Patent GB-1068166-A (GB)
Title: Method of and apparatus for measuring moisture content of granular materials
IPC: G01N22/04
Filed: 1963-12-17
Abstract: 1,068,166. Measuring moisture content electrically. S. SASAKI. Dec.17, 1963 [Dec. 30, 1962], No.49741/63. Heading G1N. In a method of measuring the moisture content of a granular material, when static or flowing, microwave energy is passed through the material and the amount of attenuation thereof due to moisture is measured and the measured amount is compensated by a factor depending on the bulk density of the material to provide a more accurate measure of the moisture content. Measuring moisture in non-flowing material. In Fig. 7 granular material is fed into a tube 19 to a level which is read on a scale 20. The tube is vibrated for a predetermined time by a vibrator 21 so that the material settles to a lower level which is noted. The difference in levels is related to the density which can be determined from curves Fig. 3 to 6 (not shown) of the results of previous experiment. A microwave output from a Klystron oscillator 11 is buffered by an attenuator 13 as it is transmitted via a waveguide 12 through the material where it is further attenuated by the moisture therein, through an adjustable attenuator 15 having a dial scale 14, to a detector 17. The detector output is indicated on indicator 16, and the attenuator 15 is then adjusted to return the indicator 16 reading to zero, whereby the amount of attenuation due to moisture content will be indicated on the scale 14. The true moisture content is obtained by using the scale 14 reading in conjunction with the scale 20 reading and the curves Figs. 3 to 6 (not shown) thereby taking into account the bulk density of the material. Measuring moisture content of flowing material. In Fig. 9 material from a main stream is diverted to a measuring tube 48 and the rate of flow therethrough is set by a valve 35 the setting of which is indicated on a scale and is related to the bulk density. Microwave energy from oscillator 40 is directed alternately to a measuring waveguide 44 and a comparison waveguide 45 by a switching device 41 driven by a motor 53. The waveguide 44 has an adjustable attenuator 47 with a dial scale and is adjusted by a two phase motor 46, while the guide 45 has a calibration attenuator 49. The output of a detector 50 is fed through a phase shifter and amplifier 51 to a stator phase winding of the motor 46, the other stator phase of which is energized by a generator 52 driven by the motor 53 and therefore synchronized with the switch 41. The detector provides a rectified output the envelope of which will have a waveform corresponding to the difference between the outputs of the two waveguides, which is related to moisture content and will rotate the motor 46 accordingly. The motor will continue to rotate and adjust the attenuator 47 until the detector output is constant, and simultaneously the rotation of the motor 46 varies the state of balance of a bridge network 55 connected to a recording device 56 calibrated to show moisture content. The latter indication and the indication of density on the valve 35 scale are used in conjunction with the said curves to obtain true moisture content. Alternatively the voltage applied to terminals 57 of the bridge circuit may be set to correspond to the bulk density value measured so that the recording device 56 will record the true moisture content.