Patent GB-1524853-A (GB)
Title: Tobacco density testing method and apparatus
IPC: A24C5/34
Filed: 1975-09-01
Abstract: 1524853 Measuring density electrically HAUNI-WERKE KÍRBER & CO KG 1 Sept 1975 [31 Aug 1974] 35927/75 Heading G1N In the capacitive checking of the density of tobacco in cigarettes &c., wherein a mean signal is formed dependent on the tobacco density and moisture content, a circuit is provided which substantially excludes signals from forming the mean value which are obtained from cigarettes having too low a density and forms a signal from the mean signal which does not have a component dependent on fluctuations in the moisture content of the tobacco. In the arrangement of Fig. 1 filter cigarettes 3 are conveyed one at a time by rotating conveyer 2 into a testing position where the cigarettes form part of the dielectric of a capacitor 24, 26 forming the frequency determining circuit of oscillator 27, the output of which is fed to input 'a' of differential amplifier 33. Initially potentiometer 41 is set so that a voltage is applied to input 'b' of amplifier 33 from generator 42 which corresponds to the voltage which would be obtained from circuit 23 corresponding to normal average tobacco moisture content. The cigarettes are then transferred to the holders 7 of conveyer 2 in which they are retained by suction. When an end Zo arrives between the electrodes of the capacitor a measurement signal is fed to the differential amplifier 33 and proximity detector 31 emits a pulse which shifts signals along in shift register 53 and is also applied to input 'b' of AND gate 57. If the two signals applied to amplifier 33 are different, a difference signal is applied to a sample and hold amplifier 34 and a comparator 51 where it is compared with a reference voltage from 52 corresponding to a too low tobacco density. If the density is too low a signal is produced at the output of 51 which is fed to the input of the shift register 53 whereby an electromagnetic valve 56 is energized and the cigarette ejected by compressed air. In addition the comparator 51 output is inverted at 58 and applied to input 'a' of gate 57 so as to disable this gate so that an enabling signal is not applied to sample and hold amplifier 34 to enable the difference signal to be applied to RC circuit 37. When the tobacco density is sufficient comparator 51 has no output signal and AND gate 5 7 is enabled thus allowing a difference signal representing changes in moisture content to be fed to the sample and hold amplifier 34 and thence to the RC circuit 37. If the moisture content decreases then a negative signal appears at the output of comparator 33 so that after several cigarettes have been tested each having a decrease in the moisture content thereof the RC mean value producing circuit 37 emits an increasing negative signal. If this is less than the reference voltage applied to comparator 44 then the latter provides an amplified signal which is fed to motor control member 39 which slowly adjusts potentiometer 41 to provide a lower output voltage at input 'b' of differentive amplifier 33 and so reduce the difference signal. Similarly if the moisture content increases then the motor 39 is operated by a signal from comparator 43 to increase the voltage applied amplifier 33. In an alternative arrangement Fig. 2 (not shown) the output signal from the oscillator 27 is applied via a switch and mean value forming circuit to the "numerator" input of a divider, to the "denominator" input of which is fed the signal from the oscillator. If the ratio from the divider output is greater than a predetermined level the  reject mechanism is actuated and the switch opened so that no further signals may be applied to the mean value forming circuit.