What are the classifications of resistance thermometers?
Resistance thermometers are divided into four categories, namely:
1. Platinum thermal resistance thermometer (-200~850 °C)
Platinum thermal resistance is characterized by high measurement accuracy, good stability and reliable
performance. However, in a reducing medium, especially at high temperatures, it is easily stained by the
vapor reduced from the oxide and becomes brittle, and the resistance is changed. The relationship between
temperatures. In order to overcome the above disadvantages, the thermal resistance core should be installed
in the protective sleeve.
2. Copper thermal resistance thermometer (-50~150°C)
Industrially used copper thermal resistance to measure the temperature range of -5O ° C ~ +15O ° C, copper is
easy to purify, the price is much cheaper than platinum, the temperature coefficient of resistance is large and the
relationship is linear, so when making a thermal resistance of a certain resistance value, Compared with platinum,
if the length of the resistance wire is the same, the copper resistance wire is fine and the mechanical strength is
lowered. If the wire diameter is the same, the length is increased by many times and the volume is increased. In
addition, copper is easily oxidized above 100 ° C and has poor corrosion resistance, so the operating temperature
does not exceed 15 ° C.
3. Nickel thermal resistance thermometer (-60~180°C)
Nickel thermal resistance has a high temperature coefficient and sensitivity higher than that of platinum and copper.
It is commonly used to measure temperatures in the range of -6O ° C to +18 ° ° C. Due to the complicated manufac-
turing process of nickel thermal resistance, it is difficult to obtain the same nickel wire of α, so its measurement accuracy
is lower than that of platinum thermal resistance. The indexing number of the standardized thermal resistance currently
specified in China is Ni100, Ni300, Ni500.
4. Semiconductor thermistor thermometer
The semiconductor thermometer is a thermistor made of a metal oxide such as manganese, nickel, copper and
iron as a temperature measuring element, and has a shape of a bead shape, a circular shape, a washer shape
and a sheet shape,and a commonly used type 61 bead shape and Miniature beaded semiconductor thermistors.
The difference from the general thermal resistance is that it is the negative resistance temperature coefficient, the
temperature rises, the resistance decreases, and the variation range is also large. The temperature coefficient of
resistance α is -2 to -7 [[%]], which is 10~ larger than the metal thermal resistance. 100 times, therefore, a display
instrument with lower precision can be used.