GB867143A - Improvements in or relating to moisture gauges - Google Patents

Abstract

867,143. Radiation control systems. INDUS- fRIAL NUCLEONICS CORPORATION. Jan. 2, 1958 [Jan. 9, 1957], No. 229/58. Class 40(3) [Also in Group XXXVI] In a moisture measuring system a moisture sensitive capacitor is incorporated in a predominately inductive branch of the tuned circuit of an oscillator the output frequency of which is converted to a signal which varies a further capacitor in a predominately capacitive branch to maintain the oscillator frequency constant. General operation (Figs. 1 and 3). The material 40 passes between the plates of the condenser forming part of the tuned circuit of an oscillator 11. Changes in total moisture content vary the oscillator frequency and this variation is detected by a limiter amplifier 13, frequency discriminator 14 and an A.C.-D.C. converter 15 which produces an A.C voltage indicative of the variation of oscillator frequency from that of a standard 12 against which the circuits are periodically checked. The output voltage drives a servomotor 17 which by variation of the further capacitor in the oscillator circuit restores the oscillator frequency and at the same time adjusts the potentiometer in a standardizing and comparator circuit 18 where it is corrected for mass variations. The mass variations are detected by a Beta ray gauge consisting of source 20 and an ionizing chamber 21 which provides the voltage which is compared with a fixed voltage in computer balancer 22. The difference voltage is fed to a servomotor 24 which marks recorder 19 at 71 to indicate mass variations and positions potentiometer slider 102 in standard circuit 23 (circuit 100 of Fig. 3). In operation (Fig. 3) servo 17 responsive to frequency variations sets the potentiometer 82 while mass variations set potentiometer 102. These mass variations alter the potential at point 92 and a circuit responsive to the difference between this potential and that at 82 and consisting of converter 109 amplifier 110 and servomotor 101 drives potentiometer 92 until the difference is eliminated and at the same time marks chart 19 at 72 in accordance with proportional moisture content. Oscillator circuit (Fig. 2) shows the oscillator in which the measuring capacitor 10 is connected in a series circuit with inductance 54. The inductive circuit provides the inductive reactants of the tuned circuit adjusting capacitor 52 is connected in parallel with capacitor 51 which with series capacitor 55 form the capacitive reactants of the tuned circuit. The arrangement is such that frequency variations produced by say 1 ÁÁf change in 50 require changes of several 100 hundred ÁÁf's in capacitor 52 to restore the frequency.