As a contact method temperature measuring element, the accuracy of the thermocouple directly affects the accuracy of the temperature value. For the platinum-rhodium thermocouple in use, and the recrystallization of the thermal electrode material under high temperature conditions, the temperature measurement error is caused by the change of the thermoelectric characteristics. Therefore, the platinum-rhodium thermocouple must be cleaned before the periodic verification to remove the impurities on the surface of the electrode. , improve its thermoelectric performance and prolong its service life. Taian Detu sincerely recommends the cleaning methods and steps of platinum-rhodium thermocouples for you:

The Platinum-rhodium thermocouple cleaning method and steps: acid cleaning and borax cleaning.

1. Pickling

The purpose of pickling is to use the oxidizing power of nitric acid to remove organic matter and general metal impurities on the surface of the hot electrode. The method is as follows: first, remove the platinum-rhodium thermocouple wire from the insulating measuring tube; secondly, coil the platinum-rhodium thermocouple bare wire into a circle slightly larger than 80mm in diameter and place it in a beaker; rinse it once with distilled water to remove the surface dust; Immerse the washed platinum-rhodium thermocouple bare wire in 30%-50% (by volume) chemically pure dilute nitric acid (or dilute hydrochloric acid) for one hour or boil for 15 minutes (nitric acid is not easy to boil), and rinse it with distilled water for several times. and boil to remove acidity completely and dry.

2. Borax wash

Borax is a good purifying agent, which can remove metal impurities and their oxides that are difficult to dissolve in acid attached to the electrode surface. The specific method is as follows: use cotton dipped in anhydrous alcohol to straighten the pickled platinum-rhodium thermocouple wire, hang the free end of the platinum-rhodium thermocouple on the cleaning and annealing rack, and the angle between the two hot electrodes is 30°, and then adjust the current, The thermocouple is heated to 1100 degrees Celsius (the platinum extremely bright temperature is about 1000-1050 degrees Celsius when measuring its temperature with an optical thermometer), the platinum wire with a diameter of 0.5mm is heated to the above temperature, and the current is about 10.5A (the diameter of the even wire is more Smaller, the smaller the incoming current, otherwise the high current may burn the hot electrode), touch the top of the free end with a little borax to melt the sodium tetraborate into droplets and flow down the electrode, and clean it for many times until the hot electrode glows. After cooling, place the thermocouple in a circle in a beaker, rinse and boil several times with distilled water to completely melt off the sodium tetraborate on the electrode. The purpose of borax washing is to clean the surface of the thermocouple and eliminate the stress inside the thermocouple, so that the metallographic phase is more regular.

After the platinum-rhodium thermocouple is cleaned, the insulating porcelain tube can be re-covered (the used thermocouple insulating porcelain tube will also be polluted, and it also needs process cleaning such as pickling and high-temperature roasting), and the thermocouple can be restored to its original state.

The DT1000 thermocouple cleaning and annealing device produced by Taian Dearto is a professional thermocouple cleaning device. The technical indicators meet and are better than the relevant regulations: "JJG75-1995" "JJG167-1995" "JJG141-2013" "JJG668-1997"