pt100 platinum resistance: How to use the standard platinum resistance thermometer correctly?

pt100 platinum resistance: The standard platinum resistance thermometer is a precision measuring instrument that measures temperature based on the characteristic that the resistance value of metal platinum changes with temperature. It consists of a temperature sensing element composed of platinum wire, an insulating skeleton, a protective cover and a wire. The molybdenum wire wrapped around the skeleton adopts a stress-free structure, so that the temperature-sensing platinum wire can freely expand and contract when the temperature changes. Under the action of external forces, such as vibration and improper operation of transporting goods, the platinum wire will deform. All parts of the platinum wire are stressed. When the temperature is above 0.01°, the resistance value of the platinum wire will increase, forming this deformed platinum wire in a stable state. Therefore, deformation and stress are important factors that lead to the unstable resistance value of the standard platinum resistance thermometer.

There are no special regulations internationally on how to properly use and maintain the standard platinum resistance thermometer. Based on decades of production experience and a large amount of reference data, it is important to keep the platinum wire temperature sensing element in a stress-free state as much as possible and try to maintain this state in the future.

1. The standard platinum resistance thermometer should be stored in a special box equipped with a thermometer when it leaves the factory. When taking out or putting in, the right hand should hold the handle of the thermometer and the left hand should hold the lead to avoid shaking. Violent shaking will cause stress on the platinum wire and cause the Rtp resistance value to change. Regardless of whether any temperature measuring medium is inserted, first wipe the thermometer with an alcohol cotton ball for several times. After cooling, slowly insert the thermometer into the measured medium. 2. When inserting the standard platinum resistance thermometer into the zinc point furnace, first insert the thermometer into the annealing furnace at 420° for preheating, and then slowly insert the thermometer into the zinc point furnace, and start measuring after reaching thermal equilibrium. The purpose of this operation is to protect the thermometer and make the zinc solidification temperature platform flatter and longer. When the standard platinum resistance thermometer is measured in a water triple point bottle, the thermometer at room temperature should be precooled in a precooling tube for 5-10 minutes, and the measurement should be started after reaching thermal equilibrium. Note that the current passing through the standard platinum resistance thermometer during measurement is 1mA. 3. When using a water tank or oil tank as a temperature measuring medium, the thermometer should be fixed with a wooden clip to avoid damage to the thermometer when stirring the water tank, but the clip should not be too tight. After measurement, take out the thermometer and wipe it with a soft cloth, especially after the thermometer is used in the oil tank, otherwise the outer tube of the thermometer is easily contaminated, and the oil on the outer wall of the thermometer will turn black due to annealing, and it will also contaminate the annealing furnace and the calibration furnace. At -50 ~ 0 °: the insertion depth of the standard platinum resistance thermometer should be 150-200 mm. When the temperature is above 50, the insertion depth of the standard platinum resistance thermometer is 200-300 mm. 4. High-temperature quenching should be avoided for standard platinum resistance thermometers. Rapid cooling will damage the thermometer, deform the platinum wire inside the thermometer, generate stress, change the resistance-temperature characteristics of the thermometer, and cause crystal absorption on the outer tube of the thermometer, thereby shortening the service life of the thermometer.

The platinum wire of the standard platinum resistance thermometer is slightly deformed, resulting in little change in the resistance value. After a short-term annealing at an appropriate temperature, the resistance value can be restored to the approximate value before deformation. However, if the large deformation is annealed at a higher temperature for a long time, the resistance value cannot be restored to the value before deformation. Therefore, the standard platinum resistance thermometer should always be checked for abnormalities or sagging of the platinum wire during use. In addition, the thermometer should always check the resistance value of the triple point of water. If it is found that the measured resistance value is very different from the value on the certificate, if the standard platinum resistance thermometer is greater than 5mK and the secondary standard platinum resistance thermometer is greater than 10mK, the thermometer should be sent for inspection in advance.