High speed bulk grain moisture measurement apparatus

Apparatus for high speed continuous monitoring of the moisture content of grain and the like is disclosed. The apparatus includes a transmitter that transmits signals having two separate frequencies through the grain that is being monitored. A receiver having an antenna placed opposite the antenna of the transmitter picks up the transmitted signals after they pass through the grain. The output of the receiver is coupled to a frequency separator which separates the signals. The two single frequency signals from the frequency separator are applied to separate inputs of a differential detector. The output, if any, from the differential detector is a measure of the moisture content of the grain.

BACKGROUND OF THE INVENTION 
This invention relates to moisture measuring apparatus, and more 
particularly, to apparatus for the high speed monitoring of the moisture 
content of grain or the like. 
Excessive moisture in bulk food grain enhances the growth of poisonous 
molds, and stimulates oxidation which produces heat sufficient to cause 
spontaneous combustion. Therefore, there is a need to monitor the moisture 
content of bulk food grains both during storage and in transit. In one 
method presently used to measure the moisture content of bulk grains, 
small samples are collected from large storage facilities and these 
samples are then analyzed in a laboratory using standard physical and 
chemical methods. This method is extremely limited in terms of reliability 
of the sample. Further, this method does not afford continuous monitoring 
of the moisture in the bulk grain. 
This invention provides for continuous monitoring of the bulk grain by 
means of electromagnetic radiation. During handling, bulk grain shipments 
usually are handled on conveyor belts or are gravity dispensed from 
hoppers into mail cars on tracks. In either case, it is relatively easy to 
pass the material through a continuous reading measurement system or port. 
The examination system hereof essentially comprises a transmit and receive 
antenna, capable of transmitting two separate frequencies through the bulk 
grain as it is carried by on a conveyor belt, or falls through a test port 
during dispensing from a storage hopper. Electromagnetic attenuation at 
VHF and UHF frequencies is found to be almost totally caused by the 
residual moisture in food grains. Systems for measuring moisture by means 
of electromagnetic radiation are known in the prior art. Examples of such 
systems are disclosed in the following U.S. Patents: U.S. Pat. No. 
3,851,244 to Mounce; U.S. Pat. No. 3,694,737 to Busker et al.; U.S. Pat. 
No. 3,693,079 to Walker; and U.S. Pat. No. 3,498,122 to Howard. 
In said U.S. Pat. No. 3,851,244 to Mounce, a rather complex microwave 
system is disclosed. Said U.S. Pat. No. 3,694,737 to Busker et al. 
discloses a microwave moisture measuring system in which the transmission 
path is changed by at least one-half wavelength. Said U.S. Pat. No. 
3,693,079 to Walker discloses moisture measuring apparatus which utilizes 
a microwave signal and a penetrating signal such as x-rays or beta rays, 
and said U.S. Pat. No. 3,498,112 to Howard discloses a microwave system in 
which two separate transmitters and receivers are provided. 
The apparatus of this invention also uses microwave energy to measure 
moisture and is primarily designed to measure the moisture content of bulk 
grain. The system of this invention is not a complex system. The system 
includes a single transmitter capable of transmitting two frequencies, a 
receiver, and signal processing circuitry. 
SUMMARY OF THE INVENTION 
This invention provides apparatus for high speed measuring of moisture; 
particularly, the moisture content of bulk food grains. The apparatus of 
this invention includes a single transmitter capable of transmitting two 
separate frequencies, a receiver, a frequency separator, a differential 
detector and a recorder and/or other metering device. 
The transmitter transmits two separate frequency signals through bulk grain 
as it is carried on a conveyor belt or falls through a test port during 
dispensing from a storage hopper. The receiver is located opposite the 
transmitter and picks up the transmitted signals after they pass through 
the grain. The output of the receiver is coupled to processing circuitry 
which processes the output signals from the receiver to provide an output 
signal that is a measure of the moisture content of the grain.

DETAILED DESCRIPTION OF THE INVENTION 
The single FIGURE illustrates a preferred embodiment of the high speed 
moisture measuring system of this invention. As shown in the drawing, the 
preferred embodiment includes a first oscillator 1 which generates a 
signal having a frequency at (f1) and a second oscillator 3 which 
generates a signal having a frequency (f2). The (f1) signal from 
oscillator 1 is applied to a first input of the hybrid junction 5 and the 
(f2) signal from oscillator 3 is applied to the second input of hybrid 
junction 5. The output of hybrid junction 5 (f1+f2) is applied to the 
input of the transmitter 7. 
Transmitter 7, which of course includes an antenna not specifically shown, 
transmits the (f1+f2) signal through the grain sample. Grain sample 9 may 
be passing past transmitter 7 on a conveyor belt for example or may be 
falling part transmitter 7 as it is dispensed from a storage hopper, for 
example. 
A receiver 11, which also includes an antenna not specifically shown, is 
located opposite transmitter 7 and picks up the transmitted signals from 
transmitter 7 after the signals pass through grain sample 9. The output 
from receiver 11 (f1+f2) is applied to a frequency separator 13. Frequency 
separator 13 separates the signals from receiver 11 into two separate 
signals, one having the frequency (f1) and the other having the frequency 
(f2). The (f1) signals, which are present on one of two outputs of 
frequency separator 13, are coupled to one of two inputs of the 
differential detector 15 through a variable resistor 17. The (f2) signals, 
which are present on the other of the two inputs of frequency separator 
13, are coupled to the second one of the two inputs of differential 
detector 15 through the variable resistor 19. 
Differential detector 15 compares the amplitude of the (f1) and (f2) 
signals and produces an output signal indicative of the difference in 
amplitude of the two signals. If the two signals are equal in amplitude, 
the output from differential detector 15 is zero. The output of 
differential detector 15, which is measure of the moisture content of 
grain sample 7 is applied to a recorder 21. Recorder 21 records the output 
signals from differential 15 and therefore provides a record of the 
moisture content of bulk grain sample 9 as the grain sample passes between 
transmitter 7 and receiver 11. Recorder 21 may be any type of recorder, 
for example a chart recorder. With a chart recorder, an immediate visual 
record of the moisture content of grain sample 9 is obtained. In addition 
to recorder 21, a meter may be connected to the output of differential 
detector 15 or if no permanent record is desired a meter alone can be 
used. 
In operation, the apparatus is first energized without any grain sample 
passing between transmitter 7 and receiver 11. The variable resistors 17 
and 19 are then adjusted until the output of differential detector 15 is 
zero. The grain is then passed between transmitter 7 and receiver 11. The 
amplitude of the output signal from differential detector 15, which is the 
difference in the amplitude of the two signals, is directly proportional 
to the moisture content of the grain passing between the two antennas. 
The derivative of signal transmission with respect to frequency is the 
gauge for measurement of moisture. 
EQU % Moisture=K [(Amplitude (f1)-Amplitude (f2))/(f1-f2)] 
This gauge is insensitive to the quantity of grain, but care must be taken 
to ensure sufficient grain is being measured to produce a difference in 
amplitudes which is well above receiver noise. In addition, care must be 
taken to ensure that the signal at the higher frequency, which is subject 
to much higher attenuation, is above the noise threshold of it's portion 
of the Differential Detector. 
The simplest frequencies to use are in the range of 50 to 1000 mega Hertz 
with one frequency selected near the low end, for example 500, and one 
selected near the high end, for example the 1000 mega Hertz frequency. 
Frequencies outside this range can be used but may require cumbersome 
antennas or result in excessive attenuation. 
This invention lends itself to continuous monitoring of bulk grain 
shipments and with proper calibration, to determine the constant of 
proportionality (K), it can be very accurate even with high flow rates of 
grain. Calibration is conveniently accomplished by placing sealed plastic 
containers having grains with a known moisture content between transmitter 
7 and receiver 11. Calibrated meters can give instantaneous readings, 
especially where the acceptable "dry" calibrated range is marked with a 
green background color, and the unacceptable excessive moisture range is 
marked with a red background color. A series of such monitoring devices 
with a recorder attached to the differential detector output, will provide 
a permanent record of the condition and moisture content of bulk grain 
during transit as it proceeds from the farm to final destination. This 
would be especially useful where the U.S. Government is responsible for 
ensuring the quality or condition of large grain shipments on the 
international market. 
From the foregoing description it is apparent that this invention provides 
a simple, effective and inexpensive method for measuring the moisture 
content of bulk grain. While the invention has been described with 
reference to a specific embodiment, it will be apparent to those skilled 
in the art that various changes and modifications can be made to the 
specific embodiment shown and described without departing from the spirit 
and scope of the invention as set forth in the claims.