The present invention relates to an electronic balance, and more particularly to an electronic balance devised so that the weighing pan encased in a weighing chamber can be protected from the air turbulence which may arise, when the door of the chamber is opened, owing to the temperature difference between the inside space of the chamber and the outer atmospheric space surrounding the chamber.
Almost all of the precision balances, not restricted to electronic ones, have their weighing pans encased in a weighing chamber so as to prevent atmospheric air streams and an operator's breathing from disturbing the stabilization of the weighing pans. The doors of the chamber are to be opened only when a sample to be weighed and balancing weights (in case of non-electronic mechanical balances) are placed on or removed from the weighing pans. A weight measuring operation is carried out with the doors kept closed.
Incidentally, in case of an electronic balance, the temperature in the weighing chamber is somewhat higher than that of the ambient atmosphere when the balance is kept ready to operate, because the electronic parts and circuits employed in the balance have been energized, therefore, when the door of the chamber is opened a temperature difference between the inside and outside of the chamber causes the warm air in the chamber to be exchanged with the cool ambient atmospheric air, and produces air turbulence in the chamber. In addition, since the cool air taken into the chamber is then warmed up by the warm floor of the chamber, there arise convectional air streams in the chamber after the door has been closed. The convectional air movement continues until a temperature equilibrium is established in the chamber. The air turbulence and convectional air movement, of course, cause the weighing pan to fluctuate, and as a result, make the balance take a long time to indicate a correct value of weight measurement.