JPS60198435A - Ir gas analyzer - Google Patents

Abstract

PURPOSE:To reduce the size and cost of the titled analyzer by measuring the concn. of the gas in a measuring cell from a difference between the detection signals of the light transmitted through the measuring cell and the light transmitted through a reference cell. CONSTITUTION:The IR rays radiated from a light source 1 are intermitted at specified time intervals by a light chopper 29 and are introduced alternately to a sample cell 2 and a reference cell 3. The light transmitted through the cell 2 or cell 3 is made incident on a detector 22 via a condenser 21. The detector 22 has two chambers 22-1, 22-2 disposed before and behind the incidence of the light. Measuring component gases are filled in the chambers 22-1, 22-2 and the chambers are sealed hermetically. The incident light enters first the front chamber 22-1 and the light transmitted therethrough enters the rear chamber 22-2. The pressure difference corresponding to the difference in light absorption in both chambers 22-1, 22-2 is detected by a pressure difference detecting element 23 provided between both chambers. The need for a temp. control mechanism is thus eliminated and the reduction in the size and cost is realized.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is an analyzer used for monitoring and controlling gas concentrations in various industrial processes, measuring exhaust gas concentrations for pollution monitoring, etc. This invention relates to a non-dispersive infrared gas analyzer that measures the concentration of a specific component in a sample gas based on the strength of infrared absorption of gas molecules using the infrared absorption effect of gas molecules.

(Prior Art) FIG. 1 shows a conventional infrared gas analyzer using a single light source. 1 is a light source, and a sample cell 2 and a comparison cell 3 are arranged parallel to each other at -1 so that the same amount of light is incident on the light source 1. A sample gas containing a component to be measured is passed through the sample cell 2, and a comparison cell 3 is filled with an inert gas such as nitrogen or air that does not absorb infrared rays. 4 is a light chopper that simultaneously interrupts the light incident on the sample cell 2 and comparison cell 3 from the light source 1; 5 and 6 are light quantities that adjust the amount of light that passes through each cell 2 and 3 and enters the detector 7; It is a regulator. The detector 7 is partitioned into two chambers 9°10 by a metal thin film 8.
It is a condenser microphone type detector in which both chambers 9 and 10 are filled with a gas to be measured and are sealed, and a capacitor is formed by a metal thin film 8 and an electrode 11 provided opposite thereto. ]2 is a signal detection circuit of the detector 7.

In this conventional infrared gas analyzer, the amount of light incident on the two chambers 9, 10 of the detector 7 is adjusted by the sight adjuster 5.6 so that it is not equal. First, N has no infrared absorption.
When an inert gas (zero gas) such as 2 is flowed into the sample cell 2, the light amount adjusters 5 and 6 are adjusted so that the amount of light incident on the detector 7 is greater on the comparison cell 3 side. Suppose there is. .

In the detector 7, since a larger amount of light enters the chamber 10 than the chamber 9, the metal thin film 8 moves toward the left.

Since the light incident on both chambers 9 and 10 of the detector 7 is simultaneously interrupted by the optical chopper 4, the metal thin film 8 also vibrates at a constant frequency, and the detection signal is as shown by symbol 15 in FIG. The amplitude of this signal is the zero point.

Next, if a similar measurement is made by flowing a gas (span gas) containing a certain concentration of the component to be measured through the sample cell 2, the sample cell 2 will absorb infrared rays and the amount of light transmitted through the sample cell 2 will decrease. The amplitude of the detection signal increases as indicated by symbol J6 in FIG. The amplitude of this detection signal 16 becomes the span point.

Then, when a similar measurement is performed by flowing the measurement gas into the sample cell 2, a detection signal with an amplitude corresponding to the concentration of the component gas is obtained as shown by symbol 17 in Fig. 2, so this is taken as the zero point. The sample gas concentration can be proportionally distributed between the span points.

In this conventional infrared gas analyzer, as described above, the transmitted light from the sample cell 2 and the comparison cell 3 are respectively incident on the separate chambers 9 and 10 of the detector 7, and the difference in the amount of re-transmitted light is reflected in the sample cell 2.
The detector 7 measures the concentration of the component gas in the sample cell 2 and the comparison cell 3 when the amount of transmitted light becomes equal.
Since the metal thin film 8 stops and detection becomes impossible, the amount of light transmitted through the sample cell 2 and the comparison cell 3 was adjusted using a light amount adjuster 5.6 so that the amounts of transmitted light were different from each other.

Therefore, when using this conventional infrared gas analyzer H1 continuously for a long time, even if a single light source is used, the zero point and span point will change due to changes in ambient temperature, deterioration of the light source, changes in detector sensitivity, etc. do. For this reason, in the conventional infrared gas analysis H1, it is necessary to adjust the temperature of the analysis section (optical system) to a constant temperature, resulting in high cost.

Furthermore, if the temperature control is not perfect, it may cause errors. Conventionally, in order to reduce these tlft differences, it was necessary to calibrate the zero point and span point by periodically flowing zero gas and span gas (more frequently in high-sensitivity analyzers) at a constant cycle.

Also, during zero point measurement, it is necessary to adjust the light balance of the optical system in order to maintain a certain difference between the amount of transmitted light on the sample cell side and the amount of transmitted light on the comparison cell side, and a light amount adjuster mechanism is required for this adjustment. was required, and man-hours were also required to adjust it.

(Purpose) 4. The present invention is capable of automatically and continuously correcting changes in ambient temperature, changes in light intensity of a light source, changes in sensitivity of a detector, etc. by processing detection signals, and is capable of automatically and continuously correcting changes in ambient temperature, changes in light intensity of a light source, changes in sensitivity of a detector, etc. The purpose of this invention is to provide a stable and low-cost infrared gas analyzer that eliminates the need for

(Structure) In the infrared gas analyzer of the present invention, one light source is used, and the transmitted light from this light source is transmitted through a sample cell and a comparison cell, respectively, and is alternately introduced into one detector. Extract the light detection signals separately.

A condenser microphone type or micro flow sensor type detector is used as the detector, and the introduction of transmitted light to the detector is controlled by optical chopper means provided on the incident side or transmission side of the sample cell and comparison cell. However, the time interval is such that the detection signal of the light transmitted through the sample cell (hereinafter referred to as the measurement signal) and the detection signal of the light transmitted through the comparison cell (hereinafter referred to as the comparison signal) do not interfere with each other (even if there is slight interference, there is no substantial effect). Both transmitted lights are introduced into the detector with a degree of

Then, the difference between the measurement signal and the comparison signal is used as an output signal, and the comparison signal is also used to detect the sensitivity of the entire optical system, and the output signal is corrected so that this sensitivity is constant. It is. Furthermore, changes in the measurement signal due to changes in the density of the sample gas due to temperature changes can be corrected by detecting the degree of sinusoidality of the measurement cell.

(Example) FIG. 3 shows an optical system according to an embodiment of the present invention.

The infrared rays emitted from the light source 1 are cut off at regular time intervals by a light chopper 20 and introduced into the sample cell 2 and comparison cell 3 alternately. Reference numeral 21 is a condensing type that makes the light transmitted through the sample cell 2 or comparison cell 3 enter the detector 22 of Jll-. The detector 22 has two chambers 22-1.22-2 arranged in front and behind the incident light, each chamber 22-1.
22-2 is filled with measurement component gas and sealed, and the incident light first enters the front chamber 22-1, and the transmitted light enters the rear chamber 22-2. A pressure difference corresponding to the difference in light absorption between the compartments 22-] and 22-2 is detected by a pressure difference detection element 23 provided between the compartments. As the pressure difference detection element 23, a condenser microphone or a microflow sensor is used.

The light chopper 20 interrupts the light beam from the light source 1 so that the light is made to enter the sample cell 2 and the comparison cell 3 alternately. Such an optical chopper 20 is, for example, as shown in FIG. 4, and an opening 24 for the sample cell 2 and an opening 25 for the comparison cell 3 are provided at positions separated from each other. 26.2
A photodetector 7 detects the timing at which the optical chopper 20 interrupts the light beam, and receives light from the apertures 28 and 29 to generate pulse signals 30 and 31 shown in FIG.

The rotational speed at which the optical chopper 20 makes light alternately enter the sample cell 2 and the comparison cell 3 is set to be slower than the response time of the detector 22. As a result, the detection signal of the detector 22 becomes a solitary wave in which the comparison signal 32 and the measurement signal 33 do not interfere with each other, as shown in FIG.

7- Next, the processing system of the detection signal of this embodiment obtained as shown in FIG. 5 will be explained with reference to FIG.

Comparison signal 32 and measurement signal 33 detected by detector 22
is amplified by the amplifier 40 and then separated into a comparison signal R and a measurement signal M at the timing of the optical chopper 20. Both signals are input to a subtracter 41 to be differentiated, and the comparison signal R is also input to a comparator 42 to obtain a reference setting voltage v.
r, and if there is a deviation from r, feedback is applied to the amplifier 40 and the gain of the amplifier 40 is controlled so that the comparison signal R becomes constant. In other words, when the amount of light in the optical system or the sensitivity of the detector changes, the signal processing system controls the sensitivity so that it remains constant.

The output of the subtracter 41 inputting the comparison signal R and the measurement signal M subjected to sensitivity correction in this manner becomes an output signal corresponding to the concentration of the component gas in the sample cell.

Reference numeral 43 denotes a comparator for performing concentration correction due to changes in the density of the measurement gas due to changes in the sample cell temperature T.

81 In this embodiment, a zero gas containing no measurement component is first flowed into the sample cell 2, and the output signal at that time is set as the zero point. In this case, if the amount of transmitted light in sample cell 2 and comparison cell 3 is made equal, the output level at the zero point will be 0 level, and even if the amount of light from the light source changes or the sensitivity of the detector changes. Even if this happens, the effect will appear on the measurement signal and the comparison signal at exactly the same rate, so the level of the zero point output as the difference between the two signals will not change.

Next, a span gas containing a certain concentration of the component to be measured is passed through the sample cell 2, and the output signal at that time is taken as the span point.

Next, the concentration of the sample gas is determined by proportionally distributing the output signal obtained by flowing the sample gas to be measured through the sample cell 2 between the previously measured span point and zero point.

The sample cell 2 may become dirty due to long-term measurement, and the measurement signal may change. Since this change occurs independently of the comparison signal, it cannot be corrected by the gain control of the amplifier 40 described above. Therefore, after measuring for a certain period of time,
By flowing the zero gas and span gas again and remeasuring the zero point and span point, it is possible to correct errors caused by such Al11 constant cell contamination.

The above embodiment is an example of the present invention, and various changes can be made within the scope of the present invention. For example, the optical chopper 20 may be of any type as long as it can introduce the light from the light source 1 alternately into the measurement cell 2 and the comparison cell 3, preferably at a slow enough speed that the measurement signal and the comparison signal do not interfere with each other, and the aperture position The shape can be modified in various ways.

The detector 22 used is of a condenser microphone type which is separated into two chambers, front and rear, relative to the incidence of light, but it may be of a condenser microphone type with a single gas chamber filled with the gas to be measured. Alternatively, a micro flow sensor type detector may be used.

In addition, the detection signal processing method is just an example; the point is that the measurement signal and the comparison signal are detected separately, the component gas concentration is determined from the difference, and the sensitivity of the detection system is kept constant using the comparison signal. Any method that controls to maintain the temperature may be used. Therefore, in addition to applying feedback to the gain of the amplifier using the comparison signal as in the embodiment, it is also possible to correct changes in the detection signal by performing digital calculations using the comparison signal.

(effect) The effects of the present invention are listed below.

(1) With conventional infrared gas analyzers, measurement values fluctuate greatly due to temperature changes, so a complete temperature control mechanism was required. However, with the present invention, even if the temperature changes, the comparison signal from the comparison cell ensures zero Since the points, span points, and measurement signals are constantly corrected, a temperature adjustment mechanism is not required, and the structure of the case is simplified, making it possible to achieve smaller size and lower cost.

(2) Since drift due to deterioration of the light source or decrease in sensitivity of the detector is automatically corrected, stability is improved compared to conventional ones.

In particular, in the present invention, it is also possible to set the zero point to the 0 level by making the amount of transmitted light of the sample cell equal to the amount of transmitted light of the comparison cell. The zero point remains unchanged, resulting in better stability.

(3) Since no temperature control mechanism is required, warm-up is short and measurements can be started immediately.

(4) If the measurement signal and the comparison signal are electrically matched, there is no need to adjust the light intensity of the measurement cell and the comparison cell, thus eliminating the need for the conventional complicated adjustment process.

(5) Processing can also be performed using a microcomputer, in which case various calibrations can be performed automatically.

[Brief explanation of drawings]

Figure 1 is a schematic partial cross-sectional view of a conventional infrared gas analyzer, Figure 2 is a waveform diagram showing the detection signal of the same analyzer, and Figure 3 is a waveform diagram showing the detection signal of the analyzer.
The figure is a schematic diagram partially showing an embodiment of the present invention in cross section, and FIG. 4 is a plan view showing an optical chopper used in the embodiment.
FIG. 5 is a waveform diagram showing a detection signal of the same embodiment, and FIG. 6 is a block diagram showing a detection signal processing system of the same embodiment. =12- 1...Light source, 2...Measurement cell, 3
... Comparison cell, 20 ... Optical chip large brim, 22 ... Detector, 23 ... Pressure difference detection element. Agent: Patent Attorney Shigeo Noguchi

Claims (1)

[Claims] (1) Infrared light from a single light source is introduced into a measurement cell and a comparison cell, and the transmitted light from both cells is intermittently introduced into a detector by a light chopper provided on the incident side or transmission side of the cell. In the gas analyzer, the detector is a condenser microphone type detector or a micro flow sensor type detector having a light receiving part of Ql-, and the optical chip means detects the light transmitted through the measurement cell and the light transmitted through the comparison cell. It has a structure in which the signals are introduced into the detector alternately at time intervals such that they do not interfere with each other, and is equipped with means for detecting the temperature of the measurement cell, while detecting changes in sensitivity using the detection signal of the light transmitted through the comparison cell. An infrared gas analyzer, characterized in that a gas concentration in a measurement cell is measured from a difference between a detection signal of light transmitted through a measurement cell and a detection signal of light transmitted through a comparison cell, and correction is performed based on temperature.