HARDNESS SENSOR

PROBLEM TO BE SOLVED: To obtain a hardness sensor whose cost is reduced and which eliminates a bonding defect by housing an ion-sensitive membrane at the bottom part of an ion electrode chamber, forming an opening part in the bottom part, installing a base member and a casing on the opening part, and housing the ion-sensitive membrane which is formed by drying an ion-sensitive solution in it. SOLUTION: An ion electrode part 3 and a comparison electrode part 4 are built in an electrode body 2, and a cylindrical ion electrode chamber 5 and a comparison electrode chamber 6 are formed. Opening parts 7, 8 are formed in respective bottom parts of the electrode chambers 5, 6, and holes 9, 10 into which an internal electrode 11 for ions and an internal electrode 12 for comparison are inserted are made at their upper parts. An ion-sensitive membrane 15 is housed on the opening part 7. An ion-electrode internal liquid 16 and an external liquid to be measured are set to a continuity state regarding specific calcium ions through the sensitive film 15. A base member 21 which is composed of a Teflon filter is placed on the opening part 7, a cylindrical casing 21 is installed on it, an ion-sensitive solution in a definite quantity is injected into it from an injection container, and the solution is dried so as to be formed.