JPS61189441A - Method for measuring concentration of solution - Google Patents

Abstract

PURPOSE:To correct the error caused by a cooler and to measure the correct concn. of a soln. by subjecting the soln. concn. determined by measuring the quantity of the reflected light which is made incident at periodically changing incident angles on the liquid surface of the soln. to the correction by the soln. temp. and the correction by the temp. of a cooling medium which cools a measuring apparatus. CONSTITUTION:The light of a light source lamp 21 is projected through a sapphire window 8 to the surface of the soln. 9 at the periodically changing incident angles and the intensity of the reflected light changing in accordance with the change of the refractive index of the light by the change of the soln. concn. is detected by a detecting part 1 consisting of a photoelectric tube 26, the output signal from which is integrated by am amplifier 2(27). The correction y1=a1(T1-T0) (a1 is a temp. correction gain and T0 is a reference soln. temp.) by the signal T1 from the temp. sensor is added to said signal. The result thereof is fed as a concn. signal to a computer 4 which corrects the concn. signal by adding the primary delay element 1/(1+taus) (tau is the delay time constant) to said signal and adding the correction quantity y2=-a2(T2-T5)Q (T5 is a reference temp. Signal, a2 is then correction factor, Q is the flow rate of cooling water) by the temp. signal T2 from a temp. sensor 7 of a cooling water piping 6.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention utilizes the fact that when the concentration of a solution changes, the refractive index of light changes and the critical angle changes. The present invention relates to a method of measuring the concentration of a solution by measuring the amount of light, and more specifically, to a correction means therefor.

[Prior Art] Conventionally, a refractive index concentration meter using the above principle has been generally used as a flat stage for continuously measuring the concentration of a process fluid. FIG. 2 shows a schematic diagram of its principle. In FIG. 2, light emitted from a light source lamp 21 is converted into parallel light beams by a convex lens 22, and becomes a light band that periodically moves from A to B by a rotating (moving) slit 23. This band of light is focused by the convex lens 24 and repeatedly moves from A to B, and the irradiation direction changes, but always
It is set to reach one point 25 of the sapphire window 8. The sapphire window 8 has a semi-cylindrical shape, and the point 25 is set to be approximately the center point of the circle. The lower plane of the sapphire window 8 in the drawing is in contact with the solution 9 to be measured.

Since sapphire has a higher refractive index than the solution 9, when the incident light is A, it is refracted from the point 25 as shown in the figure and enters the solution 9 as refracted light A'. However, when the incident light moves toward B and reaches the critical angle, the light cannot be refracted into the solution, a total internal reflection phenomenon occurs, and the strong reflected light reaches the phototube 26.

Therefore, the output of the phototube 26 is that when the incident light is at angle A, the reflected light is weak and the output is low, but it progresses toward B, and when the critical angle is reached, it is totally reflected and the reflected light is strong and the output is high, and B
It lasts until Since this is repeated periodically, the output from the phototube 26 has a waveform with peaks and valleys, as shown in FIG.

When the concentration of the solution 9 changes, the refractive index of light changes and the critical angle also changes, so the output of the phototube 26 will have a constant period, but the width of the peaks will increase and the width of the valleys will decrease, or The width of the peaks decreases and the width of the valleys increases. Therefore, by integrating the output signal from the phototube 26, a change in the critical angle can be determined from an increase or decrease in the amount of reflected light, and a signal indicating the concentration of the solution can be output.

However, the optical refractive index of a solution changes not only depending on the concentration but also on the temperature of the solution, so as shown in Figure 4, the concentration output signal is compensated by measuring the solution temperature near the measurement point. . That is, the temperature is compensated by measuring the solution temperature T1, calculating the temperature correction output y1 by multiplying the difference from the reference solution temperature To (TI-To) by the temperature correction gain a1, and adding or subtracting this to the output signal. A concentration signal is output.

[Problems to be solved] However, when the temperature of the solution is high, a cooling water pipe is installed to protect the electrical circuits of the measuring equipment from the heat, but even with this cooling water temperature, As shown in FIG. 6, it was found that an error occurred in the meter output.

[Object of the Invention] Therefore, an object of the present invention is to realize a method of correcting the error caused by the cooling device that cools the measuring instrument and measuring the correct solution concentration.

[Solution Means] In order to achieve this object, the present invention measures the reflected light beam of incident light projected onto the liquid surface of the solution at periodically changing incident angles, and corrects the measured value based on the temperature of the solution. The method for measuring the concentration of the solution is characterized in that a correction is made based on the temperature of a cooling medium that cools the measuring device.

[Function] Since the present invention has the above configuration, the amount of reflected light is measured by utilizing the fact that the critical angle changes and the amount of reflected light changes due to a change in the refractive index of light due to a change in the concentration of the solution. When outputting the concentration, along with correction by solution temperature,
Since it also corrects errors caused by the state of the equipment cooled by the cooling device, accurate measurement values can be obtained.

[Example] The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a detailed explanatory diagram of the present invention. The detection unit 1 has a configuration as shown in FIG. 2, and includes, for example, a sapphire window 8 which is in contact with a process solution flow path of a device such as a hydrogen chloride recovery device. It consists of a light emitting part, a phototube in a light receiving part, an amplifying part, etc., and, as mentioned above, changes in solution concentration are detected as changes in the amount of reflected light. The output signal from the detection section I is sent to the amplifier 2 via a cable 3. amplifier 2
Then, the rectangular waveform output signal from the phototube 26 is integrated, and the fourth
The correction yl =21 (Tt To ) shown in the figure is added to form a density signal, which is sent to the computer 4 via the cable 11.

On the other hand, the detection unit 1 is provided with a cooling water pipe 6 in order to block heat from the high-temperature solution 9 and protect the measuring device of the detection unit 1. A temperature sensor 7 is provided in this pipe. In some cases, it may be preferable to provide the temperature sensor 7 on the downstream side or both upstream and downstream of the detection section l. The signal from temperature sensor 7 is sent to computer 4 via cable 13.

In the computer 4, the concentration signal from the amplifier 2 has "fluctuations" due to vibrations of the optical system, etc., and is stabilized, smoothed, and stabilized. τ is a delay time constant, which is set to about 30 seconds in the specific example. S is the Laplace transform operator d/dt.

Also, a correction Ny2 is calculated based on the temperature signal T2 from the temperature sensor 7 of the cooling device.

y2 = -a2 (T2 - Ts) ・Qa2 is a correction coefficient based on cooling water temperature, Ts is a reference temperature signal, Q
is the cooling water flow rate. The cooling water flow 1iQ is assumed to be constant. The correction 1y2 based on this cooling water temperature T2 is added to the concentration signal to correct the concentration signal.

Next, the relationship between concentration and refractive index is as shown in Figure 5.
Since the relationship is not necessarily proportional, errors will occur if the concentration is displayed in proportion to the meter's output.

In particular, when the instrument span is narrow and a minute change in refractive index is read as a change in concentration, this error becomes a problem. Therefore, the data of the graph of the solution concentration characteristics with respect to the meter output, which varies depending on the properties of the solution to be measured, is stored in the computer as a conversion function 15, and the above-corrected signal is multiplied by this conversion function 15 to convert it into a concentration signal. The information is then output and displayed on the CRT 5, recorded on paper using a printer, or stored on a storage medium.

As described above, according to this embodiment, in the method of determining the concentration by measuring the amount of reflected light by taking advantage of the fact that the optical refractive index of a solution changes depending on the concentration, in addition to correction based on the solution temperature, a microcomputer is used. By adding the correction y2 based on the cooling water temperature, we were able to reduce the error, but in this example, we also added a -order lag element to smooth out and stabilize the "fluctuations" in the measured values. Ta.

In addition, even if the correspondence between output and concentration is non-linear due to the properties of the solution, the function is calculated accordingly, so corrections can be made according to the properties of the solution to be measured, allowing more accurate concentration measurements. I can do it.

Note that it goes without saying that the correction based on the temperature of the solution, )'1 = al (TI - To ), may also be configured to be calculated by the combiator 4.

[Effects of the Invention] As explained above, according to the present invention, when measuring the concentration of a solution, it is possible to correct the error in the measurement value caused by the thermal conditions caused by the cooling device that cools the measuring instrument, and to obtain an accurate measurement value. be able to. In addition, if configured as in the example, it is possible to stabilize the measured value by loading the -order element, and furthermore, by setting and calculating the output vs. concentration function, it is possible to stabilize the measured value by Errors can be removed depending on the properties of the solution.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the embodiment, Fig. 2 is an explanatory diagram of the principle of the refractive index concentration meter, Fig. 3 is the output pattern of the phototube, Fig. 4 is a correction block diagram based on solution temperature, and Fig. 5 is the instrument. Graph of Power vs. Concentration. FIG. 6 is a graph of cooling water temperature vs. instrument output. In the figure, ■ is the detection unit, 4 is the computer, and 5 is the CR.
T, 6 is the cooling water pipe, 7 is the temperature sensor, 8 is the sapphire window, 9 is the solution, 12 is the primary element, 14 is the cooling temperature correction, and 15 is the conversion function. Sub-agent Yukio Harada, patent attorney Figure 1

Claims (1)

[Claims] A method of measuring the concentration of the solution by measuring the reflected light beam of incident light projected onto the liquid surface of the solution at an incident angle that changes periodically, and correcting the measured value by the temperature of the solution, the method includes: A method for measuring the concentration of a solution, characterized by adding correction based on the temperature of a cooling medium to be cooled.