Method and apparatus for detecting and correcting an operating parameter during fiber web coating

In a method of direct or indirect application of a liquid or viscous coating medium onto a moving material web, specifically a paper or cardboard web, a layer of the coating medium is applied to the material web by use of an applicator unit. The coating result is then checked for deviations from the desired coating result. In the event that such deviations are detected, and in order to correct them, at least one applicator unit operating parameter is adjusted. The adjustment is made within a short time period, and with the material web running, from an initial operating parameter value that is in effect prior to detection of the deviation. Subsequently, the operating parameter is then reset to at least approximately the initial parameter value, whereby the adjustment and the subsequent resetting may be repeated if necessary. With this method, particularly with a free jet applicator, streaking in the coating profile of the applied layer, caused by dirt particles or other contaminations which have deposited themselves in the jet discharge opening of the free jet applicator, may be eliminated.