ERRORS OF MEASURING TEMPERATURE WHILE REDUCING LINEAR DIMENSIONS OF LIQUID-IN-TUBE THERMOMETERS

The methodological bases  for  the study of  the systematic error of  temperature measurement by  liquid-in-tube thermometers  and microthermometers with  diminution  of  the  capillary  diameter,  that  is, when  passing  from  thermometers  to microthermometers, in the  field of predominance of gravitational forces over surface tension  forces, are given. The existence of components of the systematic total error of temperature measurement with help of such thermometers is established with different thermometric  liquids  (water,  mercury,  alcohol).  Their  relative  weight  varies  depending  on  the  conditions  of  calibration  and application, the peculiarities of manufacturing and used structural materials,  their compatibility and wetting.  It  is shown that  the change in the linear dimensions of the thermometers, in particular their reduction in micro size, leads to the strengthening of some components  and  the  weakening  of  others.  The  equation  of  motion  of  a  thermometric  fluid  in  a  capillary  with  a  number  of parameters is derived. It is shown that the geometry of the inner surface of the capillary can become a determining factor for the formation  of  the  component  of  the  systematic  error  of  the  so-called  dead  passage. The  content  of  the  two  components  of  the systematic error due to  the deterioration of  the conditions of movement of  the liquid  in  the capillary due  to changes  in its cross section  is  revealed. The value of  the  component of  the systematic  error, determined by  the drop  in  the  internal diameter of  the capillary due to technological deviations in its manufacture, is estimated at the level of up to 1 %.