What are the cause of the effect of glass thermometer use?

Glass thermometer to measure temperature, the main source of the uncertainty of measurement, basically can be divided into two broad categories. One kind is glass thermometer when dividing or verification by the uncertainty of the standard itself and the standard equipment. Another source of uncertainty is one of the characteristics of glass thermometer and testing methods. Main performance for 6: one, the influence of people reading in the thermometer read value, if the line of sight of the eyes and the thermometer is not vertical groove, read the value will be high or low. For mercury thermometer, can by positive and the negative two aspects, and take the average deviation to eliminate or reduce the readings. Two, rod displacement influence on value because of the glass is heated to produce thermal expansion of the thermometer, lead to the internal standard thermometer scale and the relative position of capillary will produce tiny change, thus affecting temperature value, become a component of uncertainty of measurement. In general there are thermal expansion of the component can be ignored. Three, capillary uneven on the influence of value for glass thermometer at fixed point scale, calibration and verification, was conducted on the several provisions of the point. The dividing and verification method based on the capillary as a uniform, but it's actually not the case. Due to the capillary pore size is not uniform, can cause small interval scale error. Thermometer for accuracy is not high, the error is negligible, but for one, second-class standard mercury thermometer must be revised. Four, with liquid column of values in theory, the influence of total immersion type thermometer and bureau of immersion type thermometer use conditions, it shall conform to the degree of condition. But sometimes due to the limitation of conditions, full immersion bureau immersion method used to do, to reveal the influence of the fluid column will cause thermometer low value. Bureau of immersion will show liquid column in dividing with when using environmental temperature is different, impact on value. The above two cases the effects on the temperature measurement, must through the show liquid column temperature correction to eliminate this effect. Five, the time lag influence on measuring the time delay error of the thermometer expressed as a time constant. Time constant is the temperature up or down to the final value and value for the difference between the initial value of 62. 3% of the required duration. Time constant and the temperature between the type, length, thermal bubble shape and the thickness of the glass, and also with the surrounding measured medium, uniform and whether the kinds of liquid or gas. Because the thermometer has time lag error, so in use or test temperature and time must be thermometer with real measured medium reaches thermal equilibrium before reading. Six, zero change on the influence of the zero value for change is caused by the heat after effect of glass. When the temperature of the glass thermal bubble felt gradually rises, the glass molecules arranged it, temperature increase makes glass thermal bubble volume increase, if remove the thermometer from high temperature medium at this moment, all of a sudden drop in temperature can make glass molecules rearrange and couldn't keep up with the change of temperature, so that the temperature of thermal bubble volume cannot recover, this is the hot glass after effect. Due to heat after effect, thermal bubble size slightly bigger than a before use some, so will cause the lower than zero before use. Despite the lower zero is temporary, as the molecular structure of the glass slowly recovery, after thermal bubble volume will gradually recover, but need a long time. This is especially the standard thermometer thermometer zero cause of change. Zero change will directly influence on the temperature measurement uncertainty.