GB1016784A - Improvements in the measurement of the moisture content of specimens - Google Patents

Abstract

1, 016, 784. Measuring moisture content. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 1, 1963 [May 11, 1962], No.18248/62. Heading G1N . The moisture content of a specimen 11 is measured using a "Magic-T" hybrid waveguide junction by applying short-circuited terminations to two opposed arms 1, 3, placing the specimen in one of these arms, 1, applying radio frequency energy to another arm 7, and varying the effective length and attenuation in arms 1 and 3 until the energy passing into the fourth arm 5 is substantially zero, the attenuation produced by the specimen being deduced from the attenuation applied to arms 1 and 3. Arm 1 has a fixed termination 13 and contains an attenuator 15, which need not be calibrated. Arm 3 has a movable plunger 19 and a calibrated attenuator 17. Arm 5 contains a fixed padding attenuator 23 and a probe 25 connected through diode 27 and amplifier 29 to meter 31. Arm 7 is coupled to a klystron operating in the 3cm. wavelength range. Attenuator 17 is initially set to zero with no specimen 11 in place and 19 is adjusted to give a zero output on meter 31. The attenuator 17 is calibrated using a series of known specimens, or a calibration chart is prepared. During each test, attenuator 17 and plunger 19 are adjusted to give a zero output. The attenuator and plunger may be combined in a single unit by providing a cylindrical waveguide section with an absorbing tapered vane fitted into an axially adjustable plunger. The vane is rotatable through 90 degrees relative to a fixed tapered vane, axial and angular movement being independent. Attenuators 15 and 17 may be interchanged.