JPS6157841A - Humidity detecting device - Google Patents

Abstract

PURPOSE:To use a single power source and to obtain a humidity detection signal in which the influence of ambient temperature and a source voltage and characteristic variance are reduced by generating an AC waveform having a positive and a negative symmetric waveform on the basis of a reference voltage obtained by dividing the DC source voltage. CONSTITUTION:The reference voltage VB generated by a circuit B has the center value of the generated AC waveform of a circuit C, and the output V1 of the operational amplifier 4 of the circuit C is a rectangular wave having an AC waveform which has equal positive and negative amplitudes about the voltage VB. The period of this rectangular wave is equal to the frequency during the measurement of the resistance of a humidity sensor 12 and an output V2 passed through a resistance 9 and a capacitor 10 has a high frequency component reduced. When the output V2 is applied to a sensor part D, the voltage V3 at the connection point between the sensor 12 and a temperature sensing element 13 is in a shape close to the output V1 and its amplitude correspond to the humidity detected by the sensor 12. Then, a circuit F inputs the voltage V3 at a terminal (n) of an operational amplifier 15 and when it is higher than the voltage V7 at a terminal (i), the output V4 goes up to a high level to charge a capacitor 20; and the voltage V5 at the time of the completion of the charging is maintained and outputted by an operational amplifier 21 as a humidity detection signal V0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a humidity detection device that continuously detects the relative humidity of air in room air conditioners, dehumidifiers, humidifiers, and the like.

Conventional structure and problems Ceramic and organic polymer-based humidity sensors have been widely used as relatively low-cost humidity sensors.
The conventional humidity detection device using these humidity sensors was
As shown in the figure. In the figure, A' is a DC power supply, with positive and negative DC voltages Vcc.

and -Vcc. C' is operational amplifier 26
, a sine wave oscillation circuit consisting of a bidirectional Zener diode 27, a resistor, and a capacitor. D' is capacitor 11
, a humidity sensor 12 whose resistance value changes depending on the relative humidity of the air, a temperature sensing element (thermistor) 13 for temperature compensation of the humidity sensor 12, and an operational amplifier 27. F/n smoothing amplifier circuit, operational amplifier 28
, diodes 29 and 30 constitute a half-wave rectifier, a resistor 19 and a capacitor 20 smooth the signal, and the smoothed signal is buffered by an operational amplifier 21 to output a humidity detection signal 0 to the outside.

In this configuration, the humidity sensor 12i11: for example, a high-molecular organic type is used, and in this case, the resistance characteristic against the relative humidity H of the air exhibits the characteristics as shown in FIG. T1 in the diagram. T2. T3 is each humidity sensor 12
The resistance value Rs decreases as the ambient temperature increases. This change in resistance value depending on the ambient temperature is almost the same as that of a negative temperature sensing element (a so-called thermistor). Note that the resistance value Rs in FIG. 2 more accurately indicates the impedance class for alternating current. In other words, the equivalent circuit of this type of humidity sensor is similar to a parallel connection of a resistor and a capacitor, and it has some electrostatic charge, but when DC is applied, which is easy to use, the moisture in the air is ion movement occurs irreversibly, and its reliability is
In order to reduce the humidity, the voltage waveform applied to the humidity sensor 12 is used as an AC waveform, and the characteristic value for the humidity H is defined by the impedance value of ff11BfL, which is a sine wave of a predetermined frequency.

Therefore, in FIG. 5, a sine wave signal v7 of a predetermined frequency and amplitude is generated by a sine wave oscillation circuit C', and the DC component is cut using a capacitor 11, and the signal is applied to a humidity sensor 12. . The temperature sensing element 13 compensates for the temperature characteristics of the humidity sensor, and emits a sine wave signal v8 having an amplitude corresponding to the humidity H at the output end of the sensor section σ. The smoothing amplifier circuit F' is
The sine wave signal (1)8 is rectified to obtain a positive DC smoothed signal v9 that is approximately proportional to its negative peak value, and a humidity detection signal v0 corresponding to the humidity H is output from the operational amplifier 21 as a buffer.

Here, this conventional humidity detection device has its DC power source A'
It uses two power supply formats. This i-j: The humidity detection signal v0 should be set in a range from approximately zero volts (when the humidity is low) to several volts (when the humidity is high) so that it can be easily used by an external circuit.

However, in recent electronic devices using microcomputers and the like, medium power supplies are being used in order to make the devices smaller and lower in cost, and moreover, 5-inch power supplies are the mainstream. The unsteady sine wave oscillator circuit C' is relatively low cost as a circuit that generates a sine wave, but if the characteristics are stabilized, the waveform distortion becomes large, which adversely affects the output characteristics, and the oscillation frequency and amplitude are significantly reduced. changes relatively easily due to component variations, which increases the variation in the humidity detection signal vO.

1 Therefore, this conventional humidity detecting device has drawbacks in these points, and a low-cost humidity detecting device that has performance equal to or better than this conventional example has not yet been realized. .

OBJECTS OF THE INVENTION The present invention solves the conventional drawbacks and can be configured with a rat-power supply, and the characteristics of the humidity sensor or the entire device due to the influence of the ambient temperature, the influence of variations in the power supply voltage, and the variations of circuit components. It is an object of the present invention to provide a humidity detection device that reduces the degree of fluctuation as much as possible and continuously emits a humidity detection signal in response to changes in humidity.

Structure of the Invention The humidity detection device M of the present invention includes a DC power supply that supplies a single DC power supply voltage to other circuits inside the device, and a reference voltage that generates a reference voltage obtained by dividing the DC power supply voltage using a resistor or the like. A generation circuit, an oscillation circuit that generates alternating current waveforms whose positive and negative waveforms are symmetrical with respect to the reference source pressure, and a humidity sensor (mainly ceramic, organic high The sensor section consists of a temperature-compensating temperature-sensitive element (thermistor) connected in series with a temperature-compensating temperature-sensitive element (thermistor) of the humidity sensor, and an AC signal from the connection point of the humidity sensor and temperature-sensitive element is input to the non-inverting input terminal of the operational amplifier. , the output signal of the operational amplifier is rectified and smoothed using a diode, a resistor, and a capacitor, and the signal is output to the outside as a temperature detection signal, and is also transmitted from the output section through the resistor and from the DC power supply through the resistor. and a smoothing amplifier circuit, each of which is input to the inverting input terminal of the operational amplifier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A humidity detection device according to the present invention will be explained in detail by way of a practical example shown in the accompanying drawings.

FIG. 1 is a configuration diagram of a humidity detection device of the present invention.

In the figure, A is a DC power supply that provides a single DC power supply voltage Vcc, and B is a reference voltage generation circuit that generates a reference voltage VB.The DC power supply voltage Vcc is divided by resistors 1 and 2, and its value is The operational amplifier 3 converts it to low impedance and generates a reference voltage vB. C is an oscillation circuit that generates an AC waveform close to a rectangular wave, and operational amplifier 4, i
It is composed of resistors S, A, 7 capacitors 8, resistors 9, and capacitors 10. D is a sensor section, which includes a capacitor 11 for cutting the DC component, and a humidity sensor 12.
, a temperature sensing element (thermistor) 3. F is a smoothing amplifier circuit, which includes a resistor 14, an operational amplifier 15, a diode 16, a capacitor 17 for noise prevention, a resistor 18.
19, capacitor 20, operational amplifier 21, resistor 22.2
Consists of 3.24.25.

Next, the operation will be explained. The humidity characteristics of the humidity sensor 12 are as shown in FIG. 2 described above. FIG. 4 is an explanatory diagram of the operation and shows voltage waveforms at various parts in the configuration shown in FIG.

The reference voltage EVB generated by the unchanging reference voltage generation circuit B provides the center value of the AC waveform generated by the oscillation circuit C. That is, the output v1 of the operational amplifier 4 of the oscillation circuit C becomes a rectangular wave as shown in FIG. 4, but the DC power supply voltage Vcc=5V
Then, when the output is A, it will be approximately 3.7V, and the low special value will be 0.7V, and the center value will be 2.2■, so
When the reference voltage V)3=2.2v, the output (1) can be regarded as an AC waveform with equal positive and negative amplitudes centered on the reference voltage EVB.

The period T of this rectangular wave is, for example, IKHz, which is the same value as the frequency at which the resistance Rs of the humidity sensor 12 is measured. The resistor 9 and capacitor 10 having relatively low resistance value, when the rectangular wave of output 1 is applied to the humidity sensor 12,
This is a filter provided to prevent the influence of electrostatic charge from appearing on the humidity sensor 12, and the output ■2
As shown in Fig. 4, the rising edge and the falling edge are slightly blunted, and the high frequency range is reduced.

When the output v2 of the oscillation circuit C is applied to the sensor section with reference voltage vB as a reference, the humidity sensor 12 and the temperature sensing element 13
The voltage v3 at the connection point has a shape similar to the output v1 as shown in FIG. 4, and its amplitude corresponds to the humidity H detected by the humidity sensor 12. Now the amplitude of the square wave of output ■1 is E
If the resistance value of the humidity sensor 12 is Rs and the resistance value of the temperature sensing element is RT, then the amplitude of the voltage v3 with respect to the reference voltage vB is approximately E3, and Rs changes with respect to the humidity H. The amplitude E3 changes accordingly.

Next, in the smoothing amplifier circuit F, the AC voltage v3 is input to the non-inverting input terminal n, and is compared with the voltage v7 of the inverting input terminal i, and while the voltage v3 is high, the output v4 of the operational amplifier 15 is
is at the fin level as shown in Figure 4, and the diode 16
, the capacitor 20 is rapidly charged via the resistor 19. When the output v4 is at a low level, the charge in the capacitor 20 is discharged through the resistors 19 and 18, but the resistor 18 has a resistance of 1 0 .

Since the resistance value is selected to be sufficiently large compared to the resistor 19, the voltage 5 at the time when the 20 capacitors are fully charged will be maintained for a while.

This voltage v5 is impedance-converted by the operational amplifier 21 and outputted to the outside as a humidity detection signal V□. Next, the resistors 22 to 25 are connected to the inverting input terminal i of the operational amplifier 15.
It serves to determine the output gain and operating point of the humidity detection signal vo by giving a negative feedback signal to the humidity detection signal vo. Here resistance 24.25
is selected to be sufficiently small with respect to the resistance 22.23.

In this connection, the resistors 22 and 23 are selected so that when the voltage 3 is equal to the reference voltage V13, that is, when the humidity H is approximately 0%RH, the humidity detection signal V□=OV. That is, it is selected so that V 7 = V B, which is favorable for V □ = OV.

As a result, the amplitude E3 of the voltage V3 and the humidity detection signal V() have a relationship expressed by the following equation.

\Therefore, the amplitude E3 of the voltage v3 and the humidity detection voltage vo are proportional. Therefore, the humidity detection voltage V□ with respect to the humidity H detected by the humidity sensor 12 is as shown in FIG. 3, where H=40~
Appropriate characteristics are given at 70% RH culmness, and it is useful for humidity detection in air conditioning-related applications. Note that the temperature characteristics of the humidity sensor 12 are extremely well compensated for by the temperature sensing element 13, and the temperature characteristics of the humidity sensor 12 are
In the range of =40 to 70%RH, the culm degree is ±2%RH for a temperature of 0 to 408C.

This configuration is extremely convenient when determining the ratio of other circuits that share VCC, such as an AD converter, because the oscillation circuit C1, smoothing amplifier circuit F, etc. exhibit characteristics that are different from the DC power supply voltage Vcc.

1-Explained in detail with reference to an embodiment shown in FIG.
An operational amplifier 4.15i1'1' comparator may be used, and depending on the case, a resistor 24.25 may be connected to both ends of the capacitor 20 to achieve almost simultaneous characteristics.

If the operating temperature range is extremely small, such as 20°C ± 1°C, it is of course possible to replace the temperature sensing element 13 with a fixed resistor, and the value of the temperature sensing element 13 According to Takumi, the relationship between the humidity detection signal V□ and the humidity H shown in FIG.
Good characteristics can be obtained in the range of 0 to 50% RH, and the target KI5 can be designed as appropriate depending on the target.

Note that if there is a problem if the voltage applied to the humidity sensor 12 is not a sine wave, it is of course possible to use a sine wave oscillation circuit as the oscillation circuit C, and almost the same output characteristics can be obtained.

Furthermore, although one end of the resistor 22 is connected to the DC power supply voltage Vcc, it is also possible to connect it to a point that provides an appropriate DC voltage.

Effects of the Invention - As mentioned above, the humidity detection device of the present invention can operate with a single DC power supply voltage, for example +5V, and its humidity detection signal V
The output range of □ is possible from the vicinity of the DC power supply voltage (for example, almost zero volts), and a sufficiently large change in characteristics with respect to changes in humidity H can be freely obtained, resulting in low cost, miniaturization,
Extremely superior performance, with high performance and easy general-purpose integration.

It is expected to have high industrial value.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a humidity detection circuit in an embodiment of the present invention, FIG. 2 is a characteristic diagram of the humidity sensor, FIG. 3 is a characteristic diagram of the humidity detection signal in FIG. 1, and FIG. FIG. 5 is a configuration diagram of a conventional humidity detection circuit. A: DC power supply, B: Reference voltage generation circuit,
C...Oscillation circuit, D...Sensor section, F...
... Smoothing amplifier circuit, 12 ... Humidity sensor, 13
... Temperature sensing element, 15 ... Operational amplifier, 16
...Diode, 19...lf anti, 2o...
...Capacitor, 22.23.24.25...
Resistor, V+...Non-inverting input terminal, ■-...
- Inverting input terminal, Vs...Reference voltage, V□humidity detection signal.

Claims (1)

[Claims] A DC power supply that supplies a single DC power supply voltage to each of the following circuits, a reference voltage generation circuit that generates a reference voltage obtained by dividing the DC power supply voltage, and a an oscillation circuit that generates alternating current waveforms having positive and negative waveforms, a humidity sensor that changes a resistance value in accordance with a change in humidity between an output terminal of the oscillation circuit and the reference voltage, and the humidity sensor. A sensor section in which a temperature sensing element for compensating temperature characteristics is connected in series, and an output signal of an operational amplifier in which a signal at a connection point between the humidity sensor and the temperature sensing element is inputted to a non-inverting input terminal are connected to a diode, Smoothing is performed using a resistor and a capacitor, and the smoothed signal is outputted to the outside as a humidity detection signal, and a bias signal is applied to the inverting input terminal of the operational amplifier via the resistor from the DC power supply voltage, and further from the humidity detection signal. A humidity detection device comprising a smoothing amplifier circuit that provides a negative feedback signal via a resistor.