JPH06324012A - Moisture-susceptible element drive device and moisture measuring instrument - Google Patents

Abstract

PURPOSE:To improve moisture measurement accuracy with a simple circuit configuration by converting the DC current from a DC current input part to an AC current which is amplified according to the AC signal from an AC signal input part and then supplying it to a moisture-sensitive element and then detecting DC current from the DC current input part. CONSTITUTION:An AC signal input part 20 of a drive circuit 10 is connected to an AC signal generator VOSC, a DC current input part 22 is connected to a DC power supply Vcc via a current detection means A, and then an AC output part 24 is connected to a moisture-sensitive element RL. Transistors Q1 and Q2 form a B-class push-pull amplification circuit. A positive or negative current is output accordingly during the positive or negative half cycle period of AC signal from the input part 20 and the element RL is driven by the AC current. Therefore, the AC current has a proportional relationship with a DC current I form the input part 22. Therefore, when the current I is detected by a means A, current flowing through the element R is known and the resistance can be determined, thus determining the moisture of ambient environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity-sensitive element driving device for driving a humidity-sensitive element made of a ceramic material used for measuring humidity, and a humidity measuring device equipped with such a humidity-sensitive element driving device.

[0002]

2. Description of the Related Art Various measuring devices are used to measure various physical quantities. As a kind of such measuring device,
There is a humidity measuring device that measures humidity. Conventionally, the humidity is measured by using a damp hygrometer or a dry-wet bulb hygrometer as a humidity measuring device, but these humidity measuring devices have insufficient response such as measurement accuracy and changes in humidity, and It is difficult to convert the measurement result into an electric signal. Therefore, a humidity sensor has been developed which measures the humidity by utilizing the property that the property of the substance changes depending on the humidity, for example, the expansion and contraction of the substance, the change of capacitance, the change of electric resistance value, and the like.

As one of such humidity sensors, a humidity sensor using a humidity sensitive element (hereinafter also simply referred to as a moisture sensitive element) made of a ceramic material, which focuses on the fact that the ceramic material is thermally stable ( Hereinafter, it may be simply referred to as a ceramic humidity sensor). In the ceramic humidity sensor, the humidity-sensitive element adsorbs moisture in the air, so that the electric resistance value of the humidity-sensitive element changes. Therefore, the electric resistance value of the humidity sensitive element can be obtained by measuring the current flowing when a voltage is applied to the humidity sensitive element, and the relative humidity in the atmosphere in which the humidity sensitive element is placed can be obtained from the electric resistance value. .

[0004]

However, when a direct current voltage is applied to the humidity sensitive element, the humidity sensitive element causes a polarization phenomenon and the performance is deteriorated. Therefore, it is necessary to apply an AC voltage containing no DC component to the humidity sensitive element. Therefore, in order to measure the electric resistance value with the conventional ceramic humidity sensor, the AC voltage is applied to the humidity sensitive element to measure the flowing AC current, and the AC current is converted into the DC current to calculate the electric resistance value. There is a need to.

Therefore, in the conventional ceramic humidity sensor, a rectifying circuit for converting the obtained alternating current into a direct current is required, which causes a problem that the circuit configuration for driving the ceramic humidity sensor becomes complicated. There is also a problem that the humidity measurement accuracy cannot be improved due to the complicated circuit configuration.

Therefore, it is an object of the present invention to provide a humidity sensitive element driving device and a humidity measuring device capable of improving the humidity measuring accuracy with a simple circuit configuration.

[0007]

SUMMARY OF THE INVENTION To achieve the above object, a humidity-sensitive element driving device of the present invention is a humidity-sensitive element made of a ceramic material whose electric resistance value changes according to relative humidity and which is AC-driven. Is a humidity-sensitive element driving device for driving the.
Then, an AC signal input unit to which an AC signal is input, a DC current input unit to which a DC current is input, and the DC current to be input from the DC current input unit are the AC input from the AC signal input unit. An alternating current output part for converting to an amplified alternating current according to a signal and supplying the same to the humidity sensitive element, and a current detecting means for detecting a direct current flowing through the direct current input part are detected by the current detecting means. The resistance value of the humidity sensitive element is measured by the generated direct current.

In order to achieve the above object, the humidity-sensitive element driving apparatus of the present invention has a sense of driving a humidity-sensitive element made of a ceramic material whose electric resistance value changes according to relative humidity and which is AC-driven. It is a wet element drive device. Further, it has an alternating current signal input portion to which an alternating current signal is input and a direct current input portion to which a direct current is input, and the direct current input from the direct current input portion is input from the alternating current signal input portion. A class B push-pull amplifier circuit which converts the amplified AC current into an amplified AC current and supplies it to the humidity sensitive element;
A current detecting means for detecting a direct current input to the class push-pull amplifier circuit, and the resistance value of the humidity sensitive element is measured by the direct current detected by the current detecting means. .

Further, the humidity measuring apparatus of the present invention for achieving the above object generates a alternating current signal and a humidity sensitive element made of a ceramic whose electric resistance value changes according to relative humidity and which is driven by an alternating current. An alternating current signal generator, an alternating current signal input portion to which an alternating current signal generated by the alternating current signal generator is input, a direct current power source, and a direct current input portion to which a direct current supplied from the direct current power source is input, An alternating current output part for converting the direct current input from the direct current input part into an alternating current amplified in accordance with an alternating current signal input from the alternating current signal input part and supplying the alternating current output to the humidity sensitive element; A current detecting means for detecting a direct current flowing through the direct current input portion is provided, and the resistance value of the humidity sensitive element is measured by the direct current detected by the current detecting means.

Further, the humidity measuring apparatus of the present invention for achieving the above object generates a alternating current signal and a humidity sensitive element made of a ceramic whose electric resistance value changes according to relative humidity and which is driven by an alternating current. An AC signal generator, a DC power supply, an AC signal input unit to which the AC signal generated by the AC signal generator is input, and a DC current input unit to which the DC current supplied from the DC power supply is input. A class B push having the DC current input from the DC current input unit, which is converted into an AC current amplified according to the AC signal input from the AC signal input unit and supplied to the humidity sensitive element. A pull amplifying circuit and a current detecting means for detecting a direct current input to the class B push-pull amplifying circuit are provided, and the resistance value of the humidity sensitive element is measured by the direct current detected by the current detecting means. To Characterized in that was.

In the humidity sensitive device driving apparatus or the humidity measuring apparatus of the present invention, the class B push-pull amplifier circuit can be composed of a single power source type or a dual power source type amplifier circuit.

As the ceramic material used for the moisture sensitive element, Al ₂ O ₃ , Cr ₂ O ₃ , Cr ₂ O ₃ + C and Fe _{2 are used.}
O ₃ , ZnO, Fe ₃ O ₄ , CoO, Ni _1-X Fe _{2 + X} O ₄ ,
TiO ₂ + Mn ₃ O ₄ , Fe ₂ O ₃ + Li ₂ O, SnO ₂ + S
b ₂ O ₃ , BaTiO ₃ , Al ₂ O ₃ + glass, Fe ₂ O ₃ +
K ₂ O, TiO ₂ , V ₂ O ₅ + Na ₂ CO ₃ + Si, Cr ₂ O ₃
+ Glass, ZnO + Li ₂ O + V ₂ O ₅ , MgCr ₂ O ₄ +
TiO ₂ , TiO ₂ + SnO ₂ , TiO ₂ + V ₂ O ₂ , BaT
iO ₃ + SrTiO ₃ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , A
1PO ₄ , Co ₃ O ₄ + TiO ₂ , thermistor, ZnCr ₂
O ₄ + Li ₂ O, MnWO ₄ , LiNbO ₃ , zeolite +
Examples thereof include MgAl ₂ O ₄ + MgFe ₂ O ₄ and SnO ₂ + apatite.

[0013]

In the present invention, for example, a positive current corresponding to the AC signal is output during the positive half cycle of the AC signal input from the outside, and the AC signal is output during the negative half cycle of the AC signal. A negative current corresponding to is output. That is, an AC current corresponding to the input AC signal is output, and the humidity sensitive element is driven by this AC current.

On the other hand, the AC current supplied to the humidity sensitive element is obtained by controlling the DC current input from the DC current input section according to the AC signal. Therefore, the alternating current supplied to the humidity sensing element has a fixed relationship, for example, a proportional relationship, with the direct current input from the direct current input section.

Therefore, since the current flowing through the humidity sensitive element can be known by detecting the DC current, the electric resistance value of the humidity sensitive element can be known. In other words, the humidity of the surrounding environment can be measured by detecting the direct current supplied from the direct current input section.

Further, more specifically, the circuit for driving the humidity sensitive element with an alternating current can be configured by a so-called class B push-pull amplifier circuit. Then, by detecting the change in the DC power supply current supplied to the class B push-pull amplifier circuit, the humidity of the surrounding environment can be measured by the same operation as described above.

If the humidity-sensitive element driving device of the present invention is incorporated into a humidity measuring device, a rectifying circuit for converting an alternating current into a direct current unlike the conventional device is not required.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a humidity sensitive element driving device and a humidity measuring device of the present invention will be described below in detail with reference to the drawings.

FIG. 1A is a circuit diagram showing a first embodiment of the humidity measuring apparatus and the humidity sensitive element driving apparatus of the present invention.
As the drive circuit of the humidity sensing element RL, a single power supply type class B push-pull amplifier circuit is used.

The humidity measuring apparatus according to the first embodiment has an AC signal generator VOSC for generating an AC signal, a capacitor C1, a drive circuit 10, a humidity sensing element RL, a DC power supply Vcc, and a current detecting means. It consists of A and.

Further, the humidity sensitive element drive apparatus in the first embodiment comprises a drive circuit 10 and a current detecting means A.

The drive circuit 10 includes an AC signal input section 20 and
It has a DC current input section 22 and an AC output section 24, and one end of the AC signal input section 20 is connected to an AC signal generator VOSC via a capacitor C1. DC current input section 2
2 is connected to the DC power supply Vcc via the current detection means A. The AC output unit 24 is connected to the humidity sensing element RL.

The drive circuit 10 includes an NPN transistor Q.
1, a PNP transistor Q2, a bias circuit, and a capacitor C2. The bias circuit is composed of resistors R1 and R2 and diodes D1 and D2, one end of which is connected to the DC power supply Vcc and the other end of which is grounded. This bias circuit uses a DC supply current I described later when the electric resistance value of the humidity sensing element RL is a finite value.
To generate a bias signal for the transistors Q1 and Q2. The other end of the AC signal input section 20 is connected to the connection point of the diode D1 and the diode D2.

The humidity sensitive element RL is a well-known element which is made of a ceramic material, is driven by an alternating current, and changes its electric resistance value in accordance with a change in relative humidity of the surrounding environment. One terminal of the humidity sensitive element RL is connected to the capacitor C2 via the AC output section 24, and the other terminal is grounded.

As the DC power supply Vcc, for example, a +5 V DC power supply can be used.

The current detecting means A is composed of, for example, a direct current ammeter and is used to detect a current (direct current supply current) I flowing from the direct current power supply Vcc to the collector of the transistor Q1. The relative humidity can be obtained from the current value indicated by the current detecting means A. A capacitor C3 is inserted in parallel with the current detecting means A. That is,
A capacitor C3 is arranged between the DC power supply Vcc and the collector of the transistor Q1 and plays a role of smoothing the pulsating DC supply current I and bypassing a high frequency component.

In FIG. 1A, the DC ammeter as the current detecting means A is arranged so as to detect the current flowing through the collector of the transistor Q1, but it detects the current flowing through the collector of the transistor Q2. You may arrange like this. Also in this case, a detection value equivalent to the measurement of the DC supply current I is obtained.

The AC signal generator VOSC is, for example, 1 KH.
A z sinusoidal AC signal is generated. AC signal generator VOS
The output of C is input to the bias circuit (specifically, the connection point between the cathode of the diode D1 and the anode of the diode D2) via the capacitor C1 and the AC signal input unit 20. The capacitor C1 has a DC blocking function, and only the AC signal supplied from the AC signal generator VOSC is supplied to the drive circuit 1
It is added to 0 to prevent the bias from changing.

Transistor Q1 which constitutes drive circuit 10
Is an NPN type transistor. The collector of the transistor Q1 is connected to the DC power supply Vcc via the current detection means A, and the transistor Q1 has a DC power supply Vcc.
DC power is supplied from. The base of the transistor Q1 is connected to a bias circuit (specifically, a connection point between the resistor R1 and the anode of the diode D1) so that a predetermined bias signal is supplied. Furthermore,
The emitter of the transistor Q1 is connected to the capacitor C2 and the emitter of the transistor Q2.

Transistor Q2 which constitutes drive circuit 10
Is a PNP type transistor. The emitter of the transistor Q2 is connected to the emitter of the transistor Q1 and the capacitor C2 as described above. Further, the base of the transistor Q2 is connected to a bias circuit (specifically, a connection point between the cathode of the diode D2 and the resistor R1) so that a predetermined bias signal is supplied. Further, the collector of the transistor Q2 is grounded.

A capacitor C2 arranged between each emitter of the transistors Q1 and Q2 and the humidity sensitive element RL.
Are charged during the half cycle in which the transistor Q1 is operating and discharged during the half cycle in which the transistor Q2 is operating. This means that the half cycle in which transistor Q2 is operating acts as a power supply for transistor Q2. An alternating current flows through the humidity sensitive element RL according to the charging and discharging of the capacitor C2.

FIG. 2A is a circuit diagram showing a second embodiment of the humidity measuring device and the humidity sensitive element driving device of the present invention.
As a drive circuit for the humidity sensing element RL, a dual power source class B push-pull amplifier circuit is used.

The humidity measuring apparatus according to the second embodiment includes an AC signal generator VOSC for generating an AC signal, a drive circuit 10, a humidity sensing element RL, a DC power supply Vcc, and a second DC power supply Vee. , Current detection means A.

Further, the moisture sensitive element driving apparatus in the second embodiment is composed of a driving circuit 10 and a current detecting means A.

The drive circuit 10 includes an AC signal input section 20 and
It has a DC current input unit 22 and an AC output unit 24, and one end of the AC signal input unit 20 is connected to the AC signal generator VOSC. The DC current input unit 22 is connected to the DC power supply Vcc via the current detection means A. AC output unit 24
Is connected to one end of the humidity sensing element RL.

The drive circuit 10 is an NPN transistor Q.
1, a PNP transistor Q2, and a bias circuit. The bias circuit includes resistors R1 and R2 and diodes D1 and R1 as in the case of the first embodiment.
D2, one end of which is connected to the DC power supply Vcc, and the other end of which is connected to the negative side of the second DC power supply Vee. This bias circuit generates bias signals for the transistors Q1 and Q2 so that a DC supply current I described later flows when the electric resistance value of the humidity sensing element RL is a finite value. The other end of the AC signal input section 20 has a diode D1
And the diode D2.

As the humidity sensitive element RL, the same element as in the first embodiment is used. One terminal of the humidity sensing element RL is connected to the AC output section 24, and the other terminal is grounded and connected to the positive side of the second DC power source Vee.

DC power supply Vcc and second DC power supply Vee
For example, a +5 volt DC power supply can be used.

The structure and operation of the current detecting means A and the capacitor C3 are the same as those in the case of the above-mentioned first embodiment, and therefore their explanations are omitted.

The AC signal generator VOSC is, for example, 1 KH.
A z sinusoidal AC signal is generated. AC signal generator VOS
The output of C is input to the bias circuit (specifically, the connection point between the cathode of the diode D1 and the anode of the diode D2) via the AC signal input unit 20.

Transistor Q1 which constitutes drive circuit 10
Is an NPN type transistor. The collector of the transistor Q1 is connected to the DC power supply Vcc via the current detection means A, and the transistor Q1 has a DC power supply Vcc.
DC power is supplied from. The base of the transistor Q1 is connected to a bias circuit (specifically, a connection point between the resistor R1 and the anode of the diode D1) so that a predetermined bias signal is supplied. Furthermore,
The emitter of the transistor Q1 is connected to the emitter of the transistor Q2.

Transistor Q2 which constitutes drive circuit 10
Is a PNP type transistor. The emitter of the transistor Q2 is connected to the emitter of the transistor Q1 as described above. Further, the base of the transistor Q2 is connected to a bias circuit (specifically, a connection point between the cathode of the diode D2 and the resistor R1) so that a predetermined bias signal is supplied. Further, the collector of the transistor Q2 is connected to the negative side of the second DC power source Vee.

A single power source class B push-pull amplifier circuit according to the first embodiment shown in FIG.
It is essentially the same as the dual power supply class B push-pull amplifier circuit according to the second embodiment shown in FIG.

That is, the capacitor C1 in FIG.
Is inserted to prevent the DC bias from being disturbed by the signal source (AC signal generation circuit VOSC) as described above. If the impedance of the capacitor C1 can be ignored at the signal frequency, AC equivalent. Therefore, the capacitor C1 in FIG. 1A is not always necessary.

Further, the capacitor C2 in FIG.
Has a function corresponding to the second DC power source Vee in FIG. Therefore, in FIG. 2A, the one corresponding to the capacitor C2 is not provided.

In the single-power-supply class B push-pull amplifier circuit, as shown in FIG. 1B, the amplitude of the negative side by the time constant of the capacitance of the capacitor C2 and the electric resistance value of the humidity sensing element RL. 2 is different from the two-power-source class B push-pull amplifier circuit shown in FIG. 2B in that it takes time to reach a steady state. In the case of the circuit shown in FIG. 1B, a charge offset is generated in the humidity sensing element RL by the amount of time required for the negative-side amplitude to reach a steady state, but this occurs unless the capacitor C2 self-discharges. If the problem is solved by a factor such as disconnection, and if there is no discharge through the circuit of the capacitor C2, there will be no delay due to the time constant from the next operation start.

Next, the operation of the humidity measuring device and the humidity sensitive element driving device configured as described above will be described below.

As described above, the humidity measuring device and the humidity sensitive element driving device using the single power source class B push-pull amplifier circuit shown in the first embodiment are the two power sources shown in the second embodiment. This is substantially equivalent to the humidity measuring device and the humidity sensitive device driving device using the class B push-pull amplifier circuit.

Therefore, the operation of the humidity measuring device and the humidity sensitive element driving device using the dual power source class B push-pull amplifier circuit shown in FIG. 2 will be described below. here,
The class B push-pull amplifier circuit is an ideal circuit. Further, the input voltage Vi of the AC signal supplied from the AC signal generator VOSC is assumed to be a sine wave as shown in FIG.

When the input voltage Vi is in the positive half cycle, the transistor Q1 is turned on and the transistor Q2 is turned on.
Turns off. As a result, a path from the DC power supply Vcc to the ground via the transistor Q1 and the humidity sensing element RL is formed, and the DC supply current I (Ic1) flows. In other words, when the AC signal output from the AC signal generator VOSC is in the positive half cycle, a pulsating positive DC current as shown in FIG. 3C is passed. Therefore, the humidity sensing element RL is connected to the collector of the transistor Q1 from the DC power source Vcc.
A direct current that is proportional to the direct current that flows through will flow.

On the other hand, when the input voltage Vi is in the negative half cycle, the transistor Q2 is turned on and the transistor Q1 is turned off. Thereby, the second DC power source Vee
From (ground level), the humidity sensing element RL and the transistor Q
A path is formed through 2 to the second DC power source Vee,
The DC supply current IC2 flows. In other words, when the AC signal output by the AC signal generator VOSC is in the negative half cycle, a pulsating negative DC current as shown in FIG. 3D flows through the collector of the transistor Q2. In this case, the current detecting means A may be connected to the collector of the transistor Q2.

By the above operation, an alternating current alternating in every half cycle of the alternating signal causes an alternating current output section 24 of the drive circuit 10.
The output voltage VO is output from FIG.
The voltage is proportional to the input voltage Vi as shown in FIG. In this way, the alternating current that changes according to the alternating signal input from the alternating signal generator VOSC is supplied to the humidity sensing element RL via the alternating output part 24.

In this case, the transistors Q1 and Q2 act as emitter followers for the AC signal generator VOSC. Therefore, if the impedance of the AC signal generator VOSC is small to some extent, the AC voltage applied to the humidity sensing element RL becomes substantially equal to the AC signal output by the AC signal generator VOSC.

That is, assuming that the transistors Q1 and Q2 operate as an emitter follower every half cycle, the voltage gain Av = VO / Vi is calculated by the humidity sensing element RL.
Although it depends on the electric resistance value of and the characteristics of the transistors Q1 and Q2, it is about “0.99”.

Here, the relationship between the voltage gain Av in the emitter follower and the load resistance (resistance of the humidity sensitive element) RL will be examined in more detail as follows.

FIG. 4A shows an emitter follower, and FIG. 4B shows an AC equivalent circuit using the grounded-emitter hybrid model. In the AC equivalent circuit, the impedances of the input capacitor CIN and the output capacitor COUT can be ignored. Further, since it is driven by voltage (Vin), the resistor RB can be ignored. The internal resistance of the DC power supply Vcc was set to zero. Further, a combined resistance of the resistance RE and the resistance RL ′ is set as a load resistance RL.

The voltage VO at the point E which serves as an output terminal and the input current ib are expressed by the following equations, respectively. VO = (ib + hfe * ib) * RL = (1 + hfe) * ib * RL ... (1) ib = (Vi-VO) / hie ... (2) Here, when the expression (2) is substituted into the expression (1), The following formula is obtained.

[Equation 1] When the VO and Vi terms in the above equation are separated, the following equation is obtained.

[Equation 2] Therefore, the voltage gain Av is expressed by the equation (3).

[Equation 3]

In the above equation (3), hfe = 100, h
FIG. 5 shows the relationship between the load resistance RL and the voltage gain Av when ie = 1K [Ω]. As is clear from FIG. 5, the load resistance R
The voltage gain when L is 1 K [Ω] is “0.990”, and the AC voltage applied to the humidity sensing element RL has a value substantially equal to the AC signal input from the AC signal generator VOSC.

Next, the relationship between the load current io and the DC supply current Icc of the class B push-pull amplifier circuit will be described.

The relationship between the collector current IC1 on the positive side, the DC supply current Icc, and the effective value IO of the load current io flowing through the load resistor RL in the case of the above-mentioned dual power supply system is as follows.

First, since the load current io is a sine wave, it is expressed by the following equation (4). io = Im · sin ωt (4) The effective value IO of the load current io is given by the following equation (5).

[Equation 4]

Since the DC supply current ICC is an average of the collector current ic, it is expressed by the following equation.

[Equation 5] The integration range is 0 to T / 2 because only half a cycle is conducted.

From the equations (5) and (6), the detected current efficiency η is as follows.

[Equation 6]

The theoretical value calculated as described above was confirmed by experiments. The circuit used for the experiment is shown in FIG. In order to obtain a half-wave waveform, the diode D is U1B manufactured by Toshiba Corporation.
C44 was used.

For the diode D, an isolation transformer of Toyoden 100V: 140V is used, and the commercial power source A
C100V, 50Hz was boosted and supplied to 140V.
This is the pure voltage drop Vf of the diode D (about 1.0
This is to reduce the effect of V). In addition, a voltmeter HP3403C TRUE RMSVO is used to measure each voltage.
LT METER was used.

For the measurement, the voltage V1 on the anode side of the diode, the voltage V2 on the cathode side of the diode, and the voltage V3 across the resistor R2 were measured for each of the case where the switch SW was opened and the case where the switch SW was closed. .
In measuring each of the voltages V1, V2, V3, AC (effective value of only AC component), AC + DC (effective value including DC component), and DC (DC without AC component) of the voltmeter
The measurement was performed by reading three types of values of component only = DC average value). The measurement results are shown in Table 1.

[Table 1]

Detecting the current efficiency η in each case, η1 = V2 (DC) / V1 (ON) = 44.9% η2 = V2 (DC) / V1 (OFF) = 44.7% η3 = V3 (DC) / V3 (AC, ON) = 45.0% is obtained. This result agrees with the theoretical value “η = 0.450” described above with an error of 0.67% or less.

As described above, assuming that the drive circuit 10 is lossless, in other words, the transistors Q1 and Q2 are ideal transistors, 45% of the effective value of the AC drive current flowing through the humidity sensing element RL. DC supply current I (I
It will be measured by the current detection means A as C1).

Therefore, if the AC signal output from the AC signal generator VOSC is kept constant, the electric resistance value R of the humidity sensing element RL is reduced.
S is calculated by the following formula. Electric resistance value RS = k × Vosc / I / 0.45 (7) Here, Vosc is the voltage of the AC signal generated by the AC signal generator VOSC, I is the DC supply current, and k is a constant.
In the ideal case, k = 1.

Therefore, in consideration of the relative humidity-electric resistance change characteristic of the humidity sensing element RL, the voltage value of the AC signal Vosc can be measured so that the DC supply current I can be measured in a range where the sensitivity of the current detecting means A is optimized. If it is determined, the humidity can be measured with good accuracy.

FIG. 7 shows a case where a humidity sensitive element made of a ceramic material composed of SnO ₂ + apatite is used and the humidity sensitive element driving apparatus and the humidity measuring apparatus of this embodiment are used to measure the voltage V _{cc of the} DC power source Vcc. To + 4.5V, + 5.0V and +
Relationship between measurement result of electric resistance value of humidity sensitive element RL and power supply current I when changed to 5.5 V, and measurement result of electric resistance value of humidity sensitive element RL and current flowing through humidity sensitive element RL It is a figure which shows the relationship with I ', and also the ratio I / I' of the power supply current I in each electric resistance value of the humidity sensitive element RL, and the current I'flowing through the humidity sensitive element RL. The current I ′ (rms) flowing through the humidity sensing element RL is
It was calculated from the terminal voltage (rms). The vertical axis and the horizontal axis of FIG. 7 are logarithmic scales.

As can be understood from FIG. 7, the humidity sensitive element R
It was confirmed that the electrical resistance value of L and the power supply current I have a substantially logarithmic linear relationship. This means that the electric resistance value of the humidity sensing element RL, that is, the humidity value can be directly obtained by multiplying each value of the power supply current I by a predetermined coefficient.

Further, the ratio of the power supply current I and the current I ′ flowing through the humidity sensitive element RL at each electric resistance value of the humidity sensitive element RL is substantially constant. This means that the electric resistance value of the humidity sensitive element RL can be obtained by measuring the power supply current I instead of the current I ′ flowing through the humidity sensitive element RL. Therefore, the present invention, which is characterized in that the electric power supply current I is measured and the electric resistance value of the humidity sensitive element RL is obtained, should be accepted.

In the above embodiments, the case where the ceramic moisture sensitive element made of SnO ₂ + apatite is used as the moisture sensitive element RL has been described, but the present invention is not limited to the ceramics if the electric resistance value changes due to moisture absorption. Can be applied regardless of the type, and the same action and effect as those of the above-described embodiment can be obtained. Further, the frequency of the AC signal generated by the AC signal generator can be about 1 to 100 kHz. Voltage V _cc of the DC power source Vcc can be changed as appropriate. Further, the drive circuit 10 is not limited to the circuit described in the embodiment, and the design can be appropriately changed.

[0075]

As described in detail above, according to the present invention,
It is possible to provide a humidity-sensitive element driving device and a humidity measuring device that do not require a rectifying circuit or the like and can improve measurement accuracy with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram and an operation waveform diagram showing a first embodiment of a humidity-sensitive element driving device and a humidity measuring device according to the present invention.

FIG. 2 is a circuit diagram and an operation waveform diagram showing a second embodiment of the humidity-sensitive element driving device and the humidity measuring device according to the present invention.

FIG. 3 is a diagram for explaining a relationship between an input / output voltage and a current supplied from a DC power supply according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the emitter follower according to the second embodiment of the present invention.

FIG. 5 is a diagram for explaining changes in the voltage gain Av of the emitter follower according to the second embodiment of the present invention due to the load resistance RL.

FIG. 6 is a diagram showing a circuit used for an experiment of a detected current gain η according to a second embodiment of the present invention.

FIG. 7: Moisture-sensitive element RL measured using the apparatus of the present invention
Between the electric resistance value of the sensor and the power supply current I, the humidity sensing element RL
Relationship between the electric resistance of the humidity sensitive element RL and the current I ′ flowing through the humidity sensitive element RL, and the ratio I / of the power supply current I and the current I ′ flowing through the humidity sensitive element RL at each electric resistance value of the humidity sensitive element RL.
It is a figure which shows the relationship with I '.

[Explanation of symbols]

 10 Drive Circuit 20 AC Signal Input Section 22 DC Current Input Section 24 AC Output Section RL Humidity Sensing Element Q1, Q2 Transistors R1, R2 Resistance C1, C2, C3 Capacitor D1, D2 Diode A DC Ammeter Vcc, Vee DC Power Supply VOSC AC Signal generator

Claims (8)

[Claims] 1. A humidity-sensitive element driving device for driving a humidity-sensitive element made of a ceramic material, the electric resistance value of which changes according to relative humidity, and which is AC-driven, wherein an AC signal input section receives an AC signal. A direct current input portion to which a direct current is input, and the direct current input from the direct current input portion to an alternating current amplified according to an alternating current signal input from the alternating current signal input portion. And an electric current detection means for detecting a direct current flowing through the direct current input portion, and a resistance value of the humidity sensitive element based on the direct current detected by the current detection means. A humidity-sensitive element driving device, characterized in that 2. A humidity-sensitive element driving device for driving a humidity-sensitive element made of a ceramic material, the electric resistance value of which changes according to relative humidity, and which is AC-driven, wherein an AC signal input section receives an AC signal. And a direct current input part to which a direct current is input, converting the direct current input from the direct current input part into an alternating current amplified in accordance with the alternating current signal input from the alternating current signal input part. And a current detecting means for detecting a direct current input to the class B push-pull amplifying circuit, and the direct current detected by the current detecting means. The humidity sensitive element driving device is characterized in that the resistance value of the humidity sensitive element is measured by the above. 3. The humidity sensitive element drive device according to claim 2, wherein the class B push-pull amplifier circuit is a single power supply type amplifier circuit. 4. The humidity sensitive element drive device according to claim 2, wherein the class B push-pull amplifier circuit is a dual power supply type amplifier circuit. 5. A humidity sensitive element made of ceramic whose electric resistance value changes according to relative humidity and is driven by an alternating current, an alternating current signal generator for generating an alternating current signal, and an alternating current generated by the alternating current signal generator. An alternating current signal input portion to which a signal is input; a direct current power source; a direct current input portion to which a direct current supplied from the direct current power source is input; and the direct current input from the direct current input portion to the alternating current An AC output unit which converts the AC current amplified according to the AC signal input from the signal input unit and supplies it to the humidity sensitive element, and a current detection unit which detects a DC current flowing through the DC current input unit. A humidity measuring device comprising: a resistance value of the humidity sensitive element, which is measured by a direct current detected by the current detecting means. 6. A humidity sensitive element made of ceramic whose electric resistance value changes according to relative humidity and is driven by an alternating current, an alternating current signal generator for generating an alternating current signal, a direct current power supply, and the alternating current signal generator. It has an alternating current signal input portion to which the generated alternating current signal is input, and a direct current input portion to which the direct current supplied from the direct current power source is input, and the direct current input from the direct current input portion , A class B push-pull amplifier circuit for converting to an AC current amplified according to the AC signal input from the AC signal input section and supplying the AC current to the humidity sensitive element, and input to the class B push-pull amplifier circuit A humidity measuring device comprising: a current detecting means for detecting a direct current, wherein the resistance value of the humidity sensitive element is measured by the direct current detected by the current detecting means. 7. The humidity measuring apparatus according to claim 6, wherein the class B push-pull amplifier circuit is a single power supply type amplifier circuit. 8. The humidity measuring apparatus according to claim 6, wherein the class B push-pull amplifier circuit is a dual power supply type amplifier circuit.