Abstract: The measuring device comprises at least one measuring head having a reference part, which comprises a reference surface against which the moving web is supported. The reference surface comprises a measuring area in the inside of which the property of the web is measured. The reference part is arranged in connection with the measuring head in such a way that below the reference part, there is a substantially open air space. The measuring head comprises means for generating negative pressure in the air space below the reference part, and the reference part comprises holes formed through it, in such a way that the negative pressure generated in the air space affects through the reference part the space between the reference surface and the moving web in such a way that the web is supported against the reference surface substantially over the whole area of the measuring area.

Abstract: The measuring device is arranged to measure at least one property of a moving web. The measuring device includes at least one measuring head with at least one measuring element arranged in a flexible membrane that surrounds the measuring element and is arranged in connection with the measuring head such that the measuring element is movable by means of the flexible membrane perpendicularly to the moving web. The turning effect, which is caused by the pressure of the air conveyed with the moving web, and directed in the travel direction of the web at least in front of the measuring element on the web side of the flexible membrane, and turns the measuring element, is prevented by at least partly changing the amount and/or flow direction of the air conveyed with the web moving to the measuring element.

Abstract: The measuring device comprises at least one measuring head having a reference part, which comprises a reference surface against which the moving web is supported. The reference surface comprises a measuring area in the inside of which the property of the web is measured. The reference part is arranged in connection with the measuring head in such a way that below the reference part, there is a substantially open air space. The measuring head comprises means for generating negative pressure in the air space below the reference part, and the reference part comprises holes formed through it, in such a way that the negative pressure generated in the air space affects through the reference part the space between the reference surface and the moving web in such a way that the web is supported against the reference surface substantially over the whole area of the measuring area.

Abstract: The invention relates to a method of keeping a measuring window of a measuring device clean, and to a measuring device. Gas is blown onto the surface of the measuring window (2) of the measuring device (1). Gas is guided onto the measuring window (2) by a nozzle (3) which is substantially on the same level with the measuring window (2).