Process for manufacturing platinum resistance thermometer
A process for manufacturing a platinum resistance thermometer that is stable with reduced resistance value variation over service temperature range through clarification of a quantitative mechanism of resistance value variation with respect to the oxidation/reduction of platinum resistance wire. The process including the steps of (S 1 ) enclosing a purge gas containing an inert gas and oxygen in a protection tube provided with a thermosensitive part of platinum resistance wire; (S 2 ) raising the internal temperature of the protection tube to a temperature region in which the platinum is in reduced form at a partial pressure of oxygen in the purge gas as determined from platinum oxide formation free energy; (S 3 ) replacing the purge gas with an inert gas wherein oxygen is 1 kPa or below; and (S 4 ) sealing the protection tube under the replaced condition.
1. A process for manufacturing a platinum resistance thermometer provided with a thermosensitive part composed of platinum resistance wire or platinum resistance film in a protective tube, comprising the steps of:
enclosing a purge gas containing a first inert gas and oxygen in the protective tube provided with the thermosensitive part composed of platinum resistance wire or platinum resistance film;
raising the temperature inside the protective tube to a temperature region in which the platinum is in reduced form at a partial pressure of oxygen in said purge gas as determined from platinum oxide formation free energy; and
substituting said purge gas with a second inert gas in which oxygen is 1 kPa or less.
2. The process for manufacturing a platinum resistance thermometer according to claim 1 , further comprising the steps of: sealing said protective tube after said second inert gas has been substituted, such that the thermometer can be stably used to the temperature region at which the platinum is in reduced form at a partial pressure said oxygen at 1 kPa or less as determined from platinum oxide formation free energy.
3. The process for manufacturing a platinum resistance thermometer according to claim 1 , further comprising the steps of taking a gas containing oxygen as said purge gas and causing sufficient PtO 2 oxidation of the surface of said platinum resistance wire or platinum resistance film; and sealing said protective tube with the partial pressure of the oxygen in said purge gas adjusted to a partial pressure such that the use temperature region of the applicable platinum resistance thermometer falls within the temperature region of said oxidized form of PtO 2 , whereby the thermometer can be stably used in the temperature region of the applicable oxidized form by lowering the internal temperature of the protective tube, with the purge gas having been substituted with said second inert gas, to the temperature region of the oxidized form of PtO 2 , in which the partial pressure of the oxygen in said purge gas is 1 kPa or less as determined from the platinum oxide formation free energy.
4. The process for manufacturing a platinum resistance thermometer according to claim 3 in which said purge gas containing oxygen, is a gas of 100% oxygen in order to cause PtO 2 oxidation the surface of said platinum resistance wire or platinum resistance film.
5. The process for manufacturing a platinum resistance thermometer according to claim 4 , further comprising the steps of: sealing said protective tube after said second inert gas has been substituted, such that the thermometer can be stably used to the temperature region at which the platinum is in reduced form at a partial pressure said oxygen at 1 kPa or less as determined from platinum oxide formation free energy.
6. The process for manufacturing a platinum resistance thermometer according to claim 1 wherein said temperature region of platinum in reduced form and said temperature region in PtO 2 form are determined as a function of respective oxide formation free energies.
7. The process for manufacturing a platinum resistance thermometer according to claim 6 , further comprising the steps of: sealing said protective tube after said second inert gas has been substituted, such that the thermometer can be stably used to the temperature region at which the platinum is in reduced form at a partial pressure said oxygen at 1 kPa or less as determined from platinum oxide formation free energy.
8. The process for manufacturing a platinum resistance thermometer according to claim 1 wherein said first inert gas with oxygen of 1 kPa or less that is substituted is an inert gas with roughly 0% or trace amounts of oxygen.
9. The process for manufacturing a platinum resistance thermometer according to claim 8 , wherein a substance obtained by passing a specified highly pure inert gas through an oxygen getter is used as said first inert gas in which oxygen is roughly 0%.
10. A platinum resistance thermometer manufactured by of the manufacturing process according to claim 1 .