JPH0795055B2 - Water content detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electronic water content detection device, and more particularly, to the water content in a subject such as a gas phase or a liquid phase (specific examples include: (Amount of water in air, amount of water in sealing gas in insulating containers filled with insulating oil such as transformer gas and insulating oil, amount of sealing gas in various oil tanks and amount of oil in oil)
The present invention relates to a digital electronic water content detection device including a water content detection element whose electrostatic capacity is variable according to the change of.

2. Description of the Related Art Conventionally, this type of electronic water content detecting device has been constructed as shown in FIGS. 9 and 10, for example. That is, in the detection device of FIG. 9, a capacitance-type moisture content detection element C _H whose capacitance changes in accordance with a change in moisture content is used as a moisture sensor, and a constant frequency from the oscillation circuit 1 This moisture content detecting element is connected to the AC voltage via the DC blocking capacitor C _1.
The analog voltage signal, which is supplied to C _H and changes according to the change in the water content from the water content detection element C _H, is amplified by the amplifier circuit 2 and then converted into a digital signal by the analog-digital converter 3, A digital signal is sent to the microcomputer 4 to calculate the water content detected by the water content detection element C _H. A constant operating voltage is supplied from the constant voltage circuit 5 to the oscillation circuit 1, the amplification circuit 2, and the analog-digital converter 3, and R ₁ and R ₂ in the figure are resistors.

On the other hand, in the detection device of FIG. 10, two inverters 6 and 7 connected in series such as a C-MOS type Schmitt inverter and a resistor R'inserted in the feedback circuit of the inverter 6 of the preceding stage are the same as those of the preceding stage. of the connected capacitive on the input side of the inverter 6 by the water content detecting device C _H constitute a CR oscillation circuit for generating a square-wave pulse signal, the water content detecting device C _H is the frequency determining element The output frequency of the CR oscillation circuit is correspondingly changed by changing the electrostatic capacitance according to the change of the water content, and this oscillation output, that is, a square wave pulse signal is sent to the microcomputer 4, and the counter in the microcomputer 4 is The digital signal input by is counted, the output frequency of the oscillation circuit is detected, and the water content corresponding to the frequency is calculated.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the water content detecting device configured as shown in FIG. 9 described above, since a change in the detected water content corresponds to a weak analog voltage change, Errors are likely to occur due to the mixing of low-voltage noise. Also, since the circuit is composed of analog circuits such as an oscillation circuit, an amplifier circuit, a constant voltage circuit, and an analog-digital converter, the number of parts is large, and the size and size are low. There was a limit to reducing power consumption and cost.

On the other hand, in the water content detection device configured as shown in FIG. 10, the water content detection element C _H is provided between the two ends (point a).
As shown in FIG. 11, since a voltage in which an AC voltage is superimposed on a DC voltage proportional to the power supply voltage of the inverters 6 and 7 used in the CR oscillator circuit is applied, an excessive voltage causes a moisture content detection element. However, there is a drawback in that C _H is involved, which causes dielectric breakdown of the sensing element. In particular, when a voltage having a DC component is applied to a moisture content sensing element made of aluminum oxide or the like, deterioration of the characteristics of the sensing element is likely to occur due to polarization, dielectric breakdown and the like. Further, the water content detection element C _H has a temperature-dependent characteristic, and even if the water content is the same, the capacitance value of the detection element varies depending on the temperature.

Therefore, as shown in FIG. 12, in addition to the moisture content detection circuit 9 that processes the detection output of the moisture content detection element 8, a temperature detection circuit 11 that processes the detection output of the temperature detection element 10 is provided. Is connected to an analog-to-digital converter 13 via a multiplexer 12, and this multiplexer 12 is switched and controlled by a control signal from the microcomputer 4 via a control line 4a to output the water content from the water content detection circuit 9. For example, a water content detection device that alternately supplies the temperature output from the temperature detection circuit 11 to the microcomputer 4 and corrects the water content output value according to the temperature output value to prevent an error due to a temperature change. Proposed. However, if the temperature detection circuit is separately provided, the number of parts is further increased, the power consumption is increased, the size is increased, and the cost is increased.

Therefore, a main object of the present invention is to provide a compact and highly reliable digital water content detecting device having a simple circuit configuration in which a DC voltage component is not applied to the water content detecting element.

Another object of the present invention is to provide a compact and highly reliable digital water content detection device capable of correcting a detection error due to a temperature change of a water content detection element with a single simple circuit configuration. .

Means for Solving the Problems The above object is achieved by the water content detection device according to the present invention. In summary, the present invention provides a pulse signal generation circuit,
Electricity forming a CR time constant circuit between the capacitance type moisture content detection element connected to the pulse signal generation circuit and the capacitance of the moisture content detection element connected to the pulse signal generation circuit. In a water content detection device including a resistance element,
Oscillating means for outputting a pulse signal according to a change in capacitance of the water content detecting element, and counting the number of pulses of the pulse signal output from the oscillating means in a certain period of time, and based on the counting result, the water content. And a DC component removing unit that removes the DC component applied to the moisture content detecting element.

In one embodiment of the present invention, the DC component removing means is connected to an input side of the pulse signal generating circuit, and periodically switches the polarity of the moisture content detecting element to connect to the input side of the pulse signal generating circuit. It consists of two switches to connect.

In another embodiment of the present invention, the DC component removing means is an electric resistance element connected in parallel with the moisture content detecting element, and an electrostatic capacitance element connected in series with a parallel circuit of these elements. It consists of

In still another embodiment of the present invention, a temperature detecting element having an electric resistance variable according to a temperature change in a subject in which the water content detecting element is positioned is provided, and the water content detecting element due to the temperature change is provided. The detection error of is corrected.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit configuration diagram showing a first embodiment of a water content detecting device according to the present invention. In this embodiment as well, the capacitance-type water content in which the capacitance changes in accordance with the change in the water content. The sensing element C _H is used as a moisture sensor. The square wave pulse signal generating circuit 20 which is an oscillating means includes an inverter 21 such as a C-MOS type Schmitt inverter, a resistor R for determining a pulse frequency inserted in a feedback circuit of the inverter 21, and an inverter 21. _A CR oscillator circuit is composed of two analog switches SW _A and SW _B connected to the input side, and the capacitance type moisture content detection element C _H for pulse frequency determination connected between the movable contacts of these switches. is doing.
The two analog switches SW _A and SW _B are water content detecting elements.
It is a changeover switch that functions as a DC component removing means for canceling the DC voltage component applied to C _H , each having one movable contact and two fixed contacts, and through a control line 22a from a microcomputer 22 which is a digital arithmetic processing means. Each movable contact is connected to either one of the two fixed contacts by the control signal. As shown,
One of the two fixed contacts of the two switches SW _A and SW _B is connected to the input of the inverter 21, and the other fixed contact is grounded. And at the time of this figure, one switch (SW
The movable contact of _A ) is connected to the fixed contact that is connected to the input of the inverter 21, and the movable contact of the other switch (SW _B ) is connected to the fixed contact that is connected to ground. Now, when the level of the control signal from the microcomputer 22 is switched from, for example, low level to high level, the movable contacts of the two switches respectively move and become the opposite of the illustrated connection mode, and the water content detection element C _H Will be connected between the input of the inverter 21 and ground with the polarities reversed.

In the water content detection device having the above configuration, two switches SW
_{When A} and SW _B are in the connection mode shown in the drawing or the connection mode opposite to that shown above, the moisture content detecting element C _H has a DC voltage component V _DC (of the inverter 21 as shown in FIG. 2A). Power-supply voltage)
A voltage in a state in which an AC voltage is superimposed on is applied. Here, the voltage level of the control signal from the microcomputer 22 through the control line 22a is set to a high level (H) in the first half and a low level in the second half at every cycle T as shown in FIG. When the movable contacts of the two switches SW _A and SW _B are switched and connected in the first half and the second half of the cycle T, respectively, the polarity of the water content detection element C _H is switched in the first half and the second half of the cycle T. The voltage applied to the sensing element C _H becomes an alternating voltage in which the DC voltage component is canceled as shown in FIG. 2 (c). Therefore, a voltage with no DC component is applied to the moisture content sensing element C _H , so that an excessive voltage is not applied to the sensing element as in the conventional case, and polarization of the sensing element, insulation breakdown, etc. Since this does not occur, it is possible to prevent the deterioration of the characteristics of the sensing element and improve the reliability. Further, since the switch is simply added, the size of the device can be reduced.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the water content detecting device according to the present invention. In this embodiment, the analog switch as in the first embodiment is not used as the DC component removing means, Instead, connect a DC resistor R ₀ in parallel with the capacitance-type moisture content detection element C _H for determining the pulse frequency of the square wave pulse signal generation circuit 20, and connect a capacitor C ₀ in series with this CR parallel circuit. Further, the connection is made. Since the other constituent elements are the same as those in FIG. 1, corresponding elements are designated by the same reference numerals and the description thereof will be omitted.

With this configuration, the DC voltage component of the voltage applied to the water content detection element C _H is Therefore, this DC component is exclusively a series capacitor.
It is applied between C ₀ , that is, between-in the figure, and is hardly applied between both ends of the water content detection element C _H , that is, between-in the figure. Therefore, the voltage between both ends of the water content detecting element C _H becomes an alternating voltage as shown in FIG. 4 and the direct current component is removed. Therefore, as in the first embodiment, an excessive voltage is applied to the detecting element. And the polarization and dielectric breakdown of the sensing element do not occur, so that the deterioration of the characteristics of the sensing element can be prevented.

Since the voltage applied to the moisture content detecting element C _H is divided by the capacitor C ₀ connected in series, the moisture content detecting element C _H can be selected by appropriately selecting the value of the capacitor C ₀ in series. The applied voltage can be varied and thus
It is possible to reliably prevent an excessive voltage from being applied to the water content detection element C _H , and the reliability is further improved.

FIG. 5 is a circuit configuration diagram showing a third embodiment of the water content detecting device according to the present invention. This embodiment is a combination of the first embodiment of FIG. 1 and the second embodiment of FIG. It is a thing. According to the configuration of the present embodiment, the DC component of the voltage applied to the water content detection element C _H can be completely removed. Therefore, the water content detection can be performed more reliably than in the first and second embodiments. It is possible to prevent an excessive voltage from being applied to the element C _H. Thus, a compact and highly reliable water content detection device can be obtained. In FIG. 5, elements corresponding to those in FIGS. 1 and 3 are designated by the same reference numerals.

FIG. 6 is a circuit configuration diagram showing an example of a simple water content detection device to which the present invention in which the temperature detection function is added to the water content detection device can be easily applied. This moisture content detecting device is connected with a resistor R for determining a pulse frequency inserted in a feedback circuit of an inverter 21 constituting a square wave pulse signal generating circuit 20 in series with a switch SW _E consisting of a three-state buffer,
In parallel with the series circuit of the resistor R and the switch SW _E, a series circuit of a resistance change type temperature detecting element R _T such as a thermistor and a switch SW _D composed of a 3-state buffer is connected, and further the inverter 21 insert the changeover switch SW _C analog between the capacitive moisture content sensing element C _H for the input side and the pulse frequency determination, the changeover switch SW _C
Is configured to select one of the water content detection element C _H and the capacitor C _T and connect it to the input side of the inverter 21, and each switch SW _C , SW _D , SW _E has a control line 22a,
A control signal is supplied from the microcomputer 22 via 22T and 22R, respectively, and controls these switches.

In the above configuration, if the changeover switch SW _C selects the water content detecting element C _H by the control signal from the microcomputer 22, the switch SW _D is turned off, and the switch SW _E is turned on, the circuit of FIG. Since the circuit configuration is as shown in FIG. 7A, a normal water content detection circuit is configured. On the other hand, the changeover switch SW _C selects the capacitor C ₁ by the control signal from the microcomputer 22, and the switch S C
If W _D is on and switch SW _E is off, then
Since the circuit shown in the figure has the circuit configuration shown in FIG. 7 (b), it constitutes a normal temperature detecting circuit. Thus, since the moisture content detection circuit and the temperature detection circuit can be configured with one simple circuit configuration, the number of parts increases and the power consumption increases as in the case where the temperature detection circuit is provided separately. However, the disadvantages of increasing the size of the device and the cost increase are eliminated.

FIG. 8 is a circuit configuration diagram showing a fourth embodiment in which the present invention is applied to the water content detecting device of FIG. 6, and this embodiment is the same as the third embodiment of the present invention shown in FIG. This is a combination of the temperature detection functions of FIG. In the present embodiment, the capacitor C ₀ that is a series capacitance that divides the voltage applied to the moisture content detection element C _H is also used as the capacitor C _T that is the capacitance used during temperature detection. That is, one capacitor is commonly used so that the number of parts does not increase.

According to this embodiment, it is possible not only to completely prevent an excessive voltage from being applied to the water content detection element C _H , but also to correct a detection error of the water content detection element due to a change in temperature. There is a remarkable advantage that accurate and highly accurate water content detection can be performed. Further, the device can be downsized.

The above embodiments are merely examples of the present invention, and the circuit configuration, the elements to be used, and the like can be arbitrarily changed as necessary. For example, an electronic switch may be used instead of the analog switch, or an electronic switch other than a 3-state buffer, a logic gate, or an analog switch may be used. Of course, an inverter other than the C-MOS Schmidt inverter or another circuit element may be used, and a resistance change type temperature detection element or an element other than the microcomputer may be used. Further, the temperature detecting function shown in FIG. 6 can be combined with the embodiment of the present invention shown in FIGS. 1 and 3, and can of course be applied to a moisture amount detecting circuit having a circuit configuration other than that shown. . Further, the oscillating means may generate a pulse other than the square wave pulse.

EFFECTS OF THE INVENTION As described above, since the water content detecting device according to the present invention includes the DC component removing means for removing the DC component applied to the water content detecting element, an excessive voltage is applied to the water content detecting element. And the polarization and dielectric breakdown of the sensing element do not occur, so that the deterioration of the characteristics of the sensing element can be prevented. Moreover, since the DC component removing means has a simple circuit configuration, it hardly causes increase in power consumption and cost. Furthermore, the temperature detection function can be added by adding the minimum number of elements, so the size of the device can be increased without increasing the number of parts and power consumption, compared to the case where a temperature detection circuit is provided separately. There is an excellent effect that the amount of water can be detected with high accuracy by accurately correcting the temperature change, without the disadvantages of increasing temperature and increasing cost.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a water content detecting device according to the present invention. 2 (a), (b) and (c) are waveform charts for explaining the operation of the first embodiment of the present invention shown in FIG. FIG. 3 is a circuit configuration diagram showing a second embodiment of the water content detecting device according to the present invention. FIG. 4 is a waveform diagram for explaining the operation of the second embodiment of the present invention shown in FIG. FIG. 5 is a circuit configuration diagram showing a third embodiment of the water content detecting device according to the present invention. FIG. 6 is a circuit configuration diagram showing an example of a water content detection device having a simple configuration to which the present invention is preferably applied and a temperature detection function is added. FIGS. 7 (a) and 7 (b) are circuit configuration diagrams for explaining operation modes of the water content detection device of FIG. 6, respectively. FIG. 8 is a circuit configuration diagram showing a fourth embodiment of the water content detecting device according to the present invention. 9 and 10 are circuit configuration diagrams showing typical examples of conventional analog and digital water content detecting devices, respectively. FIG. 11 is a waveform diagram for explaining the operation of the conventional water content detection device of FIG. FIG. 12 is a circuit configuration diagram showing a conventional moisture content detection device provided with a temperature detection circuit separately. 20: Square wave pulse signal generation circuit 21: C-MOS Schmidt inverter 22: Microcomputer C _H : Capacitance type moisture content detection element SW _A , SW _B , SW _C : Analog switch SW _D , SW _E : 3-state buffer R, R ₀ : Resistor C ₀ : Capacitor R _T : Temperature detection element

Claims (4)

[Claims] 1. A pulse signal generating circuit, an electrostatic capacitance type moisture content detecting element connected to the pulse signal generating circuit, and an electrostatic capacitance of the moisture content detecting element connected to the pulse signal generating circuit. In a water content detection device including an electric resistance element forming a CR time constant circuit between, an oscillation means for outputting a pulse signal according to a change in the capacitance of the water content detection element, and the oscillation means The digital signal processing means for counting the number of pulses of the output pulse signal in a certain period of time and obtaining the water content based on the counting result, and the direct current component removing means for removing the direct current component applied to the water content detecting element are provided. A water content detecting device characterized by: 2. The water content according to claim 1, wherein the direct current component removing means is connected to the input side of the pulse signal generating circuit and comprises a switch for periodically switching the polarity of the water content detection element. Detection device. 3. The DC component removing means is composed of an electric resistance element connected in parallel with the moisture content detecting element and an electrostatic capacitance element connected in series with a parallel circuit of these elements. The water content detection device according to claim 1. 4. The water content detection device according to claim 1, further comprising a temperature detection device whose electric resistance value is variable according to a temperature change in a subject in which the water content detection device is positioned. apparatus.