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Influence factors of glass thermometer use

Have read 8312013-9-25 21:47:58

 

Glass thermometer measurement temperature measurement uncertainty of several main source, basically can be divided into two categories. One kind is glass thermometer the degree or verification by the standard uncertainty of itself and standard equipment brings. Another source of uncertainty is glass thermometer characteristics and test method brings. Main show is have six: thermometer

A, personnel reading influence

In the reading thermometer value, if the line of sight of eyes and thermometer scribed line not vertical, read and value will be high or low. For a minute mercury thermometer, but through the positive and negative two aspects and take its mean value, in order to eliminate or decrease the deviation of reading.

Second, the scale of displacement and the influence of the value

Due to the thermometer glass after heated produce thermal expansion, lead to internal standard thermometer of scale and the relative position of the capillary can produce a small change, thus affecting temperature and value, become a measurement uncertainty component. Generally have produced by the thermal expansion of the component can be neglected.

Three, capillary uneven and value to the influence

Glass thermometer in scale fixed point, calibration and verification, there are several provisions on the point. This kind of indexing and verification method based on the capillary as uniform, but actual condition is not such. Due to the capillary aperture is not uniform, can cause small interval scale have error. For accuracy is not high thermometer, this error can be neglected, but for one, second class standard mercury thermometer must be corrected.

Four, show liquid column to and the influence of the value

In theory, fully submerged thermometer and bureau immersion thermometer using conditions, should with dividing conditions consistent. But sometimes because of the limit of the conditions, fully submerged to do bureau immersion type use, revealing the influence of liquid column can cause thermometer and low value. Bureau immersion type will also due to show liquid column in the indexing with use in different environmental temperature, the influence and value. The above two kinds of circumstances to the impact of temperature, must through the show liquid column temperature correction to eliminate the influence.

Five, time lag the effects on the measurement

Thermometer time lag error in time constant said. Time constant is temperature and value rise or fall to end value and initial value only 62.3% of the difference between the required duration.

Time constant and the temperature of the room type, length, thermal bubble of shape and thickness of the glass relevant, and at the same time and the measured medium around the situation, the liquid or gas species and whether the uniform. Due to the thermometer have time hysteresis error, so in use or test temperature time, must will thermometer and measured medium really achieve heat balance when square reading.

Six, zero change on and the influence of the value

Zero change is the glass of heat caused by the after effect. When the glass temperature bubble felt gradually increasing temperature rises, and the glass molecules will then rearrange, temperature makes the glass temperature bubble volume increase, at this time if the thermometer from high temperature medium take out, suddenly cooling can make glass molecular rearrangement and couldn't keep up with the change of the temperature, so that the temperature heat bubble volume can't restore, this is a glass of hot aftereffect. Because of the heat after effect, make the temperature bubble of volume ratio before using some of the larger, so will cause the zero than before using reduced. Although the zero lower is temporary, later with the molecular structure of glass  thermometers, thermal bubble volume will recover gradually, but need quite a long time. This is the thermometer especially standard thermometer zero change causes. Zero changes will directly on the temperature of the uncertainty of measurement effect.