JPH04301507A - Infrared type measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an infrared measuring device, and more specifically, it projects infrared rays onto a resin coat, resin film, etc. formed on a material such as a metal plate, and measures the infrared wavelength region. This invention relates to an infrared measuring device that measures the thickness of resin coats, resin films, etc. from the characteristic absorption amount.

0002

[Prior Art] Generally, in various industrial fields such as the food industry, pharmaceutical industry, chemical industry, and semiconductor industry, there is a need to easily and non-contactly measure the concentration of components contained in liquids and the thickness of resin films, etc. .

Conventionally, measuring devices that perform this type of measurement project light (infrared rays) emitted from an infrared light source onto an object to be measured, detect the light that is reflected or transmitted from the object, and detect the infrared rays. 2. Description of the Related Art Infrared measuring devices are well known that measure the concentration or thickness of an object to be measured by measuring a characteristic absorption amount specific to the object in a wavelength region. This infrared measuring device measures the amount of light absorbed by the object based on the ratio of the light projected onto the object and the light that is transmitted without being absorbed by the object. Detecting density or thickness.

[0004] In the conventional infrared measuring device described above, unnecessary light other than the light projected onto the object to be measured from the infrared light source mixes with the light projected onto the object to be measured, affecting measurement accuracy. Therefore, in order to eliminate the influence of this mixed unnecessary light, the light emitted from the infrared light source is intensity-modulated and then projected onto the object to be measured, and the light intensity is measured in synchronization with this intensity modulation. An infrared measuring device having a configuration as shown in FIG. 13 has been proposed.

In FIG. 13, light emitted from an infrared light source 1 enters a light intensity modulator 3 called a chopper through an optical system 2 consisting of a condenser lens and a filter that transmits infrared light having a predetermined wavelength. After being periodically blocked and modulated by the light intensity modulator 3, the light is incident on the object to be measured 4. The light intensity modulator 3 chops the light emitted from the optical system 2 by rotating a semicircular light shielding plate 5 as shown in FIG. 14 using a motor M. The light intensity of the reflected light from the measurement object 4 is detected by the detector 6. Modulation timing detection circuit 7
supplies a timing signal synchronized with the light intensity modulation to the signal processing circuit 8, and processes the detection signal of the detector 6 through this signal processing circuit 8. Signal processing by this signal processing circuit 8 is shown in FIG.

FIG. 15(1) shows the detector 6 in the normal case.
is the state of the output signal. The light intensity E of unnecessary light other than the light projected onto the measurement object 4 from the infrared light source 1, the so-called background, is "bright" and "dark" during light intensity modulation.
Detected in either state. That is, in the "dark" state during light intensity modulation, the output of the detector 6 is E, and in the "bright" state of light intensity modulation, the output of the detector 6 is (E+A). Therefore, the light intensity A of the light projected onto the measurement object 4 is determined by the signal processing circuit 8 as follows:
The light intensity E(
background) and calculate the difference between the output (E+A) of the detector 6 in the "bright" state of light intensity modulation and the light intensity E, (E+A)-E (=A). , background E is removed. Thereby, it is possible to accurately detect only the light intensity A of the light projected onto the measurement object 4.

In (2) of FIG. 15, in addition to the unmodulated unnecessary component E, a new unnecessary component D of light is incident on the detector 6 from the outside, and (D+E) is simultaneously detected as the background. Indicates the condition. Also in this case, the output of the detector 6 in the "bright" state of light intensity modulation (D+E+A)
and the background (D+E), (D+E+A
)−(D+E)(=A), the background (D+E) is removed.

In the conventional device using this modulation-synchronization detection method, unnecessary light other than the light projected onto the measurement object 4 from the infrared light source 1 is removed, and only the light intensity of the light projected onto the measurement object 4 is detected. Can be measured accurately. In this conventional device, unnecessary light can be removed as long as it is not modulated by the light intensity modulator 3. For this reason, the light intensity modulator 3 needs to be placed as close as possible to the infrared light source 1 that projects the light, and usually a pre-modulation optical system is used to modulate the light before projecting the light onto the measurement target 4. The layout configuration is adopted.

[0009]

[Problems to be Solved by the Invention] In the conventional infrared measuring device described above, between the infrared light source 1 and the light intensity modulator 3,
An optical system 2 consisting of optical parts such as a spectrometer and a lens is arranged to separate the light emitted from the infrared light source 1 into a narrow wavelength range and project it onto the measurement object 4 through the light intensity modulator 3. ing. Further, in order to serve as the spectrometer, the light intensity modulator 3 itself may include optical components that constitute a part of the optical system 2.

By the way, in the infrared measuring device having the optical system 2 arranged as described above, among the unnecessary light mixed between the light intensity modulator 3 and the detector 6, the light intensity modulator 3 side The incident light may pass through a path L shown in FIG. 13, be reflected by the surface reflection of the optical components constituting the optical system 2, and then be incident on the detector 6.

In this case, the unnecessary light enters the light intensity modulator 3 and is modulated by the light intensity modulator 3, so as shown in FIG.
As shown in (3), unnecessary light is detected by the detector 6 only in the "bright" state in synchronization with the light intensity modulator 3 as shown in FIG. 15B. Then, by synchronization detection, "bright" and "dark"
If it is detected as a difference between the two, it will be detected as a measured value B that includes an unnecessary component C.

Optical components of the optical system 2 that reflect unnecessary light that enters between the light intensity modulator 3 and the detector 6 include, for example, lenses, mirrors, spectrometers, prisms, and polarizer interference filters. . These optical components are essential for constructing the optical system 2, which modulates the intensity of light from the infrared light source 1 with the light intensity modulator 3 and projects the light onto the object to be measured 4.

Furthermore, since light having a wavelength in the infrared region is used, unnecessary light that enters between the light intensity modulator 3 and the detector 6 is affected by thermal radiation other than the infrared light source 1. In the conventional infrared measuring device described above, it is possible to prevent contamination by taking measures such as shielding against heat radiation from a heat source that exists in the background, but if the object to be measured itself is high temperature, It is impossible to eliminate the effect of this thermal radiation.

For this reason, in the conventional infrared measuring device described above, the temperature of the object to be measured 4 is measured while ignoring the influence of thermal radiation from the object to be measured 4, or when measurement accuracy is required. This is handled by measuring separately and making corrections. However, even when performing temperature correction, the advantage of the conventional device is that it measures the object 4 without contacting it, so it is necessary to measure the temperature without contacting it. Due to the above accuracy, there was a problem in that the correction could not be carried out completely.

An object of the present invention is to provide an infrared method with high measurement accuracy that prevents unnecessary light from entering the detector from sources other than infrared light sources that should not normally enter the detector due to light intensity modulation. An object of the present invention is to provide a measuring device.

Another object of the present invention is to improve measurement accuracy by detecting unnecessary light components that should not normally be modulated and entering the detector, and correcting the detection value of the detector using this unnecessary light. The purpose of the present invention is to provide a high quality infrared measuring device.

[0017]

[Means for Solving the Problems] In order to achieve the above object, the invention according to claim 1 of the present application includes a projection optical system that modulates the intensity of infrared rays incident from an infrared light source and emits the infrared rays. The emitted intensity-modulated infrared rays are projected onto the measurement target, and the transmitted or reflected light from the measurement target is detected by a detector in synchronization with the intensity modulation, and the characteristics of the measurement target in the infrared wavelength region are detected. An infrared measuring device that measures the thickness or density of a measurement target based on the amount of absorption, and an optical component of the projection optical system that reflects unnecessary light traveling from the measurement target in a direction opposite to the projection direction of the infrared rays. The present invention provides an infrared measuring device characterized in that at least one optical axis of the optical axis is tilted with respect to an optical axis connecting a light source, an object to be measured, and a detector.

[0018] In order to achieve the above object, claim 2 of the present application
The invention includes a projection optical system that intensity-modulates and emits infrared rays incident from an infrared light source, and projects the intensity-modulated infrared rays emitted from the projection optical system onto an object to be measured,
This transmitted light or reflected light from the measurement object is detected by a detector in synchronization with the intensity modulation, and the thickness or concentration of the measurement object is measured from the characteristic absorption amount in the infrared wavelength region of the measurement object. type measuring device, characterized in that an anti-reflection treatment is applied to the surface of the optical component of the projection optical system that reflects unnecessary light traveling in the opposite direction to the projection direction of the infrared rays from the measurement object side. The present invention provides an infrared measuring device that

[0019] In order to achieve the above object, claim 3 of the present application
The invention includes a projection optical system that intensity-modulates and emits infrared rays incident from an infrared light source, and projects the intensity-modulated infrared rays emitted from the projection optical system onto an object to be measured,
This transmitted light or reflected light from the measurement object is detected by a detector in synchronization with the intensity modulation, and the thickness or concentration of the measurement object is measured from the characteristic absorption amount in the infrared wavelength region of the measurement object. type measuring device, which has an optical axis between the projection optical system and the object to be measured, which is inclined with respect to the optical axis of the projection optical system, and is directed opposite to the direction in which the infrared rays are projected from the object to be measured. The present invention provides an infrared measuring device characterized in that it includes an unnecessary light reflecting member that reflects unnecessary light incident on the projection optical system.

In order to achieve the above-mentioned other object, the invention according to claim 4 of the present application includes a projection optical system that modulates the intensity of infrared rays incident from an infrared light source and emits the infrared rays, and modulates the intensity of the infrared rays emitted from the projection optical system. The infrared rays are projected onto the object to be measured, and the transmitted or reflected light from the object is detected by a detector in synchronization with the intensity modulation described above, and the characteristic absorption amount in the infrared wavelength region of the object is measured. An infrared measuring device for measuring the thickness of an object, comprising: a stop means for stopping infrared rays from entering the object to be measured from an infrared light source; and a projection optical system configured to project the infrared rays from the object to be measured in a direction opposite to the direction in which the infrared rays are projected. unnecessary light measuring and recording means for measuring and recording unnecessary light incident on the system, modulated by the light intensity modulator and reflected toward the measurement target when the stop means is activated; Calculating the difference between the detected value of the transmitted light or reflected light projected onto an object and detected by the detector in synchronization with the intensity modulation and the detected value of unnecessary light recorded in the unnecessary light measurement and recording means. The present invention provides an infrared measuring device characterized by comprising a calculation means.

[0021]

[Operation] Unwanted light from sources other than the infrared light source, which should not normally enter the detector due to light intensity modulation, is deviated from the optical axis from the infrared light source to the object to be measured through the projection optical system. Therefore, even if unnecessary light is modulated by the light intensity modulator, it does not reach the detector and is therefore not detected.

Further, only the unnecessary light is separately measured, and the influence of the unnecessary light is removed by subtracting the detected value of the unnecessary light.

[0023]

According to the present invention, unnecessary light from sources other than the infrared light source, which should not originally be modulated in light intensity and incident on the detector, is removed from the optical axis from the infrared light source to the object to be measured through the projection optical system. Since the unnecessary light does not reach the detector even if it is modulated by the light intensity modulator, the influence of unnecessary light is removed and the light corresponds only to the light projected from the infrared light source onto the measurement target. Strength can be measured accurately.

Further, according to the present invention, only the unnecessary light from sources other than the infrared light source that should not normally enter the detector due to light intensity modulation is separately measured, and the detected value of this unnecessary light is subjected to subtraction processing. As a result, the influence of unnecessary light is removed, and the light intensity corresponding only to the light projected from the infrared light source onto the object to be measured can be accurately measured.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows the configuration of an embodiment of an infrared measuring device according to the present invention. Infrared light source 1 as shown in Figure 1
The light emitted from 1 is projected onto a light intensity modulator 13 through a projection optical system 12, and after being modulated in light intensity by this light intensity modulator 13, it is projected onto an object to be measured 14. When the measurement object 14 is, for example, a transparent film coated on a reflector, the projected light is transmitted to the measurement object 1.
After passing through the transparent film 4 and being reflected by the reflector 14,
The light passes through the transparent film and enters the detector 15 again. This detector 15 detects the light intensity of the incident light in synchronization with the modulation of the light intensity modulator 13. Here, in the light intensity modulator 13, in order to measure the amount of light absorbed in a plurality of wavelength ranges, three holes 16a are provided in a disk 16 that is rotationally driven by a motor M, as shown in FIG. formed, each hole 16
An interference filter 17 is attached to each of a,
The light intensity modulator 13 also serves as a spectrometer for the projection optical system 12.

The interference filter 17 causes surface reflection. In order to prevent the light due to this surface reflection from entering the detector 15 from the measurement object 14, in the embodiment shown in FIG. The light intensity modulator 13 is mounted so as to be inclined at an angle (-θ) with respect to a direction perpendicular to the direction. That is,
The optical axis of the interference filter 17 of the disc 16 of the light intensity modulator 13 is relative to the optical axis of the projection optical system 12 (-θ
) Mounted at an angle. When the disc 16 of the light intensity modulator 13 is rotationally driven by the motor M, the light projected from the projection optical system 12 passes through the interference filter 17 through the hole 16a of the disc 16, and the object to be measured is 14, and is blocked in other parts. The light emitted from the infrared light source 11 passes through the interference filter 17, passes through the optical path N shown by the solid line, and enters the detector 15, so it has no effect on the measurement. The reflected light of the light projected onto the measurement object 14 enters the detector 15, and its light intensity is detected.

Modulation timing detection circuit 18 and signal processing circuit 19 have the same configuration and function as modulation timing detection circuit 7 and signal processing circuit 8, respectively, explained with reference to FIG. That is, the modulation timing detection circuit 18 supplies a timing signal synchronized with the light intensity modulation to the signal processing circuit 19, and the processing circuit 19 processes the detection signal of the detector 15 in the same manner as the signal processing circuit 8 of FIG. Process.

In such a configuration, the optical intensity modulator 1
3 and the detector 15, for example, light due to thermal radiation of the measurement object 14, which cannot be removed by conventional infrared measuring devices, this light travels in the direction of the infrared light source 11. and enters the interference filter 17. As described above, the optical axis of the interference filter 17 is inclined at an angle (-θ) with respect to the optical axis of the projection optical system 12, so the light reflected by the interference filter 17 is indicated by the broken line P. Since the light travels in the direction and deviates from the optical axis N of the projection optical system 12, it does not enter the detector 13. by this,
Unnecessary light is not measured, and the influence of thermal radiation from the measurement object 14 is removed.

As described above, in order to prevent light reflected from the surface of the interference filter 17 from entering the detector 15 from the measurement object 14, in the embodiment shown in FIG. The light intensity modulator 13 is attached so that the light intensity modulator 16 is inclined at an angle (-θ) with respect to the direction perpendicular to the optical axis of the projection optical system 12. As shown in FIG.
The light intensity modulator 13 has a disk 16 that is connected to the projection optical system 1.
It may be attached so as to be inclined at an angle θ with respect to the direction perpendicular to the optical axis N of the lens 2, contrary to FIG. That is, the disc 16 of the optical intensity modulator 13 is connected to the interference filter 17 of the optical intensity modulator 13.
The optical axis of the projection optical system 12 may be inclined by θ with respect to the optical axis N of the projection optical system 12.

[0030] Using the infrared measuring device having the above configuration and the infrared measuring device having the conventional configuration explained in FIG. The results of measuring the thickness of the acrylic resin coat for Sample 1 and Sample 2 are shown in Tables 1 and 2 below.

[0031]

[Table 1]

[0032]

[Table 2]

As can be seen from Tables 1 and 2 above,
In an infrared measuring device having a conventional configuration, the measured thickness is affected as the sample temperature rises, but in an infrared measuring device having the configuration shown in FIG. 1, the influence of the sample temperature is removed.

In the above embodiment, the interference filter 17 is attached to the disk 16 of the light intensity modulator 13, and the light intensity modulator 13
The light intensity modulator 13 is attached so that the light intensity modulator 13 is inclined with respect to the direction perpendicular to the optical axis of the projection optical system 12. However, an interference filter is attached to the light output section of the projection optical system 12 to eliminate this interference. The optical axis of the filter is the projection optical system 1.
It may also be fixed so as to be tilted with respect to the optical axis N of the lens.

Further, the components of the interference filter 17 and the projection optical system 12 may be subjected to anti-reflection treatment to absorb unnecessary light.

Furthermore, although not shown in detail, an unnecessary light reflection device is provided between the light intensity modulator 13 and the object to be measured 14, which transmits the light from the projection optical system 12 and blocks the transmission of unnecessary light. You may make it install a member.

Next, FIG. 4 shows the configuration of the main part of another embodiment of the present invention. In the infrared measuring device shown in Figure 4,
A movable shutter 24 is installed between the projection optical system 22 of the infrared light source 21 and the optical component of the disk 26 of the light intensity modulator 23 that reflects unnecessary light. In the infrared measurement device shown in FIG. 4, the optical component that reflects unnecessary light is assumed to be an interference filter 27 attached to a hole 26a formed in a disc 26 of a light intensity modulator 23, as shown in FIG. are doing.

The shutter 24 moves as shown by arrow a so as to be able to block the infrared light source 21, and the first timing sensor 28 determines whether the light from the projection optical system 22 is blocked or transmitted. Further, the rotation timing of the disk 26 is determined by the second timing sensor 29.

A timing chart of signals from the detector 30 is shown in FIG. E1 and A1 indicate a state in which the light from the infrared light source 21 is blocked by the shutter 24 in FIG.
E2 and A2 indicate states in which light from the infrared light source 21 is transmitted. In addition, E1 and E2 indicate a state in which the light from the infrared light source 21 is blocked by the disk 26, and A1 and A2 are as follows.
A state in which light from the infrared light source 21 is transmitted through the interference filter 27 is shown. However, in A1, the light from the infrared light source 21 is blocked by the shutter 24.

From the above, in the timing chart of FIG. 6, at timings E1 and E2, unnecessary component light is not reflected and light from the infrared light source 21 is also blocked, so the incident light to the detector 30 is modulated. Not a background. At timing A1, the infrared light source 21 is blocked and only unnecessary light is reflected by the interference filter 27, so that the incident light to the detector (not shown) becomes unmodulated background and modulated unnecessary light. At timing A2, the light incident on the detector becomes unmodulated background, a modulated infrared light source, and unnecessary light.

FIG. 7 shows the configuration of the signal processing circuit. The switch 31 switches the output of the detector 30 using a switching signal synchronized with the first timing sensor 28 . shutter 2
When the shutter 4 is closed, the switch 31 connects the output of the detector 30 to the contact 31a, and when the shutter 24 is open, the switch 31 connects the output of the detector 30 to the contact 31a.
The output of 0 is connected to contact 31b.

The first hold circuit 32 holds E1 in FIG. Then, the first subtraction circuit 33 performs processing of A1-E1. The third hold circuit 36 holds A1-E1. This allows only unnecessary light to be measured.

At the timing when the shutter 24 is opened, the switch 31 connects the output of the detector 30 to the contact 31b. Then, the second hold circuit 34 holds E2. The subtraction circuit 35 performs processing A2-E2. Also, in the third subtractor 37, (A2-E2)-(A1-E2)(=
Perform the processing of A2-A1). This removes unnecessary components of reflected light. The absorbance conversion circuit 38 calculates the absorbance of the object to be measured based on the output of the third subtraction circuit 37 from which unnecessary light has been removed.

Next, FIG. 8 shows the configuration of the main part of another embodiment of the present invention. In the infrared measuring device shown in FIG. 8, a disk 46 of a light intensity modulator 43 that modulates the light intensity of the light emitted from the projection optical system 42 of the infrared light source 41 has the following configuration. That is, as shown in FIGS. 9 and 10, respectively, the surface of the disk 46 opposite to the projection optical system 42 and the surface opposite to the projection optical system 42,
6 is formed with semicircular holes 46a, and an interference filter 47 is attached to each hole 46a. And the disk 4
On the surface opposite to the projection optical system 42 of No. 6, an unnecessary light reflecting portion 46b is formed in the semicircular portion where each hole 46a remains. The timing of rotation of the disk 46 of the light intensity modulator 43 that is rotationally driven by the motor M is detected by a modulation timing detection circuit 49.

When the disk 46 of the light intensity modulator 46 has such a configuration, as can be seen from the timing charts of FIGS. 9 and 11, at E, the light from the infrared light source 41 is is shielded from light and does not reflect unnecessary components of light, so only the background can be measured. At A1, the light from the infrared light source 41 is blocked and unnecessary light is reflected by the unnecessary light reflecting section 46b, so that the background and unnecessary light are measured. And in A2, infrared light source 4
1 light, reflected light of unnecessary light, and background are measured.

FIG. 12 shows an outline of signal processing. The hold circuit 51 holds A1 output from the detector 50 according to the output timing of A1, and the subtraction circuit 52 processes A2-A1. This makes it possible to perform measurements without unnecessary reflected light. The absorbance conversion circuit 53 calculates the absorbance of the object to be measured based on the output of the subtraction circuit 52 from which unnecessary light has been removed.

Note that when a liquid is used as the object to be measured, the concentration can be measured.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of an infrared measuring device according to the present invention.

FIG. 2 is a plan view of a disk constituting a light intensity modulator of the infrared measurement device of FIG. 1;

FIG. 3 is an explanatory diagram showing the configuration of a modification of the infrared measuring device of FIG. 1;

FIG. 4 is an explanatory diagram showing a main part of the configuration of another embodiment of the infrared measuring device according to the present invention.

5 is a plan view of a disk constituting a light intensity modulator used in the infrared measuring device of FIG. 4. FIG.

6 is a timing chart for explaining the operation of the infrared measuring device of FIG. 4. FIG.

FIG. 7 is an explanatory diagram of the configuration of a signal processing circuit portion of the infrared measuring device of FIG. 4;

FIG. 8 is an explanatory diagram showing a main part of the configuration of yet another embodiment of the infrared measuring device according to the present invention.

FIG. 9 is an explanatory diagram of the surface of a disk forming the light intensity modulator used in the infrared measuring device of FIG. 8, on the opposite side to the projection optical system.

10 is an explanatory diagram of a surface of a disc constituting a light intensity modulator used in the infrared measuring device of FIG. 8, on the projection optical system side; FIG.

11 is a timing chart for explaining the operation of the infrared measuring device shown in FIG. 8. FIG.

12 is an explanatory diagram of the configuration of a signal processing circuit portion of the infrared measuring device of FIG. 8; FIG.

FIG. 13 is an explanatory diagram showing the configuration of a conventional infrared measuring device.

14 is an explanatory diagram of a light intensity modulator of the infrared measuring device of FIG. 13. FIG.

15 is a timing chart for explaining the operation of the infrared measuring device of FIG. 13. FIG.

[Explanation of symbols]

11 Infrared light source 12 Projection optical system 13. Light intensity modulator 14 Measurement object 15 Detector 16 Disc 16a hole 17 Interference filter 18 Modulation timing detection circuit 19 Signal processing circuit 21 Infrared light source 22 Projection optical system 23 Light intensity modulator 24 Shutter 26 Disk 26a hole 27 Interference filter 28 First timing sensor 29 Second timing sensor 30 Detector 31 Switcher 32 First hold circuit 33 First subtraction circuit 34 Second hold circuit 35 Subtraction circuit 36 Third hold circuit 37 Third subtraction circuit 41 Infrared light source 42 Projection optical system 43 Light intensity modulator 46 Disk 46a semicircular hole 46b Unnecessary light reflecting part 47 Interference filter 49 Timing sensor 50 Detector 51 Hold circuit 52 Subtraction circuit

Claims (4)

[Claims] Claim 1: A projection optical system that intensity-modulates and emits infrared light incident from an infrared light source, projects the intensity-modulated infrared light emitted from the projection optical system onto a measurement object, and emits the intensity-modulated infrared light from the measurement object. An infrared measuring device that detects transmitted light or reflected light with a detector in synchronization with the intensity modulation, and measures the thickness or concentration of an object to be measured from the characteristic absorption amount in the infrared wavelength region of the object. , light that connects at least one optical axis in the optical component of the projection optical system that reflects unnecessary light traveling in the opposite direction to the projection direction of the infrared rays from the measurement object side, and the light source, the measurement object, and the detector; An infrared measuring device characterized by being tilted with respect to the axis. 2. A projection optical system that modulates the intensity of infrared light incident from an infrared light source and emits the infrared light, projects the intensity-modulated infrared light emitted from the projection optical system onto an object to be measured, and emits the infrared light from the object to be measured. An infrared measuring device that detects transmitted light or reflected light with a detector in synchronization with the intensity modulation, and measures the thickness or concentration of an object to be measured from the characteristic absorption amount in the infrared wavelength region of the object. An infrared measuring device, characterized in that an anti-reflection treatment is applied to the surface of an optical component of the projection optical system that reflects unnecessary light traveling in a direction opposite to the projection direction of the infrared rays from the side of the object to be measured. 3. A projection optical system that intensity-modulates and emits infrared light incident from an infrared light source, projects the intensity-modulated infrared light emitted from the projection optical system onto an object to be measured, and emits the infrared light from the object to be measured. An infrared measuring device that detects transmitted light or reflected light with a detector in synchronization with the intensity modulation, and measures the thickness or concentration of an object to be measured from the characteristic absorption amount in the infrared wavelength region of the object. , the projection optical system has an optical axis inclined with respect to the optical axis of the projection optical system between the projection optical system and the object to be measured, and the projection optical system is arranged in a direction opposite to the direction in which the infrared rays are projected from the object to be measured side. An infrared measuring device characterized by comprising an unnecessary light reflecting member that reflects unnecessary light incident on the infrared measuring device. 4. A projection optical system that modulates the intensity of infrared light incident from an infrared light source and emits the infrared light, projects the intensity-modulated infrared light emitted from the projection optical system onto an object to be measured, and emits the infrared light from the object to be measured. An infrared measuring device that detects transmitted light or reflected light with a detector in synchronization with the above-mentioned intensity modulation, and measures the thickness of the object to be measured from the characteristic absorption amount in the infrared wavelength region of the object, which includes an infrared light source. stopping means for stopping infrared rays from being incident on the object to be measured; and a stop means for stopping infrared rays from entering the object to be measured; an unnecessary light measuring and recording means for measuring and recording the unnecessary light that is reflected toward the measurement object by the projection optical system; An infrared measuring device comprising: a calculation means for calculating a difference between a detected value of the transmitted light or reflected light and a detected value of unnecessary light recorded in the unnecessary light measurement and recording means.