saett and device maetning foer of luftgenomslaeppligheten in a materialbana, saerskilt a loepande orbit in a paper mill

摘要

The invention relates to a method of measuring the air- permeability of a material web 7, in particular a continuous press felt of a paper machine. At a nozzle 2 which is brought to bear against the web 7, a pressure drop is brought about across the web and thus an air stream which depends on the air-permeability. The pressure drop is regulated to a constant value and, at this constant value, the size of the air flow is measured as a measure of the air-permeability. The air flow is measured by a vortex measuring device 3 which is connected to the nozzle and emits an output signal with a frequency which is proportional to the speed of the air flow. The pressure drop is regulated by a precision regulator 4 which, on its secondary pressure side, is connected to the input side of the vortex measuring device 3 and which is adjusted to preferably at least 20 kPa. The nozzle 2, the vortex measuring device 3 and the precision regulator 4 are guided as a unit designed as a measuring head 1 across the web 7 to measure a transverse profile of the air-permeability of the web 7 by means of the output signal of the vortex measuring device 3. A compressed air source 9 separate from the measuring head 1 is connected to the primary pressure side of the precision regulator 4. IMAGE