JPH054628B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a cross-flow type gas analyzer, which is a type of gas analyzer used to measure the concentration (and thus the amount) of a gas to be measured in a sample gas. , a gas distribution cell, and an absorbance detector are arranged in that order so that an optical linear relationship is established, and the sample gas and zero gas are alternately switched and introduced into the gas distribution cell at a constant cycle. The present invention relates to a cross-flow type gas analyzer configured to include a gas distributor, and a synchronous rectifier amplifier that rectifies the output from the absorbance detector based on switching timing of the gas distributor. [Prior Art] FIG. 1 shows an infrared analyzer using a two-beam method, which is an example of a general cross-flow type gas analyzer. That is, as shown in the figure, a first light source 1A and a second light source 1B for irradiating an infrared beam for measurement, a first gas distribution cell 2A and a second gas distribution cell 2B, and a condenser microphone, for example. and one absorbance detector 3 consisting of a pneumatic type differential detector (a microflow type is also acceptable) are arranged in that order so that an optical linear relationship is established, and both the gas flow cells 2A and , 2B are provided with a gas distributor 4 for alternately switching and introducing sample gas and zero gas at a fixed period, and a detector 5 (for example, a photointerrupter) for detecting the switching timing of the gas distributor 4. , and a synchronous rectifier amplifier 6 that receives a signal from the switching timing detector 5 and rectifies the output from the absorbance detector 3 based on the switching timing of the gas distributor 4; An arithmetic circuit 7 outputs a concentration indication signal by performing processing such as absolute value averaging, absolute value integral averaging, or positive peak value holding on the output from the arithmetic circuit 7, and displays and displays the output from the arithmetic circuit 7. Recording display/recording circuit 8
A cross-flow gas analyzer capable of measuring the concentration of a gas to be measured in a sample gas is configured. As shown in the figure, the gas distributor 4 is normally a rotary valve having a rotary valve body 4a that is rotated at a constant cycle (for example, a frequency of 1 Hz), and the switching timing detector 5 is connected to the rotary valve body 4a. It is configured to detect the position of the rotary valve body 4a. Also, in the figure, 9
A and 9B are solid filters provided according to the gas to be measured, and furthermore, 10A and 1
0B is a flow rate control device for controlling the flow rates of sample gas and zero gas supplied to the gas distributor 4. [Problems to be Solved by the Invention] However, the cross-flow gas analyzer having the above configuration has conventionally had a major problem due to the influence of flow rate, as explained below. That is, the gas distributor 4 and the gas distribution cell 2
The lower the gas flow rate per unit time introduced into A, 2B, the greater the decrease in sensitivity due to the mixing of sample gas and zero gas in the gas distributor 4 and gas distribution cells 2A, 2B. The flow rate-sensitivity characteristics of a flow-type gas analyzer are basically as shown in Figure 4 A. Therefore, in order to keep sensitivity changes due to changes in flow rate small, it is necessary to The target flow rate Q ₀ to be introduced must be set within a large flow rate region where the basic flow rate-sensitivity characteristics of the analyzer are approximately flat. As a result, the entire device must be relatively large. On the other hand, the output of the absorbance detector 3 is also
As the gas flow rate per unit time introduced into the gas distribution cells 2A and 2B changes, the phase shifts, so the synchronous rectifier amplifier 6 provided after the absorbance detector 3 is also affected by the flow rate. Therefore, as a matter of course, the flow rate-sensitivity characteristic of the synchronous rectifier amplifier 6 itself is adjusted so as to exhibit maximum sensitivity at the target flow rate _Q0 , as shown in FIG. 4B. As a result, the actual flow rate-sensitivity characteristics of this cross-flow gas analyzer are as shown in Figure 4 C.
The maximum sensitivity is exhibited at the target flow rate _Q0 . Therefore, in order to perform accurate measurements using this cross-flow type gas analyzer, the gas flow rate per unit time introduced into the gas distributor 4 and the gas distribution cells 2A, 2B must always be adjusted to the above-mentioned target. flow rate
Q must be tightly controlled to keep it at ₀ ,
For this reason, it is necessary to adopt a very complicated configuration as the flow rate control devices 10A, 10B, and even if such precise flow rate control devices 10A, 10B are used, there will be some degree of flow rate change. The occurrence of errors due to changes in sensitivity is unavoidable. The present invention has been made in view of the above-mentioned conventional circumstances, and its object is to hardly cause a change in sensitivity due to a change in flow rate even if the target flow rate to be introduced into the gas flow cell is set to be relatively small. By doing so, the purpose is to simplify the flow rate control device, downsize the entire device, and improve measurement accuracy. [Means for Solving the Problems] In order to achieve the above object, the cross-flow gas analyzer according to the present invention has the basic configuration as described at the beginning, and is provided at the downstream stage of the absorbance detector. The flow rate of the synchronous rectifier amplifier itself −
The synchronous rectification amplifier is adjusted so that the sensitivity characteristic exhibits maximum sensitivity at a flow rate lower than the target flow rate to be introduced into the gas flow cell. [Effects] The effects achieved due to this characteristic configuration are as follows. That is, the cross-flow gas analyzer according to the present invention overcomes the disadvantageous property of the synchronous rectifier amplifier installed therein (as explained earlier, it is affected by phase shift due to flow rate changes). This was done based on the idea of using the synchronous rectification amplifier effectively, and the synchronous rectification amplifier is used in a completely different way than the normal usage. In other words, the synchronous rectification amplifier has maximum sensitivity at a flow rate lower than the target flow rate. By adopting the method of adjusting the target flow rate, the target flow rate can be adjusted to achieve the miniaturization of the entire device including the gas flow cell, as will become clear from the description of the examples described later. Although the setting is relatively small, the actual flow rate-sensitivity characteristics of the cross-flow gas analyzer are
It is now possible to obtain a substantially flat state near the target flow rate, and therefore, even if the gas flow rate introduced into the gas flow cell changes to some extent, the measurement sensitivity does not change. As a result, it has become possible to achieve significant simplification of the flow rate control device and to ensure excellent measurement accuracy. [Example] Hereinafter, an example of the present invention will be described based on the drawings (FIGS. 1 to 3). The hardware configuration of the cross-flow gas analyzer according to the present invention is the same as that shown in FIG. Only regarding the adjustment status of synchronous rectifier amplifiers and related matters.
This will be explained below. In other words, the flow rate of this cross-flow gas analyzer -
As explained earlier using FIG. 4, the sensitivity characteristics are basically as shown in FIG.
Since there is no need to set the target flow rate Q ₀ to be introduced into A and 2B within a large flow rate region where the basic flow rate-sensitivity characteristics of the analyzer are almost flat, unlike conventional methods, the gas flow cell In order to reduce the size of 2A, 2B, etc., it is set within a relatively low flow rate region. On the other hand, the synchronous rectifier amplifier 6 provided after the absorbance detector 3 has a flow rate-sensitivity characteristic of the synchronous rectifier amplifier 6 itself that is lower than the target flow rate Q ₀ as shown in FIG _. (Hereinafter, this will be referred to as a synchronously adjusted flow rate: Q ₁ <Q ₀ ). Adjustment is made so that maximum sensitivity is exhibited (peak is achieved). As a result, the actual flow rate-sensitivity characteristic of this cross-flow type gas analyzer can have a substantially flat region S near the target flow rate _Q0 , as shown in FIG. 2C. Therefore, even if the gas flow rate introduced into the gas flow cells 2A, 2B changes to some extent, the measurement sensitivity will not change. This makes it possible to ensure excellent measurement accuracy in which errors due to influences are less likely to occur. By the way, what value to set the synchronous control flow rate _Q1 to is determined by the specific use of the analyzer (length and diameter of the gas distribution cells 2A, 2B, dead space in other piping systems, etc.). Although it is not possible to specify it precisely because the flow rate is different for each individual, usually the synchronized adjustment flow rate Q ₁ is approximately 60% of the target flow rate Q ₀ .
It has been empirically found that it is sufficient to set the synchronously adjusted flow rate to approximately An almost exact value of Q ₁ can be easily determined. That is, Fig. 3A shows the basic flow rate-sensitivity characteristics in a relatively low flow rate region (0.3 to 0.7/min) of an analyzer equipped with gas flow cells 2A and 2B with a length of 30 mm and a diameter of 10 mm. Figure 3 shows a specific example of the experimentally determined flow rate (in this example, the target flow rate Q ₀ to be introduced into the gas flow cells 2A and 2B is set to 0.5/min), and the analyzer. This shows a specific example in which the relationship between the time required for replacing the sample gas with zero gas and the flow rate in the gas distribution cells 2A and 2B was determined by experiment.
In the case of this analyzer, the relationship between the time required for the replacement and the phase shift of the output from the absorbance detector 3 is
It has been experimentally determined that the speed is 241°/sec. Here, using the graph in FIG.
Calculating the flow rate-sensitivity characteristics of the device itself, () If the target flow rate Q ₀ (0.5/min) is used as the standard, as in the case of conventional means, that is, the target flow rate Q ₀ (0.05/min) ), if the synchronous rectifier amplifier 6 is synchronously adjusted so that its flow rate-sensitivity characteristic reaches its maximum sensitivity at the target flow rate Q ₀ , the phase shift will be:

[Table] Since the flow rate-sensitivity characteristics of the synchronous rectifier amplifier 6 itself are affected by the cosine phase shift (θ),

[Table], which is shown by the dotted line in Figure 3C. Therefore, it is expressed as the product of the basic flow rate-sensitivity characteristic of the analyzer shown in FIG. However, the actual (final) flow rate-sensitivity characteristic of the analyzer is shown by the dotted line in FIG. 3D. In this case, as is clear from the figure, a flat flow rate-sensitivity characteristic is not obtained near the target flow rate Q ₀ , so the gas flow rate per unit time introduced into the gas distribution cells 2A, 2B is always In order to strictly control the flow rate to maintain it at the target flow rate Q ₀ , a flow rate control device with a complicated configuration must be employed. This conventional problem cannot be solved. () Therefore, if the flow rate Q ₁ (0.3/min in this example) is smaller than the target flow rate Q ₀ (0.5/min), that is, the synchronously adjusted flow rate
When the synchronous rectifier amplifier 6 is synchronously adjusted at Q ₁ (0.3/min) so that its flow rate-sensitivity characteristic has the maximum sensitivity at the synchronously adjusted flow rate Q ₁ , the phase shift is as follows.

【table】 Then, The flow rate-sensitivity characteristics of the synchronous rectifier amplifier 6 itself are as follows:

〔Effect of the invention〕

As is clear from the detailed description above, according to the cross-flow gas analyzer according to the present invention, the flow rate-sensitivity characteristic of the synchronous rectifier amplifier itself provided after the absorbance detector is The target flow rate to be introduced into the gas flow cell can be adjusted by simply adjusting the synchronous rectifier amplifier so that it exhibits maximum sensitivity at a flow rate lower than the target flow rate to be introduced. Even if it is set to a relatively small value, there is almost no change in sensitivity due to changes in flow rate.
Excellent effects have been achieved in that the objectives of simplifying the flow rate control device, downsizing the entire device, and improving measurement accuracy can be fully achieved.

[Brief explanation of the drawing]

1 to 3 are for explaining embodiments of the present invention, and FIG. 1 shows an overall schematic configuration diagram of a general cross-flow type gas analyzer, and FIG. 2 is a graph schematically representing the basic flow rate-sensitivity characteristics of this analyzer, Figure 2B is a graph schematically representing the flow rate-sensitivity characteristic of the synchronous rectifier amplifier itself when the present invention is applied, Figure 2C shows a graph schematically representing the actual flow rate-sensitivity characteristics of the analyzer when the present invention is applied, and Figure 3B shows the specifics of the basic flow rate-sensitivity characteristics of the analyzer. Graph showing an example, Figure 3 (b) is a graph showing a specific example of the relationship between the time required to replace the sample gas with zero gas and the flow rate in the gas flow cell of this analyzer, and Figure 3 (c) is a graph in which the present invention is applied. A graph showing a specific example of the flow rate-sensitivity characteristic of the synchronous rectifier itself and a comparative example thereof in the case where the present invention is applied. 2 shows a graph representing a comparative example. Figure 4 is for explaining the problems of the conventional technology. FIG. 4C is a graph schematically representing the flow rate-sensitivity characteristic of the synchronous rectifier amplifier itself in the conventional analyzer. 1A, 1B...Light source, 2A, 2B...Gas distribution cell, 3...Absorbance detector, 4...Gas distributor, 6...Synchronous rectifier amplifier, _Q0 ...Target flow rate,
Q ₁ ...Synchronized control flow rate.

Claims (1)

[Scope of Claims] 1. A light source, a gas distribution cell, and an absorbance detector are arranged in that order so that an optical linear relationship is established, and a sample gas and a zero gas are kept constant with respect to the gas distribution cell. A cross-flow type comprising a gas distributor for alternately switching and introducing the gas at intervals, and a synchronous rectifying amplifier for rectifying the output from the absorbance detector based on the switching timing of the gas distributor. In a gas analyzer, the flow rate-sensitivity characteristic of the synchronous rectifier amplifier itself is
A cross-flow type gas analyzer characterized in that the synchronous rectifier amplifier is adjusted so as to exhibit maximum sensitivity at a flow rate lower than a target flow rate to be introduced into the gas distribution cell.