JPS61160047A - Optical cell detecting assembly and infrared spectrophotometer - 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 Field of the Invention The present invention relates to optical cell detection assemblies and infrared spectrophotometers.

BACKGROUND OF THE INVENTION Infrared spectrophotometers are used in the dairy industry for the analysis of emulsions and suspensions, for example for the fat, protein and lactose content in milk and milk products.

One such device is disclosed, for example, in US Pat. No. 4,310,763. In particular, the first part of the attached drawings
In the figure, “Multispec I
An example of a device known as an instrument is shown.

In this device, two beams of different wavelengths of infrared radiation are directed alternately to an elliptical mirror through an optical cell containing the sample to be tested. From this mirror, the beam is
focused on an infrared detector. The signal from the detector is
It can be analyzed by techniques well known in the art, where the components in the sample are reliably determined.

The so-called “double beam J (double-b
The above device uses an e-am-in-wavelength) system.

Analyze fat, protein and lactose in milk.

The device requires a reference filter for each sample wavelength, as well as a filter at the appropriate wavelength for each component. Additionally, O-balance systems typically incorporate damping comb servos and electronics that are fairly expensive.

Various factors affect the performance of such devices. For example, the presence of water vapor in the optical path of the device selectively absorbs portions of the infrared signal, causing interference.

Therefore, in order to conserve energy, water vapor within the device must be reduced and the length of the optical path must be minimized.

Furthermore, the presence of large spheres in the emulsion or suspension being tested scatters the infrared radiation, thus causing errors in the optical measurement of the components of the milk sample.

Since the amount of radiation scattering is proportional to the diameter of one sphere, it is necessary to apply a high-pressure homogenizer to the sample to break the spheres. For example, the need to homogenize milk samples significantly increases the manufacturing cost of suitable analytical equipment. oval mirror is
It is quite expensive and thus increases the manufacturing cost of the entire device.

What is needed, therefore, is an apparatus that is inexpensive and has an accuracy suitable for use in the dairy industry.

(Means for Solving the Problems) An object of the present invention is to provide an inexpensive apparatus for analyzing a sample, which overcomes the above-mentioned drawbacks.

According to the invention, there is provided an optical cell detection assembly for a spectrophotometer, comprising: a sample cell having walls of transparent material for defining a sample cavity; and a radiation detector proximate to the sample cavity.

and a lens adjacent the opposing wall, thereby concentrating radiation passing through the cell.

The invention also provides an infrared source, a detector therefor, and an optical device for focusing the beam onto the sample cell.
and a chopper device for periodic clouding of the beam, wherein the sample to be tested consists of an aqueous emulsion;

A patent variant is provided, characterized in that the filter is selected to determine the concentration of non-aqueous components of the emulsion by measuring the water replaced by the components.

By arranging the detectors in close proximity or in contact, the sample cell reduces the length of the radiation path and eliminates the ellipsometer mirrors traditionally used, and also as described in e.g. US Pat. No. 4,310,736. Since the temperature of the cell is controlled, as described in , the temperature of the detector can be tracked and controlled. especially.

Due to the large spheres within the sample being tested, the effect of #turbulence is greatly reduced.

This is because even the scattered light is collected close to the sample by the detector. There, the homogenization of the sample being tested is reduced and completely eliminated. The detector can replace part or the entire wall of one cell.

The device according to the invention is used in particular for dairy products and dairy products. The most important measurements required then concern the solid content of fat and non-fat in the sample.

In the device according to the invention, by using a "fat" filter, such as a 5.7 micron filter, and a "water" filter, such as an 8.64 micron or 4.7 micron filter, the amount of each of the above components can be reduced. , easily and accurately 8
11 determined.

One embodiment of the device according to the invention comprises a microcomputer, a small display keypad, an optical unit, electronic control components and a pump homogenizer. The optical unit is linear and includes an infrared M source and a detector on both sides of each beam path, and a chopper, filter, and cell in between. Chopper is a "window"
It has the same area as , and has a reflective surface. The speed of this chopper is variable and controlled by a microprocessor. Between the chopper and the cell, a filter is placed 6. Different filters may be activated by means of a rotating wheel 7 on which the filter is placed. 6 The rotating wheel is rotated to suitably place the desired filter. The cell is placed in a pump homogenizer.

Within the optical unit, infrared radiation is emitted from an infrared source. This radiation is incident on a convex lens which focuses the beam onto a chopper driven by a motor.

The choppers have the same number of reflective surfaces and windows and transmit or block the beam in proportions based on the triangular frequency.

After traversing a suitable filter, the transmitted beam is focused by a second convex lens onto the sample cell. There, the transmitted radiation is incident on an infrared detector. An alternating current signal is generated that indicates the amount of absorption that has occurred within the cell.

The spectrophotometer changes the filter, reads the milk sample in the cell, and compares this to the moisture sample reading in the cell. This reading represents a simple percentage of the sample's transmission (absorption) at one or more selected wavelengths and at the reference wavelength.

One this ratio measurement is highly inaccurate due to variations in detector sensitivity, so the O-balance method is preferred. but,
According to recent improvements in detection techniques, such ratio methods exhibit sufficient accuracy.

Significantly reduce costs.

For each sample, the cell is equipped with a pump homogenizer, each filter is placed in the appropriate position and a measurement is performed.

The concentration of components of interest in the sample, such as fat and SNF or fat, protein and lactose, is measured, calculated and displayed. To make this calculation, several reference measurements are required. For this purpose, a diluted water sample is introduced.

In this embodiment, the board clock calendar is equipped with a microcomputer, so a reference sample is required on the device itself in the absence of an operator. The frequency required for the reference sample is based on the temperature and humidity stability within the instrument.

However, before measurement, it is necessary to process the optical signal reaching the detector and convert it into a digital format. This conversion is performed in four stages as follows.

a) A detector generates a small electronic signal.

b) An amplifier amplifies this to a useful level.

C) A programmable gain amplifier placed under computer control compensates for the different signal levels from the different filters.

d) A12-bit analog-to-digital converter
The signal is converted to digital form at a rate of over 1000 samples per second.

Typically, a tuned filter and a synchronous rectifier (lock-in amplifier), coupled with a low-pass filter, are used and one composite DC signal is picked up by a computer. By taking AC signals and processing them with a computer, accuracy can be significantly increased with fewer electronic components.

This method also allows for fewer noise generators, resulting in lower noise levels, lower manufacturing costs, and can be changed to triangular frequencies without any hardware changes.

From time to time, a signal is taken and between 1 and 2000 data points, the signal is stored. This data is then filtered using a finite impulse response digital filter with a narrow passband, at triangular frequencies.

Filtered. The amplitude of the composite signal is proportional to the magnitude of the optical signal.

Also, a fast Fourier transform is performed and the amplitude at the triangular frequency is directly calculated. Time is calculated by fast Fourier transform. Although the fast Fourier transform consumes more time than the method of filtering and approximating the amplitude under certain conditions, since in this case only one point of frequency is calculated.

This method is faster.

In either case, the method for ascertaining the magnitude of the optical signal is based on digital signal processing by a computer. For example, in methods such as milk sample analysis, a cell is filled with milk and read at 5.7 microns and 8.64 microns.

Similar measurements have already been carried out with diluted water in cells.

The difference between the milk and water readings at 5.7 microns determines the fat content of the milk sample.

At 8.64 microns. The difference between the milk and water readings determines the total solids content in the milk.

The difference between the two readings, total solids and fat, then determines the value of "non-fat solids" in the milk.

Although other wavelengths of "water filters" can be used, such as 4.7 microns, we have found good results at 8.64 microns, with a standard deviation of less than 0.04%. .

Determination of fat and SNF levels is of paramount importance in milk analysis.The microprocessor in this example allows direct reading of the two levels to be programmed without the need for an operator to calculate. I can do it.

In one embodiment of the present invention, the optical device includes only two lenses, does not include an elliptical or concave mirror, and furthermore, a cell and a detector are arranged, so that the homogenizer is omitted. You can. The manufacturing cost of this embodiment can be significantly lower than that of conventional analytical devices.

The spectrophotometer operates by changing the filter, reading the milk sample in the sample cell, and comparing this value to a similar value, such as a reference value for water in the sample cell.

Without significantly increasing cost, the readings can be calculated as simple percentages of transmission (absorption) at one or more sample wavelengths and reference values, preferably using a microprocessor, before comparing and integrating the readings. show.

The advantage of this device is that it has only one cell.

The cell was first filled with dilution water and then the 6th order measured at 8.64 microns and 5.7 microns.

The cell is filled with milk sample and m is determined. The cell is then filled with milk sample and the measurement repeated. Since the moisture measurement is stored in the device, there is no need to repeat the moisture determination in each subsequent milk sample. So one beam at one wavelength passes through one cell at any time.

With memorized water reference information, without reducing speed,
Compared to a double boom device, manufacturing costs of the optical device can be saved.

The apparatus according to the present invention has various desired uses, has been improved in various aspects, and its superior computer equipment allows for versatile analysis of proteins, lactose, fats, etc.

(Example) In the drawings, the cell detection device designated by special number (16) is made of an optically transparent material such as silver iodide, calcium fluoride, germanium, zinc sulfide or potassium bromide for infrared analysis. A pair of cell walls (12) (14
) equipped.

The cell walls (12) (14) are secured by bolts (18).
They are held within the body (16) in a known manner and define a sample cavity (20) therebetween.

The sample cavity (20) has an inlet hole (26) and an outlet hole (2) for the fluid sample by passageways (22) (24).
8).

A radiation detector (30) having a radiation transparent window (32) and a detection element (34) is mounted on one cell wall (12).
is installed.

Near the other cell wall (14), there is a cell wall (12) (1
Lenses made of optically transparent materials similar to those in 4) (
36) is attached to 6. Radiation (38) of a specific wavelength is directed at the lens (36) from the rest of the device, as detailed below.

The radiation (38) is focused by the lens (36) through the sample cell detection window (32) onto the detection element (34).

The radiation detector (36) has a diameter of 1oIII1, for example.
A version with one or more relatively large windows (32) is preferred. This makes it possible not only to focus the radiation (38) into the receiving area of the detection element (34), but also to collect all the light scattered within the cell, so that, according to the invention, the spectrometer sensitivity is improved.

Elliptic chains and their associated optical path lengths are eliminated.

Further, since the body (16) is temperature controlled to control the temperature of the cell, as disclosed in U.S. Pat. No. 4,310,763, a radiation detector ( 3o) is also temperature controlled, thereby reducing or eliminating drift of the radiation detector (3o) due to temperature changes.

In use, a comparison sample is placed within the cell and different amounts of radiation having different selected wavelengths are absorbed by the filter and their levels are recorded.

The milk sample then absorbs much better than water, so the optical signal at the radiation detector (3o).

The size varies depending on the component concentration and the filter selected. This optical signal is an alternating current signal generated by the action of the chopper. From the data recorded in this way, an estimate of the concentration of important components of the milky white can be obtained by calculation.

Other filters can be used to obtain information regarding protein and lactose, if desired. Cross-correction of interfering components
) can be done using equations that are known per se,
And these corrections can be programmed when using a microprocessor.

Furthermore, the simplifications made to the spectrophotometer according to the invention allow the production of spectrophotometers of very small dimensions. This further allows the spectrophotometer to be incorporated into equipment or equipment for process control.

In another embodiment, part or all of the exit cell wall (12) may be replaced so that the radiation detector is actually incorporated within the cell.

FIG. 3 shows other parts of the optical system that make the photometer low cost.

The infrared rays generated from the infrared ray generation source (40) are transmitted through a lens,
Or, by the lens group (42), the chopper (44)
focused on. The chopper (44) has its drive motor (
The infrared beam is alternately passed through and blocked at a frequency determined by the speed of 46).

If the radiation detector (30) is a photon detector.

For example, a high chopper frequency of 200c, ρ, s, is preferred. However, in the case of slow-acting radiation detectors, very low frequencies are used, for example IO~25c,p,s.

As is well known to those skilled in the art, the electronic technology of radiation detectors is dependent on the speed of the chopper. and is determined by it.

A replaceable filter (48) is arranged between the chopper (44) and the lens (36).

In normal use, when analyzing a milk sample, the cell is first filled with reference water and filtered (
48) selects 5.7 microns in the fat rAJ frequency band.

Measurements are taken both with the infrared beam (38) passing through and with the beam interrupted to measure the background level.

The filter (48) is then replaced with a "water filter" with high water absorption, for example 8.64 microns, and the same measurements are taken. This sequence is repeated for the milk sample in the cell.

In the case of 5.7 microns, by the difference in milk and water measurements corrected for background.

The fat content of the milk sample is determined. The difference between the milk and water measurements corrected for background at 8.64 microns determines the total solids content of the milk.

As a result, the difference between total solids and fat content determines the "non-fat solids" or SNF content of the milk.

Fat and SNF levels are particularly important measurements for analyzing milk. The microprocessor within the spectrophotometer can be programmed so that these two levels can be read directly without any calculations.

In this way, the most important parameters for milk analysis can be measured with sufficient accuracy using very low cost equipment.

Although the above-described embodiment is an apparatus for analyzing milk and milk products, and a suitable growth filter has been selected to achieve the objective in parentheses, the invention is not limited thereto. do not have. Other icy emulsions can be analyzed and in this case an appropriate filter can be selected.

In addition to the filters with the specific values mentioned above, other filters can also be used in the analysis of milk.

For example, other filter wavelengths that may be used to analyze milk fat include 3.46 microns and 6.84 microns.

As explained above, the present invention has important significance in the dairy industry as it provides a fast and reliable method for confirming the quality of milk samples at a relatively low cost.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a cell detection device according to the present invention. FIG. 2 is a cross section 1Ii showing the optical path by simplifying FIG. 1.
FIG. 3 is a schematic diagram of a spectrometer incorporating the cell detection device. (io) Cell detection device (12) (14) Cell wall
(16) Main body (18) Bolt (20) Sample cavity (22) (24) Passage (26) Inlet hole (28) Outlet hole (30) Radiation detector (
32) Radiation transparent window (34) Detection element (36)
Lens (38) Radiation (40) Infrared source (42) Lens, lens group (44) Chopper (46) Drive motor (48)
Filter hand *i'1. :? rf? +TI3 71 sun=(
Method) February 4, 1985 Michibe Uga, Director General of the Patent Office1, Indication of the case Patent Application No. 252974 of 19852, Name of the invention Optical cell detection assembly and infrared spectrophotometer 3, Make corrections Relationship with patent applicant Name: Shields Instruments Limited 4, Agent 5, Date of amendment order: January 8, 1985 (Delivery date: January 28, 1988)

Claims (10)

[Claims] (1) a sample cell having a wall made of an optically transparent material to define a sample cavity; a radiation detector disposed close to the sample cavity; and adjacent to the wall on the opposite side from the detector; and a lens for focusing radiation passing through the cell onto the detector. (2) The optical cell detection assembly according to claim (1), wherein the detector is in contact with the sample cell wall. (3) An optical cell detection assembly as claimed in claim (1), wherein the detector forms part or all of one of the sample cell walls. (4) an infrared radiation source, a converging lens, a chopper,
The optical cell detection assembly of claim 1, further comprising a filter. (5) an infrared source and a detector therefor, an optical device for focusing the beam on the sample wall, a chopper device for periodically interrupting the beam, and a filter for selecting one or more wavelengths from the beam; an infrared spectrophotometer comprising an apparatus, wherein the sample to be tested consists of a water emulsion, and the concentration of non-water in the emulsion is determined by measuring the water displaced by the constituents. An infrared spectrophotometer characterized in that a filter is selected to measure. (6) At least two filters, one of which
Infrared spectroscopy according to claim 5, wherein one filter selects a wavelength that is strongly absorbed by water and the remaining filter selects a wavelength to be absorbed by one of the components of the sample. Photometer. (7) Infrared spectroscopy according to claim (6), comprising one cell filled with water to make a reference measurement and then filled with a sample to make a sample measurement. Total. (8) An infrared spectrophotometer as claimed in claim (7), further comprising a processor device for storing and comparing reference measurements, each successively measuring the sample. (9) The claim according to any one of claims (5) to (8), comprising a filter that selects a wavelength of 8.64 microns and a filter that selects a wavelength of 5.7 microns. Infrared spectrophotometer. (10) A device for amplifying the alternating current signal from the detector, a device for correcting the different signal levels from different filters, and an analog-digital device for converting said signal into digital form for calculation. An infrared spectrophotometer according to any one of claims (5) to (9), comprising a converter.