The working principle of the negative pressure weighing cover (chamber) is to establish a pressure environment lower than the external atmospheric pressure in the room, so that the indoor air will not naturally flow to the outside, forming a negative pressure environment, which effectively prevents the leakage of indoor pollutants and reduces the risk of cross-contamination between different drugs. This ensures the cleanliness and safety of the room.

The negative pressure weighing cover chamber adopts the form of vertical unidirectional flow, and the direction of flow is vertical downward. Part of the clean air circulates in the work area and part is discharged to the nearby area, so that the work area produces a negative pressure environment. The air inlet of the negative pressure weighing hood must first undergo the pre-filtration of the initial effect filter and the medium effect filter, filter out the obvious large particle dust particles in the air stream, and preliminarily purify the air to protect the fan and the high efficiency filter.