The characteristics of the gas pressure type thermometer and use the matters needing attention

Gas pressure type thermometer bulb in the changing process of gaseous medium is equivalent to a constant volume heat process, the amount of gas under the condition of fixed volume for heating or cooling. By the second law of thermodynamics: gas P ₁ / P ₁ ₂ = T/T ₂ pressure P and temperature T is linear, the relationship between the uniform and its scale is equal. Gas pressure type thermometer heat medium is commonly nitrogen, its stable physical and chemical properties, and a linear relationship between temperature and pressure, pressure is not due to a sharp increase with the rising of temperature. So that the upper limit of the thermometer temperature relative to the upper limit temperature of the steam pressure type thermometer is much higher, generally is 500 ℃ Around 600 ℃. If the gas pressure type thermometer original charging - high in the system, capillary liquid column in the height of the system error is relatively small. So the effect of liquid column height can be neglected. For gas pressure type thermometer, the initial filling pressure inside the closed system is higher. So the atmospheric pressure fluctuations will not cause too much additional error. For gas pressure type thermometer, if heat medium and the coefficient of expansion of capillary material, spring tube material is different, can produce error of measurement environment temperature changes. In order to reduce this error, the manufacturer of a kind of practice is another reload a compensation of capillary and spring tube. This method can also compensate capillary tube and spring error caused by ambient temperature changes, but its cost is higher; Another method is the spring tube free end with the introduction of a bimetallic strip between transmission amplification mechanism. Environmental temperature change, bimetallic strip produce corresponding deformation, in order to compensate for spring tube around the error due to environment temperature change. And one way is to place a thin metal wire in the capillary, when the environment temperature changes, the inner wall of the capillary and wire ring which is formed by the empty asked between internal volume change instead of just the volume change of the liquid is equal, in order to compensate the temperature of the capillary additional error. The simplest approach is to use common increase temperature tolerance to reduce the error. Thermometer bulb volume is large, so large thermal inertia. Before the article has introduced the features and the use the matters needing attention of steam pressure type thermometer, as shown in table is steam pressure type thermometer and the difference between the gas pressure type thermometer, have a clear understanding of.