U.S. patent number 3,766,471 [Application Number 05/204,577] was granted by the patent office on 1973-10-16 for method and apparatus for determining moisture content of tobacco.
This patent grant is currently assigned to Liggett & Myers Incorporated. Invention is credited to James O. Pullman.
United States Patent |
3,766,471 |
Pullman |
October 16, 1973 |
METHOD AND APPARATUS FOR DETERMINING MOISTURE CONTENT OF
TOBACCO
Abstract
A method and apparatus for determining the moisture content of
freshly prized remoistened tobacco compressed into hogs-heads. An
alternating voltage is applied to a pair of electrodes connected in
a circuit and thrust into the hogshead. A phase sensitive voltmeter
connected to the electrode circuit measures the component of the
current in that circuit which is in phase with the alternating
voltage, and hence the resistive component of the impedance between
the electrodes. A logarithmic converter transforms this resistive
component into a signal varying linearly with moisture content.
Inventors: |
Pullman; James O. (Chapel Hill,
Triangle Township, NC) |
Assignee: |
Liggett & Myers
Incorporated (New York, NY)
|
Family
ID: |
22758500 |
Appl.
No.: |
05/204,577 |
Filed: |
December 3, 1971 |
Current U.S.
Class: |
324/694; 324/705;
324/709 |
Current CPC
Class: |
G01N
27/223 (20130101); G01N 27/048 (20130101) |
Current International
Class: |
G01N
27/22 (20060101); G01N 27/04 (20060101); G01r
027/02 () |
Field of
Search: |
;324/65R,57R |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
2661734 |
December 1953 |
Holzer et al. |
|
Foreign Patent Documents
Primary Examiner: Krawczewicz; Stanley T.
Claims
What is claimed is:
1. A method for determining the moisture content of freshly
re-moisturized tobacco, comprising the steps of:
a. placing a quantity of said tobacco in a container,
b. inserting a pair of separated electrodes connected in a circuit
into the tobacco, said circuit partially comprising said
tobacco,
c. applying a reference alternating voltage to said electrodes
through said circuit to thereby generate an alternating current in
said circuit, said alternating current passing through said
tobacco,
d. measuring the relative magnitude of that component of said
alternating current which is in phase with said reference
alternating voltage by means of a phase-sensitive voltmeter,
e. placing other quantities of tobacco separately into said
container, each of said other quantities being equal to said
quantity, each of said other quantities having a known moisture
content, each of said moisture contents being different,
f. repeating steps (b) through (d) on each of said other quantities
of tobacco, and
g. determining from the measurements of steps (e) and (f) the
relation between the magnitude of in-phase alternating current
measured in said quantity of tobacco and the moisture content
thereof, and
h. determining from said relation of step (g) the moisture content
of said quantity of tobacco.
2. The method of claim 1, in which the tobacco is compressed in a
hogshead and said electrodes have an elongated rod configuration,
in which:
the step of inserting the electrodes into the tobacco comprises
forcing the electrodes through the walls of the hogshead.
3. The method of claim 1, in which the step of applying an
alternating voltage comprises:
applying an alternating voltage having a frequency of 1 KHz.
4. The method of claim 1, in which step (d) comprises:
a. passing said alternating current through a resistor
b. applying the voltage drop across said resistor to a second input
of a phase sensitive voltmeter, said voltmeter having first and
second voltage inputs and being capable of producing an output
proportional to the magnitude of the component of the voltage
across said second input which is in phase with the voltage across
said first input,
c. applying said alternating reference voltage to said first input
of said phase sensitive voltmeter, and
d. measuring at the output of said phase sensitive voltmeter the
magnitude of the component of said voltage drop which is in phase
with said reference alternating voltage.
5. The method of claim 1, in which step (d) comprises:
a. passing said alternating current through a resistor
b. applying the voltage drop across said resistor to a second input
of a phase sensitive voltmeter, said voltmeter having first and
second voltage inputs and being capable of producing an output
proportional to the magnitude of the component of the voltage
across said second input which is in phase with the voltage across
said first input
c. applying said alternating reference voltage to said first input
of said phase sensitive voltmeter, and
d. measuring at the output of said phase sensitive voltmeter the
magnitude of the component of said voltage drop which is in phase
with said reference alternative voltage
e. applying said output of said voltmeter to a logarithmic
converter which produces an output proportional to the logarithm of
the output of said voltmeter, so that the output of said converter
is proportional to the moisture content of the tobacco.
6. The method of claim 1, in which step (a) comprises:
placing the tobacco in a hogshead and positioning the hogshead
beneath said electrodes, for insertion of said electrodes into said
tobacco.
7. Apparatus for measuring the moisture content of freshly prized
tobacco comprising:
a. a frame
b. a pair of electrodes connected in a circuit and movably mounted
to said frame for selective insertion into the tobacco,
c. power means connected to said circuit for applying an
alternating voltage between said electrodes to generate an
alternating current in said circuit,
d. means connected to said power means to said circuit for
measuring the magnitude of said alternating current which is in
phase with said alternating voltage
whereby the relative magnitude of the resistive component of the
impedance between said electrodes may be measured, and the moisture
content of said tobacco may be determined by comparing the relative
magnitude of said resistive component with the relative magnitude
of the resistive component of the impedance between said electrodes
when said electrodes are inserted into tobacco having a known
moisture content.
8. The apparatus of claim 7, in which said measuring means
comprises:
a. a resistor serially connected in said circuit, and
b. a phase sensitive voltmeter having
i. a first input connected to said power means to receive said
alternating voltage,
ii. a second input connected across said resistor to apply the
voltage drop of said alternating current across said resistor to
said second input, and
iii. means for producing an output signal whose magnitude is
proportional to the magnitude of the component of said voltage drop
which is in phase with said alternating voltage.
9. The apparatus of claim 8, further comprising:
a logarithmic converter having an input connected to the output of
said phase-sensitive voltmeter for producing an output which is
proportional to the logarithm of said output signal of said
phase-sensitive voltmeter,
whereby the output of said logarithmic converter is proportional to
the moisture content of the tobacco.
10. The apparatus of claim 7, in which
said electrodes have an elongated rod configuration.
11. The apparatus of claim 10, further comprising:
means connected to said electrodes for forcing said electrodes into
said tobacco, whereby said electrodes may be forced through the
walls of a container into which the tobacco is placed.
12. The apparatus of claim 11, in which said forcing means
comprises:
a. a pneumatic cylinder connected between said frame and said
electrodes, and
b. pneumatic power means for actuating said pneumatic cylinder.
13. The apparatus of claim 7, in which:
said power means comprises:
a. a square wave generator having its output connected to the input
of a selective amplifier to convert said square waves to sine
waves.
14. A method for determining the moisture content of freshly
re-moisturized tobacco, comprising the steps of:
a. inserting a pair of electrodes connected in a circuit into the
tobacco,
b. applying a reference alternating voltage to said electrodes
through said circuit to generate an alternating current in said
circuit,
c. determining the relative magnitude of the component of said
alternating current which is in phase with said reference
alternating voltage, said determination further comprising the
steps of:
i. passing said alternating current through a resistor,
ii. applying the voltage drop across said resistor to a second
input of a phase sensitive voltmeter, said voltmeter having first
and second voltage inputs and being capable of producing an output
proportional to the magnitude of the component of the voltage
across said second input which is in phase with the voltage across
said first input,
iii. applying said alternating reference voltage to said first
input of said phase sensitive voltmeter, and
iv. measuring at the output of said phase sensitive voltmeter the
magnitude of the component of said voltage drop which is in phase
with said reference alternating voltage, and
d. comparing said relative magnitude of said in-phase component of
said alternating current with the in-phase magnitude of said
alternating current when said electrodes are inserted into tobacco
having a known moisture content.
15. A method for determining the moisture content of freshly
re-moisturized tobacco, comprising the steps of:
a. inserting a pair of electrodes connected in a circuit into the
tobacco,
b. applying a reference alternating voltage to said electrodes
through said circuit to generate an alternating current in said
circuit,
c. determining the relative magnitude of the component of said
alternating current which is in phase with said reference
alternating voltage, said determination further comprising the
steps of:
i. passing said alternating current through a resistor,
ii. applying the voltage drop across said resistor to a second
input of a phase sensitive voltmeter, said voltmeter having first
and second voltage inputs and being capable of producing an output
proportional to the magnitude of the component of the voltage
across said second input which is in phase with the voltage across
said first input,
iii. applying said alternating reference voltage to said first
input of said sensitive voltmeter,
iv. measuring at the output of said phase sensitive voltmeter the
magnitude of the component of said voltage drop which is in phase
with said reference alternative voltage, and
v. applying said output of said voltmeter to a logarithmic
converter which produces an output proportional to the logarithm of
the output of said voltmeter, so that the output of said converter
is proportional to the moisture content of the tobacco, and
d. comparing said relative magnitude of said in-phase component of
said alternating current with the in-phase magnitude of said
alternating current when said electrodes are inserted into tobacco
having a known moisture content.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and apparatus for determining the
moisture content of tobacco in hogsheads, particularly the moisture
content of freshly prized tobacco which has been recently
remoistened.
2. Description of the Prior Art
In the process of curing tobacco, an important step includes a
procedure known as "remoistening." Tobacco having a moisture
content of approximately 20 percent is dried to a moisture level of
about 4 to 7 percent and subsequently moisture, in the form of
steam or water, is added, in order to bring the moisture content up
to approximately 10 to 12 percent. This remoistened tobacco is then
compressed and sealed into wooden containers known as "hogsheads."
The tobacco in the hogsheads is then removed to a storage area, for
aging, during which time curing effects take place.
It is important that the moisture increase in the tobacco resultant
on remoistening be accurately known and controlled. If the moisture
content of the tobacco is insufficient after remoistening, the
subsequent aging process takes much longer than it would if the
moisture level were in the presecribed 10 to 12 percent range. On
the other hand, if too much moisture is injected into the tobacco
immediately prior to aging, the tobacco can spoil and become
useless.
Many different methods and devices have been used in the past to
accurately measure the moisture level of tobacco in hogsheads. One
such method is moisture testing by hand, which is done by a trained
and experienced sampler who, within limits, can gauge the moisture
of the tobacco simply by its "feel." Besides requiring an
individual with long experience in this art, this method has not
been completely satisfactory, because even the most skilled sampler
cannot always detect the moisture level of tobacco with sufficient
accuracy.
Another method of testing moisture content is by removing a sample
of tobacco from the hogshead, weighing it, and subsequently drying
and reweighing the sample. This method can be quite accurate, but
requires approximately 20 minutes for each test. Because tobacco is
remoistened on a continuous basis, the time required for this type
of testing is excessive. It is necessary to maintain an almost
continuous sampling of the moisture content of tobacco hogsheads,
in order that the information thereby obtained may be fed back to
the remoistening machines, so that continual adjustment in the
amount of moisture injected into the tobacco can be made as
needed.
This need has led to the use of various electronic instruments
which can make relatively fast moisture determinations, without the
need for a highly skilled and experienced operator. One of these
electronic techniques involves passing microwave energy through
samples of the tobacco, and measuring the microwave energy loss
occurring as the waves pass through the tobacco.
Another method has been to place samples of the tobacco between the
plates of a capacitor, and to subsequently measure the dielectric
constant of the tobacco.
Both of these two latter techniques have proved to be
unsatisfactory in measuring moisture content of freshly prized
tobacco. (The tobacco, immediately after remoistening, and
compressing into a hogshead, is referred to as "freshly prized").
The reason for this is related to a problem which is uniquely
associated with measuring the moisture content of remoistened
tobacco shortly after the remoistening process.
This problem is accountable to two factors. First, the freshly
prized tobacco is not, at first, uniformly moistened. It takes a
certain amount of time, for "equilibration" of the moisture
throughout the tobacco to take place. Secondly, and more
importantly, it is known that, when moisture is added to tobacco,
it remains in a free state for a period of time, and subsequently
gradually becomes "bonded" i.e., molecularly bound, to the tobacco
itself.
It is further known that, as this binding takes place, the
dielectric constant of the tobacco decreases, and so does the
ability of the tobacco to attenuate microwaves passing through it.
Therefore, it can be seen that moisture readings taken by
instruments which measure dielectric constant or microwave loss in
the tobacco will vary according to the amount of time elapsed since
the remoistening process and according to the relative fraction of
the total moisture which is freshly applied. This phenomenon will
take place notwithstanding the fact that the moisture content
remains relatively stable throughout the "bonding" period. It can
thus be seen that the electronic techniques discussed here, while
they might be quite satisfactory for use with "equilibrated"
tobacco, are not suitable for freshly prized tobacco, due to the
bonding process, and the variations it induces in moisture
measurements made with the instruments.
It is also noteworthy that the hand sampling and oven drying
methods and apparatus for measuring moisture in freshly prized
tobacco involve the necessity for removing a sample of the tobacco
from the hogsheads and placing it in some sort of test cell for the
actual measurement. This requires more effort and time than would
be the case if a measurement could be made of the entire tobacco
sample within a hogshead, without the necessity for removing any of
the tobacco therefrom.
Another type of moisture detector is disclosed in the May, 1946,
issue of "Electronics" magazine, on page 180, by John H. Jupe. This
detector includes a test cell into which a sample of material to be
evaluated is placed, the cell having electrodes attached to an AC
voltage source. An alternating voltage is applied across the test
cell, and a voltmeter is provided to measure the alternating
current in the electrode circuit which bears a predetermined phase
relationship to the main supply. This apparatus, however, when
adjusted to the manner recommended in the article, is unsuitable
for measuring the moisture content of freshly prized tobacco in a
hogshead, and the article reveals no appreciation of the problems
of such measurement.
Moisture has also been measured by simply testing DC resistivity.
This method is subject to substantial inaccuracies, due to effects
of electrolytic polarization and other factors.
It is therefore an important purpose of this invention to provide a
moisture detector for freshly prized tobacco which is responsive to
the total moisture content of the tobacco, without regard to the
fraction of that moisture which may be bonded to the tobacco.
It is a further purpose of this invention to provide a moisture
detector for freshly prized tobacco which is operable by an
individual not having the benefit of extensive experience in
determination of tobacco moisture content.
It is another purpose of this invention to provide a moisture
detector for freshly prized tobacco which enables very rapid
determination of moisture content of the tobacco.
It is a still further purpose of this invention to provide a
moisture detector for freshly prized tobacco which is capable of
making moisture measurement on entire hogsheads of tobacco without
the necessity for removing samples of the tobacco from the
hogsheads.
BRIEF SUmMARY OF THE INVENTION
This invention includes driving a pair of electrodes through a wall
of a tobacco hogshead, and applying a 1 KHz alternating voltage
across the electrodes. The alternating current thus impressed
between the electrodes is input to a phase-sensitive voltmeter
which compares the current in the electrode circuit with a
reference voltage which is taken from the AC voltage source. The
phase-sensitive voltmeter is designed to provide an output which is
proportional to the magnitude of the component of the alternating
current in the electrode circuit which is in phase with the
alternating voltage. This output is fed into a logarithmic
converter which produces a signal in proportion to the log of the
input from the voltmeter, which signal varies in magnitude in
linear proportion to the moisture content of the tobacco between
the electrodes.
It is noteworthy that the electrodes are constructed in the form of
elongated probes, and are made of a relatively tough material, so
that they are susceptible of being forced through the walls of the
tobacco hogshead. A pneumatic system is provided in order to
selectively force the probes through the hogshead.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the moisture determining apparatus
of this invention, showing the electrode probes in phantom lines in
their extended positions.
FIG. 2 is a block diagram of the moisture detector of this
invention.
FIG. 3 is a detailed schematic drawing of the electronic circuitry
of the moisture detector of this invention.
FIG. 4 is an elevation view of the electrode probes comprising the
moisture detector of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the basic mechanical structure of the
apparatus of this invention includes upright support columns 10, to
the base of which are attached guardrails 12. Crossbars 14 extend
between the upper ends of support columns members 10. Attached to
crossbars 14 are vertical cylinder supports 16. Pneumatic cylinders
18 are fastened in a vertical fashion to cylinder supports 16, and
electrodes 20 are attached to the pistons of cylinders 18. The
electronic components of this apparatus are contained within box
24, which is fixed to crossbars 14.
Photocells 13 and light sources 13a are mounted on guardrails 12
and function to direct a light beam across the assembly, the
interruption of which indicates when a hogshead of tobacco is
properly positioned for insertion of the electrode probes 20 into
the hogshead.
Pneumatic cylinders having pistons 18 are driven by a pneumatic
pressure system of a known type, which is not shown. upon actuation
of the pneumatic system, the pneumatic cylinders drive electrodes
20 through the wooden walls of the hogshead and into the
tobacco.
Notwithstanding that this specification is directed primarily to
piercing the walls of a wooden hogshead with the probes, it is
comtemplated that this device has analogous utility when employed
to detect the moisture level of freshly re-moistened tobacco in
open containers, such as bins, not requiring any piercing of the
container walls in order to reach the tobacco with the probes.
referring to FIG. 4, it can be seen that the electrode probes 20
have a generally elongated rod-like configuration, tapering toward
the lower ends thereof, at 21. Electrodes 20 are secured to the
pistons of penumatic cylinders 18 in such a way that contact 20b,
which is electrically attached to probe 20, is insulated, along
with probe 20 from the pneumatic system itself, to wit, the
pneumatic cylinders. This is accomplished by means of nylon
threaded bushing 20c, the threads of which engage and are screwed
onto threads 20a at the top of each of probes 20. Threaded bushing
20c is then in turn screwed into member 20d which is fixed with
respect to the pistons of pneumatic cylinder 18. In this way, the
electrical contact 20b is fully insulated from all other portions
of the apparatus except the probe 20 to which it is attached.
Probes 20 are connected electrically to the electrical box 24 by
means of flexible cables 20e.
Electrodes 20 are suitably made from a touch material, such as
stainless steel. They are approximately 1 foot in length. Pneumatic
cylinders 18, however, have a path of travel which is somewhat
longer than 1 foot in order to insure that the entire length of the
electrodes can be driven into the hogshead in which the tobacco to
be evaluated is contained.
Referring now to FIG. 2, there is illustrated a block diagram of
the electronic circuitry involved in the apparatus of this
invention. Electrode probes 20 are shown having resistor R and
capacitor C in parallel between them, these two elements
representing schematically the complex impedance between the probes
which is presented by the re-moistened tobacco located between
them.
An alternating reference voltage is applied beween electrode probes
20 by oscillator 50. This voltage is applied from terminals 52
located on oscillator 50 to terminals 53 and 54, as indicated in
FIG. 2. The current generated by application of this reference
voltage flows between electrode probe 20 and through one of the
sampling resistors R.sub.s, the particular one of the R.sub.s
resistors in the circuit being dictated by the position of switch
S.sub.1.
Also included in the circuitry is phase sensitive voltmeter 70,
having first input 72 and second input 73. Phase sensitive
voltmeter 70 produces at its output 70a a signal which is
proportional to that component of the voltage presented to second
input 73 which is in phase with the reference voltage input at
first input 72. The reference voltage is input at 72 from terminals
52 by means of the voltage thereby generated across the secondary
at transformer T.sub.2. A voltage drop proportional to the current
in the electrode probe circuit is impressed on second input 73 by
means of the voltage drop across the resistor R.sub.s which is in
the electrode probe circuit, which generates a voltage across the
secondary of transformer T.sub.3. It can be seen that, if R.sub.s
is not excessively large, with respect to the value of R, the
presence of R.sub.s will not appreciably distort the current in the
electrode probe circuit. It can also be seen that the voltage
appearing at second input 73 will be approximately in phase with
the alternating current in the electrode probe circuit.
Therefore, the output 70a of phase sensitive voltmeter 70 will have
a magnitude which is directly proportional to that component of the
alternating current in the electrode probe circuit which is in
phase with the reference voltage applied at first input 72 from
oscillator 50. This means, in effect, that the output from
voltmeter 70 will be in approximate inverse proportion to the
resistive component R of the complex impedance between electrodes
20, which resistive impedance indicates, by a logarithmic relation,
the moisture content of the tobacco.
The resistive component R of the impedance in moisturized tobacco
varies in approximate inverse logarithmic relation with respect to
actual moisture content M of the tobacco, such that M.alpha.log 1/
R. Therefore, it is contemplated that logarithmic converter 80 can
be employed to receive the output of voltmeter 70, and to itself
produce an output which is proportional to the value of the
logarithm of the magnitude of the said output of voltmeter 70.
The addition of logarithmic converter 80 thereby enables the
obtaining of an output signal, which may be measured as at meter
90, which signal is linearly proportional to the actual moisture
content of the tobacco.
Power for oscillator 50, voltmeter 70 and logarithmic converter 80
is provided, as is shown in FIG. 2, by power supply 30, which, by
way of its output 32, supplies power to the aforementioned elements
at terminals 51, 71, and 81, respectively. Power source 30 also
supplies power to various internal components of these elements in
a manner described below.
A better understanding of the electronic functioning of the
apparatus of this invention may be had by referring to FIG. 3,
which shows a detailed schematic drawing of the circuitry
therein.
Power supply 30 is supplied with conventional 115 volt ac at its
input 31, and produces its output at terminals 32. Applicant has
found that a suitable power supply for this apparatus is a Burr
Brown Dual Power Supply Model 501.
The oscillator circuitry is designated generally by the dotted line
defining zone 50, and consists primarily of square wave oscillator
55, and a square to sine wave converter including amplifier A.sub.1
and its attendant conversion and stabilization circuitry,
designated within box 60, and as C.sub.1 and R.sub.1. Square wave
oscillator 55 is supplied with power at terminals 51 from output
terminals 32 of power supply 30. Suitable hardware for the square
wave oscillator may be a Fork oscillator, type G, manufactured by
Fork Standards, Inc. The output from square wave generator 55 is
input to the primary winding of transformer T.sub.1.
The secondary windings of transformer T.sub.1 are connected to
input terminals 56 of convertor amplifier A.sub.1. Square wave
conversion and stabilization circuitry, indicated within box 60 and
as capacitor C.sub.1 and resistor R.sub.1, operate in conjunction
with amplifier A.sub.1 to produce an output at terminals 52 which
is approximately a sinusoid having the same frequency as square
wave oscillator 55. This frequency, as noted hereinabove may
satisfactorily be 1,000 Hz. Amplifier A.sub.1 is provided with
power from output terminal 32 of power supply 30 at terminals 57.
For simplicity, the connection between terminals 32 and 57 is not
shown. Also, amplifier A.sub.1 is provided with balance circuitry
indicated at 61. Amplifier A.sub.1 may suitably be a Burr Brown
Model 3241.
It is understood that oscillator 50 need not have the specific
circuitry described herein, but can be any constant voltage
oscillator capable of producing a sine wave of any frequency
appropriate for the measurement contemplated, at a suitable energy
level.
The output of oscillator circuitry 50 is input at terminals 52 to
the primary windings of transformer T.sub.2. The output of the
secondary windings of transformer T.sub.2 is connected to terminals
72, the first input of phase sensitive voltmeter 70, which first
input is connected to phase detector circuitry 75, as indicated in
the box bearing that designation. The voltage at oscillator output
52 is also connected to electrode probes 20 to form the electrode
circuit. Connection is made to one of the probes between the
uppermost of terminals 52 and terminal 53. The other probe is
connected to the lower terminal 52 through the one of resistors
R.sub.s which is connected in series with the electrode probe
circuit, by way of terminal point 54.
The operator of this apparatus may select which of resistors
R.sub.s he desires to insert into the electrode probe circuit by
appropriate positioning of switch S.sub.1. The particular one of
resistors R.sub.s which is in the circuit is indicated by the
illumination of one of the lamps L which are connected to an
independently supplied AC circuit. Switch S.sub.2 being ganged with
switch S.sub.1, determines which of lamps L is lighted, in
accordance with which resistor is in the electrode circuit.
The reason for provision of a choice of resistors R.sub.s of
varying value is to permit measurement of a wide range of moisture
levels and testing of different tobaccos, which may vary in
impedance from one type to another, although moisture content is
the same. Applicant has found that suitable values of resistors
R.sub.s are 10, 100, and 1,000 ohms, respectively, enabling
measurement of impedance in the respective ranges of 10.sup.5
-10.sup.3, 10.sup.6 -10.sup.4, and 10.sup.7 -10.sup.5 ohms.
The voltage drop across the one of the resistors R.sub.s which is
in the electrode probe circuit, which voltage drop is of course,
generated by the alternating current flowing in that circuit, is
impressed on the primary windings of transformer T.sub.3.
Transformer T.sub.3, amplifier A.sub.2 and phase detector circuitry
75 are the principle components of phase sensitive voltmeter 70,
indicated within the dotted lines in FIG. 3.
Detector amplifier A.sub.2 is provided with power from output 32 of
power supply 30 through terminals 71, the actual connections being
omitted here for simplicity. The output of the secondary windings
of transformer T.sub.3 is input at terminals 73 of amplifier
A.sub.2. Amplifier A.sub.2, which has been found to be suitably
provided by a Burr Brown Model 3308 amplifier, is provided with
associated balance circuitry 77 and gain control circuitry 78. The
output of amplifier A.sub.2 is input to phase detector circuitry
75.
The output of phase sensitive voltmeter 70, which appears at
terminal 70a, is proportional to that component of current flowing
in the electrode circuit (as sensed by the voltage drop across
R.sub.s) which is in phase with the reference voltage output of
transformer T.sub.2 which is input to voltmeter 70 by way of first
input terminals 72.
Thus, the output of voltmeter 70 will be inversely proportional to
the value of the resistive component of the complex impedance
between electrode probes 20.
The resistive component of the complex impedance of freshly
re-moistened tobacco is related to the moisture content of the
tobacco by an approximate inverse logarithmic function. Therefore,
it can be seen that if the output of voltmeter 70 is converted such
that an output is obtained which is proportional to the value of
the logarithm of the output of voltmeter 70, then a signal is
obtained which is linearly related to the actual moisture content
of the tobacco.
This function is provided by the inclusion of logarithmic converter
80, indicated within the dotted lines on FIG. 3. Converter 80
consists primarily of drive amplifier A.sub.3 and linear-to
log-amplifier A.sub.4, which are connected in series, as shown in
FIG. 3. Amplifiers A.sub.3 and A.sub.4 are supplied with power from
output terminals 32 of power supply 30 via terminals 81 and 87,
respectively. Gain control is provided for amplifiers A.sub.3 and
A.sub.4 by means of gain control elements 84 and 89, respectively,
and balance resistors 85 and 88.
Applicant has found that suitable amplifiers for supplying drive
amplifier A.sub.3 and linear-to log-amplifier A.sub.4 are Burr
Brown Models 3241 and 4007, respectively.
Functionally speaking, output 70a is applied to input terminal 83
of drive amplifier A.sub.3. The signal is amplified and passed in
series to inputs 86 of linear-to log-amplifier A.sub.4, where it is
converted to a logarithmic function of the signal at output 70a of
voltmeter 70. The output of the log converter ranges in logarithmic
fashion relative to the input thereto, from a relatively large
positive output when the input from the phase sensitive voltmeter
is near zero, to a relatively large negative output when the input
has a relatively high positive value.
The output of converter 80, appearing at terminals 91, is thus a
linear function of the moisture content of the tobacco sampled
between electrode probes 20. Because resistance R of the complex
impedance of the tobacco is reduced as the moisture content thereof
increases, the co-efficient of linearity between the signal at
output 91 and the actual moisture content will be negative. An
ammeter 90 may be provided to receive the signal at terminal 91 in
order to indicate its value. Ammeter 90 is of a type which yields
left-hand deflections for negative voltages and right-hand
deflections for positive voltages. Ideally, the ammeter can be
caused to show upward (right-hand) deflections corresponding to
high moisture content (negative outputs of the log converter) by
connecting it "backward" to the log converter, so that maximum
positive voltage (low moisture) gives a full left deflection.
This apparatus can be calibrated for varying moisture levels of
tobacco, by simply taking measurements of a number of tobacco
samples, noting the meter deflections which are obtained in those
measurements, and determining the precise moisture content of each
of the samples by means of conventional, analytical methods, such
as the oven drying process described hereinabove. Applicant
believes that the method and apparatus taught in this application
has solved a longstanding problem in the measurement of moisture
levels on freshly re-moistened tobacco, which problem has been
peculiar to measurement of such levels in the past.
For a very long time, tobacco processors have had difficulty in
determining moisture content of freshly re-moistened tobacco. To
Applicant's knowledge, and based on his extensive tests, no
previous attempts to test moisture levels in such tobacco have been
able to avoid the deceptive influence of moisture progressively
bonding to the tobacco. Only this invention has been able to
accomplish this purpose. The apparatus and method of this invention
avoid almost entirely the influence of the degree of such bonding
on moisture readings.
It is to be understood that these disclosures are illustrative
only, and that one of ordinary skill in this art could modify,
alter, or depart from the specific embodiments taught without
deviating from the spirit of this invention.
* * * * *