Abstract:
The present invention provides an improved ion measuring composite electrode, measuring instrument incorporating the composite electrode, and a manufacturing method for forming a preform of a composite double glass pipe for forming the ion measuring composite electrode. A hollow inner pipe and a hollow outer pipe are axially aligned with an elongated member having liquid absorption capacity. The inner pipe is welded to the outer pipe to form an annular space there between for receiving reference electrode liquid. The elongated member insures electrical conductivity even in the presence of air bubbles so that the measuring instrument is operatable and an appropriate weld can be easily manufactured to improve productivity.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an improved ion measuring composite electrode, a measuring instrument incorporating such a composite electrode, and manufacturing method for a double glass pipe. 
   2. Description of Related Art 
   When measurement is performed for ion concentration of a sample, such as a pH value in a liquid, there has been used an ion measuring composite electrode constructed, as an integral one piece of a glass pipe serving as a measuring electrode and a glass pipe installed for a reference electrode. Generally, since an ion measuring composite electrode is relatively complicated in structure the resulting electrode can be relatively large in size, and it is difficult to manufacture an equivalent electrode that is small in size. 
     FIG. 4  is a schematic view showing a construction of a pH composite electrode  20  employing a double pipe structure, in which a responsive section for an ion concentration, such as a pH value, is formed as a long and narrow channel, and which has been developed to enable an ion concentration of a very small amount of a solution, such as a measuring specimen, to be measured. Furthermore,  FIGS. 5A and 5B  are views describing a manufacturing method for this type of double pipe structure. 
   In  FIGS. 4 , and  5 A and  5 B, a numerical symbol  2  denotes an outer pipe and  3  denotes an inner pipe of the double pipe structure. The outer pipe  2  is formed so that a distal end  2   a  thereof is sealed and is of an extremely narrow diameter, in the order of several mm, wherein a diameter of the proximal end  2   b  assumes a large value so as to be connectable to a body  20   a  side of the pH composite electrode  20 . Furthermore, a pH responsive section  4  made from a glass that is responsive to an ion, such as a pH value, is provided at the distal end  2   a  of the outer pipe  2 . 
   The distal end  3   a  of the inner pipe  3  is expanded at an outer diameter thereof and the expanded outer periphery is glass-welded to the inner peripheral surface of the outer pipe  2  to thereby create a separate space  5  in the interior of the inner pipe  3  for communicating with a pH responsive section  4 . The space  5  extends through the inner pipe  3  from an annular space  6  formed between the outer pipe  2  and the inner pipe  3  with the result that a construction is formed so that the space  5  can be filled with a measuring electrode internal liquid  7  and the space  6  can be filled with a reference electrode internal liquid  8 . 
   A liquid connecting section  9  made of a ceramic filling a small hole is formed in the outer pipe  2 , and is located near the lower end of the annular space  6  to communicate with the outside of the outer pipe  2 . An internal electrode  10  is immersed in a measuring electrode internal liquid  7  in the space  5 , and a reference electrode  11  is immersed in the reference electrode internal liquid  8  in the space  6 . Therefore, when a pH composite electrode  20  is constructed, a measurement of a pH value is enabled for even a very small amount of a measuring specimen when the liquid connecting section  9  and the pH responsive section  4  is immersed in the solution, as a measuring specimen. 
   In the fabrication of a double pipe structure with the outer pipe  2  and the inner pipe  3 , as shown in  FIG. 5A , a technique has been adopted in a prior art practice where the opening at the distal end  3   a  of the inner pipe  3  is expanded so that the outer periphery of the opening becomes close to the inner peripheral surface of the outer pipe  2  to form a flange section  12 . The inner pipe  3  thus worked is inserted into the outer pipe  2  with the distal end  3   a  as a leading head. At this time, the proximal end  3   b  of the inner pipe  3  is carefully fixed with a bushing or the like (not shown) so that the distal end  3   a  is aligned with the outer pipe  2   a  with respect to the center axes. Then, heat is applied on the outer peripheral surface of the outer pipe  2  using a gas burner  17  while rotating the outer and inner pipes  2  and  3  using a lathe or the like to thereby weld the flange section  12  to the inner peripheral surface of the outer pipe  2 . 
   In such a welding, however, a problem of a defective welding has arisen as shown in  FIG. 5B  since the inner pipe  3  can move to create a positional instability in the outer pipe  2  so that the outer pipe  2  and the inner pipe  3  are insufficiently aligned with each other with respect to the center axes at the distal ends  2   a  and  3   a  thereof. 
   Also a problem of transferring more heat than necessary from the gas burner  17  to the flange section  12  in those portions where the inner pipe  3  is closer to the outer pipe  2  can occur, which can cause fusion of the glass over a wide range to cause the outer pipe  2  to be placed in wide contact with the inner pipe  3  in a portion  12   a  apart from a target portion. Additionally, in those portions where the inner pipe  3  is positioned farther away from the outer pipe  2 , welding can produce a clearance  12   b , which can permit the spaces  5  and  6  to communicate with each other. This problem can occur since heat from the gas burner  17  is hard to be transferred to the flange section  12 . 
   In addition, since the outer and inner pipes  2  and  3  are formed in an extremely narrow offset, difficulty has accompanied the aligning of both the center axes. That is, not only is there a shift in a center axis between the distal ends  2   a  and  3   a  which is hard to visually recognize from outside the outer pipe  2 , but difficulty also arises in visual judgment on a value of a force imposed on a site where the flange section  12  is in contact with the inner peripheral surface of the outer pipe  2 , if any. Hence, even though the welding work is done with deliberate attention thereto and with extra time, a case can arise where a shift between the center axes is occurs, and defective weld happens, resulting in a poor production rate. 
   Moreover, a necessity exists for the interiors of the inner and outer pipes of the formed double pipe structure to be completely filled with an internal liquid, and with a decrease in diameters of the outer and inner pipes  2  and  3 , the space  6 , which is the gap between the outer and inner pipes  2  and  3 , can become too narrow; therefore, the reference electrode internal liquid  8  can be difficult to evenly spread within the space  6  to every part thereof and a bubble can be produced between the reference electrode  11  and the liquid connecting section  9  to cause an electrically open state, leading to a problem of disabling a measurement. In a case where the reference electrode internal liquid  8  decreases, a bubble can also be incorporated into the space  6  when the reference electrode internal liquid is supplemented. 
   Thus the prior art is still seeking both an improved method of manufacturing concentric small diameter glass tubes and a resultant improved ion measuring composite electrode with improved production rates. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in light of the above circumstances and it is an object of the present invention to provide a manufacturing method for a double glass pipe and an ion measuring composite electrode, not only making it easy to manufacture a glass composite pipe of a double structure for constructing an ion measuring composite electrode, but also capable of insuring a setoff space between an outer glass pipe and an inner glass pipe of a formed double structure is electrically conductive even if the presence of a bubble occurs in the space. 
   In order to achieve the above object, a manufacturing method for a composite double glass pipe of the present invention is characterized by an inner pipe and an outer pipe having a diameter whose lower section is designed so as to be narrower than that of the proximal end thereof, an opening at the distal end of the inner pipe is expanded so that the outer periphery of the opening becomes close to the inner peripheral surface of the outer pipe, a string-like or elongated member is wound on an outer peripheral surface of the inner pipe such as in the form of a spiral and the inner pipe is inserted into the outer pipe while holding a constant spacing between the inner pipe and the outer pipe around the inner pipe, and thereafter, the distal end of the inner pipe is welded to the inner peripheral surface of the outer pipe. 
   Therefore, the string-like member, wound on the outer peripheral surface of the inner pipe, can be elastically deformed and simultaneously brought into contact with the outer peripheral surface of the inner pipe and the inner peripheral surface of the outer pipe to thereby impose a force uniformly in every direction so as to expand a gap between the inner pipe and the outer pipe, thereby enabling neither play nor positional instability between the inner pipe and the outer pipe to occur. The gap between the inner pipe and the outer pipe is held at a constant value around the inner pipe with the help of the string-like member. That is, when the distal end of the inner pipe is welded to the outer pipe, the centers of the distal ends of the inner pipe and the outer pipe can be aligned with each other precisely. Furthermore, a worker can perform such centering between the inner pipe and the outer pipe with extreme ease and quickness with a result of effectively preventing any fusion over a wide range which can cause the outer pipe to be put into wide contact with the inner pipe in a portion except for a target region to be welded, thereby enabling a formation of a glass pipe in a double structure with a good production yield. 
   As a string-like member, there can be used, for example, a string such as a cotton string. A string capable of being elastically deformed to a predetermined extent is desirable in order to perform centering between the inner pipe and the outer pipe, and a string can employ other kinds of materials with sufficient elasticity and high water absorption capacity, for example rubber and sponge, both having being water absorption-treated, and having communicating air bubbles therein, and in addition, a net tube and water absorbing tube. 
   An ion measuring composite electrode of the present invention can include an outer pipe in which not only is a distal end thereof closed, but a diameter of a lower section is also narrower than that of a proximal end thereof, and which includes an ion responsive section and a liquid connecting section; an inner pipe in which a distal end thereof is welded to an inner peripheral surface of the outer pipe in a state where the inner pipe is inserted in the outer pipe to thereby form an annular space between the outer pipe and the inner pipe; and a string-like member, having a water absorption capacity, and disposed in the annular space in a state where the string-like member is wound on the inner pipe. 
   The string-like member having sufficient water absorption capacity is located in the annular space between the inner pipe and the outer pipe and thereby can absorb an internal liquid. With such a nature of the member, even if an air bubble is mixed into the annular space, electrical conduction through the space is still secured by transmission through the string-like member, which can serve as a salt bridge, in a practical sense, thereby enabling a measurement. Furthermore, it is possible to secure a flow path filled with the internal liquid in which the internal liquid is easy to flow through the string-like member, making it easy for the internal liquid to prevail in a narrow gap to every part thereof. 
   In addition thereto, since the string-like member works as a spacer between the outer pipe and the inner pipe because of its location in the annular space between the inner pipe and the outer pipe, the string-like member can contribute to an improvement in durability in even a double glass pipe structure formed in an extremely narrow way so as to enable a measurement of an ion concentration in a very small amount of a solution, as a measuring specimen. That is, there can be formed an ion measuring composite electrode excellent in durability, though it is small-sized by supporting the glass pipes and absorbing shock energy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings. 
       FIG. 1  is a view showing a construction of an ion measuring composite electrode of the present invention; 
       FIG. 2  is an exploded perspective view of a double glass pipe structure of the ion measuring composite electrode; 
       FIGS. 3A and 3B  are views disclosing a manufacturing method for a double glass pipe and workings thereof; 
       FIG. 4  is a view showing a construction of a prior art ion measuring composite electrode; and 
       FIGS. 5A and 5B  are views describing a manufacturing method for a double glass pipe structure of a prior art ion measuring composite electrode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the intention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. For example, details of a measuring instrument with a composite electrode are known and shown in  FIG. 4  and accordingly only the improved elements are set forth herein. 
   A description will now be given of details of the invention below with reference to the accompanying drawings. 
     FIG. 1  is a view showing one example of a construction of an ion measuring composite electrode  1  (in this example, a pH composite electrode) of an extremely narrow type according to the present invention.  FIG. 2  and  FIGS. 3A and 3B  are views describing a manufacturing method for the pH composite electrode  1 . In  FIGS. 1 ,  2 , and  3 A and  3 B, constituents denoted with the same symbols as respective constituents in  FIGS. 4 and 5  are equivalent to the respective constituents in  FIGS. 4 and 5 , and as such, detailed descriptions thereof are not repeated. 
   In a pH composite electrode  1  of the present invention, an elongated or a string-like member  13  with a water absorption capacity and a pre-determined elasticity is wound on an outer peripheral surface of the inner pipe  3 , for example, in the form of a spiral. Alternatively, other elongated material with sufficient water absorption capacity including sponge material can be used. The form of the member  13  can be altered to be a tube or an elongated net configuration to provide both spacing and liquid retention. 
   As string-like members  13  with a water absorption capacity and elasticity, there can be exemplified: a cotton string (a kite string) rich in hydrophlicity and with a proper elasticity slightly thicker than a gap between the outer pipe  2  and the inner pipe  3 . 
   An adhesive  14  adhering to an end  13   a  of the cotton string  13  is positioned in the vicinity of the distal end  3   a  of the inner pipe  3 , such as a silicon resin (for example, made by Shin-Etsu Chemical Industry Co., Ltd. with a trade name of KE-66) without an influence or interference on an reference electrode internal liquid. 
   As a method of winding the cotton string  13 , an end  13   a  of the cotton string  13  is attached to a position in the vicinity of the distal end  3   a  of the inner pipe  3  with the adhesive  14 , and the inner pipe  3  is, as shown with an arrow symbol A in  FIG. 2 , rotated while pulling the inner pipe  3  toward the proximal end thereof with a proper force. The cotton string  13  is cut almost at a position past a section where a diameter of the inner pipe  3  increases to adhere the other end  13   b  to the side surface of the inner pipe  3 . 
   Note that the end  13   a  of the cotton string  13  is desirably located at the closest possible point to the liquid connecting section  9  and the other end  13   b  is, while the inner pipe  3  is inserted into the outer pipe  2 , desirably disposed at a position just past a section where the cotton string  13  is sandwiched between the inner pipe  3  and the outer pipe  2 . 
   Not only is the inner pipe  3 , on which the cotton string  13  is wound, assembled so as to be aligned with the outer pipe  2  to provide concentric circles at the proximal end using assembly caps  15  and  16  shown in  FIG. 2 , but also the inner pipe  3  is, as shown in  FIG. 3A , inserted into the outer pipe  2  and thereby is brought into contact with the outer peripheral surface of the inner pipe  3  and the inner peripheral surface of the outer pipe  2  to slightly perform an elastic deformation of the cotton string  13 . At this time, the inner pipe  3  is guided in the insertion while performing centering so as to align the center of the inner pipe  3  with the center of the outer pipe  2  with certainty by a elastic deformation of the cotton string  13 . 
   Heat is then applied to a portion of the outer pipe  2  corresponding to the flange section  12  formed by expanding the opening of the distal end  3   a  of the inner pipe  3  so as to be close to the inner peripheral surface of the outer pipe  2 . The heat can be applied from the gas burner  17  or the like to an outer peripheral surface of the outer pipe  2 , thereby enabling the flange section  12  to be welded to the outer pipe  2 . 
   At this time, since the centers of the outer and inner pipes  2  and  3  are aligned with certainty through the elastic deformation of the cotton string  13 , no unbalanced transfer of heat occurs in the welding of the flange section  12  and the flange section  12  is properly welded at its outer periphery to the inner peripheral surface of the outer pipe  2 . A controlled separation can accordingly be realized between the space  5  in the inner pipe  3  and the annular space (gap)  6  sandwiched between the inner pipe  3  and the outer pipe  2 . 
   In a pH composite electrode  1  manufactured with this type of preform of composite glass tubes, the space in the inner pipe  3  is filled with a glass electrode internal liquid  7  and the annular space  6  is filled with the reference electrode internal liquid  8 . 
   At this time, since the reference electrode internal liquid  8  is not only absorbed in the bulk of the cotton string  13 , but also is attached to a peripheral surface thereof. A flow path  18  (see an enlarged view) in the form of a spiral filled with the reference electrode internal liquid  8 , as shown in  FIG. 3B , is formed around the cotton string  13  by a surface tension of the liquid. On the other hand, a discharge path  19  in the form of a spiral of air bubbles may be formed between pairs of windings of the cotton string  13 . That is, a pH composite electrode  1  of the present invention is wound with the cotton string  13  in the form of a spiral to thereby not only facilitate the reference electrode internal liquid  8  to be introduced into the annular space  6  in the double pipe formed in an extremely narrow way, but also to facilitate positioning air bubbles in the space  6 , if any is mixed therein. 
   Even if air bubbles are mixed into the space  6 , the flow path  18  filled with the internal liquid absorbed into the cotton string  13  and positioned around the periphery can serve as a salt bridge; therefore, no electric conduction is disconnected because of the location of bubbles, if any, between the liquid connecting section  9  and the reference electrode  11 . Therefore, if a bubble or bubbles are mixed into the space  6  by tilting the pH composite electrode  1  in a situation with a small amount of the reference electrode internal liquid  8  remaining therein, the measurement won&#39;t be disabled. 
   While in the examples, the double pipe structure is part of the pH composite electrode  1  having the pH responsive section  4  formed at the distal end, the present invention is not limited to a measurement on a pH value. The present invention can also apply to an ion measuring composite electrode with an ion responsive section suitable for measuring a concentration of any of a variety of various kinds of ions in a similar manner. Furthermore, in the above example, the electrode construction is exemplified in which the ion responsive section  4 , exposed to the space  5 , is formed at the distal end  2   a  of the outer pipe  2  and the liquid connecting section  9  is formed in a portion communicating with the annular space  6  in the vicinity of the ion responsive section  4 , 
   According to the present invention, not only is the manufacturing of a pH composite electrode  1  facilitated with a better product yield, but also a pH composite electrode  1  can be formed with adaptability even for the case of a mixing-in of air bubbles through a salt bridge effect by the cotton string  13  and therefore, a higher reliability. Note that by providing the shape of a string of almost uniform thickness and elasticity, the string-like member  13  is particularly suited for positioning of the inner pipe  3  with the outer pipe  2  with respect to the centers (centering), but the string-like member is not necessarily limited to natural or artificial fibers as a material and various modifications such as an elongated sponge can be considered. 
   While an elastic force of the string-like member  13  is desirably strong in order to assist positioning of the inner pipe  3  within the outer pipe  2  and further improves durability, various other kinds of material can be employed as long as the material does not adversely influence the internal liquid  8 . In addition, considering the welding of the flange section  12 , a certain degree of heat resistance is desirably imparted to the string-like member  13 . 
   Likewise, as long as the elongated or string-like member  13  is made of a material rich in water absorption capacity and hydrophilicity and can function as a salt bridge, there is no necessity that the string-like member be limited to fabric. 
   Furthermore, in order to perform sufficient centering of the inner pipe  3  with the outer pipe  2 , it is desirable that the string-like member  13  is densely wound in the form of a spiral, while in order to perform attraction and absorption of the internal liquid  8 , and removal of bubbles, it is desirable that the string-like member  13  is sparsely wound. Accordingly, in winding of the string-like member  13  described in  FIG. 2 , a possible modification can be considered where the string-like member  13  is densely wound at the distal end  3   a  and more sparsely wound toward the proximal end. 
   Moreover, the string-like member  13  can be comparatively densely wound in a first stage operation and when welding of the flange section  12  is completed, a density of the windings of the string-like member  13  is reduced by pulling it off the inner pipe  3 , thereby enabling the windings to be sparse. 
   With implementation of the present invention, precise centering can be ensured in welding glass pipes into a double structure, and a construction is obtained with a positional stability between the outer and inner pipes. Additionally, fusion over a wide contact area in portions different from a target portion can be prevented with the result of a better product yield and improvement of productivity. Since there is provided a string-like member with a water absorption capability between the inner pipe and the outer pipe, the internal liquid can be easily spread through the gap to every part thereof and even in a case where a bubble or bubbles are generated between the internal electrode and the liquid connecting section, the electric conduction is ensured, thereby enabling a measurement on an ion concentration. 
   Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the amended claims, the invention may be practiced other than as specifically described herein.