Presize moisture control system for a papermaking machine

Claim 2

In a machine for making a continuous web of paper having a size press, a main dryer section, a vernier dryer section between said main dryer section and said size press, a first valve for supplying steam to said main dryer section and a second valve for supplying steam to said vernier dryer section, a presize moisture control system comprising means providing a signal indicative of the actual moisture contained in said web at a location between said vernier dryer section and said size press, first comparator means for comparing said actual moisture signal with a moisture set point signal to provide a first error signal representative of any difference between said moisture signals, second comparator means for comparing the value of said first error signal with a signal indicative of a desired steam pressure for said vernier dryer section to provide a second error signal representative of any difference therebetween, means responsive to the value of said second error signal for positioning said second valve in accordance with the value of said second error signal, third comparator means for comparing the value of said first error signal with a pressure set point signal to provide a third error signal representative of any difference therebetween, a deadbanded controller responsive to upper and lower limits of said third error signal for providing an output signal representative of values above and below said levels, and fourth comparator means for comparIng the value of said output signal with a signal indicative of the steam pressure at said main dryer section to provide a fourth error signal in accordance with any difference therebetween for positioning said first valve in accordance with the value of said fourth error signal, whereby said vernier dryer section will operate between pressure limits determined by the dead band of said controller.

Claim 3

In a machine for making a continuous web of paper, a moisture control system comprising first means for supplying heat to a first portion of said web, first control means responsive to the actual moisture content of said web at a given location therealong for controlling said first heat-supplying means, second control means controlled by said first control means for controlling said second heat-supplying means when said actual moisture content has increased to a predetermined value, said second control means including a controller having a dead band representative of upper and lower limits for said first heat-supplying means to increase the flow of heat supplied by said second means when said upper limit is reached and to decrease the flow of heat when said lower limit is reached.

Claim 4

In a machine for making a continuous web of paper having a first dryer section and a second dryer section, first means for supplying heat to said first dryer section and second means for supplying heat to said second dryer section, a moisture control system comprising means providing a signal indicative of the actual moisture content of said web after said web has passed through said first and second dryer sections, first comparator means for comparing said actual moisture signal with a moisture set point signal to produce an error signal representative of any difference therebetween, second comparator means for comparing said error signal with a set point signal representative of a desired amount of heat to be supplied by said first dryer section to produce a second error signal representative of any difference therebetween, means for adjusting said second heat-supplying means to change the amount of heat supplied to said second dryer section so as to reduce any difference between said actual moisture signal and said moisture set point signal, third comparator means for comparing said first error signal with a signal representative of the heat supplied by said second dryer section to produce a third error signal for controlling the first heat-supplying means, and fourth comparator means for comparing said second error signal when above or below prescribed limits with a signal representative of the heat supplied by said first dryer section to produce a fourth error signal for controlling said second heat-supplying means.