Electric conductivity-measuring cell

Abstract: An electric conductivity measuring cell comprises a pressure container (1), serving also as an outer electrode, an inlet port (2) for a liquid to be measured, an outlet port (3), and an inner electrode (11) provided within said pressure container (1) so as to simplify construction and improve measurement accuracy.

Description: The present invention relates to an electric conductivity-measuring cell used for measuring an electric conductivity of chemical substances, which are used in a production of semiconductors and gaseous at normal temperature and pressure, under the condition of liquefied gases and for a control of water quality of industrial water, water supplied for a boiler, various kinds of washing water and the like, in particular to an electric conductivity-measuring cell suitable for a measurement of an electric conductivity of liquids, which exist under the high-temperature and high-pressure condition, such as a primary cooling water in a nuclear power plant. Description of the Prior Art High-purity halogen gases, inorganic hydrides, such as hydrogen halide gases, and the like have been used as dry etching gases in the production of semiconductors and various kinds of gas, such as SiH 4 , Si 2 H 6 and SiH 2 Cl 2 , have been used in the formation of thin films of Si, SiO 2 , Si 3 N 4 and the like hut even though a remarkably very small quantity (for example a ppb-level) of impurities are contained in these gases, a bad influence upon a manufacturing process of LSI and the like by said impurities is increased as a pattern is fined and thus also a gas piping system itself is seriously influenced. So, it has been desired to accurately measure a concentration of the impurities at a ppb-level and control it. In addition, various kinds of impurity, such as corrosion products by an electrolysis, are formed with an operation of a reactor in a reactor-cooling water circulating through a primary cooling system of a boiling water reactor. In particular, when said electric conductivity is increased with an increase of electrolyzed components, a corrosion speed of structures in said system is rapidly accelerated and said corrosion products are radioactivated by neutrons to increase a radioactive level within the system while said electrolytic impurities are settled on a surface of fuel rods to hinder a smooth thermal conductance, whereby reducing an operating efficiency of the reactor, so that said primary cooling water is suitable refined to a high purity or newly replenished to be controlled so that a constant water quality may be always kept. In particular, the control of the electric conductivity as an index for a quantity of said electrolyzed components is an important item for the control of water quality of the primary cooling water. Prior art document DE-C-968 548 discloses a cell for measuring the electrical conductivity comprising an outer electrode and an inner electrode which are concentrically arranged. The outer electrode comprises slots serving as inlet and outlet ports for the liquids to be measured. Similar measuring cells are also described in documents Nouvel Automatisme, vol. 29, no. 48, September 1984, Paris FR, pages 56 - 62, and Patent Abstracts of Japan, vol. 10, no. 344 (P-518)(2400), November 20, 1986. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric conductivity-measuring cell capable of measuring an electric conductivity of a liquid to be measured with high accuracy and inexpensively. To achieve this object, the present invention provides an electrical conductivity measuring cell as specified in claim 1. Preferred embodiments are described in the subclaims. An electric conductivity-measuring cell comprises a pressure container serving also as an outer electrode and provided with an inlet port of a liquid to be measured and an outlet port and an inner electrode provided within said pressure container. In this case, an inner surface of the pressure container and an outer surface of said inner electrode may be subjected to an electro-polishing, an oxidative passivating treatment, or a fluorinative passivating treatment. A cylindrical portion connected with the pressure container is provided with a stepped portion formed therewithin, a diffused-diameter portion being formed midway in the longitudinal direction of the inner electrode, a first insulating spacer comprising a cylindrical reduced-diameter member airtightly put in a separate cylindrical diffused-diameter member having a larger diameter and a smaller length as compared with those of said cylindrical reduced-diameter member in a tapered manner and a first sealing ring being put on one side of the inner electrode so that said first sealing ring may be closer to said diffused diameter portion of the inner electrode, a second sealing ring being put on a reduced-diameter portion of said first insulating spacer, and a stepped second spacer and a thrust bearing being put on the other side of the inner electrode so that said second insulating spacer may be closer to the diffused-diameter portion of the inner electrode, whereby the first sealing ring may be pressedly put between the first insulating spacer and the diffused-diameter portion of the inner electrode and the second sealing ring may lie pressedly put between said stepped portion of said cylindrical portion and the first insulating spacer by fastening a cap nut engaged with the cylindrical portion. In this case, the diffused-diameter portion of the inner electrode may be provided with a concave portion to fixedly hold the first sealing ring by means of said concave portion. And, in the above described electric conductivity-measuring cell, the liquid to be measured is introduced into the pressure container through said inlet port to be measued on the electric conductivity thereof within the time when it passes through a gap between the pressure container serving also as said outer electrode and the inner electrode. And, the liquid to be measured is discharged through the outlet port. And, in the above described electric conductivity-measuring cell, the stepped first insulating spacer is airtightly put in a separate cylindrical diffused-diameter member having a larger diameter and a smaller length as compared with those of the cylindrical reduced-diameter member in a tapered manner and comprises the reduced-diameter portion and the diffused-diameter portion, so that the diffused-diameter portion and the reduced-diameter portion can be individually finished, in particular both end faces of the diffused-diameter portion as sealing surfaces of the first insulating spacer can be mirror-finished. Accordingly, it is unnecessary to press the sealing rings by an excessive power and thus the first insulating spacer is not damaged. In addition, in the case where the diffused-diameter portion of the inner electrode is provided with a curved concave portion on a sealing surface thereof to fixedly hold the first sealing ring, not only an airtightness can be improved but also a positional relation between the inner electrode and the pressure container as the outer electrode can be fixedly set at a desired positional relation, so that the measurement can be achieved in higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention is shown in Figs. 1 to 10, in which Fig. 1 is a longitudinal sectional view showing an electric conductivity-measuring cell; Fig. 2 is a longitudinal sectional view showing a construction of essential parts of said cell; Fig. 3 is a disintegrated perspective view showing a construction of an inner electrode and a sealing construct ion; Fig. 4 is a drawing showing one example of a first insulating spacer; Fig. 5 is a drawing showing a sealing structure between said first insulating spacer and a diffused-diameter portion of said inner electrode; Fig. 6 is a circuit diagram showing one example of an electric construction in the case where an electric conductivity is measured by the use of said cell; Fig. 7 is a drawing showing one example of a detected output; Fig. 8 is data showing an airtightness of the cell; Fig. 9 is a diagram showing a relation between a concentration of impurities and an electric conductivity in case of liquefied hydrogen chloride; and Fig. 10 is a diagram showing a relation among a quantity of impurities and a temperature and said electric conductivity. An example of another electric conductivity measuring cell is shown in Figs. 11 to 13, in which Fig. 11 is a longitudinal sectional view showing an electric conductivity-measuring cell; Fig. 12 is a longitudinal sectional view showing a construction of essential parts of said cell; and Fig. 13 is a disintegrated perspective view showing a construction of an inner electrode and a sealing construction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 is a longitudinal sectional view showing an electric conductivity-measuring cell A (hereinafter referred to as a cell) according to a preferred embodiment of the present invention. Referring to Fig. 1, reference numeral 1 designates a pressure container serving also as an outer electrode serves as an electrode on the side of a lower impedance in an alternating bielectrode method and is provided with an inlet port 2 of a liquefied gas to be measured on a lower side thereof and an outlet port 3 of said liquefied gas on an upper side thereof. Said pressure container 1 is made of corrosion resistant metals, such as stainless steels, and an inner surface of the pressure container 1 is subjected to an electro-polishing, an oxidative passivating treatment or a fluorinative passivating treatment to be improved in chemical resistance and corrosion resistance. And, the pressure container 1 has a highly airtight construction, as detailly described later. Said inlet port 2 is connected with a gas-liquefying apparatus or a liquefied gas cylinder (not shown) through a coupling 4. In addition, said outlet port 3 is connected with pipings to an apparatus for producing semiconductors and the like (not shown) through a coupling 5. And, reference numeral 6 designates a cylindrical member electrically and mechanically connected with the pressure container 1 and provided with a cylindrical hole 7 opened at one end and a hole 8 having a diameter smaller than that of said cylindrical hole 7 connected with the cylindrical hole 7 formed therewithin and a tapped portion 9 formed on an outer circumeference thereof, as shown also in Fig. 2. Also an inner surface of said cylindrical member 6 is subjected to an electro-polishing, an oxidative passivating treatment or a fluorinative passivating treatment. Reference numeral 11 designates an inner electrode arranged concentrically with the pressure container 1 in an upper space within the pressure container 1. That is to say, in said cell A used in this preferred embodiment, a measuring electrode is composed of the pressure container 1 serving also as said outer electrode and said inner electrode 11 arranged in a highly insulating connection with the pressure container 1. And, it is necessary to determine a cell constant of said measuring electrode depending upon a sample but this cell constant is determined by an inner surface area of the pressure container 1 in a portion where the pressure container 1 and the inner electrode 11 are opposite to each other, an area of an outer surface, with which the inner electrode 11 is connected, and a distance from the pressure container 1 to the inner electrode 11. The inner electrode 11 is, as shown also in Figs. 2, 3, provided with a hollow member 12 opened on the side of one end and closed on the side of the other end and a diffused-diameter portion 13 having a diameter smaller than an inside diameter of the cylindrical member 6 formed in a midway portion in the longitudinal direction. An outside diameter of said diffused-diameter portion 13 of the inner electrode is set so that a clearance having an appointed high insulating power may be formed between the inner electrode 11 and said inner surface of the cylindrical member 6 under the condition that the inner electrode 11 is arranged within the pressure container 1, as shown in Fig. 1. And, the inner electrode 11 is made of corrosion resistant metal, such as stainless steel, and said outer surface of the inner electrode 11 is subjected to an electro-polishing, an oxidative passivating treatment or a fluorinative passivating treatment. In addition, the inner electrode 11 is provided with a tapped portion 14 formed at an end portion on the opened side thereof and a temperature sensor 15 is inserted into said hollow member 12 from the opened side until the vicinity of a closed portion. Said temperature sensor 15 is inserted into an inside of the hollow member 12 of the inner electrode 11 and not brought into direct contact with a liquefied gas, so that it is not necessary to subject the temperature sensor 15 to a chemical resisting treatment, a corrosion-resisting treatment and the like. Furthermore, hereinafter a reduced-diameter portion from the diffused-diameter portion 13 of the inner electrode to an end portion on said closed side is referred to as an inward portion 16 of the inner electrode and a reduced-diameter portion from the diffused-diameter portion 13 of the inner electrode to an end portion of the opened side is referred to as an outward portion 17 of the inner electrode. Reference numeral 18 designates a C-ring as a first sealing ring made of metals, such as nickel, and put on said inward portion 16 of the inner electrode so as to be adjacent to one side of the diffused- diameter portion 13 of the inner electrode. Reference numeral 19 designates a first stepped insulating spacer put on the inward portion 16 of the inner electrode and composed of a cylindrical reduced-diameter member 20 airtightly put in a separate cylindrical diffused-diameter member 21 having a larger diameter and a smaller length as compared with those of said cylindrical reduced-diameter member 20 in a tapered manner and comprises a reduced-diameter portion 19A and a diffused-diameter portion 19B. A construction of said first insulating spacer 19 will be below described in detail with reference to Figs. 3 and 4. The most part of a trunk portion of the reduced-diameter member 20 is formed so as to have an outside diameter slightly smaller than a diameter of said hole 8 provided between the pressure container 1 and said cylindrical member 6 but a tapered surface 23 is formed so as to be thicker toward the end portion side over a certain length from the side of one end. And, the reduced-diameter member 20 is provided with a through hole 24 having a diameter slightly larger than that of the inward portion 16 of the inner electrode at a center of an axis thereof. In addition, said diffused-diameter member 21 has an outside diameter slightly smaller than that of the hole 7 of the cylindrical member 6 and is provided with a through hole 26 surrounded by a tapered surface 25 corresponding to said tapered surface 23 of the reduced-diameter member 20. The reduced-diameter member 20 and the diffused-diameter member 21 are made of highly insulating materials such as ceramics. And, outer surfaces including both end faces of the reduced-diameter member 20 and the diffused-diameter member 21 are subjected to a mirror-polishing, in particular said both end faces 27 and 28 of the diffused-diameter member 21 are subjected to a high mirror-polishing so that Ra (mean roughness on a central line) may be reduced to for example 0.08 µm or less and a surface accuracy may be improved to an extent of for example 0.5 µm or less. In addition, the tapered surfaces 23 and 25 of the reduced-diameter member 20 and the diffused-diameter member 21 are improved in airtightness by a mutual rubbing. And, the reduced-diameter member 20 is inserted into said through hole 26 of the diffused-diameter member 21 from the side of reduced-diameter thereof and airtightly engaged in a tapered manner, as shown in Fig. 4, to form the stepped first insulating spacer 19 composed of said reduced-diameter portion 19A (consisting of said straight trunk portion 22 of the reduced-diameter member 20) and said diffused-diameter member 19B (substantially consisting of the diffused-diameter member 21), but, as enlargedly shown in Fig. 4, an end face 29 of the reduced-diameter member 20 is adapted to slightly (for example about 0.2 mm at maximum) project from said end face 27 of the diffused-diameter member 21. In short, both end faces 27 and 28 are adapted to form a slight step 30 therebetween. The reduced-diameter portion 19A of the first insulating spacer 19 having the above described construction is, as shown in Figs. 1, 2, inserted into the hole 8 of the cylindrical member 6 so that a pointed end thereof may arrive at the vicinity of the outlet port 3 of the pressure container 1. Although the cell constant is determined by said areas of the inner and outer electrodes and said distance from the inner electrode to said outer electrode, as above described, it can he regulated also by regulating a length of the reduced-diameter portion 19A of the first insulating spacer 19 in addition to regulating a length of the inner electrode 11. In addition, the reduced-diameter portion 19A reduces a contribution to the cell constant in said portion serving as a stagnant portion of the liquefied gas in the cell by increasing a substantial length between the inner electrode and the outer electrode in said portion positioned above the outlet port 3 within the pressure container 1 to improve an accuracy of measurement of an electric conductivity meter. Referring to Figs. 1 to 3, reference numeral 31 designates a C-ring as a second sealing ring made of metals such as nickel put on the reduced-diameter portion 19A. Reference numeral 32 designates a second insulating spacer put on said outward portion 17 of the inner electrode so as to he adjacent to the other side of the diffused-diameter portion 13 of the inner electrode, composed of a reduced-diameter portion 33 having a diameter slightly smaller than that of the hole 7 of the cylindrical member 6 and a diffused-diameter portion 35 having a diameter larger than that of said reduced-diameter portion 33 but slightly smaller than an inside diameter of a cap nut 34 screwed on the cylindrical member 6, and provided with a hole 36 having a diameter slightly larger than that of the outward portion 17 of the inner electrode passing therethrough. And, also said second insulating spacer 32 is made of highly insulating materials, such as ceramics, and an outer surface including both end faces of the second insulating spacer 32 is subjected to a mirror-polishing. Reference numeral 37 designates a thrust bearing and reference numeral 38 designates a voltage terminal for applying a voltage to the inner electrode 11. One example of procedures for arranging the inner electrode 11 within the pressure container 1 will be below described. The first sealing ring 18 is put on the inward portion 16 of the inner electrode 11 with the temperature sensor 15 inserted into the hollow member 12 so as to be adjacent to one side of the diffused-diameter portion 13 of the inner electrode and then the first sealing ring 18 is put on the first insulating spacer 19. And, the second sealing ring 31 is put on the reduced-diameter portion 19A of the first insulating spacer 19 while the second insulating spacer 32 is put on the outward portion 17 of the inner electrode 11 so as to be adjacent to the other side of the diffused-diameter portion 13 of the inner electrode and then the thrust bearing 37 is put on the second insulating spacer 32. The inner electrode 11, on which the respective members have been put in the above described manner, is inserted into the pressure container 1 with the side of the closed portion as the head through the cylindrical member 6. And, the cap nut 34 is put on the cylindrical member 6 to be screwed up. When the cap nut 34 is screwed up, a torque in the direction of rotation is let escape by an action of the thrust bearing 37 and thus a force acts merely in the direction shown by an arrow B in Fig. 1, whereby the first sealing ring 18 is strongly put between one side of the diffused-diameter portion 19B of the first insulating spacer 19 and the diffused-diameter portion 13 of the inner electrode and the second sealing ring 31 between a stepped portion 6a (refer to Fig. 2) of the cylindrical member 6 and the other side of the first insulating spacer 19 without damaging the sealing portion. As a result, the inner electrode 11 is held within the pressure container 1 concentrically with the pressure container 1 and the rings 18, 31 are evenly smashed to seal up the inner electrode 11 and the first insulating spacer 19 by means of the ring 18 and seal up the cylindrical member 6 of the pressure container 1 and the first insulating spacer 19 by means of the ring 31, whereby maintaining an airtightness within the pressure container 1. And, in this preferred embodiment, as shown in Fig. 5, the diffused-diameter portion 13 of the inner electrode is provided with a concave portion 39 having for example a curved section at a portion corresponding to the first sealing ring 18 on the sealing surface 13a thereof, so that the first sealing ring 18 can be held in said concave portion 39 with being engaged with said step 30 of the first insulating spacer 19 and thus a position of the sealing ring 18 can be fixedly set. Accordingly, not only the airtightness in this portion can be improved but also a position of the inner electrode 11 within the pressure container 1 can be fixedly determined, whereby a sure cell constant can be obtained and thus the highly accurate measurement can be achieved. In addition, in this preferred embodiment, as shown in Fig. 2, a concave portion 40 similar to the concave portion 39 is formed also in a step 6a of the cylindrical member 6 so as to fixedly set a position of the second sealing ring 31. Fig. 6 is a circuit diagram showing one example of an electric construction in the case where an electric conductivity is measured by the use of the cell A. Referring to Fig. 6, reference numeral. 41 designates a transmitter tranmitting an alternating signal of for example about 900 Hz which is applied to the inner electrode 11. And the pressure container 1 serving also as the outer electrode is earthed. In addition, reference numeral 42 designates a fixed resistance. Voltages at both ends of said fixed resistance 42 are put in a processor 43 as detected outputs. Fig. 7 shows one example of said detected outputs. However, in the case where the pressure container 1 is made of the stainless steel, if said alternating voltage of about 900 Hz is applied between the inner electrode and the outer electrode in the above described manner, the detected outputs are influenced by a dielectric constant to deteriorate a surmounting, whereby resulting an error. In order to prevent this, for example it is thought to coat the inner surface of the pressure container 1 with platinum but the expensiveness cannot be avoided. So, in said processor 43 a synchronism with a transmission frequency is conducted not to adopt portions, of which wave form is disturbed, as signals and to take out merely shaded portions in Fig. 7 as signals, whereby solving a problem that said surmounting is deteriorated. In addition, such the taking-out of signals is effective also in the case where the inner surface of the pressure container 1 is subjected to the electro-polishing and the like taking the corrosion resistance and the chemical resistance into consideration. Fig. 8 is data showing measured results on an airtightness of a cell A having the above described construction. As shown in Fig. 8, said cell A exhibits a slight increase of leakage rate at - 10 °C or less but this does not have substantial influence upon the measurement, that is it is found that the cell A is remarkably superior in airtightness. In addition, a plot at said leak rate of 1.5 x 10 -11 Torr· ℓ/s shows a detction limit of a He leak detector. In addition, in the case where the airtightness within the pressure container 1 is insufficient, not only the liquid to be measured introduced into the pressure container 1 is leaked out but also water outside of the pressure container 1 is diffused into the pressure container 1 by a differential concentration. As a result, not only an error of measurement is produced but also the piping system incorporated in the pressure container 1 is damaged. In a process, in which said Liquid to be measured is introduced into and guided out from the pressure container 1, its electric conductivity is measured by means of the pressure container 1 and the inner electrode 11 but the measured electric conductivity can be easily converted into a concentration of impurity by data showing for example a relation between a concentration of impurity in liquefied halogen gases and an electric conductivity with a logarithm of concentration of water as an axis of abscissa and a logarithm of electric conductivity as an axis of ordinate, as shown in Fig. 9, and thus a concentration of a very small quantity of impurities contained in the liquid to be measured can be measured. Because, in the case where water exists in the liquefied gases, such as liquefied hydrogen chloride, the electric conductivity is greatly changed due to the dissociation as shown by the following chemical equation (1). In addition, it goes without saying that the electric conductivity is greatly changed due to the dissociation of merely water. HCl + H 2 O ↔ H 3 O + + Cl - In addition, in the case where the impurities, such as H 2 SO 4 and SiO 2 , exist in liquefied hydrogen chloride, water is produced to be dissociated in the same manner as above described, as shown by the following chemical equations (2), (3), whereby greatly changing the electric conductivity, and thus the concentration of impurities, such as H 2 SO 4 and SiO 2 , can be measured in the form of a value converted into water. H 2 SO 4 + HCl ↔ HSO 3 Cl + H 2 O SiO 2 + 4HCl ↔ SiCl 4 + 2H 2 O Furthermore, Fig. 10 plots a relation between a temperature and an electric conductivity for two kinds of liquefied hydrogen chloride gas. In order to liquefy chemical substances, which are gaseous at normal temperature and pressure, they are pressurized or cooled but the electric conductivity is changed with a temperature-change, as shown in Fig. 10, so that it is desirable to keep said temperature constant or compensate the electric conductivity by the use of the data showing said relation between a temperature and an electric conductivity for the liquefied hydrogen chloride gas as shown in for example Fig. 10. In addition, not only the pressure container 1 is made of corrosion-resisting metal but also the inner surface of the pressure container 1 and the outer surface of the inner electrode 11 are subjected to the electro-polishing, the oxidative passivating treatment or the fluorinative passivating treatment, so that, even though the impurities are contained in the liquefied gases, the impurities are not adsorbed on and desorbed from the pressure container 1 and the inner electrode 11 as measuring electrodes and the cell A itself does not generate impurities and additionally also aggressive gases can be adopted as an object to be measured. In addition, in the above described preferred embodiment, in the cylindrical member 6 connected with the pressure container 1 the first sealing ring 18 and the first stepped insulating spacer 19 are put on one side of the inner electrode 11 so that the first sealing ring 18 may be closer to the diffused-diameter portion 13 of the inner electrode, the second sealing ring 31 being put on the reduced-diameter portion 19A of the first insulating spacer 19, the second stepped insulating spacer 32 and the thrust bearing 37 being put on the other side of the inner electrode 11 so that the second insulating spacer 32 may be closer to the diffused-diameter portion 13 of the inner electrode, and the cap nut 35 screwed on the cylindrical member 6 being screwed up to put the first sealing ring 18 between the first insulating spacer 19 and the diffused-diameter portion 13 of the inner electrode and the second sealing ring 31 between the stepped portion 6a of the cylindrical member 6 and the first insulating spacer 19, so that the high airtightness can be kept within the pressure container. For example, the leak rate is reduced to the detection limit (about 1.5 x 10 -11 Torr·l/s or less) of the He leak detector and thus not only the liquefied gas can be prevented from being leaked out of the pressure container 1 but also gases can be prevented from entering the pressure container 1 from outside. And, the stepped first insulating spacer 19 comprises the cylindrical reduced-diameter member 20 airtightly put in the separate cylindrical diffused-diameter member 21 having a larger diameter and a smaller length as compared with those of the cylindrical reduced-diameter member 20 in a tapered manner and comprises the reduced-diameter portion 19A and the diffused-diameter portion 19B, so that the diffused-diameter portion 19A and the reduced-diameter portion 19B can be individually finished, in particular both end faces 27 and 28 of the diffused-diameter portion 19B as the sealing surfaces of the first insulating spacer 19 can be mirror-finished. Accordingly, it is unnecessary to press the sealing rings 18 and 31 by an excessive power and thus the first insulating spacer 19 is not damaged. In addition, since the diffused-diameter portion 13 of the inner electrode is provided with the concave portion 39 on the sealing surface 13a thereof to fixedly hold the first sealing ring 18, not only an airtightness can be improved but also a positional relation between the inner electrode 11 and the pressure container 1 as the outer electrode can be fixedly set at the desired positional relation, so that the measurement can be achieved in higher accuracy. Furthermore, the thrust bearing 37 is provided between the cap nut 35 and the second insulating spacer 32, so that an advantage occurs also in that a turning force of the cap nut 35 does not directly act upon the second insulating spacer 32. And, the cell A can be used for not only measuring a very small quantity of impurities contained in the chemical substances, which are gaseous at normal temperature and pressure, but also measuring the electric conductivity in the control of water quality of industrial water, water supplied for a boiler, various kinds of washing water and the like, in particular suitably used for measuring the electric conductivity of liquids, which exist under the high-temperature and high-pressure condition, such as a primary cooling water in a nuclear power plant. Although the stepped first insulating spacer 19 to be put on the inward portion 16 of the inner electrode comprises the cylindrical reduced-diameter member 20 airtightly put in the separate cylindrical diffused-diameter member 21 having a larger diameter and a smaller length as compared with those of the cylindrical reduced-diameter member 20 in a tapered manner so as to form the reduced-diameter portion 19A and the diffused-diameter portion 19B in the above described preferred embodiment, a first insulating spacer 51 having the following construction may be used. That is to say, Figs. 11 to 13 show an example of another electric conductivity measuring cell. Said first insulating spacer 51 in this example comprises a reduced-diameter portion 52 having a diameter slightly smaller than that of a hole 8 provided between a pressure container 1 and a cylindrical member 6 and a diffused-diameter portion 53 having a diameter larger than that of said reduced-diameter portion 52 but slightly smaller than that of a hole 7 of said cylindrical member 6 and is provided with a hole 54 having a diameter slightly larger that of an inward portion 16 of an inner electrode passing therethrough. And, the first insulating spacer 51 is made of highly insulating materials, such as ceramics, and an outer surface thereof including both end faces is mirror-finished. And, the reduced-diameter portion 52 of the first insulating spacer 51 is, as shown in Figs.11 and 12, inserted into said hole 8 of the cylindrical member 6 so that a pointed end thereof may arrive at the vicinity of an outlet port 3 of the pressure container 1. Although a cell constant is determined by areas of the inner and outer electrodes and a distance from the inner electrode to said outer electrode, as above described, it can be regulated also by regulating a length of the reduced-diameter portion 52 of the first insulating spacer 51 in addition to regulating a length of the inner electrode 11. In addition, the reduced-diameter portion 52 reduces a contribution to the cell constant in said portion serving as a stagnant portion of the liquefied gas in the cell by increasing a substantial length between the inner electrode and the outer electrode in said portion positioned above the outlet port 3 within the pressure container 1 to improve an accuracy of measurement of an electric conductivity meter. Besides, in this example, other constructions are same as in the preferred embodiment, so that they are designated by the same reference numerals as in the preferred embodiment and their detail descriptions are omitted. And, the operation and effects by this example are almost same as those in the preferred embodiment, so that their detail description is omitted. As above described, according to the present invention, the electric conductivity of various kinds of liquid to be measured can be accurately and simply measured. And, the sizes of the respective portions, in particular the cell constant, are stabilized, so that the electric conductivity of the liquid to be measured can be accurately measured. And, in the case where the stepped first insulating spacer to be put on the inward portion of the inner electrode comprises the cylindrical reduced-diameter member airtightly put in the separate cylindrical diffused-diameter member having a larger diameter and a smaller length as compared with those of the cylindrical reduced-diameter member in a tapered manner, the reduced-diameter portion and the diffused-diameter portion can be separately finished, so that they can be more precisely and easily mirror-finished and thus not only the cell is more easy in assembly but also the the cell is remarkably improved in yield.

Claims: An electrical conductivity measuring cell for measuring the conductivity of a fluid, said cell comprising: a diffused-diameter portion (13) formed at a midway portion of a longitudinal direction of an inner electrode (11), a first sealing ring (18) and a first (19) insulating spacer, a second insulating spacer (32) fitted into an outward portion (17) of said diffused-diameter portion (13); a second sealing ring (31), and a nut (34) whose tightening allows said first sealing ring (18) to seal said inner electrode (11) and said first insulating spacer (19) and said second sealing ring (31) to seal a cylindrical member (6) and said first insulating spacer (19), characterized in that said first sealing ring (18) and said first insulating spacer (19) are fitted into an inward portion (16) of said diffused-diameter portion (13) in this order, said cylindrical member (6) is connected to a pressure container (1) which also serves as an external electrode, a stepped portion (6a) is provided at said cylindrical member (6), said second sealing ring (31) is located between said first insulating spacer (19) and said stepped portion (6a), and said first insulating spacer (19) comprises a cylindrical reduced-diameter member (20) airtightly put in a separate cylindrical diffused-diameter member (21) having a larger diameter and a smaller length as compared with those of said cylindrical reduced-diameter member (20) in a tapered manner. The electrical conductivity measuring cell as set forth in claim 1, characterized in that an inner surface of the pressure container (1) and an outer surface of said inner electrode (11) are subjected to an electro-polishing, an oxidative passivating treatment or a fluorinative passivating treatment. The electrical conductivity measuring cell as claimed in claims 1 or 2, characterized in that said first sealing ring (18) is put on one side of the inner electrode (11) so that said first sealing ring (18) may be closer to said diffused diameter portion (13) of the inner electrode (11), said second sealing ring (31) is put on a reduced-diameter portion (19A) of said first insulating spacer (19), and said second insulating spacer (32) and a thrust bearing (37) are put on the other side of the inner electrode (11) so that said second insulating spacer (32) may be closer to the diffused-diameter portion (13) of the inner electrode (11), whereby the first sealing ring (18) is pressedly put between the first insulating spacer (19) and the diffused-diameter portion (13) of the inner electrode (11) and the second sealing ring (31) is pressedly put between said stepped portion (6a) of said cylindrical portion (6) and the first insulating spacer (19) by fastening said nut (34) engaged with the cylindrical portion (6). The electrical conductivity measuring cell as set forth in claim 3, characterized in that the diffused-diameter portion (13) of the inner electrode (11) is provided with a concave portion (39) on a sealing surface (13a) thereof to fixedly hold the first sealing ring (18) by means of said concave portion (39).

Inventors: FUKUSHIMA RYOSUKE, ISHIHARA YOSHIO, OHMI TADAHIRO, FUKUSHIMA, RYOSUKE, ISHIHARA, YOSHIO, OHMI, TADAHIRO
Applicants: HORIBA LTD, NIPPON OXYGEN CO LTD, OHMI TADAHIRO, HORIBA, LTD., NIPPON SANSO CORPORATION, OHMI, TADAHIRO
Application year: 1992
Main classification: G01N27
IPC codes: G01N27, G01R27, G21C17