Patent ID: 8157890

Claim:
A filter assembly for electric cabinets, the filter assembly comprising a filter cloth, a conveying sump, a fan operating at a fan power and a flow-rate sensor; wherein the conveying sump comprises a wall with a Venturi-shaped hole in the wall; wherein the Venturi-shaped hole communicates with an interior of the electric cabinet; wherein the conveying sump connects the filter cloth to the fan and is between the filter cloth and the fan; wherein the flow-rate sensor is adjacent the Venturi-shaped hole in the conveying sump; wherein the flow-rate sensor has a thermal capacity such that the flow-rate sensor is self-heating in unmoving air; wherein the flow-rate sensor has a cooling capacity which changes as a function of air flow crossing the flow-rate sensor; wherein the flow-rate sensor determines the temperature of the flow-rate sensor at multiple times; wherein the difference between the temperatures of two of the multiple times is directly related to air speed in the hole; wherein the air speed in the hole is a function of the fan power; wherein the conveying sump is equipped with at least one opening for re-circulating internal air in the electric cabinet; and wherein the opening is separate from the inlet, outlet or Venturi-shaped hole.