GB1416640A - Moisture tester - Google Patents

Abstract

1416640 Moisture measurement DICKEYJOHN CORP 16 Nov 1973 53190/73 Heading G1N The invention relates to measuring moisture as a percentage by weight (e.g. in grain). A capacitor measuring cell is mounted on a spring- loaded weighing frame which operates a switch to initiate a rapid moisture measurement when the predetermined weight is poured into the cell. The measurement is in the form of a frequency count taking less than 1 millisecond. A temperature compensation signal may be added DETECTOR-CELL CONSTRUCTION FIG 3 and Figs 1, 2, 4, 5 (not shown) The weighing platform, capacitor cell, circuit boards, and batteries are mounted in a sheet metal housing 4 with a handle (9) Fig. 5 at one end and a top member 6. The capacitor cell 52 has a control cylindrical electrode with a conical dielectric cap, mounted in a cylindrical container forming the other electrode. A thermister (120) is mounted in the cell on the container wall. The weighing platform comprises upper and lower angle bars 72, 74, hinged by blade-springs (76) to the wing-members 46 of a chassis formed by a channel (36) depending from the top plate. When the capacitor is full the platform moves down against the bias of coil springs 112 to close switch 94. CIRCUIT FIG. 6. Moisture measurement. The outputs of variable oscillator 130 tuned by the capacitor cell and reference oscillator 132 are fed to mixer 144 and the difference frequency abstracted through lowpass filter 146. A counting time base is provided by a 12-stage frequency divider fed from the reference oscillator. The output of the 11th stage opens AND gate 156 passing the differency frequency through OR-gate 160 to a 3-decade counter and L.E.D. readout. The 12th-stage output inhibits the input OR-gate 152 thus stopping the count. (With a frequency of about 2 MHZ this takes less than one millisecond.) Power supply. The measuring circuit is only energized for a short while after the weight-switch 94 is closed. Power is supplied by a multivibrator 180 which is kicked into oscillation by a pulse from transistor 176 when the switch closes. R-C circuit 170, 172 provide a small time delay before transistor 176 fires. Œ Temperature correction relative to 25‹C is then initiated by button 34 which resets flip-flop 168 to close gate 148 in the moisture measuring circuit and trigger "one-shot" 214 and enable AND-gates 216 and 217 so that pulses from stage 1 of the divider 154 are fed to the counter until the "one-shot" reset. This resetting time is determined by thermister 120 and is arranged so that at 25‹C, 1000 pulses are added to the three-decade counter, rolling it through zero to its initial setting. In an alternative circuit arrangement Fig 9, (not shown) the moisture-variable frequency is applied to the divider as a variable time-base during which reference frequency pulses are counted. CALIBRATION. A capacitor (302) in series with the measuring capacitor may be used to vary the slope of the response curve for different grains.