| 摘要 |
The invention relates to a control system for the ventilation of a paper machine drying hood (10), by which both the exhaust-air stream (m2) diverted from the hood and the replacement air stream (m1) fed to the hood are measured and controlled. In the process, the moisture level and the temperature of the exhaust-air flow are measured. The control system comprises two control loops. With the first control loop (23, 24, 26, 27, 30, 31, 32, 33), the moisture level of the exhaust-air flow is measured and, by influencing the amount of exhaust air (m2), its moisture level is controlled to a predetermined value by a setpoint unit (33). With the second control loop (14, 15, 16, 17, 19, 20, 21, 22) of the control system, the 0 point of the difference between internal pressure and external pressure of the hood (10) to be ventilated, i.e. the so-called 0 level of the hood, is kept at a constant level by measuring the amount of exhaust air (m2), controlled by the first control loop, and setting the setpoint of the amount of replacement air (m1) of the second control loop to a value corresponding to the constant 0 level of the hood (10), determined in advance (Fig. 2) and introduced into the control loop or stored. <IMAGE>
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