Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a moisture meter for
determining the water content of a specimen through measuring
the electrical resistance of the specimen, and more particu-
larly to such a moisture meter provided with temperature
compensation.
In the accompanying drawings:-
Fig. 1 shows a graph illustrating the relationbetween the water content and the electrical resistivity of
grain at a constant temperature;
Fig. 2. illustrates by way of example a circuit -
diagram of a moisture meter according to an embodiment of
this invention; and
Fig. 3 illustrates by way of example a circuit
diagram of a moisture meter according to another embodiment
of this invention.
In grain such as rice and wheat, the water content
has a correlation with the electrical resistivity and hence ~-
it can be determined by measuring the electrical resistivity.
The electrical resistivity of grain with a constant
water content, however, shows a temperature dependence cor-
responding to the water content of + 1.0~ for a temperature
change of + 10C. Thus, temperature compensation is necessary
in determining the water content of a grain specimen from
the electrical resistivity. This has been done by compen-
sating the determined result according to a temperature
compensation table, or with a compensating quantity which is
arranged to be directly read from a thermometer. "Grain
moisture meter, model SP-l" (since April, 1967) of Kett
Electric Laboratory in Japan and "moisture meter, model TW73"
(trade name "Protimeter Grain-master") (Since 1973) of
Protimeter Ltd. are examples of these methods. Such methods
of temperature compensation are troublesome and time-consuming.
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It has been known that at a constant temperature the
electrical resistivity of grain varies with the water content
as is shown in Fig. 1, i.e. it varies exponentially in a water
content range of 12 to 20% and relatively linearly in a water
content range of 20 to 30%. As a result, the provision of a
- moisture meter having only one range of reading is difficult
and involves an extremely complicated circuit structure which
is extremely difficult to adjust. Thus, it can be considered
necessary to divide the whole range into a low water content
- 10 range of 12 to 20% and a high water content range of 20 to 30%.
As an attempt in linearizing the indication scale in a --
- moisture meter, Japanese Patent Publication No. 35039/1973
to Susumo Yagyu discloses an electrical resistance measuring ~ -
apparatus in which an electrical signal is amplified in an
amplifying transistor in the low water content range, in -~
which i~ is difficult to measure fine differences in the
water content because of the high resistivity, an electrical
signal is by-passed through a compensating transistor used
in diode-like manner in the high water content range to
decrease the rate of change of the signal with change of
water content, and the water content signal is preliminarily
converted into a current flowing through a reference resis-
tance and indicated on a meter to enable direct reading.
In this apparatus, however, no consideration is made of the
temperature compensation which is indispensable in the water
content measurement of grain specimens.
This invention improves upon these conventional
;; techniques and is intended to eliminate the drawbacks thereof.
An object of this invention is to provide a moisture
meter capable of automatic temperature compensation in the
accurate determination of the water content of specimens
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1()38931
- using a relatively simple circuit structure which is easily
brought into practical use.
According to this invention there is provided
apparatus for determining the water content of a specimen
. whose electrical resistivity varies non-linearly with the
, water content, comprising sensing means for producing a first
; electrical signal dependent upon the electrical resistivity
of the specimen; linearizer means for producing from the first
: electrical signal a second electrical signal which varies
linearly with the water content of the specimen; indicator
means responsive to the second electrical signal to provide an
indication of the water content of the specimen; and tempera-
ture compensating means for responding to the temperature of
the specimen to shift the zero point of the indicator means
according to the temperature of the specimen thereby to provide -
temperature compensation of said indication.
According to an aspect of the invention there is provided
apparatus for determining the water content of a specimen whose
electrical resistivity varies non-linearly with the water con- .
tent in one water content range and substantially linearly with
- the water content in another water content range, comprising:
sensing means for producing a first electrical signal
dependent upon the electrical resistivity of said specimen;
linearizer means for producing from said first electrical
signal a second electrical signal which varies linearly with the
: water content of the specimen in said one water content range;
. indicator means for providing a water content indication
,; in response to a signal supplied thereto;
change-over means for selective connection of said linear-
izer means between said sensing means and said indicator means to
~. cause a selected one of said first and second electrical signals
: to be supplied to said indicator means; and
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- temperature compensating means responsive to the temper-
ature of the specimen to shift the zero point of the indicator
- means according to the temperature of the specimen, the linear-
izer means being adjusted or adjustable so that said temperature
compensating means provides accurate temperature compensation for
both said one and another water content range. ~ -
According to another aspect of the invention there is
provided a moisture measuring apparatus for electrically measur-
ing the water content of a specimen which has a correlation with .
the electric resistivity of the specimen, comprising~
- means for providing a stabilized d.c. power source of a
relatively high voltage; ~: .
means for detecting the electric resistivity of the speci-
men in the form of an electric quantity by the application of . ~
; said d.c. voltage through a resistance connected in series to ~ .
said power source and said specimen, said means including a pair : :
of electrode members disposed so as to contain said specimen and
to make pressed contact with said specimen, said specimen having : -
such a property that its electric resistivity varies non-linearly ~ -
in one water content range and linearly in another water content
range with respect to the water content;
linearizer means including a plurality of active elements
and connected to the output terminal of said detecting means
.. . . .
through said resistor for converting a non-linearly varying signal
from said detecting means into a linearly varying signal;
temperature compensator means including a voltage dividing
circuit having a temperature detecting element the resistance of
~ which varies substantially linearly with respect to the tempera-
ture of the specimen, for temperature-compensating the water
content measurement by varying the voltage dividing ratio
.: according to the detected temperature; and
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~'- 103893~, ,'.
.; indicating means including another voltage dividing
circuit for providing a voltage dividing ratio corresponding
to one of the linearly varying detection signal and the
linearized detection signal from said detecting means and a
water-content-scaled indicator; said another voltage dividing
circuit, said indicator and the voltage dividing circuit of
said temperature compensator means forming a bridge circuit,
and said indicator being connected at the balancing tapping
points of said bridge so as to indicate the measured water
content.
The invention will be further understood from the
following detailed description of embodiments thereof.
Fig. 2 of the drawings illustrates a moisture meter in
which a dc power source E, e.g. 6V, such as a battery is con- -
nected through a power switch PS to an inverter circuit IN
- including a first transistor Trl of NPN type and an inverter
transformer T. The output of the inverter circuit IN is
rectified by a diode D and smoothed by a smoothing circuit
FC. Thus, a low dc voltage, e.g. 6V, from said dc power source
E is converted to a relatively high dc voltage, e.g. 20V or
above.
Lines Ql and Q2 are connected to the positive and the
, negative terminals of said smoothing circuit FC. Between the
lines Ql and Q2 are connected a voltage dividing series circuit
formed of resistors Rl and R2 and a first field effect transis-
- tor FETl of N-channel type having a drain connected to the
line Ql through a series circuit of a resistor R3 and
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103B931
a first variable resistor VRl and a source to the line Q2
~- through a series circuit of a second variable resistor VR2 and
, a resistor R4, a linearizer LC comprising a second and a third
transistors Tr2 and Tr3 of PNP type, and a fourth transistor
Tr4 of NPN type, in which the transistors Tr3 and Tr4 are
complementally connected. In said linearizer LC, the second ~ -
transistor Tr2 has an emitter connected to a base of the ~ :
fourth transistor Tr4, a collector to the line Q2' and a base ~ -
to the line Q2 through a parallel circuit of a resistor R6 and
; 10 a potentiometer PM and to the line Ql through the movable
terminal of the potentiometer PM and a resistor R7 in series
connection. The fourth transistor Tr4 has a collector con-
nected to the base of the third transistor Tr3, an emitter to
- the collector of the third transistor Tr3 and to the line Q2
through a resistor R8. The third transistor Tr3 has an emitter
connected to the line Ql through a r~sistor Rg. A resistor R5
is connected between the gate of the first field effect tran-
sistor FETl and the line Q2. Further, between the lines Ql and
Q2 are connected a second field effect transistor FET2 of N- ~-
channel having a source connected to the line Q2 through a
resistor Rlo, and a temperature compensating circuit TCC
including a third and a fourth field effect transistor FET3 and
FET4 of N-channel and a temperature detecting circuit TC having
a thermistor TH of negative characteristic (its resistance
decreases with an increase in temperature) for detecting the
temperature of a grain specimen to be described later. In the ^ '~
temperature detecting circuit TC, the thermistor TH has one end
~' connected to the line Ql through a resistor Rll and the other
~' end to the line Q2 through resistors R12 and R13 and a third
-, 30 variable resistor VR3 connected in series, and a resistor R14
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is connected in parallel with the series connection of the
thermistor TH and the resistor R12. In the temperature compen-
sating circuit TCC, the third field effect transistor FET3 has
a drain connected to the line Ql' a source to the line Q2 -~
through a resistor R15, and a gate to the drain of the fourth
field effect transistor FET4. Further, the fourth field effect
transistor FET4 has a drain connected to the line Ql through a
resistor R16, a source to the line Q2 through a series con-
nection of a resistor R17 and a fourth variable resistor VR4,
and a gate to the interconnection point of the thermistor TH
and the resistor R12. The second field effect transistor FET2
has a gate connected to the line Q2 through a resistor R21 and
to a change-over switch CS3, a drain connected to the line Ql'
and a source connected to the line Q2 through a resistor Rlo.
Between the sources of the second and the third field effect .
transistors FET2 and FET3 is connected a series connection of
a fifth variable resistor VR5, a resistor R18 and a water
content meter M. A pair of electrodes Pl and P2 are provided.
One electrode Pl is connected to the line Ql through a "dry"
contact Dl of a first change-over switch CSl and to the inter-
connection point of the resistors Rl and R2 through a "wet"
contact Wl of the change-over switch CSl, and the other elec-
trode P2 to the emitter of the second transistor Tr2 through
a series connection of a "dry" contact D2 of a second change-
over switch CS2 and a resistor Rlg and to the gate of the
first field effect transistor FETl through a "wet" contact W2
of the second change-over switch CS2. Further, the gate of
the second field effect transistor FET2 is connected to the
emitter of the third transistor Tr3 through a series connection
of a "dry" contact D3 of a third change-over switch CS3 and a
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resistor R20, and to the drain of the first field effect tran-
sistor FETl through a "wet" contact W3 of the third change-over
switch CS3. Here, the respective change-over switches CSl, CS2 ~
and CS3 are mutually interlocked so that the on-off operation -
of the "dry" contacts Dl, D2 and D3 and the "wet" contacts Wl,
W2 and W3 are respectively synchronous. A grain specimen G
such as rice or wheat is disposed between the electrodes Pl
and P2. Here, an ammeter is used as the water content measuring
meter M, in which a current scale is replaced with a correspon-
ding water content scale.
In the above circuit, when the water content of a grain
specimen G is in the low water content range of 12 to 20~, the
"wet" contacts Wl, W2 and W3 of the respective change-over
switch CSl, CS2 and CS3 are opened and the "dry" contact Dl,
D2 and D3 are closed to interpose the linearizer LC between
the electrode P2 and the gate of the second field effect tran-
sistor FET2. In this state, when the power switch PS is thrown
in, the emitter potential of the second transistor Tr2, i.e. -
the base potential of the fourth transistor Tr4 of the linear-
izer is established according to the electric resistance of
the grain specimen G between the two electrodes Pl and P2 and
those of the transistors Tr2, Tr3 and Tr4. In a transistor, ,~
the collector current varies exponentially with respect to the -
base-emitter voltage. Thus, the operation characteristics of ;$
the transistors Tr2, Tr3 and Tr4 can be predetermined to generate
an electric signal output changing linearly with the water con-
tent in the grain specimen G from the exponential variation of
the resistivity of the grain specimen G with the water content.
Thus, the linearizer LC generates an output signal changing
linearly with the water content. The output of the linearizer
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; LC, i.e. the emitter output of the third transistor Tr is
supplied to the gate of the second field effect transistor
FET2 which has a linear gate-source voltage vs. drain current
characteristic. Hence, the second field effect transistor
FET2 controls the drain current in proportion to the water
content of the grain specimen G and changes the source potential
linearly with the water content of the grain specimen G. As a
result, the current flowing through the meter M varies linearly
with the water content of the grain specimen G, and the needle
of the meter M moves linearly thereby.
- When the water content of a grain specimen is in the
~- high water content range of 20 to 30%, the "dry" contacts Dl,
D2 and D3 of the respective change-over switches CSl, CS2 and
- CS3 are opened and the "wet" contacts Wl, W2 and W3 thereof
are closed to interpose the first field effect transistor FET
between the electrode P2 and the gate of the second field
effect transistor FET2. When the power switch PS is thrown in
this state, the gate potential of the first field effect
- transistor FETl is established in accordance with the electric
resistance of the grain specimen G between the electrodes P
and P2 to activate the transistor FETl accordingly. Here,
:~ the field effect transistor changes the drain current linearly
with the gate-source voltage. Thus, the linear change of the
electric resistivity with the water content in the grain speci-
men produces a corresponding linear change of the drain output
of the first field effect transistor FETl. As the drain out-
put of the first field effect transistor FETl is applied to
the gate of the second field effect transistor FET2, the second
field effect transistor FET2 controls the drain current in pro-
portion to the water content of the grain G and changes the
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` 1038931 : ~
source potential linearly therewith, similar to the case of
the low water content range. In this case also, the current
flowing through the meter M varies linearly with the water
content of the grain specimen G and the needle in the meter M
moves linearly thereby.
- Therefore, it is possible by the adjustment of the
first, the second and the fifth variable resistors VRl, VR2 and
VR5 and potentiometer PM to arrange the linear movement of the
needle in the meter G in both the low and the high water content
ranges and the water content scale with equal gaps. Thus,
reading of the meter G is made easy.
~ On the other hand, in the temperature compensator TCC,
the resistance of the thermistor TH varies according to the
temperature of the grain specimen G and the gate potential of
the fourth field effect transistor FET4 is changed thereby. The
drain output of the fourth field effect transistor FET4 con-
trolled by the resistance of the thermistor settles the gate ,~
potential of the third field effect transistor FET3 to control
it accordingly. Here, the resistance of the thermistor TH does
; 20 not necessarily change linearly with the temperature, but the
gate potential of the fourth field effect transistor FET4 can - -
be predetermined to change substantially linearly with the
temperature of the grain G. The field effect transistors FET3
and FET4 provide drain currents changing linearly with the
gate-source voltages. Thus, the source voltage of the third
field effect transistor FET3 changes linearly with the tempera-
ture of the grain G. Namely, the temperature compensator TCC
linearly controls the current flowing through the water content
meter M with respect to the temperature of the grain specimen
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Thus, when the circuit is so arranged that the changes
in the output of the temperature compensator TCC (the source
voltage of the third field effect transistor FET3) compensates
the changes in the source voltage of the second field effect
transistor FET2 due to the temperature variation, the current -
flowing through the water content meter M does not change with
the temperature of the grain specimen G but only with the water
content of the grain specimen G. Therefore, the meter G can
indicate the true water content of the grain G.
As is described above, the water content of a grain
- specimen is measured by measuring the electric resistance of
the grain specimen through a linearizer in the low water con-
tent range and directly in the high water content range, and
thereby the water content of the grain can be read out with
temperature-compensation throughout the low and the high water
content ranges by a common temperature compensator.
Therefore, the temperature compensation for the water
content of grain specimens can be done automatically with a
simple circuit structure and the water content of grain speci-
mens can be measured easily and highly accurately.
; A simplified embodiment of the moisture meter according
to this invention is shown in Fig. 3, in which similar parts
with those of Fig. 2 are indicated by similar reference marks.
In this circuit, a change-over switch CS5 is provided at the
interconnection point of the emitter of a fourth transistor Tr4
- and the collector of a third transistor Tr3. A "wet" contact
W5 of the switch CS5 i8 connected to a line Q2 through a bias-
ing series connection of a resistor R4 and a variable resistor
VR2, and a "dry" contact D5 thereof to the line Q2 through a
resistor R8. The emitter of the third transistor Tr3 is con-
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1~38931
nected to the line Ql through a potentiometer VR6 and a resis-
tor Rg and to the line Q2 through a resistor R21. The moving
contact of the potentiometer VR6 is connected to a meter M
through a series connection of a resistor R18 and a variable
resistor VR5. The base for the fourth transistor Tr4 is con-
nected to an electrode P2 through a resistor Rlg. The other
electrode Pl is connected to the line Ql The interconnection
point of a voltage dividing circuit consisting of resistors
R6 and R7 is connected to the base of a second transistor Tr2
of PNP type. The collector of the transistor Tr2 is connected
to the line Q2. A change-over switch CS4 is provided at the
, interconnection point of the resistor Rlg and the base of the
- fourth transistor Tr4, and has a "dry" contact D4 connected
; to the emitter of the second transistor Tr2 and a "wet" contact
connected to the line Q2 through a parallel circuit of a capa- ` -
citor and a resistor R5. The change-over switches CS4 and CS5
are interlocked in relation with the selection of the water
content range of the specimen. In this embodiment, for the
measurement in the high water content range the transistor
Tr2 is isolated by the change-over switch CS4 and the emitter
resistance for the transistor Tr4 is changed to high by the
change-over switch CS5 so as to increase the input impedence `~
for the transistor Tr4 and to change the base potential of the
transistor Tr4 linearly with the water content of the grain
specimen G. It is apparently possible to provide an appro- ;
priate amplifier to linearly amplify the output signal for
improving the sensitivity. -
. - . .
In the above embodiments, description of the lineari-
zer was limited to ones including the second, the third and
the fourth transistors. It will be apparent, however, that
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- the linearizer is not limited to the described ones. Further,
although the specimen was grain in the above embodiments, it
- is also apparent that the specimen is not limited to grain.
,- Yet further, it is apparent that the circuit structure of the
temperature compensator is not limited to those of the above
embodiments.
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