Experiences with an On-Press Densitometer in the Production on a Web-Offset Press.

An 8-channel, 4-filter web densitometer has been developed at the Technical Research Centre of Finland. The densitometer has been in productional use at a Finnish board printing plant for about six months. A short description of the microcomputer-controlled device has been given. The test targets for each of the inks and for each of the eight measuring heads may be positioned in relation to the image as desired and independently of the others. The co-ordinates of the test points are given by means of a keyboard. The instrument is equipped with two display units. One display unit shows the profile of the eight parallel densities either as absolute print density values or as deviations from the accepted density values. They are measured by the system after a make-ready. The second display is a 3-digit display giving an accurate density value of a selected measuring head and measuring filter. A short description of the microcomputer-controlled device has been given. The test targets for each of the inks and for each of the eight measuring heads may be positioned in relation to the image as desired and independently of the others. The co-ordinates of the test points are given by means of a keyboard. The instrument is equipped with two display units. One display unit shows the profile of the eight parallel densities either as absolute print density values or as deviations from the accepted density values. They are measured by the system after a make-ready. The second display is a 3-digit display giving an accurate density value of a selected measuring head and measuring filter. Experiences with the instrument in the web-offset press have been given based on the measurements made during normal production with the equipment.