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Platinum rhodium thermocouple in the testing before the cleaning, acid, borax and notice what is _ instrument

by:JVTIA     2020-10-30
Cleaning precious metal thermocouples must be cleaned before test, to eliminate the hot electrode surface impurities, organic matter and oxide, thus reducing the hot electrode contamination, thermoelectric properties stable, prolong service life. Cheap metal thermocouple can often not to clean, when the electrode is dirty, can use wire brush to remove dirt and scale. Thermocouple don't need to be cleaned. Pickling is used to remove heat organic matter and part of the oxide on the surface of the electrode. Platinum rhodium thermocouple the pickling method of thermocouple plate into not less than 80 mm diameter circle in the concentration of about 30% of chemically pure hydrochloric acid solution soak 1 h or boil 15 min, take out after several times with distilled water is boiling, until thoroughly eliminate acid. Short type work with a series of platinum-rhodium thermocouple pickling method will thermocouple in no less than 60 mm diameter circle, on with the concentration of 30% ~ 50% of chemically pure hydrochloric acid solution soak 1 h or boil 15 min, take out after several times with distilled water is boiling, know thoroughly eliminate acid. Gold - Platinum thermocouple the pickling method of cleaning before unloaded thermocouple clamp, and cut off the thermocouple measuring the welding head, pickling of platinum and gold respectively. The platinum wire in about 30% of chemically pure hydrochloric acid or nitric acid solution soak 1 h, and take out after several times with distilled water is boiling, know thoroughly eliminate acid. Dip gold by 15 g, 100 g water, bleaching powder, 15 g, 5 g of salt and sodium bicarbonate and become the hot solution 2 h, then use 1 kg clean hot water add 25 g of sodium bicarbonate configuration solution. Thermocouples should be paid attention to during pickling acid concentration of 30% 50% is refers to the percentage of solvent for safe operation, should be add distilled water into the beaker when making up, and then pour acid. Borax washing borax is a kind of colorless, transparent crystal, heating is about 400 ℃, the dehydrated sodium tetraborate. The melting point of sodium tetraborate is very low, at 878 ℃ melting into the vitreous body. Contains sodium borate and boron bottles. Melting borax can be dissolved metal oxide and stable glass compound and the oxide generated, so that you can remove hot metal oxide on the surface of the electrode. Borax is a good metal cleaning agent. This method is to use borax has the ability of dissolving metal oxide at high temperature, thermocouple to precious metal surface cleaning. Thermocouple used after pickling and borax cleansing, new thermocouple needn't to clean borax. When cleaning, expand the hot electrode, the reference side suspension respectively in cleaning with platinum hook holder, two electrode Angle should be less as far as possible. Slowly adjust the input current, platinum rhodium - 10 Platinum thermocouple, platinum rhodium - 13 Platinum thermocouple bubbled into 10. 5 a current, platinum rhodium - 30 Platinum rhodium thermocouple 6 into 11 a current, make the hot electrode heating to ( 1100 ~ 1150) ℃, chemically pure borax piece of thermal contact reference electrode near end, melt borax into drops, suitable electrode flow, several after cleaning, the hot electrode will appear metallic luster. By repeated cleaning (if More than 3 times) Hot electrode black there is still a serious phenomenon that appearance is unqualified, not to show his value verification. Borax, after cleaning to reduce electric current and cut off the power supply should be slowly, take thermocouple, again into the corresponding circle, into the distilled water to boil, know the dissolve vitreous material on the electrode. Platinum rhodium thermocouple just for platinum borax wash, according to the above method into the current to 10. 5a。 Don't for borax clean rhodium wire. Note ( 1) Hot with platinum electrode hook should have a good contact; ( 2) Hanging hot electrode, should make the Angle is small, as far as possible to reduce the thermal stress electrode, make the melting borax easy electrode flow; ( 3) Should strictly control the heating temperature. Temperature is too low, melting borax condensation easily, affect the cleaning effect; Temperature is too high, the electrode grain growth, reduce the service life.
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