CA1038931A - Direct-reading moisture meter with temperature compensator - Google Patents
Direct-reading moisture meter with temperature compensatorInfo
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- CA1038931A CA1038931A CA248,035A CA248035A CA1038931A CA 1038931 A CA1038931 A CA 1038931A CA 248035 A CA248035 A CA 248035A CA 1038931 A CA1038931 A CA 1038931A
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- water content
- specimen
- temperature
- transistor
- indicator
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Abstract
ABSTRACT OF THE DISCLOSURE
Apparatus for electrically measuring the water content of a specimen such as grain the electric resistivity of which had a correlation with the water content, comprising a linear-izer for converting the measured electric resistivity in the low water content region in which the electric resistivity of a grain specimen changes non-linearly with the water content into an electric quantity linearly changing with the water content, and a temperature compensator including a temperature sensitive element for generating a linearly changing electric signal with temperature, the temperature compensator generating a temperature-compensating electric signal from said linearly changing temperature signal, the temperature compensation of the measured value being commonly done with said temperature compensator in both the low and the high water content ranges by adding a linearly changing electric quantity corresponding to the measured water content and the compensating electric signal.
Apparatus for electrically measuring the water content of a specimen such as grain the electric resistivity of which had a correlation with the water content, comprising a linear-izer for converting the measured electric resistivity in the low water content region in which the electric resistivity of a grain specimen changes non-linearly with the water content into an electric quantity linearly changing with the water content, and a temperature compensator including a temperature sensitive element for generating a linearly changing electric signal with temperature, the temperature compensator generating a temperature-compensating electric signal from said linearly changing temperature signal, the temperature compensation of the measured value being commonly done with said temperature compensator in both the low and the high water content ranges by adding a linearly changing electric quantity corresponding to the measured water content and the compensating electric signal.
Description
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,1~3~93'1 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 _ 2 -- . . . . . - ~ .: . . .
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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.; 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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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 . " j~! . .
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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 7 ~ n .
1038931 :
; 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 - ' ' ~ ' " ' ~ ,, ' ` 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 .; ~ .
G.
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,, , . , , ,! ' , . ' '. ', - : : ' '.: ' : ... ,... . ' : - ' - 1~38931 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-,:
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 ,. - - 11 - . ~ ' .' . . . ..
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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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,1~3~93'1 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 _ 2 -- . . . . . - ~ .: . . .
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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.; 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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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 . " j~! . .
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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 ......
~. ~
: `
:. 1038931 .
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 7 ~ n .
1038931 :
; 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 - ' ' ~ ' " ' ~ ,, ' ` 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 .; ~ .
G.
'' '`': ' ' ' :- :
'~' ' '"'' ~ :
,, , . , , ,! ' , . ' '. ', - : : ' '.: ' : ... ,... . ' : - ' - 1~38931 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-,:
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 ,. - - 11 - . ~ ' .' . . . ..
. . , , " , , " , , , ,, " ~ " , , ", , ~ , :, - . ~ , - - , ,., . ~ :
- 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.
... : .~ .
:. :
~: ' ' . . , .':
. .
' ~: ,: -; ;:' , -.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. 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 resis-tivity 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 temperature 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.
indicator means responsive to the second electrical signal to provide an indication of the water content of the specimen;
and temperature 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.
2. Apparatus according to claim 1 wherein said linearizer means comprises a first bipolar transistor, whose base and collector are connected to receive biasing voltages in opera-tion, and a second bipolar transistor, complementary to the first transistor, whose base is coupled to the emitter of the first transistor and is arranged to be supplied with the first electrical signal from the sensing means.
3. Apparatus for determining the water content of a specimen whose electrical resistivity varies non-linearly with the water content 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 elec-trical 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 linearizer 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 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 linearizer means being adjusted or adjustable so that said temperature compensating means provides accurate temperature compensation for both said one and another water content ranges.
sensing means for producing a first electrical signal dependent upon the electrical resistivity of said specimen;
linearizer means for producing from said first elec-trical 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 linearizer 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 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 linearizer means being adjusted or adjustable so that said temperature compensating means provides accurate temperature compensation for both said one and another water content ranges.
4. Apparatus according to claim 1, 2, or 3 wherein the temperature compensating means comprises a first voltage divider and the indicator means comprises a second voltage divider and means responsive to a voltage difference between the voltage dividing points of the first and second voltage dividers for providing said water content indication.
5. A moisture measuring apparatus for electrically measuring 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 specimen 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 speci-men 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 res-istance of which varies substantially linearly with respect to the temperature of the specimen, for temperature-compensating the water content measurement by varying the voltage dividing ratio according to the detected temperature; and 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.
means for providing a stabilized d.c. power source of a relatively high voltage;
means for detecting the electric resistivity of the specimen 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 speci-men 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 res-istance of which varies substantially linearly with respect to the temperature of the specimen, for temperature-compensating the water content measurement by varying the voltage dividing ratio according to the detected temperature; and 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.
6. A moisture measuring apparatus according to claim 5, wherein said linearizer means comprises at least a first transistor having an emitter connected to the output terminal of said detecting means, a base connected to a biasing source for determining the rising threshold voltage for operation, and a collector connected to the ground, and a second transistor being complementary to said first transistor and having a base con-nected to the emitter of said first transistor, and a collector connected to the voltage dividing point of said another voltage dividing circuit of said indicator.
7. A moisture measuring apparatus according to claim 5, wherein the voltage dividing circuit of said temperature compen-sator means includes a thermistor constituting the temperature detecting element and a plurality of resistance elements connected in series to said thermistor, and connected between the two terminals of said d.c. power source with an adjustable volt-age dividing ratio, and said indicator means includes an ammeter having terminals connected between the voltage dividing terminals of said voltage dividing circuits.
8. A moisture measuring apparatus according to claim 5, further comprising a first change-over switch connected between said detector means and said indicator for connecting and dis-connecting said linearizer means therebetween, a second change-over switch interlocked with said first change-over switch for changing over the voltage applied to the electrodes of said detecting means corresponding to the selection of said water con-tent ranges, a potentiometer for adjusting the level of the detected signal in said another water content range, and another potentiometer provided in the voltage dividing circuit of said indicator for adjusting the voltage dividing ratio.
9. A moisture measuring apparatus according to claim 5, further comprising first and second transistors each having an emitter, a base and a collector in said linearizer means, and first and second change-over switches interlocked to each other, said second transistor having the base connected to one of said pair electrodes through a resistor, the collector being the output terminal and connected to the voltage dividing cir-cuit of said indicator, for the measurement in said one water content range said first transistor having the emitter connected to the input base of said second transistor through said first change-over switch, the base connected to a bias source for setting the rising threshold point and the collector grounded, said second transistor having the emitter connected to a first biasing means through the second change-over switch thereby linearizing the detected resistance signal, while for the measurement in said another water content range said first trans-istor being isolated by said first change-over switch and said second transistor having the base grounded through the first change-over switch and a resistive bias and the emitter connected to a second biasing means through the second change-over switch, thereby to amplify the detected resistance signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,035A CA1038931A (en) | 1976-03-16 | 1976-03-16 | Direct-reading moisture meter with temperature compensator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,035A CA1038931A (en) | 1976-03-16 | 1976-03-16 | Direct-reading moisture meter with temperature compensator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038931A true CA1038931A (en) | 1978-09-19 |
Family
ID=4105476
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,035A Expired CA1038931A (en) | 1976-03-16 | 1976-03-16 | Direct-reading moisture meter with temperature compensator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1038931A (en) |
-
1976
- 1976-03-16 CA CA248,035A patent/CA1038931A/en not_active Expired
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