JPH0419499B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a densitometer for suspended matter, and more specifically, it detects the optical density due to absorption of a suspension by using diffused light as incident light to measure the concentration of suspended matter in a suspension. It relates to a measuring device.

In general, optical measurement methods are often used to measure the concentration of suspended matter such as microorganisms in a culture solution, and the concentration of suspended matter in water quality tests of rivers, lakes, reservoirs, and the like. In this optical measurement method, light is first introduced into the suspension, and the transmitted light is detected to determine the optical density (Optical Density=-log
The intensity of transmitted light/intensity of incident light (hereinafter referred to as OD) is determined, and then the concentration of the suspended matter is determined from this OD.

Typical conventional devices for measuring the concentration of suspended matter include a turbidity meter and a colorimeter. A turbidity meter makes parallel light enter a suspension and uses a lens, pinhole, etc. (without detecting the light that hits the suspended matter in the liquid and scatters)
Only parallel transmitted light is detected by a photodetector. When the concentration of suspended matter is low, a linear (proportional) relationship is maintained between OD and concentration, and the sensitivity characteristics are excellent. However, as the concentration increases, the linear relationship breaks down, which is a drawback. Therefore, for example, it was not suitable for continuous measurement of the growth rate of bacteria in a culture solution, that is, for continuous measurement of the concentration of suspended matter ranging from low concentration to high concentration. On the other hand, in a colorimeter, divergent light or parallel light from a light source lamp is made incident on a suspension, and the transmitted light is detected by a photodetector. Because it detects not only parallel transmitted light but also part of the light scattered by particles, it is more suitable for measuring relatively high concentration ranges than a turbidity meter. There was no linear relationship between them, so correction was required.

In this way, conventional suspension concentration measurement devices
There was an inconvenience that a linear relationship between OD and the concentration of suspended matter was not maintained from low to high concentrations, and correction was required depending on the measured concentration. Particularly in the field of fermentation industry, for automatic control of cultures of Escherichia coli, Bacillus subtilis, yeast, etc. (control of fermentation process), it is possible to measure from low to high concentration ranges, and the device configuration is simple. A densitometer is desired.

The present invention is applicable to concentrations ranging from low concentration range to high concentration range.
The purpose of the present invention is to provide a densitometer for suspended solids that has an improved linear relationship with OD.

The purpose of this is to provide a light source for inputting light into the first light diffusing plate, first and second light diffusing plates arranged outside the storage space for the suspension, and a light source for inputting light into the first light diffusing plate, and a first and second light diffusing plate arranged outside the storage space for the suspension. This is achieved by a densitometer having a photodetector that receives light entering the light diffuser and exiting the second light diffuser plate.

With this configuration of the present invention, diffused light (light whose intensity distribution is uniform in all directions) is absorbed through the suspension, and the amount of unabsorbed diffused light is linearly related to the concentration of the suspension. It can be measured as

First, the principle of the present invention will be explained below with reference to the accompanying drawings. FIGS. 1A and 1B are diagrams explaining the principle of the densitometer of the present invention. First and second light diffusing plates 3 and 4 are arranged outside the storage space 2 for the suspension 1, and the light is made to enter the suspension from the first light diffusing plate 3, and the second light diffusing plate A photodetector 5 is configured to detect the transmitted light from 4. In the case of Fig. 1A, parallel light is
The case shown in FIG. 1B is a case in which diverging light from the light source lamp 6 is used. In either case, the incident light is converted into diffused light by the first light diffusing plate, and the OD generated when this diffused light is absorbed by the suspension.
is detected. The second light diffusing plate is used to function in the same way as opal glass used for measuring absorption spectra in spectroscopic measurements. In other words, as much light as possible that is scattered by the suspension is collected by this second light diffusion plate and then enters the photodetector, so that the OD due only to the absorption of the suspension can be determined with high accuracy. There is.

In this way, in the present invention, the first light diffusing plate is used to illuminate the suspension with diffused light, and the suspension 1
The diffused light passing through is absorbed by the suspended matter, and the remaining diffused light is collected by the second light diffusion plate 4 and sent to the photodetector 5, so that only the diffused light is used to eliminate the absorption by the suspended matter. It is measured using. Therefore, as shown by the solid line in FIG. 2, a linear relationship is maintained between OD and concentration from low to high concentrations.

As shown for comparison in Figure 1 C or D, when parallel light or diverging light is directly incident light, the second
As shown by the dotted line in the figure, there is no linear relationship between OD and concentration in the low concentration region, but a curved, nonlinear relationship. This is measured using the absorption of parallel light or diverging light by suspended matter when the concentration is low even if parallel light or diverging light is incident, but when the concentration becomes high to a certain extent, the parallel light or diverging light becomes diffused. This nonlinearity occurs because the absorption coefficient of parallel light or diverging light is different from the absorption coefficient of diffused light. It is. Based on this understanding, the inventor of the present invention eliminates nonlinearity by performing measurements using the absorption of only diffused light (light whose intensity distribution is uniform in all directions).

The light diffusing plate used in the present invention is preferably one that completely diffuses light, such as opal glass with a thin opalescent layer on one half of transparent glass, opal glass entirely made of opalescent material, opalescent plastic board, or parchment paper. Select and use as appropriate.

Furthermore, the arrangement of the light diffusing plates is not limited to the facing arrangement as shown in Fig. 1 A or B, but may also be arranged as shown in Fig. 3 A or B, but in either case, it is difficult to store the suspension. Light diffusing plates 3 and 4 are arranged outside the space,
First light diffusing plate 3 - Suspension 1 - Second light diffusing plate 4
The structure is configured so that the light passes in this order.

Further, as the photodetector, a photomultiplier tube, a phototransistor, etc. may be appropriately selected and used.

FIG. 4 is a partially sectional front view of one embodiment of the present invention. FIG. 5 is a front view showing an enlarged section of a part of FIG. 4. Figure 6 is A-A of Figure 5.
FIG. 3 is a plan view showing a cross section in the direction of arrows. Light from a light source (not shown) passes through an optical fiber 8 disposed in an outer cylinder 7, is bent by 90 degrees by a mirror 10 in a mirror holding cylinder 9, and is directed from a first opal glass 11 to a suspension liquid. It is configured to pass through the storage space 12 -> second opal glass 11'-> mirror 10'-> optical fiber 8' and to be detected by a photodetector (not shown). 13 is a cap that can be attached to and detached from the outer cylinder 7, and has an inlet 14 and an outlet 15 for the suspension.
is provided on the side perpendicular to the optical path, and a fine wire mesh 16 is placed at the inlet to prevent air bubbles from flowing in. The flow of the suspension that entered the cap 13 from the inlet 14 is accelerated in the narrow storage space 12 formed between the mirror holding tubes 9 and 9' and reaches the outlet 15, so that air bubbles are absorbed by the wire mesh 16 at the inlet. Even if air bubbles enter the cap without being removed, they will not stagnate in the storage space. Therefore, the OD due to air bubbles
The influence on the measurement can be largely avoided. 17 is a cap nut, which is designed to be divided.

FIG. 7 is a graph showing the relationship between yeast concentration and OD obtained using the densitometer of this example.
Helium neon laser (5mW.632.8nm) as light source
and a tungsten lamp (30W), and a silicon photocell (Hamamatsu TV KK.5876) as a photodetector.
It was carried out using Regardless of the type of light source, both the concentration and OD range from low to high concentration.
A linear relationship was maintained, the concentration of bacteria in the culture solution could be measured, and the growth rate of the bacteria could be continuously monitored, which was extremely convenient for automatic culture management. In addition, the structure is compact, and it can be used without any problems even in a small culture tank. Furthermore, since there is no light source or photodetector inside the outer tube that is inserted into the culture solution or other suspension, high-pressure steam sterilization can be carried out with the concentration meter inserted in the culture tank, and contaminants can be removed. Contamination could be easily avoided.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a graph showing the relationship between the concentration of suspended matter and OD, and FIG. 3 is a diagram showing another embodiment of the arrangement of the light diffusing plate used in the present invention.
FIG. 4 is a front view partially showing an embodiment of the concentration meter of the present invention in cross section, FIG. 5 is a front view showing a partially enlarged cross section of FIG. 4, and FIG. FIG. 7 is a plan view taken in the cross section taken along the line A-A, and is a graph showing the relationship between the concentration of yeast and OD obtained in Examples of the present invention. Codes in the figure: 1... Suspension liquid, 2... Suspension liquid storage space, 3, 4... First and second light diffusion plates, 5...
Photodetector.

Claims (1)

[Claims] 1 first and second light diffusing plates arranged outside the suspension storage space; receiving light entering the storage space from the first light diffusing plate and exiting from the second light diffusing plate; A suspension densitometer characterized by being equipped with a photodetector.