JPH0230458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field This application relates to a frustrated multiple total, internal reflection absorption spectrophotometer.
spectrometer). In more detail,
This application relates to a spectrometer that employs a circular rod with a conical end face that is immersed in a flowing sample fluid. Two identical mirror unit magnification systems are advantageously used to focus the radiation from the radiation source onto one conical end face and to collect and focus the radiation from the other end face onto a single detector. The spectrophotometer of the present invention is much more energy efficient than conventional spectrophotometers, providing a signal-to-noise ratio 100 times higher than previously possible. A radiation filter is placed on a rotating wheel between the radiation source and the detector to aid in sample composition determination.

BACKGROUND ART “APPARATUS FOR ANALYZING A” according to the invention of Paul A. Wilks, Jr. et al.
CONTINUOSLY MOVING STRIP BY
MEANS OF ATTENUATED TOTAL
In U.S. Pat. A circular rod is disclosed for analyzing a strip or web moving past the rod.

“FRUSTRATED MULTIPLE INTERNAL” invented by Paul A. Wilks, Jr. et al.
REFLECTION ROD WITH VARIABLE
LENGTH FLUID CONTAINING
In U.S. Pat. No. 3,370,502 (issued February 27, 1968) entitled ``ENCLOSURE MEANS,'' Wilks discloses how rods of this type are utilized in analyzing the flowing fluid surrounding them. ing.

In these earlier patents, Mr. Wilks disclosed the use of a conventional thin lens to illuminate one end of the rod, to collect the radiation emanating from the other end of the rod, and to feed it to a spectrometer. ing. In U.S. Patent No. 3,370,502
Mr. Wilks also proposed conical mirrors surrounding each end of the rod to collect the collimated illuminating radiation at one end of the rod, and to collect and collimate the radiation emanating from the other end of the rod. Discloses that it will be used.

DISCLOSURE OF THE INVENTION We herein employ opposed mirrors used between the illumination source and one end of the rod, and between the other end of the rod and the detector, which are much more efficient than those employed in the prior art. discovered an optical system. These same optical systems employ two opposing mirrors with the same radius, separated so that the conjugate image plane is on the outside of each mirror, and each mirror has an aperture in its center. have. We have found that by using these mirror relay systems, the signal-to-noise ratio can be increased by a factor of 100 in infrared spectrometers.

The spectrophotometer preferably employs a rotating disk having a plurality of apertures consisting of suitably selected filters.

OBJECTS OF THE INVENTION One object of the invention is therefore to provide an incompletely multiplexed total internal reflection absorption spectrophotometer.

Another object of the present invention is to provide a spectrophotometer that utilizes a rod with conical ends in which total internal reflection occurs.

Yet another object of the invention is to provide a spectrophotometer of this type with higher sensitivity.

Yet another object of the invention is to provide a spectrophotometer of this type with improved illumination means.

A further object of the invention is to provide a spectrophotometer of this type with improved radiation collection means.

A further object of the invention is to provide a spectrophotometer of this type which employs simple radiation analysis means.

Another object of the invention is to provide a spectrophotometer for analyzing flowing fluids.

Other objects of the invention are in part obvious and in part will become apparent below.

Accordingly, the present invention includes features of structures, elements, and arrangement of parts as exemplified by the structures described below.

The scope of the invention is set forth in the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. 1, a spectrophotometer in accordance with the present invention includes a circular cylindrical rod 20, the material of which transmits radiation provided by a radiation source 22. It is formed of. Rod 20 is mounted within a sample chamber 24, which may be made of glass, by caps 26, 28 and seals 30, 32. A fluid sample may be introduced into the sample chamber 24 through an inlet 34 and exit through an outlet 36 . The rod 30 has conical ends 38 and 4.
0.

In the infrared spectrophotometer shown in FIG. 1, the radiation source 22 may be a heated wire or other infrared source. Rod 20 is made of a material that transmits infrared rays, such as sapphire, diamond, zinc selenide, tin sulfide, germanium, silicon, and KRS-5 (thallium bromide iodide eutectic), and the material has a higher refractive index than the sample. By selecting such a rod, the infrared rays passing through the rod are subjected to multiple reflections due to total internal reflection, as shown in the figure.

Total internal internal reflection is a surface phenomenon and involves a slight seepage of infrared radiation into the sample 42 surrounding the rod 20. A certain amount of infrared radiation is then absorbed and this absorption is measured in a known manner.

The problems with the prior art are the irradiation applied to the rod 20, the amount of radiation that passes through the rod 20 with multiple internal reflections, and, to some extent, the amount of radiation that passes through the rod 20 with multiple internal reflections.
The aim was to maximize the amount of radiation absorbed by the rod and collected by the rod. For this purpose we have placed a pair of spherical mirrors 44 and 46 between the radiation source and the conical end face 40. Each mirror is 48 and 5
It has a circular central aperture, generally designated 0.

The radiation source 22, mirrors 44 and 46 have an exit window 5 which is transparent to infrared radiation, such as barium fluoride.
4 may be suitably mounted within a housing generally indicated at 52.

The apex angle of cone 40 is preferably equal to the cone formed as the center or average of the radiation bundles indicated generally at 56 and 58. This angle is chosen such that all of the radiation flux within the rod 50 undergoes total internal reflection at an angle greater than the critical angle defined by the ratio of the refractive index of the rod 20 and the refractive index of the sample 42. By making the angles of the radiation bundles 56 and 58 equal to the apex angle of the cone 40, radiation transmission within the rod 20 is maximized. By making the angle of reflection as close as possible to the critical angle, radiation seepage into the sample 42 is maximized.

A baffle 60 is provided to prevent direct radiation from the radiation source 22 from entering the rod 20 and causing total internal reflection, thereby causing noise in the system. This baffle is preferably made to tightly close the cone between the innermost radiation bundles 62 and 64 reflected by mirror 46. It is also preferred that this baffle is actually placed close to the end face 40, for example on the exit window 54 as shown, to block stray light.

A chopper disk 66 for spectroscopic analysis is provided; see also FIGS. 2 and 3. These chopper disks are, for example, 68, 70, 72 and 7.
4. It includes a plurality of apertures, generally indicated at 4. It is also possible to have more apertures, or even just two apertures. These openings have at least two
Two transmitting means are provided, as _shown in _{FIG .} The filter is designed to transmit radiation having a wavelength of λ ₂ , which is greatly influenced by the filter to be transmitted and the material to be analyzed. Disc 66 is connected to motor 76 (FIG. 1) and generally 7
It is rotated by a gear shown at 8.

Additionally, additional filters may be added to determine more than one component for sample 42.
For example, to determine the concentration of three components, four types of filters are used, namely λ ₁ , λ ₂ , as shown in FIG.
λ ₃ and λ ₄ are used.

Light is collected from a conical end face 38 extending from rod 20 using the same optical system as the illumination optics. The focusing optics includes circular mirrors 80 and 82 with equal cone angles 84 of 60 DEG, aligned with the 60 DEG cone angle of the conical end face of rod 20. Mirrors 80 and 82 are mounted within a single housing, generally indicated at 86, as is an infrared detector, indicated generally at 88. The baffle 90 is preferably mounted inside a cone formed by the innermost radiation bundle 92 reflecting from the mirror 82.
This attachment may be done by a spider 94. Buffle 90 is placed close to detector 88 to block stray light as well as direct light from rod 20. However, as shown at 96, it may be installed so as to simply block only direct light, or it may be omitted in some cases.

As one of ordinary skill in the art would understand, the motor 76
provides a synchronization output signal on line 98 which is combined with the detector signal on line 100 (which varies over time by the action of chopper filter 66) and is processed by suitable electronic means. The component concentration of the sample 42 is then determined.

Referring now to FIG. 4, a rod 120 having a concave conical end surface having a cone angle substantially equal to the angle between optical axis rays 56 and 58 in FIG. 1 may be used in place of the example described above. is depicted. The rod is mounted within chamber 24 using end caps 26, 28 and resilient seals 30, 32 shaped as shown. End caps 26 and 28 slightly clamp the ends of sample chamber 24 and clamp resilient seals 30 and 32 surrounding rod 120. This end seal 3
0,32 may be tetrafluoroethylene or a similar material that is impermeable to the sample 42.

As will be understood by those skilled in the art, the illumination system is retained within housing 52 and the radiation collection system is optionally retained within housing 86, forming a relay magnification system unit. That is, they image the end face 40 of the rod 20 onto the radiation source 22 and vice versa with the same dimensions, and likewise the end face 38 of the rod 20 with the same dimensions onto the detector 86.
is imaged. These mirrors have a radius of, for example, 6 inches, and their conjugate image planes are located at the housing 52.
and spaced a sufficient distance outside of 86. Thus housings 52 and 8
6 may include windows 48 and 148 that are complete, completely sealed, and made of a material that transmits infrared radiation.

As will be understood by those skilled in the art, similar systems with rods made of sapphire, plastic or diamond are available in the visible spectrum, and similar systems using sapphire rods in the ultraviolet range, each with appropriate radiation. a source and a detector of its selected radiation.

It will be appreciated that the objects originally stated as well as those identified in the foregoing description may be effectively achieved and that considerable changes may be made to the system described above without departing from the scope of the invention. Therefore, it will be understood that all matters shown in the above description and the accompanying drawings are illustrative only and are not meant to be construed as limiting.

It will also be understood that the claims are intended to cover all expressions that fall within the scope of the invention in language, as well as generic and specific features of the invention.

We describe in the claims the matters for which our invention is newly claimed and which we wish to be protected by a letter of patent.

[Brief explanation of drawings]

FIG. 1 diagrammatically represents a spectrophotometer according to the invention. FIG. 2 schematically represents the filter stopper of the spectrophotometer shown in FIG. FIG. 3 represents a cross-section taken along line 3--3 in FIG. FIG. 4 diagrammatically represents an alternative embodiment of the invention to that shown in FIG.
FIG. 5 schematically represents another chopper filter for the spectrophotometer depicted in FIG. Like numbers refer to like elements in each figure. 20,120: rod, 22: radiation source, 2
4: Sample chamber, 34: Inlet, 36: Exit, 38, 4
0; 122, 124: Conical end surface, 42: Sample, 44, 46, 80, 82: Spherical mirror, 52, 8
6: Housing, 60, 90, 96: Batsuful,
68, 70, 72, 74: Filter, 48, 5
0,148: Central opening.

Claims (1)

[Scope of Claims] 1. A radiation transmitting rod having both conical end faces, a radiation source, a radiation detector, and the radiation source and the conical one end face of the radiation transmitting rod. a housing disposed between the housing and having a central opening on an optical axis connecting the radiation source and one conical end surface of the rod; and a housing disposed within the housing for forming an image of the conical one end surface of the rod. A total internal reflection absorption spectrophotometer comprising a pair of opposed spherical mirrors for 2. The spectrophotometer according to claim 1, wherein the optical system forms an image of the conical end surface without enlarging it. 3. The spectrophotometer according to claim 1 or 2, wherein one baffle is provided in the optical system to prevent direct light not reflected by the mirrors from forming an image. Total. 4. The spectrophotometer of claim 3, wherein said baffle extends through the smallest cone of radiation flux between said end face of said rod and said mirror furthest from said rod. 5. The spectrophotometer according to claim 3, wherein the mirrors are spaced apart from each other so that the end face and its image are located outside of the mirrors. 6. The spectrophotometer according to claim 5, wherein both mirrors have the same radius. 7. The spectrophotometer according to claim 1 or 2, wherein both mirrors have the same radius. 8. The spectrophotometer according to claim 7, wherein the mirrors are spaced apart from each other so that the end face and its image are located outside of the mirrors. 9. The spectrophotometer according to claim 1 or 2, comprising an identical optical system located at the other end of the rod. 10. The spectrophotometer according to claim 9, wherein the average angle of the radiation bundles reflected by the mirrors is substantially equal to the apex angle of the conical end surface. 11. The spectrophotometer according to claim 1 or 2, wherein the average angle of the radiation fluxes reflected by the mirrors is substantially equal to the apex angle of the conical end surface. 12 Radiation from the radiation source at least 2
A spectrophotometer according to claim 1 or 2, comprising a chopper located between the radiation source and the detector and having an aperture for transmitting radiation in two different spectroscopic regions. Total.