Volumetric moisture tester

A moisture tester for grain and like materials is disclosed. The tester includes a walled test chamber including spaced apart electrodes which form an electrical coaxial capacitor, the electrodes being located so that the dielectric constant of the capacitor is modified in accordance with the dielectric constant of a test material sample introduced into the test chamber. To limit the volume, and to configure and pack the volume of test material introduced into the tester in a predetermined way, a funnel arrangement is provided at the tester top. A lower portion of the funnel directs inflowing grain over an axially aligned, centrally located finger which forms one of the electrodes. A pour spout is provided for pouring test sample material from the test chamber after test completion.

BACKGROUND OF THE INVENTION 
This invention relates generally to moisture testing apparatus, and more 
particularly concerns a device for testing the moisture content of grains. 
Determining the moisture content of grains by sampling methods is an 
important activity in modern agriculture. One grain sample moisture 
testing device which has met with commercial success is that disclosed and 
claimed in U.S. Pat. No. 3,794,911. In this device, a sample of grain is 
introduced into a test chamber and is weighed, and data corresponding to 
the moisture content of the grain is visually displayed upon a suitable 
screen. 
It is a general object of the present invention to provide a moisture 
tester for grain and the like which is highly reliable and rugged in 
operation, yet which provides data sufficiently reproducible and accurate 
for many important uses. Among these uses are the discernment of trends in 
moisture variations when a series of samples are compared. 
Another object is to provide a moisture tester into which a fixed volume of 
test material is introduced into the test cell, and is packed into the 
test cell in a preordered, uniform manner. The tester itself is calibrated 
to give a relatively accurate reading of moisture on a percent of total 
sample weight basis. 
Another object of the invention is to provide such a moisture tester which 
can be offered at low cost to the marketplace. 
Yet another object is to provide such a device which can be used by even 
inexperienced personnel and which will nevertheless provide reliable, 
reproducible results within an acceptable range of error. 
Other objects and advantages of the invention will become apparent upon 
reading the following detailed description and upon reference to the 
drawings. Throughout the drawings, like reference numerals refer to like 
parts.

DETAILED DESCRIPTION 
While the invention will be described in connection with a preferred 
embodiment, it will be understood that it is not intended to limit the 
invention to this embodiment. On the contrary, it is intended to cover all 
alternatives, modifications and equivalents as may be included within the 
spirit and scope of the invention as defined by the appended claims. 
Turning first to FIGS. 1 and 2, there is shown a moisture tester device 10 
which embodies the present invention and is adapted for use with grains 
such as corn and the like. In general, this device 10 includes a test 
chamber 11 which is defined by a cylindrical wall 12 and an annular bottom 
13. Electrical components described below with respect to FIG. 3 are 
interconnected in an electrical circuit constructed upon a circuit board 
14 which is here mounted on the side of the test chamber 11. This circuit 
is powered by a battery 16 carried in a battery housing 17. To 
conveniently operate the device, a circuit-energizing thumb switch 20 is 
mounted immediately above a hand or finger-accommodating handle 21 in a 
position which permits the tester 10 to be held and the switch 20 to be 
operated by one hand. Data relating to the moisture content of any grain 
sample contained within the test chamber 11 is displayed on a display 
screen 23 which is here conveniently mounted above the actuator switch 20. 
To minimize test chamber end capacitance leakage, a grounded metal 
capacitance shield plate 24 is affixed in the device bottom. 
Atop the test chamber 11, a funnel device 30 is formed. In the illustrated 
device, this funnel 30 includes an upper portion 33 extending outwardly 
and upwardly from the remaining portions of the tester 11, and a lower 
portion 34 terminating in a lower margin 36 which is located at a fixed 
position relative to the test chamber. 
In operation, a quantity of grain or other granular substance to be tested 
for moisture content is introduced into the upper portion 33 of the funnel 
30. This material slides through the funnel and falls out the lower funnel 
margin 36 where it impinges upon and is deflected by a finger 40 carried 
within the annular bottom 13 of the test chamber 11. This finger 40 
comprises a cylindrical mediate portion 41 formed of a material comprising 
one of the two test chamber electrodes, and a conical top 42, the tip 43 
of which is aligned with the axis A of the funnel 30 and cylindrical test 
chamber 11. This grain flow deflecting action encourages even distribution 
and random mixing of the grain particles within the test chamber, and 
provides a uniformly dense, evenly distributed, fully representative 
sample in the test cell 11 for moisture testing. When the device is used 
with known grains, the process of fully filling the test cell and 
uniformly packing the test sample will provide moisture data readings of 
accuracy sufficient for many uses. 
As the material flow rises within the test cell, the flow covers a bottom 
test chamber cylindrical wall 45 comprising the other of the two 
electrodes. In the illustrated embodiment, an outer nonconductive lower 
portion of the wall 47 covers this interior electrode 45 and protects it 
from damage which might be encountered during use. 
Additional sample grain material introduced into the funnel 30 continues to 
flow into the test chamber until sufficient material has been received 
within the cell to fill it to a level providing a top material cover layer 
or covering R as shown especially in FIG. 2. Additionally added material 
will simply pile or back up within the lower portion 34 of the funnel 30. 
When stored in this location, this material in the funnel 30 will have 
little or no effect upon the dielectric constant of the material located 
within and near the coaxial electrodes 45 and 41. That test material 
sample in the test cell, however, will always be of a predetermined amount 
and configuration. This constant sample configuration equalizes 
electrode-end fringe effect and other factors from test sample to test 
sample. Thus the test sample material configuration will have little or no 
effect upon the signal issued by the electrical circuit and the data 
displayed on the data display 23. The tested material can be poured from 
the tester 10 by simply tipping it; material then runs out a pour spout 
37. 
When the operator has filled the tester 10 to a level which clearly covers 
the bottom margin 36 of the funnel device 30, he presses the actuator 
switch 20 to energize the electrical circuit (including the temperature 
compensator) and readout or display 23. To this end, a switch finger 51 
abuts an extension 52 of an electrical contact 53, and moves this contact 
53 into a closed position against a second contact 54, thereby completing 
the circuit energization. 
With reference to FIG. 3, there is shown a schematic diagram of an 
electronic circuit which may be utilized in accordance with the principles 
of the present invention. The circuit of FIG. 3 comprises a 
fixed-frequency or "reference" oscillator 110 comprising an oscillator 
transistor 111 and its associated circuitry. The circuitry of FIG. 3 also 
includes a variable-inductance coil 112 for calibrating the circuit 
initially when the device of the invention is manufactured and, if 
necessary, for recalibration from time to time throughout the life of the 
device. The output of oscillator transistor 111 is applied to a first 
counter-decoder stage 121 of a three-stage decade counter-display unit 120 
by means of a coupling capacitor 113 and a NOR gate 114. The reference 
oscillator signal is applied to the "clock enable" input terminal 2 of the 
first counter-decoder stage 121 of counter-display unit 120, as 
hereinafter discussed in greater detail. 
The circuit of FIG. 3 also includes a variable frequency or "test" 
oscillator 130 which comprises a pair of oscillator transistors 131 and 
132. The variable frequency oscillator 130 also includes means for 
adjusting the "empty-chamber" frequency of the oscillator which comprises 
a variable-inductance coil 133 and a variable capacitor 134, both of which 
are connected in parallel with a capacitance that has a value which is 
determined primarily by the series combination of the capacitor 135 and 
the coaxial capacitor formed by coaxial electrodes 41 and 45 of the test 
chamber 11, as described above. Moreover, the value of capacitor 135 may 
be selected to produce the desired frequency-readout characteristic (e.g., 
a direct readout of percent of moisture content as a linear function of 
the changes in oscillator frequency) for the particular type of grain 
being tested. Similar to variable-inductance coil 112 of reference 
oscillator 110, the variable-inductance coil 133 and the variable 
capacitor 134 of test oscillator 130 are adjusted initially at the factory 
with test chamber 11 being empty, so that the frequency of variable 
frequency oscillator 130 may be calibrated to a standard frequency which 
has a predetermined relationship with respect to the reference frequency. 
Moreover, an additional capacitor 136 physically located within the test 
chamber 11 and having a predetermined temperature coefficient may be 
provided in parallel with the tuning circuitry of test oscillator 130 to 
provide automatic temperature compensation. If the frequency of the test 
oscillator tends to increase with an increase in temperature, for example, 
a capacitor having a negative temperature coefficient would be used to 
compensate so that readings made when the ambient temperature is above 
25.degree. Centigrade are decreased in value and those made below 
25.degree. Centigrade are increased, with the amount of increase or 
decrease in value being determined empirically. 
The output signal of variable frequency or test oscillator 130 is applied 
to twelve stages of a commercially available 14-stage divider circuit 140 
by means of a NOR gate 141 and a diode 142. Although any suitable 12-stage 
divider may be utilized for divider 140, a well-known integrated circuit 
made by RCA Corporation, for example, and known as a "CD4020, 14-stage 
ripple-carry binary counter-divider" has been found particularly well 
adapted for use in the illustrated embodiment of the invention. With this 
circuit, input pulses from test frequency oscillator 130 are applied to 
the input terminal 10 of the divider 140 and the output pulses of the 11th 
stage (Q.sub.11) are available at an output terminal 15 of divider 140 for 
application to the "clock" terminal 1 of the decade counter-decoder 121 of 
the counter-display unit 120. Decade counter-decoder 121 corresponds to 
the least significant digit of counter-display unit 120, which is the 
tenths digit in the embodiment of the invention illustrated in FIG. 3. The 
output of the 12th stage (Q.sub.12) of divider 140 is returned (via diode 
143) to input terminal 10 to lock or "clamp" divider 140 to thus terminate 
the count. Thus, one output pulse at output terminal 15 is produced for 
each 2.sup.10 input pulses (i.e. 1024 pulses) applied to input terminal 
10, and the duration of this pulse is the length of time it takes for the 
test oscillator to generate an additional 2.sup.10 pulses. The output 
pulses at terminal 15 of divider 140 thus effectively gate counter-display 
unit 120. Consequently, the higher the frequency of the test oscillator, 
the lower or shorter is the time duration of the control pulse from 
divider 140, and vice versa. 
The counter-display unit 120, as shown in the embodiment of the invention 
illustrated in FIG. 3, comprises three decade counters-decoders 
(seven-segment) 121, 122 and 123 such as SSL4426 manufactured by Solid 
State Scientific Inc. Respectively associated with these counter-decoders 
121, 122 and 123 are current-limiting resistor networks 121a, 122a and 
123a, along with seven-segment display units 121b, 122b and 123b, each 
display unit having its seven segments labeled "a"through "g"in the 
customary fashion and displaying the tenths, units and tens digits, 
respectively. Display units 121b, 122b and 123b are located behind the 
display screen 23 of FIG. 1. Of course, any number of stages may be 
employed, depending upon the particular application of the invention. 
When actuator switch 20 is pressed, the voltage "v"supplied by a battery 
source 150 (here comprising the battery 16) is applied to the various 
portions of the circuit where indicated by the reference character "u"to 
initiate operation of the circuit. The battery voltage is simultaneously 
applied to the input of a pair of NOR gates 151 and 152 which operate as a 
monostable multivibrator or "one-shot" to generate a reset pulse that is 
applied to the reset terminal of divider 140 as well as to each of the 
counter-decoders 121, 122 and 123 so that all four of these circuits are 
reset to the zero count. At the end of the reset pulse, divider 140 begins 
its count. NOR gates 151 and 152, as well as NOR gates 114 and 141, may be 
of any suitable type; however, one integrated circuit particularly adapted 
for use in the illustrated embodiment of the invention is a "CD4001, 
quadruple two-input NOR gate" manufactured by RCA Corporation, for 
example. The CD4001 IC is manufactured in complementary metal-oxide 
semiconductor (CMOS) form and has a very high input impedance and high 
noise immunity. 
By applying the output signal from reference oscillator 110 to the "clock" 
enable terminal 1 of the first counter-decoder stage 121 of display 
circuit 120, and simultaneously applying the output signal from test 
oscillator 130 (as divided by divider 140) to the "clock" terminal 1 of 
counter-decoder 121, the length of time that the counter is permitted to 
count the reference oscillator signal is effectively controlled by the 
frequency of the test oscillator to thus generate a digital representation 
of the moisture content of the material in test chamber 11 which is 
displayed by seven-segment display units 121b, 122b and 123b.