JP4532357B2 - Concentration measuring device - Google Patents

Description

  The present invention relates to a concentration measuring apparatus that measures, for example, the salt concentration of saline, and more particularly to a technique for improving measurement accuracy.

  As a salinity meter used for measuring the salinity concentration, for example, as described in Japanese Patent Application Laid-Open No. 2002-5862 (Patent Document 1), two electrodes are inserted into a liquid, and between these electrodes A system is known in which an AC voltage is applied to the current, the current value flowing at this time is measured, and the salinity concentration is measured based on this current value.

  FIG. 7 is an explanatory view schematically showing the measurement principle of a conventional salinity concentration measuring device. As shown in the figure, two electrodes 103 and 104 are inserted into a container 101 filled with a saline solution 102. An AC voltage is applied between the two electrodes 103 and 104 from the power source 105. Then, a current flows in the saline 102 through a path as indicated by arrows Y1 and Y2 in the figure, and the flowing current is measured by the ammeter 106.

Then, by calculating (measurement current) / (applied voltage), the electrical conductivity g of the saline solution 102 is obtained, and based on the correspondence between the electrical conductivity and the salinity concentration, the obtained electrical conductivity g is calculated. The corresponding salinity concentration is obtained and the obtained salinity concentration is displayed on the display means.
JP 2002-5862 A

  However, in the above-described conventional salinity meter, the current does not flow only between the two electrodes 103 and 104, and the current flows also on the back side and the periphery of the electrode as shown by the arrow Y2 in FIG. Depending on the amount of the target saline solution 102 and the size of the container 101, the current value varies greatly, and there is a drawback that it is impossible to detect the concentration with high accuracy.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a concentration measuring apparatus capable of measuring the concentration of a measurement object with high accuracy from a small amount of liquid sample. Is to provide.

In order to achieve the above object, the invention according to claim 1 of the present application is a concentration measuring apparatus for measuring the concentration of a measurement object dissolved in a liquid, and has an upper expanded cylindrical shape and injects the liquid. A sample stage, a first electrode provided at a substantially central portion of the sample stage, a second electrode provided on the same plane as the first electrode and around the first electrode; Power supply means for supplying AC power between the first electrode and the second electrode; a peripheral electrode provided at a peripheral portion of the second electrode and having the same potential as the second electrode; Detection means for measuring a voltage generated between the first electrode and the second electrode and a current flowing between the first electrode and the second electrode, conductance of the measurement object, and the measurement object Characteristic curve data showing the relationship with the concentration of Concentration measuring means for obtaining the conductance of the measurement object based on the current value and the voltage value detected by the means, and for obtaining the concentration of the measurement object with reference to the characteristic curve data based on the obtained conductance; And a display means for displaying the obtained concentration.

The invention described in claim 2 is characterized in that the second electrode is disposed so as to substantially surround the periphery of the first electrode .

According to a third aspect of the present invention , a buffer amplifier is provided between the second electrode and the surrounding electrode, so that the second electrode and the surrounding electrode have the same potential. .

According to a fourth aspect of the present invention, the power supply means is a voltage source that outputs a constant alternating voltage, and the detection means is a shunt provided between the power supply means and the first or second electrode. A current detecting means for obtaining a current flowing between the first electrode and the second electrode based on a resistance and a voltage generated at both ends of the shunt resistor; and between the first electrode and the second electrode Voltage detecting means for detecting a voltage, wherein the concentration measuring means obtains conductance from the current detected by the current detecting means and the voltage detected by the voltage detecting means, and the measurement object is based on the conductance. It is characterized by determining the concentration of the object .

The invention according to claim 5 is characterized in that the liquid is a saline solution and the concentration of the measurement object is a salinity concentration .

In the first aspect of the present invention, since the peripheral electrode having the same potential as the second electrode is provided in the peripheral portion of the second electrode, the current flowing between the first and second electrodes is It is possible to prevent leakage to the surroundings. Therefore, it is not affected by the shape of the solution injection region around the second electrode, and high-precision concentration measurement is possible even when the amount of liquid as a sample is small. In addition, characteristic curve data indicating the relationship between the conductance and the concentration of the measurement object is provided. When the conductance is obtained, the conductance is substituted into the characteristic curve data to obtain the concentration of the measurement object. As a result, the calculation load can be reduced.

In the invention of claim 2 , since the second electrode is arranged so as to substantially surround the periphery of the first electrode, a stable current can flow between the two electrodes, and the measurement accuracy can be improved. .

In the invention of claim 3 , since the buffer amplifier is provided between the second electrode and the surrounding electrode, the second electrode and the surrounding electrode can be easily set to the same potential. In addition, since no current flows from the second electrode to the surrounding electrodes, it is possible to measure the concentration with high accuracy.

In the invention of claim 4 , since the current is measured using a shunt resistor provided on the electric wire connecting the power supply means and the electrode, and the voltage between the first and second electrodes is further measured by the voltage detecting means. Therefore, it becomes possible to measure current and voltage with high accuracy, and in turn, it is possible to calculate conductance with high accuracy.

In the invention of claim 5 , since the salinity concentration is measured as the measurement object concentration, the salinity concentration can be measured with high accuracy and a simple operation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an external view showing a configuration of a salinity concentration measuring apparatus as a concentration measuring apparatus according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of the salinity concentration measuring apparatus. As shown in the figure, the salinity concentration measuring device 1 has a casing structure that is entirely covered by an upper case 2 and a lower case 3, a substrate 4 on which various electronic components are mounted, and a measurement target The sample stage 11 that forms the region where the saline solution to be injected is injected, the display unit (display means) 9 such as a liquid crystal display that displays the salinity concentration that is the measurement result, and operations such as start of processing and zero adjustment Operation switches 10a and 10b to perform are provided. An electrode substrate 5 is provided below the sample stage 11.

  FIG. 3 is a partially broken perspective view of the sample stage 11. As shown in the figure, the sample stage 11 has an upper expanded cylindrical shape, and a liquid is provided in the lower opening of the sample stage 11. The electrode substrate 5 is disposed via the sealing O-ring 12 (see FIG. 2), and a portion surrounded by the sample stage 11 and the electrode substrate 5 is an injection region of a saline solution to be measured.

  The electrode substrate 5 includes a first electrode 8 formed at the center of the circular opening of the sample stage 11, and the periphery of the first electrode 8 with the first electrode 8 as the center. A second electrode 7 is provided so as to cover it. Furthermore, the lower circumferential surface of the sample stage 11 is a guard electrode (peripheral electrode) 11a made of a conductor.

  FIG. 4 is a block diagram showing a control unit of the salinity concentration measuring apparatus 1 according to the present embodiment. As shown in the figure, the control unit includes a signal generator (power supply means) 22 that generates an AC voltage signal having a predetermined frequency, and an output amplifier circuit 23 that amplifies the AC signal output from the signal generator 22. The output terminal of the output amplifier circuit 23 is connected to the second electrode 7 via the shunt resistor 21. The first electrode 8 is grounded.

  Further, the second electrode 7 is connected to the guard electrode 11 a via the buffer amplifier 26, and is connected to a voltage detection circuit (detection means) 25 that detects a voltage applied to the second electrode 7. Further, both ends of the shunt resistor 21 are connected to a current detection circuit (detection means) 24, and a current flowing through the shunt resistor 21 is obtained based on a voltage generated in the shunt resistor 21.

Each output terminal of the current detection circuit 24 and the voltage detection circuit 25 is connected to an AD conversion circuit 27 for converting an analog signal detected by the detection circuits 24 and 25 into a digital signal. Further, the AD conversion circuit The output terminal 27 is connected to a CPU (concentration measuring means) 28. The CPU 28 obtains the conductance g of the saline solution injected between the second electrode 7 and the first electrode 8 based on the current detected by the current detection circuit 24 and the voltage detected by the voltage detection circuit 25. Process. Furthermore, characteristic data indicating the relationship between conductance and salinity as shown in FIG. 6 is provided, and the salinity of the injected saline is obtained by substituting the obtained conductance g into this characteristic data. .

  The display unit 9 displays the salinity concentration obtained by the CPU 28.

  Next, the processing operation of the salinity concentration measuring apparatus according to the present embodiment configured as described above will be described. When an activation signal is sent from the CPU 28 to the signal generator 22 in a state in which a saline solution to be measured is injected into the sample stage 11 shown in FIGS. 1 to 3, an AC voltage having a predetermined frequency is sent from the signal generator 22. A signal is output.

  The output voltage signal is amplified by the output amplifier circuit 23 and then applied to the second electrode 7 via the shunt resistor 21. Further, since the first electrode 8 formed at the center of the sample stage 11 is grounded to the ground, a current flows from the second electrode 7 toward the first electrode 8 in the saline solution.

  At this time, since the second electrode 7 and the guard electrode 11a are connected via the buffer amplifier 26, the second electrode 7 and the guard electrode 11a have the same potential. Further, since the impedance when the guard electrode 11a is viewed from the second electrode 7 is infinite, no current flows from the second electrode 7 to the guard electrode 11a side.

  Further, even in the saline solution injected into the sample stage 11, the second electrode 7 and the guard electrode 11a have the same potential, so that no current flows between them. This will be described with reference to the schematic diagram shown in FIG. 5. The second electrode 7 is provided in an arc shape centered on the first electrode 8, and further covers the periphery of the second electrode 7. Since the second electrode 7 and the guard electrode 11a are at the same potential, the current flowing from the second electrode 7 to the first electrode 8 is entirely in an arc shape. It flows inside the electrode 7. Accordingly, a current corresponding to the concentration of the saline solution flows between the two electrodes 7 and 8 without being affected by the amount of the saline solution injected as a sample and the surrounding shape.

  On the other hand, since the current flowing between the two electrodes 7 and 8 flows to the shunt resistor 21, a voltage having a magnitude proportional to the current is generated at both ends of the shunt resistor 21. Based on the voltage generated in the resistor 21 and the resistance value of the shunt resistor 21, the current flowing through the shunt resistor 21 is obtained, and the obtained current data is output to the AD conversion circuit 27. The AD conversion circuit 27 digitizes the current data and outputs it to the CPU 28.

  The voltage generated at the second electrode 7 is detected by the voltage detection circuit 25, and the detected voltage is digitized by the AD conversion circuit 27 and output to the CPU 28.

Thereafter, the CPU 28 obtains the conductance g from the obtained voltage (V) and current (I) using the relational expression g = I / V. Further, by substituting the conductance g into the characteristic data shown in FIG. 6, the salinity concentration is obtained, and the obtained salinity concentration data is output to the display unit 9. Thus, the salinity concentration is displayed on the display unit 9, and the operator can know the salinity concentration of the saline injected as a sample.

  Thus, in the salinity concentration measuring apparatus according to the present embodiment, the second electrode 7 is provided around the first electrode 8, and the guard electrode 11 a is covered so as to cover the periphery of the second electrode 7. In addition, since the second electrode 7 and the guard electrode 11a have the same potential, when an AC voltage is applied to the second electrode 7, current leaks to the outside of the second electrode 7. Can be avoided. Therefore, since the current flowing from the second electrode 7 to the first electrode 8 is limited to the inside of the second electrode 7, highly accurate salinity concentration measurement is not affected by the amount of saline solution injected or the shape of the surrounding portion. Is possible.

  In addition, since the salinity concentration can be measured with a small amount of sample that is filled between the second electrode 7 and the first electrode 8, the measurement operation can be simplified.

Further, since the voltage detection circuit 25 is directly connected to the second electrode 7 to detect the voltage, it is possible to detect the voltage with high accuracy, to obtain the conductance g with high accuracy, and thus to measure the salinity concentration. Accuracy can be improved.

Further, the CPU 28 has characteristic data (FIG. 6) showing a relationship between a preset conductance g and a salinity concentration, and obtains the salinity concentration by substituting the obtained conductance g into the characteristic data. Therefore, the conductance g can be easily converted into the salinity concentration with high accuracy.

  The concentration measuring apparatus of the present invention has been described based on the illustrated embodiment. However, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

For example, in the embodiment described above, the voltage detection circuit 25 is used to measure the voltage between the two electrodes 7 and 8. However, the voltage output from the output amplifier circuit 23 is between the two electrodes 7 and 8. It is also possible to measure the conductance g as a voltage of With such a configuration, the voltage detection circuit 25 can be omitted, so that the circuit configuration can be simplified.

In the embodiment described above, a constant level AC voltage signal is output from the signal generator 22, and the conductance g is obtained based on the current flowing at this time. The conductance g may be obtained by outputting a signal and measuring the voltage generated between the two electrodes 7 and 8 at this time.

Furthermore, in the above-described embodiment, the salinity concentration measuring device for measuring the salinity concentration contained in the saline solution has been described as an example. However, the concentration measuring device according to the present invention is not limited to this, and liquid It is also possible to employ other substances to be measured whose conductance changes depending on the concentration of the substance dissolved therein.

  It is extremely useful for easily and accurately measuring the salinity in saline.

It is an external view of the density | concentration measuring apparatus which concerns on one Embodiment of this invention. It is a disassembled perspective view of the density | concentration measuring apparatus which concerns on one Embodiment of this invention. It is a partially broken perspective view which shows the structure of a sample stage part. It is a block diagram which shows the structure of the control part of the density | concentration measuring apparatus which concerns on one Embodiment of this invention. It is explanatory drawing which shows typically the positional relationship of a 1st electrode, a 2nd electrode, and a guard electrode, and an electric current path | route. It is a characteristic view which shows the relationship between salt concentration and conductance . It is explanatory drawing which shows the measurement principle of the conventional salt concentration measuring apparatus.

Explanation of symbols

1 Salinity concentration measuring device (concentration measuring device)
2 Upper case 3 Lower case 4 Substrate 5 Electrode substrate 7 Second electrode 8 First electrode 9 Display unit (display means)
10a, 10b Operation switch 11 Sample stage 11a Guard electrode (peripheral electrode)
12 O-ring 21 Shunt resistor 22 Signal generator 23 Output amplifier circuit 24 Current detection circuit (current detection means)
25 Voltage detection circuit (voltage detection means)
26 Buffer amplifier 27 AD conversion circuit 28 CPU (concentration measuring means)

Claims (5)

In a concentration measuring device that measures the concentration of a measurement object dissolved in a liquid,
A sample stage for injecting the liquid;
A first electrode provided at a substantially central portion of the sample stage;
A second electrode provided on the same plane as the first electrode and around the first electrode;
Power supply means for supplying AC power between the first electrode and the second electrode;
A peripheral electrode provided around the second electrode and having the same potential as the second electrode;
Detecting means for measuring a voltage generated between the first electrode and the second electrode, and a current flowing between the first electrode and the second electrode;
Characteristic curve data indicating the relationship between the conductance of the measurement object and the concentration of the measurement object is provided, and the conductance of the measurement object is obtained based on the current value and the voltage value detected by the detection means. Based on conductance, referring to the characteristic curve data, a concentration measuring means for determining the concentration of the measurement object;
Display means for displaying the determined concentration;
A concentration measuring apparatus comprising: The concentration measuring apparatus according to claim 1, wherein the second electrode is disposed so as to substantially surround the periphery of the first electrode . 3. The method according to claim 1, wherein a buffer amplifier is provided between the second electrode and the surrounding electrode, whereby the second electrode and the surrounding electrode have the same potential. concentration measuring apparatus crab according. The power supply means is a voltage source that outputs a constant AC voltage,
The detecting means includes a shunt resistor provided between the power supply means and the first or second electrode, and a voltage between the first electrode and the second electrode based on a voltage generated at both ends of the shunt resistor. Current detecting means for obtaining a current flowing through the first electrode, and voltage detecting means for detecting a voltage between the first electrode and the second electrode,
The concentration measuring means obtains a conductance from the current detected by the current detecting means and the voltage detected by the voltage detecting means, and obtains the concentration of the measurement object based on the conductance. The concentration measuring apparatus according to any one of claims 1 to 3 . 5. The concentration measuring apparatus according to claim 1, wherein the liquid is a saline solution, and the concentration of the measurement object is a salinity concentration .

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