JPH0989765A - Infrared ray gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared gas analyzer for measuring the humidity of a wet gas or mixture. SOLUTION: The infrared gas analyzer comprises a sample cell 65 being set in a gas flow, an infrared radiation source 61 of selected wavelength passing the sample cell 65, and an infrared detector 69 receiving infrared rays transmitted through the sample cell 65. Concentration of a selected substance in gas flow is measured based on one selected wavelength being absorbed by a gas to be measured using infrared rays incident on the infrared detector 69. In a preferable method, the infrared gas analyzer is used as a temperature sensor for a medical respiration circuit where at least one selected wavelength is absorbed significantly by water. A heating means is coupled with a sample cell in order to evaporate water intruding into the sample cell which is provided with an inner baffle for retarding precipitation and condensation of water on a radiation window.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is particularly, but not exclusively, concerned with an infrared gas analyzer for in-line sensing of the humidity of a humidified gas stream. Applications of this infrared gas analyzer include, for example, detection of the humidity of humidified respiratory gas supplied to patients in hospitals.

Humidity sensors currently in use often have a slightly slower reaction time and are usually not suitable for use at high relative humidity. High in the biomedical industry (60-10
It is desirable to measure the absolute temperature of a moving air stream at 0% relative humidity with a fast response time. One example of this application is the measurement of humidity in the breathing circuit of a patient with an air inhaler. In this case, in the flow of air moving at high speed,
Moreover, it is desirable to know the cumulative humidity for each breath or for each certain period without being affected by the condensation of water. The air flow in the device is warmer than the surrounding wall of the tube, so that water droplets form on the wall of the tube and in the air. It is also desirable to measure the humidity of the breathing circuit without using a sampling device (such as an inhalation pump or bypass tube). This type of device, called "mainstream", has the advantages of speed, simplicity, and quiet operation. In addition, the humidity sensor must not be affected by the humidity it is measuring at any size.

[0003]

BACKGROUND OF THE INVENTION Existing commercial instruments for measuring humidity operate on the basis of several well-known principles and are without exception pros and cons. A dry-wet bulb thermometer is a device that measures the temperature difference between a wet thermometer and a dry thermometer. They are commonly used in meteorological observations or in rooms or chambers where moist air is stationary or slowly moving and there is little risk of contamination.

There are many devices consisting of polymeric films or porous ceramics that can adsorb the moisture of moist air on their surface. This leads to changes in the measurable physical properties of the device, such as resistance and capacitance. These devices are inexpensive and popular in HVAC and consumer products. The disadvantages of these devices are that they are inaccurate and they tend to "drip" at high relative humidity due to deviations and contamination of the adsorption surface after long-term use. Such drawbacks result in limited application in medical breathing circuits, which often have high relative humidity.

Although an apparatus for measuring the dew point of moist air using a cooled mirror is expensive, it is very suitable and highly accurate for measuring high relative humidity. The drawback of this technique is that the mirror surface is easily polluted and the device works well in still air. There are also several commercially available devices that measure the thermal conductivity of moist air using a heated temperature sensor. These devices are sensitive to the absolute humidity of the air and are sufficiently sensitive to high humidity. But,
Measurements can also be affected by differences in air flow and gas composition. There can be high levels of oxygen and anesthetic gases in the breathing circuit that can affect the measured humidity.

Humidity analysis by infrared rays is one of the humidity measurement methods that is insensitive to fast response time, air movement speed and changes in gas components. One of the objects of the present invention is to provide a device for measuring the humidity of moist gases or gas mixtures which overcomes the above-mentioned drawbacks. A further object of the invention is
An object is to provide an improved infrared gas analyzer.

[0007]

A preferred embodiment of the infrared gas analyzer of the present invention, although the application of the present invention is not so limited, is of the present invention for measuring the humidity of a stream of breathing air. It will be described with reference to the application. When the near-infrared or mid-infrared (IR) spectrum passes through the sample, the absorption band showing the chemical composition of the sample can be known. There are five major components in air: nitrogen, oxygen, argon, carbon dioxide and water vapor. Of course, these are symmetrical structures, so nitrogen, oxygen, and argon do not absorb infrared radiation. Carbon dioxide has a strong absorption band at a wavelength of 4.3 μm, and water vapor is 1.35 to 1.45 μ.
m, 2.6 to 2.8 μm wavelength and 5.5 to 6.5 μm wavelength. In a medical environment, gases with absorption bands at different wavelengths (such as anesthetic gases) are present in the air.

An apparatus that uses infrared absorption to measure humidity is constructed as follows. An infrared radiation source (comprising a narrow band or narrow band filter) is provided so that the radiation is collimated into the beam. The beam passes through a chamber (sample cell) containing sample air and finally enters an infrared detector which measures the radiant intensity. The infrared filter is selected to pass only one of the radiation in the absorption band of water. The device is heated with a heating coil to stop the condensation in the measurement sample cell, ie the infrared radiation intensity is large enough to stop the condensation. Adding some modulation to the light source is essential to reduce noise and improve long-term stability of the device. This is accomplished by directly modulating the light source or using some form of mechanical radiation chopper.

In practice, the arrangement is similar to a chamber containing dry air used as a reference (reference sample cell). The difference in the amount of radiation incident on the sample detector and the reference detector is the amount of radiation absorbed by the water vapor. This difference is related to the amount of water vapor in the sample cell, ie the absolute humidity. This type of device is known as a two beam, single wavelength device and is well known in the art. A disadvantage of the two-beam, single-wavelength device is that the deposition of contaminants on the window of the sample cell reduces the measurement accuracy.

An alternative to the two-beam method is to use a sample cell, but two different wavelengths pass through the sample cell. One of the wavelengths is located inside the water absorption band (measurement wavelength), and the other wavelengths are located outside the water absorption band (reference wavelength). The two wavelengths are usually directly modulated by two infrared radiation sources, wavelength modulated by a single infrared radiation source, several bandpass interference filters are interleaved in the radiation path, or bandpass interference filters are used. It is generated by modulation. The amount of radiation incident on the infrared detector depends on the amount of water vapor in the sample cell through which the measurement wavelength is passing, and is independent of the amount of water vapor passing through the reference wavelength. Therefore, a small AC signal is present at the output of the infrared detector and is proportional to the amount of radiation absorbed by the water vapor of the sample cell for a constant output of the infrared radiation source. This is related to the amount of water in the sample cell, ie absolute humidity.

Single beam, dual wavelength devices of this type are well known in the art. The advantages of this type of device are:
Any degradation of the sample cell window surface affects both the measured and reference wavelengths (assuming the wavelengths are close together) and does not affect the absolute humidity measurement accuracy. Devices for humidifying the breathing air delivered to a patient are well known and may be provided in a form similar to that shown in FIG. Please refer to FIG. The humidifier is designated by reference numeral 1 with a bottom 2 and comprises an electronic control circuit with a heating element in a heater plate 3, which is in contact with the bottom of the humidification chamber 4. The humidification chamber has a gas input 5 and a gas output 6. Gas output 6 is breathing conduit end 8
Is provided for connection to a breathing conduit 7 which supplies humidified gas to an infrared radiation source. Infrared radiation source
For example, a face mask or tube may be connected to the inserted patient. The heating element 9 is also provided in the breathing conduit and helps prevent the condensation of the moist gas as it moves through the breathing conduit. The water present in the humidifying chamber 4 humidifies the gas in the humidifying chamber by the heater plate 3 to heat it to a desired temperature and humidity. Condensation typically occurs in a respiratory conduit connecting a patient admitted to a hospital to a medical breathing circuit and includes a ventilator and a humidifier that provide a source of humidified gas. Condensation occurs in the respiratory conduit because the walls of the respiratory conduit are usually at a low temperature (close to the temperature of the surrounding atmosphere) compared to the temperature of the humidified gas supplied by the device.
Until now, there has been no humidity sensor in a breathing conduit that is not affected by water condensation and at the same time measures the humidity of a rapidly moving air stream with sufficient speed and accuracy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described.
FIG. 2 shows a block diagram of a single beam, dual wavelength infrared humidity sensor including a sample cell as an integral unit. Radiation from an infrared radiation source comprising a single multiple wavelength infrared radiation source 61 is collimated by a lens 62 into a beam 99. This beam passes through a rotating dual segment filter assembly driven by a motor 64. A rotating dual segment filter assembly first gates one wavelength and then two narrow band interference filters 8 that pass other wavelengths through the rotating dual segment filter assembly as the filter rotates.
Including 5,86. The bandpass interference filter 85 allows infrared rays in the absorption band of water to pass through. The band pass interference filter 86 avoids the water absorption band and constitutes the reference band pass interference filter 86.

The beam then passes through the sample cell, through which the detected gas 66 flows, reflects off the mirror 67 and returns through the sample cell 65 twice. The beam is focused by a lens 68 onto a point on an infrared detector 69 of the germanium photodiode type. It should be noted that the beam may be reflected multiple times through the sample cell 65 to improve radiation absorption by water vapor, or it may pass through the sample cell 65 only once but not reflected at all.

The signal from the infrared detector 69 is amplified by a preamplifier 70 and the output signal produces an output signal 71 which is synchronously detected by a lock-in amplifier or synchronous demodulator 72. The output of the lock-in amplifier is processed by the signal processing and display circuit 37 and indicates the magnitude of absolute humidity. Position sensor 7 of reflected light sensor type
4 is used to detect the mark 75 on the rotating dual segment filter assembly 63. The output signal 80 from this sensor is the phase locked loop 76.
And the phase from the signal from the position sensor 74 is synchronized with
A signal 77 having a 50% duty cycle is provided. The variable phase delay circuit 78 is the same as the signal 77,
It provides a synchronization signal 79 that is shifted by a fixed phase angle. The phase delay is adjusted so that the sync signal 79 exactly matches the timing of the light beam changing from one half of the rotating dual segment filter assembly to the other. The signal 79 is used to synchronize the lock-in amplifier 72.

The speed of the motor 64 is determined by the phase comparator 81.
To control the phase of signal 81 and the reference frequency signal from oscillator 82. The output of the phase comparator 81 passes through a loop filter 83 and into an amplifier 84 which supplies power to the motor. This configuration forms a phase locked loop that controls the speed of the motor, and the oscillator 82
Equalize the frequencies of.

The infrared radiation source 61 is preferably a semiconductor infrared radiation source such as an incandescent lamp or an infrared light emitting diode (LED). The use of LEDs as the infrared radiation source allows the amount of current supplied to be varied to enable high speed modulation of the light output. The wavelength range of the infrared radiation source 61 should be selected to cover the reference and measurement wavelengths.

When dry air passes through the sample cell,
The output signal 71 of the infrared detector preamplifier changes between two levels, the measurement wavelength signal and the reference wavelength signal. These are usually not equal due to the transmission difference of the bandpass interference filters 85, 86, the output difference of the infrared radiation source 61 depending on the wavelength, the wavelength response difference of the infrared detector 69 and other factors. In order to "balance" the device, or to make the measurement and reference signal levels equal to the output signal 71, the amount of current supplied to the infrared radiation source 61 is between two levels when the filter wheel is rotating. Can be changed with. This is the two voltages 88, 8 supplied from the reference voltage 81A.
Infrared radiation source 6 from V / C converter 87 with input switched by analog switch 90 between 9
It can be achieved by driving 1. Switch 90 is a dual segment filter that rotates the current to infrared radiation source 61.
It is controlled by a sync signal 79 to switch between two levels as the assembly 63 rotates. The two voltages 88, 89 are adjusted using an adjustable voltage divider 91 so that the output signal 71 has two equal signal levels corresponding to the measurement wavelength and the reference wavelength. The device is then considered "balanced" with dry air and a zero signal is output at the output of the lock-in amplifier 72. The humidity entering the sample cell also attenuates the signal at the measured wavelength above the reference wavelength, which causes the output signal 71 to vary between two different signal levels, causing the output of the lock-in amplifier 72 to be non-zero and absolute. Proportional to humidity.

FIG. 3 shows a front view of a rotating dual segment filter assembly 63 which takes one possible configuration. The two band-pass interference filters 85 and 86 divided into halves each have a semicircular shape and are combined to form a filter 92. The filter 92 fits into a filter holder 93 that also includes ribs 94. Rib 94
Connects to the shaft of the motor 64 to support the filter as it rotates. The rib 94 covers the joint between the filters 85 and 86 to prevent infrared rays from leaking.

A typical output signal 71 is shown in FIG. Two signal levels 95, 96 corresponding to the measurement wavelength and the reference wavelength
There is. This occurs when the radiation beam 99 passes through the bandpass interference filters 85, 86, respectively. The areas designated by reference numerals 97, 98 are the ribs 9 of the rotating dual segment filter assembly 63 where the radiation beam 99 rotates.
4 corresponds to the time of partial or complete interruption. At this time, since the signal 71 becomes somewhat undefined, it is interrupted by the signal 71 of zero level while the radiation beam is being cut by the ribs 94, or level 9 during the period 97.
It is beneficial to hold level 97 during periods 5 and 98 and ignore some of these signals. The signal processing unit 70A that implements these methods can be inserted between the preamplifier 70 and the lock-in amplifier 72. The output signal 71 is thus defined at all times.

Since some of the optical elements can be temperature sensitive, the optical configuration is temperature controlled according to conventional methods. A second embodiment of the present invention of a dual wavelength, dual beam device will be described with reference to FIG. Again, the sample cell is part of the device. Two separate infrared radiators 10
0, 101 form an infrared radiator, the radiation from each of which is reflected by lenses 102, 103 into two vertical beams 104,
Collimated to 105. Infrared radiation sources 100, 10
1 is a narrow band type or a broadband infrared radiation source used with a narrow band filter. First infrared radiation source 100
Defines the measurement wavelength with a wavelength selected to match the absorption band of water. The other infrared radiation source 101 is selected to avoid the water absorption band and defines the reference wavelength.

The two infrared radiation sources 100 and 101 switch the currents supplied to them and switch on and off alternately. The oscillator 112 supplies two switching signals 113 and 114 that are rectangular waves, and the signal 114 is 180 ° out of phase with the signal 113. The voltage level of each square wave is reduced using an adjustable voltage divider 115, 116 to provide two square wave signals 11 with different amplitudes.
7 and 118 are supplied. The signals 117, 118 are provided to V / C converters 119, 120 which drive the two infrared radiation sources 100, 101.

The beams 104, 105 are arranged to intersect at a beam splitter 106 having a transmission / reflection ratio of about 1: 1 and split each beam 104, 105 into beams 107, 108 substantially evenly. Two infrared beams 1
One of the 08 passes through a sample cell 109 filled with water vapor containing the gas to be measured and collimated by a lens 110 to a point on the infrared detector 111. Radiation beam 10
8 reflects multiple times through the sample cell 109, increasing the radiative absorption due to water vapor. The signal from the infrared detector 111 is amplified by the preamplifier 121 and the detected signal 1
22 is output. The lock-in amplifier 123 synchronously detects the detection signal and outputs an output signal 124 proportional to the absolute humidity. The sync signal is provided to the lock-in amplifier 123 by the oscillator 112. The output signal 124 is processed by the signal processing and display circuit 125 to indicate the magnitude of absolute humidity.

Infrared radiation sources 100, 101 of this embodiment
Produces two different radiation beams 104, 105 which have two different wavelengths and which are switched on and off alternately. This form of sequential gate for each wavelength is the same as the rotating dual segment filter assembly used in the first embodiment. The output intensity of each radiation beam 104, 105 is determined by each adjustable voltage divider 105, 106. Adjustable voltage dividers 115, 116 are adjusted so that the two alternating levels of signal 122 are equal when water vapor is not present in sample cell 109. The device is considered "balanced" and lock-in amplifier 12
The output of 3 becomes zero. The water vapor entering the sample cell 109 then causes the two alternating levels of the signal 122 to differ, making the output 124 of the lock-in amplifier 124 proportional to absolute humidity.

In a refinement of this embodiment, means are provided for stabilizing the output of the infrared radiation source. Lens 12
6 is a radiation beam 10 at a point on the second infrared detector 127.
Focus on 7. The signal from the infrared detector 127 is amplified by the preamplifier 128, and the lock-in amplifier 129
Provides a signal 130 that is the magnitude of the imbalance of the two wavelengths prior to entering the sample cell, detected synchronously by. The signal 130 controls the amount of current supplied to each infrared radiation source 100, 101 to provide two radiation beams 104,
Used in a control loop that keeps the ratio of 105 constant. In this way, the calibration of the infrared humidity sensor is extended. Because any variation in the radiation output of the infrared radiation sources 100, 101 will change the balance of the signal 130,
The current supplied to the infrared radiation sources 100, 101 is adjusted so that the radiation output is the same as before. This concept can also be used in the first embodiment in which a second infrared detector is inserted in the radiation path before the rotating dual segment filter assembly to feed back to the power source of a single infrared radiation source.

Suitable sample cells for the second and third embodiments described above are shown in FIGS. The arrow 14 by the user is shown in FIG.
In response to the movement in the direction indicated by 0, the infrared humidity sensor
It is an external view of a wearable sample cell 138 into which a unit 139 can be fitted. The advantage of the attachable sample cell is that when the sample cell is contaminated, it can be replaced with a new sample cell without spending time cleaning the contaminated useless sample cell. This is especially important in medical applications.

When using an infrared humidity sensor in a medical breathing circuit, care must be taken that water that may be present in the breathing circuit does not interfere with the optical path or settle in the window of the sample cell. This can be accomplished by heating the sample cell to prevent condensation, or by using a water baffle or water bypass tube around the sample cell window, or through a porous membrane that allows air and humidity but not water to pass through. Can be used around to prevent.

FIG. 7 shows a sample cell formed as a tube having a rectangular central portion and gas inlets / outlets 131 and 132 at each end. These gas inlets and outlets are equipped with standard medical breathing circuit connectors so that the sample cell can be connected to the medical breathing circuit. The gas to be measured can be input and output from the sample cell through the gas inlets and outlets 131 and 132. Infrared radiation is on windows 133 and 132
Through the sample cell. Baffles 135 and 136 are provided around the windows 133 and 134, and these baffles are used for gas inlet / outlet 131, 13
It prevents water from flowing to the windows 133 and 134 through 2. In fact, this water is sent around the window and the gas inlet / outlet 13
It is forcibly discharged through 1, 132. Instead of a water baffle, water is used to pass around the window of the sample cell.

The sample cell is entirely heated by a heater 137 which is part of the infrared humidity sensor unit 139. This heater contacts the sample cell 138 when the sample cell is inserted into the infrared humidity sensor. The purpose of the heater 137 is to prevent condensation anywhere on the sample cell. The amount of power supplied to the heater is carefully adjusted so that the air passing through the sample cell is not heated or cooled by the sample cell. Air entering and exiting the sump cell at the same temperature is important. The reason is that when the sensor changes the temperature, the humidity sensor changes the device to be measured.

It is also necessary to prevent airborne particles and water droplets dripping onto the window of the sample cell. To prevent this, one can use a "beaded" baffle as shown in FIG. This sample cell is of the same type as shown in Figure 7, but with additional baffles 141,142. These baffles force the air to move around it, causing any large water particles to drop onto the baffle surface.

It is very important to keep the window of the sample cell of the infrared gas analyzer clean and in good working order.
To assist this, a window cover is provided that is removed prior to fitting the sample cell into the sensor unit. This prevents inadvertent fingerprints, dust and scratches that may occur during handling. Before using the infrared humidity sensor, it must be calibrated with a sample cell filled with dry air. This is necessary because each sample cell has different infrared transmission characteristics. It is not always always convenient to do this with a source of dry air, so the end cap completely seals the sample cell,
It is recommended to fill the dry air and provide it to the user. This means that the user must attach the sample cell to the infrared humidity sensor, perform a calibration, and remove the end cap for the humidity sensor to operate correctly.

[0031]

The infrared gas analyzer comprises a sample cell placed in a gas, an infrared radiation source of a selected wavelength that passes through the sample cell, and an infrared detector that receives the infrared radiation that passes through the sample cell. Suitable for use as a humidity sensor in medical breathing circuits.

The present invention has remarkable effects as compared with the conventional device, such as reduction of precipitation and condensation of water on the radiation window, high-speed response time and insensitivity to movement of air and changes in gas components.

[Brief description of drawings]

FIG. 1 is a diagram showing an appearance of a humidifying device.

FIG. 2 is a block diagram of an infrared gas analyzer according to a first embodiment of the present invention.

3 is a plan view of the rotating dual segment filter assembly of the infrared gas analyzer shown in FIG. 2. FIG.

FIG. 4 is a diagram showing an output waveform of an infrared detector of the infrared gas analyzer shown in FIG.

FIG. 5 is a diagram showing a block diagram of an infrared gas analyzer according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the appearance of an infrared gas analyzer unit and a removable sample cell.

FIG. 7 is a vertical cross-sectional view of the first form of the sample cell.

FIG. 8 is a vertical cross-sectional view of a second form of the sample cell.

[Explanation of symbols]

 2 ... Bottom 3 ... Heater plate 4 ... Chamber 5,131 ... Gas inlet 6,132 ... Gas outlet 7 ... Breathing conduit 8 ... Breathing conduit end 9 ... Heating element 61 ... Single multiple wavelength infrared radiation source 62,68, 102, 103, 110, 126 ... Lens 63 ... Rotation dual segment filter assembly 64 ... Motor 65, 109, 138 ... Sample cell 67 ... Mirror 69, 111, 127 ... Infrared detector 70, 121, 128 ... Preamplifier 72, 123,129 ... Lock-in amplifier 73, 125 ... Signal processing and display circuit 74 ... Position sensor 75 ... Mark 76 ... Phase locked loop 78 ... Variable phase delay circuit 81 ... Phase comparator 82, 112 ... Oscillator 83 ... Loop filter 84 ... Amplifier 85,86 ... Band pass interference filter 8 ... V / C (voltage / current) converter 90 ... Switch 91, 115, 116 ... Adjustable voltage divider 92 ... Filter 93 ... Filter holder 94 ... Rib 100, 101 ... Infrared radiation source 106 ... Beam splitter 133, 134 ... Window 135, 136, 141, 142 ... Baffle 137 ... Heater 139 ... Infrared humidity sensor unit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Paul John Seekins New Zealand, Auckland, Panmuir, Carvine Road 25

Claims (10)

[Claims] 1. An infrared gas analyzer comprises an infrared radiator (61, 100, 101) which emits infrared radiation having at least two selected wavelengths and is strongly absorbed by the selected gas to constitute the measurement wavelength. A second selected wavelength selected to minimize absorption by the selected gas to form a first selected wavelength and a reference wavelength; and a sample cell of gas, the infrared ray passing through the sample cell. (65, 109) through which the gas in use passes and an infrared detector (6) suitable for detecting the selected infrared rays.
9, 111), and a radiation path determining means (62) for forming a radiation path between the infrared radiator and the infrared detector through the sample cell arranged between the infrared radiation source and the infrared detector. , 67, 68, 102, 106, 110) and the first and second selected wavelengths are alternately output to a radiation path, and the infrared detector (69, 111) passes through the sample cell (65, 109). Gate means (63,
118, 119) and a synchronization signal (79, 11) used for switching the gate.
3) generating synchronization signal generating means (74, 75, 11)
2), a lock-in amplifier (72, 123) for converting the output of the infrared detector (69, 111) and a signal proportional from the infrared detector to a selected concentration of gas passing through the sample cell, A power supply (81A, 112) to the infrared radiator and switching means (90, 112, 115, 116) for switching between the two levels and the power supply output are provided, and the switching means comprises the synchronization signal (79, 113). ) In synchronization with the sample cell (65,
109) An infrared gas analyzer, which is predetermined to make the amplitude of the output signal from the infrared detector (69, 111) constant when the concentration of the selected gas in (109) becomes zero. 2. The infrared gas analyzer according to claim 1, wherein the infrared radiator comprises a single infrared radiation source (61) for generating the selected at least two wavelengths, and an infrared ray having a measurement wavelength and a reference wavelength. A rotating dual segment filter assembly (63) located in the radiation path (99) before the sample cell (65) capable of alternately transmitting the sync signal generating means for generating a sync signal. 2 of the rotating dual segment filter assembly passing through the radiation path (99)
An infrared gas analyzer comprising a position sensor (74) for detecting transitions between two segments and generating an electrical signal indicative of these transitions. 3. The infrared gas analyzer according to claim 2, wherein the output of the position sensor is supplied to a phase locked loop (76) to generate a signal having a duty cycle of 50%, An infrared gas analyzer which is in turn fed to a variable phase delay circuit (78) to generate a synchronization signal (79). 4. The infrared gas analyzer according to claim 2, wherein the rotating dual segment filter assembly (6).
Detection means for detecting the interruption interval when the element (94) other than the filter of 3) passes through the radiation path, and gate means (7A) for inserting a zero signal from the output of the infrared detector into the signal during the interruption period. And an infrared gas analyzer comprising. 5. The infrared gas analyzer according to claim 4, wherein the gate means holds the signal from the infrared detector at a level immediately before the cutoff period during the detected cutoff period.
An infrared gas analyzer comprising A). 6. The infrared gas analyzer according to claim 1, wherein the infrared radiator comprises a first infrared radiation source (100) for infrared radiation of the selected first wavelength, and the selected second infrared radiation source (100). A second infrared radiation source (101) of infrared radiation of a wavelength, of the radiation path in front of the sample cell for combining radiation from the first infrared radiation source and radiation from the second infrared radiation source. Radiative coupling means (106), wherein the power source is a first power source (119) switched to the first infrared radiation source and a second power source switched to a second infrared radiation source. The switching means (112) alternately activates the first and second infrared radiation sources, and alternately switches the outputs of the first and second power sources. , Synchronize the phase with the synchronization signal, The synchronization signal is an electronic oscillator (112)
Generated by an infrared gas analyzer. 7. Infrared gas analyzer according to claim 6, wherein said radiative coupling means comprises radiative splitting means for driving a subsequent radiative path (107) of the coupling, said infrared gas analyzer further comprising: A second infrared detector (127) arranged in the radiation path, a second lock-in amplifier (129) supplied from the output of the second infrared detector, a first and a second infrared radiation source The synchronization signal (113) for generating the signal (130) indicating the imbalance of the radiation intensity generated by each of (100, 101) is provided, and the radiation intensity ratio from the first and second infrared radiation sources is made constant. Means for responding to the unbalanced signal (130) controlling both power supplies to be maintained. 8. The infrared gas analyzer according to claim 1, further comprising a device for measuring a humidity of a gas or a gas mixture flowing through a medical breathing circuit, which is used for intrusion of water or a sample cell. An infrared gas analyzer further comprising waterproofing means (135, 136, 137, 141, 142) for preventing water from being generated, said waterproofing means comprising a heater (137) provided around said sample cell. 9. An infrared gas analyzer as claimed in claim 8, wherein the sample cell comprises at least one radiation transmission window (133, 134) and the waterproofing means prevents water from contacting the window surface. A baffle (13) disposed in the sample cell around the at least one window to prevent
5, 136) including an infrared gas analyzer. 10. The infrared gas analyzer according to claim 9, wherein the second set of baffles (141, 142) comprises:
Prior to traversing the window surface, it is placed in the sample cell to form a labyrinthine path through which gas must pass, thereby guiding the water contained in the gas to guide the baffle. Infrared gas analyzer for precipitation onto the second set.