here, a case where data separated by three times the gas switching period is used will be described.

  As shown in FIG. 4, the drift amount increases every time the solenoid valve is switched. For example, the measurement gas detection data = C + Δd + b at the timing (4), and the comparison gas pre-detection data = Δd−z at the timing (1). And after the comparison gas detection data = Δd + f is acquired at the timing of (7).

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 10]
First difference data = measurement gas detection data of (4) −pre-comparison gas detection data of (1)
= C + Δd + b− (Δd−z) = C + b + z

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 11]
Second difference data = measured gas detection data of (4) −post-comparison detection data of (7)
= C + Δd + b− (Δd + f) = C + b−f

  Subsequently, the arithmetic control unit 18 performs averaging. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 12]
Averaged data = (C + b + z + C + b−f) / 2 = C + b− (f−z) / 2

  Here, assuming a linear function in which the drift amount is an inclination α and changes in the gas switching period T, when the height of b is regarded as a reference (= 0), −z = −3αT, b = 0, f = Since + 3αT, b− (f−z) / 2 = 0 when substituted into the above formula. Therefore, the averaged data = C, and the drift is removed. The concentration from which the drift is removed is calculated by converting the averaged data into a concentration.

  When generalized, the detection data before the comparison gas is acquired before the gas switching period n times (n is an odd number) than the measurement gas detection data. The post-comparison gas detection data is acquired after a gas switching period n times (n is an odd number) than the measurement gas detection data.

  Here, the meaning of using the difference value / average value is examined. In the description, it is assumed that the gas switching period is 1 time. When taking the difference between the measurement gas detection data of (2) and the detection data before the comparison gas of (1) and the detection data after the comparison gas of (3) at a gas switching cycle of 1 time, the following equation is obtained.

[Equation 13]
First difference data = measured gas detection data of (2) −pre-comparison gas detection data of (1)
= C + Δd− (Δd−z) = C + z> C

[Formula 14]
Second difference data = measured gas detection data of (2) −detection data after comparison gas of (3)
= C + Δd− (Δd + a) = C−a <C

The difference value shows a behavior that rises and falls with respect to the density value C.
Therefore, when these data are averaged, the upper and lower portions are erased and approach zero.

[Equation 15]
Averaged data = (first difference data + second difference data) / 2
= {(C−a) + (C + z)} / 2 = C− (a−z) / 2.

  Here, if the slope of the change in drift is the same, the difference in change (here, z, a) is substantially equal, and the calculation result is substantially equal to C.

  Further, when taking the difference between the measured gas detection data of (4) and the pre-comparison gas detection data of (3) or the post-comparison gas detection data of (5) at a gas switching cycle of 1 time, the following equation is obtained. .

[Equation 16]
First difference data = measured gas detection data of (4) −pre-comparison gas detection data of (3)
= C + (Δd + b) − (Δd + a) = C + (b−a)> C

[Equation 17]
Second differential data = Measured gas detection data of (4) −Comparative gas post-detection data of (5)
= C + (Δd + b) − (Δd + c) = C + (b−c) <C

The difference value shows a behavior that rises and falls with respect to the density value C.
Therefore, when these data are averaged, the upper and lower portions are erased and approach zero.

[Equation 18]
Averaged data = (first difference data + second difference data) / 2
= {C + (b−c) + C + (b−a)} / 2 = C + (2b−c−a) / 2

  Here, if the slope of the change in drift is the same, the difference between the changes (here, (b−a), (c−b)) is substantially equal (the right term (2b−c) of Equation 18). -A) can be expanded as (ba)-(cb)), and the above calculation result is almost equal to C.

  Further, when taking the difference between the measurement gas detection data of (6) and the detection data before comparison gas of (5) and the detection data after comparison gas of (7), which are different at a gas switching cycle of 1 time, Become.

[Equation 19]
First difference data = measured gas detection data of (6) −detection data before comparison gas of (5)
= C + (Δd + e) − (Δd + c) = C + (e−c)> C

[Equation 20]
Second differential data = Measured gas detection data of (6) −Post-comparison detection data of (7)
= C + (Δd + e) − (Δd + f) = C + (ef) <C

The difference value shows a behavior that rises and falls with respect to the density value C.
Therefore, when these data are averaged, the upper and lower portions are erased and approach zero.

[Equation 21]
Averaged data = (first difference data + second difference data) / 2
= {C + (ec) + C + (ef)} / 2 = C + (2e-cf) / 2

  Here, if the slope of the change in drift is the same, the difference between the changes (here, (e−c), (f−e)) is almost equal, and the above calculation result is almost equal to C. Become.

  The same applies to the following, and the error with respect to the measured value is half of the difference for each change.

  In such an infrared gas analyzer, the concentration conversion is performed last, but when the detection data is acquired, the concentration conversion may be performed and then registered as detection data. These forms are appropriately selected.

  Next, another form of infrared gas analyzer will be described. The previous embodiment was a single beam type infrared gas analyzer, but the present invention can also be applied to a double beam type infrared gas analyzer. An infrared gas analyzer using such a double beam system will be described.

  As shown in FIG. 5, the infrared gas analyzer 2 includes a motor 11, a chopper 12, an infrared light source 13, a detector 15, an amplifier 16, an AD converter 17, an arithmetic control unit 18, an SSR 19, and a first flow path switching electromagnetic valve. 20, a second flow path switching electromagnetic valve 21, an output unit 22, a distribution cell 30, a first measurement cell 31, and a second measurement cell 32. This embodiment is different in that a distribution cell 30, a first measurement cell 31, and a second measurement cell 32 are disposed in place of the measurement cell 14 in the infrared gas analyzer 1 described with reference to FIG. In the following, the same components as those in the previous embodiment are given the same reference numerals and redundant description is omitted, and differences will be mainly described.

  Two first measurement cells 31 and two second measurement cells 32 having the same length provided with infrared transmission windows (not shown) at both ends are arranged in parallel. The distribution cell 30 is disposed at one end of the first measurement cell 31 and the second measurement cell 32. The distribution cell 30 has a function of equally distributing the infrared rays from the infrared light source 13 to the first measurement cell 31 and the second measurement cell 32. Between the distribution cell 30 and the infrared light source 13, a chopper 12 for interrupting (chopping) infrared rays at a constant period is disposed.

  A detector 15 for simultaneously detecting the infrared light from the first measurement cell 31 and the second measurement cell 32 is disposed at the other end of the first measurement cell 31 and the second measurement cell 32. The two first measurement cells 31 and the second measurement cell 32 are respectively piped so that the reference gas and the measurement gas are introduced, and the first flow path switching electromagnetic valve disposed immediately before the introduction port. 20, the flow path is switched at a constant cycle by the second flow path switching electromagnetic valve 21, and the reference gas and the measurement gas are alternately introduced into the first measurement cell 31 and the second measurement cell 32. The first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 are specific examples of the flow path switching section of the present invention.

  The detector 15 takes a difference in the amount of infrared light transmitted from the two first measurement cells 31 and the second measurement cell 32 and outputs a detection signal which is a difference signal. This detection signal is input to the arithmetic control unit 18 through the amplifier 16 and the AD converter 17.

  Even in a state where infrared absorption does not occur in the first measurement cell 31 and the second measurement cell 32 (zero state), the transmitted light amounts from the two first measurement cells 31 and the second measurement cell 32 are completely balanced. (Optical unbalance), and the optical unbalance changes with time due to contamination of the first measurement cell 31 and the second measurement cell 32 and deterioration of parts. A drift in which the measured concentration value changes occurs, but the following signal processing is performed to remove the drift.

Subsequently, an analysis process including removal of a drift amount that characterizes the present invention will be described.
First, as shown in FIG. 2, the arithmetic control unit 18 functions as the flow path switching unit 181, causing the measurement gas to flow into the first measurement cell 31 and the comparison gas to flow into the second measurement cell 32. As shown in FIG. 1, the arithmetic control unit 18 sends a switching control signal to the SSR 19, and the SSR 19 connects the second flow path switching electromagnetic valve 21 to the normally closed terminal (NC) and supplies the measurement gas to the first measurement cell 31. In addition, the first flow path switching electromagnetic valve 20 is connected to the normally closed terminal (NC), and the reference gas is caused to flow to the second measurement cell 32. Infrared light emitted from the infrared light source unit 2 is converted into an optically modulated infrared light beam that is intermittent in the open / close cycle of the chopper 13, and the infrared light beam is transmitted to the first measurement cell 31 and the second measurement cell 32. Incident. In the first measurement cell 31 and the second measurement cell 32, in the process of transmitting the infrared light flux, infrared light in a wavelength band specific to each gas component constituting the measurement gas is absorbed according to the concentration of the gas component. The detector 15 is reached.

  The detection signal output from the detector 15 is amplified by the amplifier 16, is AD converted by the AD converter 17, becomes detection data, and is sequentially taken into the arithmetic control unit 18. As shown in FIG. 2, the arithmetic control unit 18 functions as the detection data storage unit 182 and registers the detection data in a storage device (not shown).

  Subsequently, the arithmetic control unit 18 functions again as the switching control means 181, causing the comparison gas to flow into the first measurement cell 31 and the measurement gas to flow into the second measurement cell 32. The first flow path switching electromagnetic valve 20 is connected to the normally open terminal (NO), and the reference gas is supplied to the first measurement cell 31, and the second flow path switching electromagnetic valve 20 is connected to the normally open terminal (NO). Then, the measurement gas is caused to flow to the second measurement cell 32. Infrared rays are incident on the first measurement cell 31 and the second measurement cell 32, and in the process of passing through the first measurement cell 31 and the second measurement cell 32, infrared rays absorbed according to the concentration of the gas component are detected. The container 15 is reached. The detection signal output from the detector 15 passes through the amplifier 16 and the AD converter 17 and becomes detection data, which is sequentially taken into the arithmetic control unit 18. The arithmetic control unit 18 functions as the detection data storage unit 182 and registers the detection data in a storage device (not shown).

  Thereafter, the switching of the measurement gas and the comparison gas is repeated. It is necessary to acquire data necessary for concentration conversion over a predetermined period. At first, in order to accumulate data, the flow path switching unit 181 and the detection data storage unit 182 are repeated to obtain necessary data.

  The detection data acquired in this way has a trapezoidal waveform as shown in FIG. 6, for example. The behavior of this concentration is stable at a small value when the gas in the first measurement cell 31 is the reference gas and the gas in the second measurement cell 32 is the measurement gas. As the gas in the cell 32 is changed, the value gradually increases, the first measurement cell 31 and the second measurement cell 32 are completely replaced, and the gas in the first measurement cell 31 becomes the measurement gas. Further, when the gas in the second measurement cell 32 is replaced with the reference gas, the constant value is stably maintained, and then gradually as the gas in the first measurement cell 31 and the second measurement cell 32 is replaced. As the value decreases, the first measurement cell 31 and the second measurement cell 32 are completely replaced, and the gas in the first measurement cell 31 becomes the reference gas, and the gas in the second measurement cell 32 measures. When the gas is replaced Maintaining the value, it is that repeat the same behavior following.

  Thus, in the present invention, for the sake of convenience, the name of the data is given with reference to the gas filled in the measurement cell 1, the data appearing at the timing when the measurement gas enters the first measurement cell 31 is taken as the measurement data, Data appearing at the timing when the reference gas enters the first measurement cell 31 is used as comparison data. However, the name of the data may be attached based on the gas filled in the second measurement cell 32.

Next, calculation of concentration including drift removal will be described. Generalized as follows.
The arithmetic control unit 18 functions as an extraction unit 183 that extracts measurement gas detection data, pre-comparison gas detection data, and post-comparison gas detection data from the behavior of the detection data.

  This pre-comparative gas detection data is obtained before a gas switching period n times (n = 1, 3,... Odd) than the measurement gas detection data. In this embodiment, n = 1, and the detection data before the comparison gas is data obtained immediately before the measurement gas detection data is acquired.

  The post-comparison gas detection data is obtained after a gas switching period n times (n is an odd number) than the measurement gas detection data. In this embodiment, n = 1, and the detection data after comparison gas is data obtained immediately before the measurement gas detection data is acquired.

The gas switching cycle is a cycle in which the first flow path switching electromagnetic valve 20 and the second flow path switching electromagnetic valve 21 are switched in order to switch the gas flowing into the measurement cell. At this time, as shown in FIG. 6, the first measurement cell 31 has a period starting from the switching from the reference gas to the measuring gas and the first measuring cell 31 until the switching from the measuring gas to the reference gas. The switching cycle. Similarly, a period in which the period from the measurement gas to the comparison gas in the first measurement cell 31 is set as the initial period and the period from the first measurement cell 31 to the period in which the measurement gas is switched to the measurement gas is determined as a gas switching period. Detection data is acquired for each gas switching period.
The timing for obtaining the measurement gas detection data, the detection data before the comparison gas, and the detection data after the comparison gas is the switching timing of the first flow path switching solenoid valve 20 and the second flow path switching solenoid valve 21.

  The arithmetic control unit 18 functions as a difference unit 184 that obtains a difference value using these data. Specifically, it functions as a first difference data calculation unit that obtains the first difference data by taking the difference between the measurement gas detection data and the detection data before the comparison gas. Similarly, it functions as a second difference data calculation unit that obtains the second difference data by taking the difference between the measurement gas detection data and the detection data after the comparison gas.

The arithmetic control unit 18 functions as an averaging unit 185 that averages the first difference data and the second difference data to obtain averaged data.
Then, the arithmetic control unit 18 functions as a density conversion unit 186 that performs density conversion processing thereafter to obtain density data.
Finally, the arithmetic control unit 18 functions as an output unit 187 for outputting the density data to an output unit such as a monitor / printer.

Next, a specific description will be given. First, a case where the drift amount is almost constant will be described. In this embodiment, n = 1 and a gas switching cycle of 1 time.
For example, as shown in FIG. 6, the arithmetic control unit 18 detects the measurement gas detection data at the timing (4), the detection data before the comparison gas at the timing (3), and the detection after the comparison gas at the timing (5). Get the data. These data are as follows.

[Equation 22]
Detection gas before comparison gas (3) = − C + Δd
Measurement gas detection data of (4) = C + Δd
Detection data after comparison gas of (5) = − C + Δd

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 23]
First difference data = measured gas detection data of (4) −pre-comparison gas detection data of (3)
= C + Δd + C−Δd
= 2C

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 24]
Second differential data = Measured gas detection data of (4) −Comparative gas post-detection data of (5)
= C + Δd + C−Δd
= 2C

  Subsequently, averaging is performed. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 25]
Averaged data = 4C / 2 = 2C

  This averaged data coincides with the double value of the density equivalent C, and the desired density can be obtained by dividing by 2 and converting the density.

  Here, Δd is a drift amount, but this Δd is constant and can be eliminated as described above. Even if Δd is not constant, if it is a fluctuation in a sufficiently long unit with respect to the gas switching period, the change can be ignored, and even in this case, the drift can be eliminated.

Next, as shown in FIG. 7, the case where the drift amount changes quickly with respect to the gas switching period (such as the drift amount increasing for each measurement as shown in FIG. 7) will be described.
As shown in FIG. 7, the drift increases every time the solenoid valve is switched. For example, the measurement gas detection data = C + Δd + b at the timing (4), the comparison gas pre-detection data at the timing (3) = − C + Δd + a, Further, it is assumed that the detection data after comparison gas = −C + Δd + c is acquired at the timing of (5).

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 26]
First difference data = measured gas detection data of (4) −pre-comparison gas detection data of (3)
= C + [Delta] d + b-(-C + [Delta] d + a) = 2C + b-a

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 27]
Second differential data = Measured gas detection data of (4) −Comparative gas post-detection data of (5)
= C + Δd + b − (− C + Δd + c) = 2C + b−c

  Subsequently, averaging is performed. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 28]
Averaged data = (first difference data + second difference data) / 2
= (2C + ba-2C + bc) / 2 = 2C + b- (a + c) / 2

  Here, assuming a linear function in which the drift amount has an inclination α and changes in the gas switching period T, when b is regarded as a reference height (= 0), a = −αT, b = 0, c = + αT Therefore, when substituting into the above equation, b- (a + c) / 2 = 0. Therefore, the averaged data = 2C, and the drift is removed. By dividing the averaged data by 2 and converting the concentration, the concentration from which the drift is removed is calculated.

  In addition, when taking the difference, the comparison gas pre-detection data 3 or 5 times before the gas switching cycle is used from the measurement gas detection data, and the comparison after 3 or 5 times the gas switching cycle from the measurement gas detection data. Gas post-detection data may be used. Here, a case where data separated by three times the gas switching period is used will be described.

  As shown in FIG. 7, the drift amount increases every time the solenoid valve is switched. For example, the measurement gas detection data = C + Δd + b at the timing (4), and the detection data before the comparison gas = −C + Δd− at the timing (1). z and the detection data after comparison gas = −C + Δd + f are acquired at the timing of (7).

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measurement gas detection data and the pre-comparison gas detection data.

[Equation 29]
First difference data = measurement gas detection data of (4) −pre-comparison gas detection data of (1)
= C + Δd + b − (− C + Δd−z) = 2C + b + z

  Subsequently, the arithmetic control unit 18 obtains a difference value between the stored measured gas detection data and the comparison gas post-detection data.

[Equation 30]
Second difference data = measured gas detection data of (4) −post-comparison detection data of (7)
= C + Δd + b − (− C + Δd + f) = 2C + b−f

  Subsequently, averaging is performed. In this case, this is achieved by adding the first difference data and the second difference data and dividing by two.

[Equation 31]
Averaged data = (2C + b + z + 2C + b−f) / 2 = 2C + b− (f−z) / 2

  Here, assuming a linear function in which the drift amount has an inclination α and changes in the gas switching period T, when b is regarded as a reference (= 0), −z = −3αT, b = 0, and f = + 3αT. Therefore, when substituting into the above equation, b− (f−z) / 2 = 0. Therefore, the averaged data = 2C, and the drift is removed. By dividing the averaged data by 2 and then converting the concentration, the concentration from which the drift is removed is calculated.

When generalized, the detection data before the comparison gas is acquired before the gas switching period n times (n is an odd number) than the measurement gas detection data. The post-comparison gas detection data is acquired after a gas switching period n times (n is an odd number) than the measurement gas detection data.
Such a form may be adopted.

The infrared gas analyzer of the present invention has been described above.
In this infrared gas analyzer, the calculation timing of the concentration value is set immediately after the timing for switching from the measurement gas to the comparison gas, and immediately after the timing for switching from the comparison gas to the measurement gas, and is synchronized with the switching cycle managed by the arithmetic control unit. Therefore, since data is acquired, it is possible to reliably acquire data at the same timing as the gas switching cycle.
Furthermore, as a result of acquiring data at the same timing as the gas switching cycle, data is acquired at a relatively stable time after the change, so that the vertical movement of the concentration data is reduced and the original measured value is output. Is possible.

  Especially when the detector signal fluctuates immediately after the start-up of the device, when the detector signal fluctuates due to rapid temperature fluctuations, and even if the detector fluctuations are particularly small, even a slight fluctuation will affect the measured value. When it is easy to give, the effect becomes big.

  The infrared gas analyzer of the present invention is most suitable for measuring flue gas such as boilers and garbage incineration. In addition, gas analysis for steel [blast furnace, converter, heat treatment furnace, sintering (pellet equipment), coke oven], fruit and vegetable storage and ripening, biochemistry (microorganism) [fermentation], air pollution [incinerator, flue gas desulfurization / Denitration], automobile exhaust gas (remove tester), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refinery plant, petrochemical plant, gas generation plant], It is also useful as an analyzer for environmental [landing concentration, tunnel concentration, parking lot, building management], and various physics and chemistry experiments.

1, 2: Infrared gas analyzer 11: Motor 12: Chopper 13: Infrared light source 14: Measurement cell 15: Detector 16: Amplifier 17: AD converter 18: Operation control unit 181: Channel switching means 182: Detection data storage Means 183: Data extraction means 184: Difference means 185: Averaging means 186: Concentration conversion means 187: Output means 19: SSR
20: 1st flow path switching solenoid valve 21: 2nd flow path switching solenoid valve 22: Output part 30: Distribution cell 31: 1st measurement cell 32: 2nd measurement cell

Claims (4)

Infrared gas that irradiates infrared rays to the reference gas and measurement gas introduced alternately into the measurement cell, and obtains detection signals according to the concentrations of these comparison gas and measurement gas from the detector to measure the concentration of the measurement gas In the analyzer
Measurement gas detection data detected for the measurement gas, comparison gas detection data detected at a time n (n is an odd number) times before the gas switching cycle from the measurement gas detection, and gas switching n times from the measurement gas detection Data extraction means for extracting the detection data after the comparison gas detected at the time after the cycle, respectively, from the detection data;
First difference data calculation means for obtaining first difference data based on a difference between the measurement gas detection data and the detection gas pre-detection data;
Second difference data calculation means for obtaining second difference data based on the difference between the measured gas detection data and the detection gas post-detection data;
Averaging means for averaging the first difference data and the second difference data to obtain averaged data;
An infrared gas analyzer comprising: The infrared gas analyzer according to claim 1,
A flow path switching unit for switching the gas flowing into the measurement cell is provided.
An infrared gas analyzer characterized in that the timing for obtaining the measurement gas detection data, the detection data before the comparison gas, and the detection data after the comparison gas is a switching timing of the flow path switching unit. In the infrared gas analyzer according to claim 1 or 2,
An infrared gas analyzer characterized by a single beam system having one measuring cell. In the infrared gas analyzer according to claim 1 or 2,
An infrared gas analyzer characterized by a double beam system having two measuring cells.

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