Patent GB-939289-A (GB)
Title: Improvements in or relating to moisture analysis apparatus
IPC: G01N27/42
Filed: 1962-05-15
Abstract: 939,289. Measuring sample moisture content electrically. CONSOLIDATED ELECTRODYNAMICS CORPORATION. May 15, 1962 [May 25, 1961], No. 18619/62. Class 40 (1). A moisture analysis apparatus (Fig. 1) comprises an electrolytic cell 28 which produces a signal dependent on its own rate of moisture absorption and which is connected to a controllable means such as an R.F. heating coil 18, for releasing moisture from a source 16 by signal responsive means such as temperature regulator 23, so that the rate of moisture release is controlled in a predetermined relation to the cell signal. Dry gas from a container 10 is passed through a regulator 13, over a platinum boat 17 containing the sample 16, and then through the cell 28, the sample 16 and R.F. heating coil being located in a refractory lined oven 14. The gas, which now contains moisture, passes through cell 28 which comprises a pair of helical platinum electrodes 30, 31, bridged by a film of hygroscopic material 33 such as phosphorus pentoxide. A voltage from a battery 39 is applied to the electrodes and when the hygroscopic material becomes conductive upon the absorption of moisture, an electrolytic path exists between the coils and in the regions of conductivity the water is electrolysed into hydrogen and oxygen so that the hygroscopic material is continuously regenerated and a current which flows is a measure of the quantity of moisture absorbed. This current produces a voltage across resistor 45 which after amplification at 43, is passed to temperature regulator 23. The cell output voltage is also connected to an integrating meter 42, such as a permanent magnet, low inertia D.C. motor the speed of which is proportional to the applied voltage and which drives an indicator 58 (Fig. 3) directly calibrated in units of moisture weight absorbed by the cell. The temperature regulator 23 comprises cell signal input terminals 50, 53 (Fig. 3) connected to a D.C. amplifier 43 which produces a signal controlling the magnitude of oscillations produced by an R.F. oscillator 75, so that an increase in cell signal causes a reduction in R.F. power. A strip recorder may be connected to terminals 52, 53. A gain control 73 determines the maximum temperature achieved by the coil 18 for any quantity of moisture absorbed by the cell. When sample 16 is heated and rises in temperature as shown by curve 101 (Fig. 2), moisture is released, as is shown at 102. The cell 28 thus produces a signal and due to the inverse relationship between cell 28 and R.F. coil 18 outputs, attenuates the moisture output which again causes a corresponding rise in temperature, this cycle continuing until all moisture is driven off the sample, as shown by the curve 102 at the point 107. The integrator 42 measures the cell output in coulombs and thus integrates the total area under the curve 102 between the points 104, 107 and thus indicates the sample's total moisture content. The maximum temperature and hence the rate of moisture release is dependent upon the over-all gain of amplifier 43 set on the control 73 and this can be regulated so as to provide a practically constant output so that a " lapsed time current integrator may be used which operates at a predetermined level of moisture release and stops when the cell output falls below it. The system described may be adapted to control the humidity of a room.