Patent GB-1371110-A (GB)
Title: Device for the regulation of the operational conditions in drying  plants particularly for agricultural crops
IPC: F26B21/06
Filed: 1971-11-24
Abstract: 1371110 Controlling the operation of drying plant CLAAS MASCHINENFABRIK GmbH Gebr 24 Nov 1971 [26 Nov 1970] 54504/71 Heading F4G An agricultural crop drum drier is controlled by a control system in which the temperature Te of the existing gas is compared at 3 with a preset value Tsoll to give a difference signal #Te which controls by a regulator R 1  the output of a burner 5, the output Q of the burner 5 is compared with a pre-set value Qp to give a difference signal #Q which controls by a regulator R 2  the input rate Gw of the crop into the drier, and the entry temperature Ta of the heated drying air is compared with a pre-set value TR and also is maintained constant by a regulator R 3  in a separate circuit. The input rate Gw of crop may be compared at 11 with the rate Gwd determined by the signal #Q, so that a difference signal #Gw controls the regulator R 2 , or the signal #Q may control R 2  directly. Crop is fed into the drum drier 1 by means of a variablespeed endless belt 13 co-operating with a metering device 10 and with a moisturemeasuring or weighing device 9, and the exiting gas passes through a separator 2. Control circuit of Fig. 3.-The exit gas temperature Te is measured in the separator 2 by a resistance thermometer and amplified at 15 to give a signal which is compared at 3 with a preset value selected by a potentiometer 16, and the difference signal #Te is fed via voltage stabilizer 17 to a regulator 19 controlling a servomotor 20 which adjusts the fuel and air supply to the burner 5. A signal representing the adjustment of the servomotor 20 (corresponding to output Q) is fed from potentiometer 21 via differential amplifier 22 to position 18 to reduce time lag in the system, and via amplifier 23 to position 7 where the signal is compared with a pre-set value for burner output from potentiometer 24 to give a difference signal #Q. The signal #Q is fed via a proportional integral regulator 26 and amplifier 27 to a servomotor 28 which adjusts potentiometer 29 to give a pre-set value of crop input rate which is compared at 11 with the actual rate Gw derived from weighing device 9 and the difference signal #Gw controls the regulator 33 controlling a servomotor 34 which determines the speed of the belt 13. The actual entry temperature Ta of the air is compared at 14 with a pre-set value on potentiometer 25 to give a difference signal #Ta which is fed to a regulator 37 controlling a servomoto 38 to adjust the position of a flap 4 past which fresh air is admitted to the dryer at V ML . The potentiometer 16, 24, 25 may be coupled to give simultaneous adjustment of Te, Q and Ta, or operated by a programme card. Regulators 19, 33, 37.-The direct voltage difference signal is compared with separate negative and positive sawtooth voltages having a frequency between 0À01 and 10À0 kHz and is amplified to switch one of a pair of thyristors only when the magnitude of the signal exceeds the sawtooth voltage and the signal is of opposite polarity. The thyristors supply current to the corresponding motor 20, 34, 38.