Patent GB-939669-A (GB)
Title: Improvements in and relating to methods and apparatus for measurement of the mass and/or moisture content of dielectric materials
IPC: G01N27/22
Filed: 1961-07-11
Abstract: 939,669. Determining relative quantities of constituents. INDUSTRIAL NUCLEONICS CORPORATION. July 11, 1961 [July 11, 1960], No. 25138/61. Class 37. In a system for measuring the amount of at least one constituent in a material having a number of constituents with different dielectric characteristics, wherein the material is passed between the plates of a capacitor, the plates are energized from a number of A.G. sources of different frequency, the number being the same as the number of constituents. The invention is particularly directed to determining the weight and moisture content of a cigarette rod during manufacture. Bridge 10, Fig. 1, including capacitive probe 12 is fed with frequencies f 1 , f 2  from sources 16, 17 over transformer 13, 14, 15 and an initial balance is obtained by the adjustment of resistorcapacitor network 22, the outputs at the two frequencies being selected by filters 25, 26 after amplification in amplifiers 23, 24. The detected signals S L , S H  are applied to a computer 29 to determine the weight p and moisture content q which are indicated on meters 31, 32, respectively. Curves S L , S H , Fig. 3, and a derived function S L /S H /S H  for a range of moisture content from 0-30% obtained with frequencies of 50 kc/s. and 3 mc/s. are used as a basis for the computer design, the computer relating the derived function shown as K(q) with q in accordance with the relation shown graphically to exist. The signals S L , S H  are applied to a subtraction circuit 44, Fig. 4, and the resulting signal is applied with a signal KS H  derived from the input S H  by a wiper 48 on a potentiometer 47, to an amplifier 46 feeding a servomotor 49. The servomotor which establishes the fractional position K of the wiper is ganged to a further wiper 51 on a potentiometer 52 which establishes a signal K(Q) on an input lead 53 to an amplifier 55 feeding a winding of a further servomotor 56. The potentiometer is fed with a constant voltage through a limiting amplifier 66 and drives the servomotor 56 to a position where the potential tapped from a potentiometer 58 wound in accordance with the q/K(q) relationship of Fig. 3 equals the potential on line 53, when it stops. The position of wiper 57 is equal to the value q and the value is indicated at 83 by an indicator connected to an auxiliary wiper 81 on potentiometer 82 the potentiometer being energized from a constant source. The filling factor P is determined both for high and low frequencies by averaging the tapping outputs from potentiometer 86, 87, wound respectively according to the functions f H (q) and f L (Q) and supplied respectively with signals S H  and S L . A correction for P may be made in accordance with the indication in 92 of the difference between the values of P obtained at the two frequencies. The change of values of K(Q) on either side of q = 10% approximately is corrected for by antiphase voltages being applied simultaneously to the limiting amplifier 66, the supply from source 69 taking over when the signal S L  falls below the value corresponding with the peak of K(q). A simple linear computer which may be used when the moisture content is known to be within a predetermined narrow range, is described with reference to Figs. 6 and 7 (not shown) in another linear servo arrangement for a range of about 10% of moisture content, signals S H  and S L , Fig. 8, are reduced by adjustable reference voltages selected by wipers 117, 119 which determine the location of the range and applied with the signals S H , S L  to chopper stabilized amplifiers 118, 121, the former including a phase inverter stage 122 to obtain an output on terminal 123 of opposite polarity to that on 124. Servomotor 130 sets to a position representative of moisture content, which is indicated on meter 139, in response to the potential at point 127 and the potential tapped off by wiper 133 from potentiometer 131, 132 supplied by signal S H . The filling factor P which is proportional to S H/q  is derived from a potentiometer 141 the wiper 142 of which is also driven by motor 130. Variations in output from H.F. generator 16 may be compensated by comparison of the output from 142 with a supply from generator 16 applied at 145 and adjusted by potentiometer 146 to balance the signal at 142. As the output at 142 may be indicative of a design requirement, a change from balance of the two signals indicates deviation from design, and control may be effected.