GB732969A - Improvements in and relating to the measurement of moisture - Google Patents

Abstract

<PICT:0732969/III/1> <PICT:0732969/III/2> A moisture-sensitive unit comprises an aluminium wire 12, Fig. 1c, part of whose surface is anodized to form a thin layer 11 of aluminium oxide, which is almost completely covered with finely-divided graphite 13, so that the conductivity and/or capacity between the aluminium wire 12 and the graphite coating 13 is affected by the humidity of the atmosphere and may be measured. In one form of measuring circuit (Fig. 2, not shown), the sensitive unit, in conjunction with an interrupter operating at constant frequency, is alternately charged by a battery and discharged through a meter whose <PICT:0732969/III/3> deflection is proportional to the capacity, and hence indicative of the moisture absorbed by the aluminium oxide from the atmosphere. In another measuring circuit, Fig. 3, the unit 26 is one arm of a D.C. bridge, the unbalance current being amplified by a push-pul amplifier with negative feed-back, and measured at terminals T. The unit may be made in sheet form, and may be used against a surface by covering it with a layer of insulating plastic. Calibration.-A saturated air source at a controlled temperature is obtained by pumping air at 41, Fig. 4, into a saturator 42, where it passes through a diaphragm 45 of filter paper dipping into a reservoir 46 and through an outlet pipe 47 to affect the sensitive unit 49. The temperature of the saturator 42 is maintained constant by a circulating liquid at a thermostatically controlled temperature in the jacket 43. The apparatus may be used to measure partial pressures of the vapour of alcohol, acetone, ether, naphthalene, acetamide, ammonia, methylamine, dimethylamine, and trimethylamine. It may also be used to measure the salinity of salt solutions, and in the measurement of moisture content of foodstuffs, building materials, timber and raw materials generally. Specification 559,240, [Group XXXVI], is referred to.