Patent ID: 8394449

Claim:
A method of calibrating a coating sensor device for measuring the amount of coating material on a coated sheet substrate, such coating sensor device having (i) a first basis weight gauge that includes a first radiation source and first radiation detector with a first gap therebetween for directing a first radiation along a first path towards a sheet substrate and for detecting the amount of first radiation transmitted through the sheet substrate wherein the transmitted first radiation being a measure of the basis weight of the sheet substrate and (ii) a second basis weight gauge that includes a second radiation source and second radiation detector with a second gap therebetween for directing a second radiation along a second path towards the coated sheet substrate after the sheet substrate had been coated and for detecting the amount of second radiation transmitted through the coated sheet substrate wherein the transmitted second radiation being a measure of the basis weight of the coated sheet substrate, wherein the amount of coating material on the coated sheet substrate is determined by measurements from the first and second basis weight gauges, the method comprising the steps of: (a) constructing a first calibration curve for the first basis weight gauge showing basis weight versus a function of transmission ratio, the first calibration curve being constructed without simulated dirt; (b) constructing as second calibration curve for the first basis weight gauge showing basis weight versus a function of transmission ratio, the second calibration curve being constructed with simulated dirt; (c) constructing a third calibration curve for the second basis weight gauge showing basis weight versus a function of transmission ratio, the third calibration curve being constructed without simulated dirt; (d) constructing a fourth calibration curve for the second basis weight gauge showing basis weight versus a function of transmission ratio, the fourth calibration curve being constructed with simulated dirt; (e) constructing a transformation curve based on the first calibration curve and the third calibration wherein the transformation curve predicts the basis weight measurement of the uncoated sheet which would be yielded by the second basis weight gauge if performing an actual measurement of the uncoated sheet; and (f) constructing a coat weight calibration curve that yields the basis weight of the coated material that is on the sheet substrate based on measurements from the first gauge and the second gauge.