JP2010256015A - Sensor device - Google Patents

Abstract

The present invention is capable of detecting a liquid level with high accuracy even if the dielectric constant or temperature of a liquid to be measured is changed without providing a complicated arithmetic device, and also provides a signal and liquid quality representing the liquid level. It is an object of the present invention to provide a sensor device that can output a signal representing the above-described signal using only two power lines.
The sensor device of the present invention includes a circuit that generates a first DC voltage proportional to the liquid level and a circuit that generates a second DC voltage proportional to the liquid quality, and each DC voltage is After limiting to a voltage range that does not overlap with each other, the voltage value is alternately pulse-width modulated at a constant period in the switching circuit 99, and a current switching circuit 77 is provided for switching the output current between two levels of magnitude by this modulation signal. The output current is superimposed on the power supply line as a digital signal representing the liquid level and liquid quality.
[Selection] Figure 8

Description

  The present invention relates to a sensor device that detects a plurality of physical quantities, and more particularly to a sensor device that detects physical quantities such as engine oil and fuel liquid levels and liquid quality of automobiles and construction machines.

  As sensor devices for detecting physical quantities such as engine oil and fuel liquid levels of automobiles and construction machines, those shown in FIGS. 12 and 13 are known (see Patent Document 1). FIG. 12 is a front view of a detection unit of a conventional sensor device. In FIG. 12, reference numeral 1 denotes a rectangular substrate extending vertically, and a first detection of a comb-like shape is provided at the lower end of the substrate 1. The electrode 2 is provided with a comb-shaped second detection electrode 3 at a substantially central portion. The first detection electrode 2 is composed of a plurality of linear electrodes arranged at predetermined intervals in the vertical direction, and these are alternately arranged on the lead lines 4 and 5 extending vertically along both side edges of the substrate 1. It is connected. The second detection electrode 3 is composed of a plurality of linear electrodes arranged so as to extend from the upper end to the lower end with a predetermined interval on the left and right sides, and these linear electrodes have a lead wire 6 at the upper end. , 7 are alternately connected.

  At the time of liquid level measurement, the detection unit is immersed in the liquid to be measured. At this time, the first detection electrode 2 is always arranged to be immersed in the liquid to be measured. On the other hand, the second detection electrode 3 intersects the liquid surface to be measured, and the portion immersed in the liquid increases and decreases as the liquid level rises and falls.

  FIG. 13 is a detection circuit diagram using the above-described detection unit, and includes an oscillation circuit 8 and a processing circuit 9. The oscillation circuit 8 includes inverters 10, 11, 12 and a resistor 13, and the first and second detection electrodes 2, 2 in the detection unit are connected between the inverters 11, 12 via analog switches 14, 15, respectively. 3 is connected. The processing circuit 9 having a microcomputer first closes the analog switch 14 and calculates and stores the dielectric constant of the liquid to be measured from the oscillation frequency determined by the resistance 13 and the capacitance of the first detection electrode 2. . Subsequently, the processing circuit 9 closes the other analog switch 15 in place of the one analog switch 14, and the oscillation frequency determined by the resistor 13 and the capacitance of the second detection electrode 3 and the dielectric constant of the liquid to be measured. From this, the liquid level is calculated and output to the output line 16, so that the accurate liquid level can be known even when the dielectric constant of the liquid to be measured fluctuates. Reference numeral 17 denotes a power supply line.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

JP-A-63-79016

  However, in the conventional sensor device described above, the dielectric constant of the liquid to be measured is calculated from the oscillation frequency of the oscillation circuit 8 determined by the capacitance between the first detection electrodes 2 that is always immersed in the liquid to be measured. After storing, the oscillation frequency of the oscillation circuit 8 determined by the capacitance between the second detection electrodes 3 that intersects with the liquid surface to be measured and is increased or decreased as the liquid level rises or lowers. Since the liquid level of the liquid to be measured is calculated from the dielectric constant of the liquid to be measured, there is a problem that the calculation device becomes complicated and large. In addition, since the above-described conventional sensor device requires three wires, that is, a power supply line and an output line, there is a problem that handling is troublesome and the manufacturing cost is increased particularly in a vehicle having a long electric wire extension distance. Had.

  The present invention solves the above-mentioned conventional problems, and can detect the liquid level with high accuracy even if the dielectric constant or temperature of the liquid to be measured is changed without providing a complicated arithmetic device. It is an object of the present invention to provide a sensor device capable of outputting a signal representing a position and a plurality of signals representing liquid quality and the like with only two power supply lines.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention includes a first circuit that converts a first physical quantity into a first DC voltage, a second circuit that converts a second physical quantity into a second DC voltage, A first voltage limiting circuit that limits a voltage value of the first DC voltage to a first range; and a voltage value of the second DC voltage is limited to a second range that does not overlap the first range. A second voltage limiting circuit and a switching circuit that outputs each of the output voltages of the first and second voltage limiting circuits at a constant cycle are provided, and an output from the switching circuit is provided on the output side of the switching circuit. A circuit that modulates the voltage to a pulse width, and a current switching circuit that switches the output current from the current source between two levels, large and small, according to the modulation signal modulated to the pulse width, and the magnitude 2 that is switched by the current switching circuit Level output current of the first The digital signal representing the quantity and the second physical quantity is superimposed on the power supply line. According to this configuration, a plurality of signals can be output by only two power supply lines. It has the effect of being able to provide a sensor device that can be easily handled and reduced in manufacturing cost in a device having a long extension distance of an electric wire.

  According to a second aspect of the present invention, there is provided a first detection electrode that is always immersed in a liquid to be measured and that measures the capacitance between the electrodes without being affected by the dielectric constant of the liquid to be measured. A second detection electrode that is always immersed in the liquid to be measured and that is affected by the dielectric constant of the liquid to be measured, and that measures the capacitance between the electrodes; and a third that measures the liquid level of the liquid to be measured. The detection electrode and a fourth detection electrode that is always outside the liquid to be measured are provided in the detection unit, and charged for a time proportional to the length of the portion where the third detection electrode is immersed in the liquid to be measured. And repeating the operation of discharging the charged electric charge for a time proportional to the length of the portion where the third detection electrode is outside the liquid to be measured, thereby generating a first DC voltage proportional to the liquid level. And a circuit that generates the static electricity measured by the second detection electrode. Charge for a time proportional to the difference between the quantity and the capacitance measured at the first sensing electrode, and charge the charged charge for a time proportional to the capacitance measured at the first sensing electrode. A circuit for generating a second DC voltage proportional to the liquid quality by repeating the operation of discharging, a voltage limiting circuit for limiting the voltage value of the first DC voltage to a first range, and the first A voltage limiting circuit that limits a voltage value of the DC voltage of 2 to a second range that does not overlap the first range, and a switching circuit that outputs each of the output voltages of the voltage limiting circuit at a constant period, On the output side of the switching circuit, there is a circuit for modulating the output voltage of the switching circuit to a pulse width, and a current switching circuit for switching the output current from the current source to two levels of large and small by the modulation signal modulated to the pulse width. And superimposing two or two levels of output current switched by the current switching circuit on a power supply line as a digital signal representing the liquid level and the liquid quality. Without being provided, a signal that accurately represents the liquid level and a signal that represents the liquid quality can be output at all times even when the dielectric constant or temperature of the liquid to be measured changes, and a signal that represents the liquid level; A signal representing the liquid quality can be output with only two power lines, thereby providing a sensor device that is easy to handle and has low manufacturing costs, particularly in vehicles with a long cable extension distance. It has a working effect.

  As described above, the sensor device of the present invention includes a first circuit that converts a first physical quantity into a first DC voltage, a second circuit that converts a second physical quantity into a second DC voltage, A first voltage limiting circuit that limits the voltage value of the first DC voltage to a first range; and a second voltage that limits the voltage value of the second DC voltage to a second range that does not overlap the first range. And a switching circuit that outputs each of the output voltages of the first and second voltage limiting circuits at a constant cycle, and further, an output voltage from the switching circuit is provided on the output side of the switching circuit. And a current switching circuit for switching the output current from the current source between two levels, large and small, according to the modulation signal modulated to the pulse width, and the large and small two levels switched by the current switching circuit Output current of the first Since the digital signal representing the physical quantity and the second physical quantity is superimposed on the power supply line, a plurality of signals can be output with only two power supply lines. It is possible to provide a sensor device that can be easily handled in a long device and can reduce the manufacturing cost.

The block diagram which shows the structure of the sensor apparatus in one embodiment of this invention (A)-(d) The characteristic view for demonstrating operation | movement of the voltage conversion circuit in the sensor apparatus (A) (b) Voltage waveform diagram for explaining the operation of the pulse width modulation circuit in the sensor device (A)-(e) Voltage waveform diagram for explaining the operation of the switching circuit, waveform shaping / frequency dividing circuit, pulse width modulation circuit, and sawtooth generator in the sensor device The circuit diagram which shows the method of transmitting the digital signal showing the 1st and 2nd physical quantity from the sensor apparatus to the position distant The front view of the detection part of the sensor apparatus in other embodiment of this invention Sectional drawing which shows the structure of the 1st detection electrode in the detection part of the sensor apparatus Detection circuit diagram of the sensor device (A)-(l) Voltage waveform diagram for explaining circuit operation of the sensor device (A)-(d) The characteristic view for demonstrating operation | movement of the voltage conversion circuit in the sensor apparatus (A)-(e) Voltage waveform diagram for explaining the operation of the switching circuit, waveform shaping / frequency dividing circuit, pulse width modulation circuit, and sawtooth generator in the sensor device Front view of detection unit of conventional sensor device Detection circuit diagram of conventional sensor device

  Hereinafter, a sensor device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a sensor device 20 according to an embodiment of the present invention. As shown in FIG. 1, an arbitrary first physical quantity such as a temperature or a liquid level is changed to a first DC voltage. The first circuit 21 for conversion and the second circuit 22 for converting the second physical quantity to the second DC voltage are set to the output terminal 23 and the second potential (V ₂ ) at the first potential (V ₁ ). It is connected between an output terminal 25 of a certain constant voltage source 24. The output DC voltage of the first circuit 21 is limited to the first voltage range by the first voltage limiting circuit 26, and the output DC voltage of the second circuit 22 is the second voltage limiting circuit 27. It is limited to a second voltage range that does not overlap the first voltage range. The output of the first voltage limiting circuit 26 is applied to the first input of the switching circuit 28, and the output of the second voltage limiting circuit 27 is applied to the second input of the switching circuit 28. Further, the output of the switching circuit 28 controlled by the output of the waveform shaping / dividing circuit 29 is connected to a first input in the pulse width modulation circuit 30. 31 is a sawtooth generator, and its output is connected to the second input in the pulse width modulation circuit 30 and is applied to the waveform shaping / frequency dividing circuit 29. The output of the pulse width modulation circuit 30 is connected to the control input of a current switching circuit 33 connected between the power supply terminal 32 and the constant voltage source 24.

Next, the operation of the first and second voltage limiting circuits 26 and 27 will be described with reference to FIGS. 2 (a), (b), (c) and (d). FIG. 2A is a characteristic diagram showing the relationship between the first physical quantity and the output DC voltage (V ₂₁ ) of the first circuit 21. Here, the first physical quantity is normalized and represented by 0 to 100%, and the output DC voltage (V ₂₁ ) is normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. 0 to 100%. Similarly, FIG. 2B is a characteristic diagram showing the relationship between the second physical quantity and the output DC voltage (V ₂₂ ) of the second circuit 22. Here, the second physical quantity is normalized and represented by 0 to 100%, and the output DC voltage (V ₂₂ ) is normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. 0 to 100%. FIG. 2C shows the first physical quantity and the first voltage limiting circuit 26.

It is a characteristic view which shows the relationship. here

Is represented by 0 to 100%, normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. From FIG. 2C, the first voltage limiting circuit 26 representing the first physical quantity

Is compressed to 10-40% and added to the first input of the switching circuit 28. Similarly, FIG. 2D shows the second physical quantity and the second voltage limiting circuit 27.

It is a characteristic view which shows the relationship. Where

Is represented by 0 to 100%, normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. From FIG. 2D, the second voltage limiting circuit 27 representing the second physical quantity

Is converted to 60-90% and added to the second input of the switching circuit 28. By converting the voltage in this way, the first voltage limiting circuit 26 representing the first physical quantity is converted.

And the second voltage limiting circuit 27 representing the second physical quantity.

It always takes a voltage value in a different range.

  Next, the operation of the pulse width modulation circuit 30 will be described with reference to FIGS. FIG. 3A shows the output of the sawtooth wave generation circuit 31 applied to the second input in the pulse width modulation circuit 30. The output voltage of this sawtooth wave generation circuit 31 is

Rises from the first potential (V ₁ ) to the second potential (V ₂ ) and then decreases linearly.

To reach the first potential (V ₁ ). further

Rises from the _first potential (V ₁ ) to the second potential (V ₂ ) and then decreases linearly.

To reach the first potential (V ₁ ). Thereafter, the same operation is repeated. FIG. 3B shows a signal output from the pulse width modulation circuit 30. The first input of the pulse width modulation circuit 30 includes, for example, the first voltage limiting circuit 26 representing the first physical quantity.

Is added,

, The voltage applied to the second input in the pulse width modulation circuit 30 is

The output of the pulse width modulation circuit 30 rises to high (V _H ) and maintains that state. Then, the voltage applied to the second input in the pulse width modulation circuit 30 is again

When it reaches

The output of the pulse width modulation circuit 30 transitions to low (V _L ) and maintains its state. further

The voltage applied to the second input in the pulse width modulation circuit 30 is

The output of the pulse width modulation circuit 30 rises to high (V _H ) and maintains that state. Then, the voltage applied to the second input in the pulse width modulation circuit 30 is again

When it reaches

The output of the pulse width modulation circuit 30 transitions to low (V _L ) and maintains its state. Thereafter, the same operation is repeated.

  Next, operations of the switching circuit 28, the waveform shaping / dividing circuit 29, the pulse width modulation circuit 30, and the sawtooth generator 31 will be described with reference to FIG.

FIG. 4A shows an output signal of the sawtooth generator 31, and this output signal is applied to the waveform shaping / dividing circuit 29 and the pulse width modulation circuit 30. In the waveform shaping / dividing circuit 29, the output signal of the sawtooth wave generator 31 is shaped into the rectangular pulse wave shown in FIG. 4 (b), and then divided by 4 to obtain the rectangular pulse wave shown in FIG. 4 (c). It is output as a control signal for the switching circuit 28. Then, as shown in FIG. 4 (d), the switching circuit 28 is connected to the first voltage limiting circuit 26 from the time when the control signal of the switching circuit 28 falls (t _p0 ).

The second potential (V ₂ ) is applied to the first input of the pulse width modulation circuit 30 from the time when the next control signal rises (t _p1 ). Next, the switching circuit 28 starts the second voltage limiting circuit 27 from the time when the next control signal falls (t _p2 ).

The first potential (V ₁ ) is applied to the first input of the pulse width modulation circuit 30 from the time when the next control signal rises (t _p3 ). Thereafter, the same operation is repeated. The pulse width modulation circuit 30 performs pulse width modulation on the second input signal from the sawtooth wave generation circuit 31 with the first input signal from the switching circuit 28 to generate a voltage signal as shown in FIG. Add to 33 control inputs. Thus, after outputting the voltage signal representing the first physical quantity a predetermined number of times (eight times), outputting the voltage signal representing the second physical quantity a predetermined number of times (eight times) is repeated.

  The current switching circuit 33 switches the output current between two levels of magnitude according to the modulation signal modulated to the pulse width. In one embodiment of the present invention, when the voltage applied to the current switching circuit 33 is high, The current switching circuit 33 outputs a large current. On the other hand, when the voltage applied to the current switching circuit 33 is low, the current switching circuit 33 is configured to output a small current. As a result, the sensor device 20 according to the embodiment of the present invention outputs the output current of two levels of magnitude, switched by the current switching circuit 33, from the output terminal 23 as a digital signal representing the first and second physical quantities. It is something that can be done.

  Next, a method for transmitting a digital signal representing the first physical quantity and the second physical quantity from the sensor device 20 in one embodiment of the present invention to a position away from the sensor device 20 will be described with reference to FIG. As shown in FIG. 5, the power supply terminal 32 of the sensor device 20 and the hot side of the direct current are connected to one of the power supply lines 41, and the output terminal 23 of the sensor device 20 and the input side of the amplifier 42 are connected to the power supply. Connect to the other side of the line 41. A pull-down resistor 43 is connected between the input side of the amplifier 42 and the ground. The output current from the output terminal 23 is current-voltage converted by a pull-down resistor 43 and an amplifier 42. The output voltage from the amplifier 42 is applied to a signal processing device 44 connected to the subsequent stage of the amplifier 42 and processed and used as a control signal.

  As is apparent from the above description, the sensor device according to the embodiment of the present invention can output a plurality of signals by only two power supply lines, and thereby, particularly in a device having a long extension distance of the electric wire. The sensor device is advantageous in that it can be easily handled and the manufacturing cost can be reduced.

  In the sensor device according to the embodiment of the present invention, signals representing the first and second physical quantities are superimposed on the power supply line, but signals representing two or more physical quantities are supplied from the power source. It is also possible to overlap the line.

  FIG. 6 shows a front part of a detection unit of a sensor device according to another embodiment of the present invention. In FIG. 6, reference numeral 51 denotes a detection unit made of a rectangular polyimide film or the like extending vertically. A pair of first detection electrodes 52 made of comb-shaped carbon is provided at the lower end of 51. Further, a pair of second detection electrodes 53 made of comb-shaped carbon is provided on the first detection electrode 52, and the comb-shaped carbon is also formed on the second detection electrode 53. A pair of third detection electrodes 54 are provided, and a pair of fourth detection electrodes 55 made of comb-shaped carbon is also provided at the upper end of the detection unit 51. The first, second, third, and fourth detection electrodes 52, 53, 54, and 55 are connected to terminals 56, 57, 58, 59, and 60 by lead wires extending vertically.

  FIG. 7 is a cross-sectional view taken along line AA of the first detection electrode 52 in FIG. 6. As shown in FIG. 7, the first detection electrode 52 provided at the lower end of the detection unit 51. Is configured by covering the entire opposing electrode 61 with a metal layer 63 via an insulator 62. With this configuration, the lines of electric force generated between the opposing electrodes 61 are covered. Since it does not pass through the measurement liquid, the capacitance between the opposed electrodes 61 measured by the first detection electrode 52 is not affected by the dielectric constant of the liquid to be measured.

  As the insulator 62, it is desirable to select a liquid to be measured, a solid material impregnated with the liquid to be measured, or a substance having substantially the same dielectric constant temperature characteristics as the liquid to be measured. Thereby, the influence of the temperature change in liquid quality measurement can be removed.

  During the operation of the sensor device according to another embodiment of the present invention, the first detection electrode 52 and the second detection electrode 53 are always immersed in a liquid to be measured having high thermal conductivity such as oil. The temperatures of the first detection electrode 52 and the second detection electrode 53 can be considered to be substantially equal.

FIG. 8 shows a detection circuit diagram of a sensor device according to another embodiment of the present invention. In FIG. 8, the terminal 56 of the detection unit 51 is an output terminal 71 at a _first potential (V ₁ ). Connect to. The terminals 57, 58, 59 and 60 of the detection unit 51 are connected to the second resistor of the constant voltage source 76 via the first resistor 72, the second resistor 73, the third resistor 74 and the fourth resistor 75, respectively. Connected to an output 78 at a potential (V ₂ ). Reference numeral 77 denotes a current switching circuit connected between the constant voltage source 76 and the power supply terminal 79. As a result, the first detection electrode 52, the second detection electrode 53, the third detection electrode 54, and the fourth detection electrode 55 are respectively connected to the first resistor 72, the second resistor 73, the third resistor 74, Connected to the fourth resistor 75.

  At this time, a time constant determined by the interelectrode capacitance of the second detection electrode 53 and the second resistor 73 in a state where the second, third, and fourth detection electrodes 53, 54, and 55 are all outside the liquid to be measured. The time constant determined by the interelectrode capacitance of the third detection electrode 54 and the third resistor 74 and the time constant determined by the interelectrode capacitance of the fourth detection electrode 55 and the fourth resistor 75 are substantially equal. It is intended to be equal to. The time constant determined by the first detection electrode 52 and the first resistor 72 is determined by the interelectrode capacitance of the second detection electrode 53 and the second resistance 73 in a state of being immersed in the liquid to be measured. It is made smaller than the time constant.

  Further, the midpoint potential of the first resistor 72 and the first detection electrode 52 is compared with the threshold value generating means comprising resistors 81 and 82 in the first comparing means 80 comprising a comparator. Similarly, the midpoint potential between the second resistor 73 and the second detection electrode 53, the midpoint potential between the third resistor 74 and the third detection electrode 54, and the fourth resistance. 75 and the fourth detection electrode 55 have a midpoint potential in the second comparing means 83, the third comparing means 84, and the fourth comparing means 85 each comprising a comparator, and a threshold value generating means comprising resistors 81 and 82, respectively. Compared with The output signals of the second, third, and fourth comparison means 83, 84, and 85 are input to a first logic circuit 86 made up of logic elements. The output signals of the first and second comparing means 80 and 83 are input to a second logic circuit 87 made up of logic elements.

Further, a first analog switch 88 and a second analog switch 89 that are controlled to be opened and closed by an output signal of the first logic circuit 86 are provided at the subsequent stage of the first logic circuit 86. Reference numeral 90 denotes a fifth resistor having one end connected to the midpoint of the first analog switch 88 and the second analog switch 89 and the other end connected to the first low-pass filter 91. A capacitor 92 has one end connected to the output terminal 71 at the first potential (V ₁ ) and the other end connected between the fifth resistor 90 and the first low-pass filter 91.

Furthermore, a third analog switch 93 and a fourth analog switch 94 that are controlled to open and close by an output signal of the second logic circuit 87 are provided at the subsequent stage of the second logic circuit 87. A sixth resistor 95 has one end connected to the midpoint of the third analog switch 93 and the fourth analog switch 94 and the other end connected to the second low-pass filter 96. A capacitor 97 has one end connected to the output terminal 71 at the first potential (V ₁ ) and the other end connected between the sixth resistor 95 and the second low-pass filter 96. The output of the first low-pass filter 91 is applied to the first input in the switching circuit 99 via the first voltage conversion circuit 98. The output of the second low-pass filter 96 is applied to the second input of the switching circuit 99 via the second voltage conversion circuit 100. The output of the switching circuit 99 controlled by the output of the waveform shaping / frequency dividing circuit 101 is connected to the first input in the pulse width modulation circuit 102. Reference numeral 103 denotes a sawtooth wave generator whose output is connected to the second input of the pulse width modulation circuit 102 and applied to the waveform shaping / frequency dividing circuit 101. The output of the pulse width modulation circuit 102 is connected to the control input of the current switching circuit 77.

  Next, the circuit operation of the sensor device according to another embodiment of the present invention will be described with reference to FIG. 9 (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) show voltage waveforms at various parts of the sensor device. Is.

  The detection unit 51 of the sensor device shown in FIG. 6 is immersed in a liquid to be measured such as engine oil in an oil pan (not shown). At this time, the first detection electrode 52 and the second detection electrode 53 are always immersed in the liquid to be measured, and the fourth detection electrode 55 is always disposed outside the liquid to be measured. And the 3rd detection electrode 54 cross | intersects the to-be-measured liquid surface, and the part immersed in a liquid increases / decreases with the raising / lowering of a liquid level.

In the sensor device according to another embodiment of the present invention, the electrode pair of the first, second, third, and fourth detection electrodes 52, 53, 54, and 55 is in an initial state (t ₀ ) before power-on. Since there is no electric charge between them, the midpoint potential between the first resistor 72 and the first detection electrode 52, the midpoint potential between the second resistor 73 and the second detection electrode 53, and the third resistor 74 The midpoint potential of the third detection electrode 54 and the midpoint potential of the fourth resistor 75 and the fourth detection electrode 55 are all at the first potential (V ₁ ).

When the power is turned on (t ₀ ), the midpoint potential between the fourth resistor 75 and the fourth detection electrode 55 is the first potential (V ₁ ) as shown in FIG. Toward the second potential (V ₂ ) exponentially with a time constant determined by the fourth resistor 75 and the interelectrode capacitance of the fourth detection electrode 55. Further, the midpoint potential of the third resistor 74 and the third detection electrode 54 goes from the first potential (V ₁ ) to the second potential (V ₂ ) as shown in FIG. 9B. Thus, it rises exponentially with a time constant determined by the third resistor 74 and the interelectrode capacitance of the third detection electrode 54. At this time, since a part of the third detection electrode 54 is in the liquid to be measured, the time constant determined by the third resistance 74 and the capacitance of the third detection electrode 54 is the fourth resistance. It becomes larger than the time constant determined by 75 and the fourth detection electrode 55. Further, the midpoint potential of the second resistor 73 and the second detection electrode 53 is changed from the _first potential (V ₁ ) to the second potential (V ₂ ) as shown in FIG. 9C. On the other hand, it rises exponentially with time constants determined by the second resistance 73 and the interelectrode capacitance of the second detection electrode 53, respectively. At this time, since the second detection electrode 53 is always immersed in the liquid to be measured, the time constant determined by the second resistor 73 and the capacitance of the second detection electrode 53 is the third constant. It becomes larger than the time constant determined by the resistor 74 and the third detection electrode 54. Further, the midpoint potential of the first resistor 72 and the first detection electrode 52 goes from the first potential (V ₁ ) to the second potential (V ₂ ) as shown in FIG. As a result, each of the first resistors 72 and the first detection electrode 52 increase exponentially with time constants determined by the interelectrode capacitance. At this time, as described above, the time constant determined by the first detection electrode 52 and the first resistor 72 is the interelectrode capacitance of the second detection electrode 53 and the second capacitance when immersed in the liquid to be measured. It is set to be smaller than the time constant determined by the resistor 73.

Thereafter, when the midpoint potential of the fourth resistor 75 and the fourth detection electrode 55 reaches the threshold voltage V _th determined by the resistors 81 and 82, the output of the fourth comparison means 85 comprising a comparator is as shown in FIG. As shown in (e), the transition is made from high to low (t ₁ ). Similarly, when the midpoint potential of the third resistor 74 and the third detection electrode 54 reaches the threshold voltage V _th determined by the resistors 81 and 82, the output of the third comparison means 84 comprising a comparator. Transition from high to low as shown in FIG. 9 (f) (t ₂ ). When the midpoint potential of the first resistor 72 and the first detection electrode 52 reaches a threshold voltage _Vth determined by the resistors 81 and 82, the output of the first comparison means 80 comprising a comparator is as shown in FIG. As shown in (h), the transition is made from high to low (t ₃ ). Further, when the midpoint potential of the second resistor 73 and the second detection electrode 53 reaches the threshold voltage _Vth determined by the resistors 81 and 82, the output of the second comparing means 83 comprising a comparator is shown in FIG. As shown in FIG. 9 (g), the charge is accumulated in the first, second, third, and fourth detection electrodes 52, 53, 54, and 55 at the time of transition from high to low (t ₄ ). Is discharged to the first potential (V ₁ ) via the element 104, so that the midpoint potential of the first resistor 72 and the first detection electrode 52, the second resistor 73 and the second potential The midpoint potential of the detection electrode 53, the midpoint potential of the third resistor 74 and the third detection electrode 54, and the midpoint potential of the fourth resistor 75 and the fourth detection electrode 55 are all the first. returning to the potential (V _1), and said first, second, third, fourth comparison means 80, 8 Each output of 84, 85 Figure 9 (h) (g) ( f) a transition from low to high as shown in (e) (t _5).

Thereafter, the midpoint potential of the fourth resistor 75 and the fourth detection electrode 55, the midpoint potential of the third resistor 74 and the third detection electrode 54, the second resistor 73 and the second resistor As shown in FIGS. 9 (a), 9 (b), 9 (c) and 9 (d), the midpoint potential of the first detection electrode 53 and the midpoint potential of the first resistor 72 and the first detection electrode 52 are the same as shown in FIGS. From the first potential (V ₁ ) to the second potential (V ₂ ), the interelectrode capacitance of the fourth resistor 75 and the fourth detection electrode 55, and the third resistor 74 and the third detection, respectively. An exponential function with a time constant determined by the interelectrode capacitance of the electrode 54, the interelectrode capacitance of the second resistor 73 and the second detection electrode 53, and the interelectrode capacitance of the first resistor 72 and the first detection electrode 52 Rises. Thereafter, the output of the fourth comparison means 85 changes from high to low (t ₆ ), the output of the third comparison means 84 changes from high to low (t ₇ ), and the output of the first comparison means 80. Transition from high to low (t ₈ ), the output of the second comparison means 83 transitions from high to low (t ₉ ), and thereafter the same operation as before is repeated.

  The output signals of the second, third, and fourth comparison means 83, 84, and 85 are input to a logic circuit 86 composed of logic elements, and the first analog switch 88 is shown in FIG. 9 (i). The signal shown in FIG. 9J is output to the second analog switch 89. Similarly, the output signals of the first and second comparing means 80 and 83 are inputted to a logic circuit 87 made up of logic elements, and the third analog switch 93 has a signal shown in FIG. 9 (k). However, the signal shown in FIG. 9L is output to the fourth analog switch 94.

In this case, the analog switch is “closed” when the signal input to each analog switch is high, and “open” when the signal is low. Accordingly, the first analog switch 88 is “closed” and the second analog switch 89 is “open” at times t _{1 to} t ₂ and t _{6 to} t ₇ in FIG. The capacitor 92 is charged through the fifth resistor 90 from (V ₂ ). ₉ , since the first analog switch 88 is “open” and the second analog switch 89 is “closed” at time t _{2 to} t ₄ and t _{7 to} t 9 in FIG. The discharged electric charge is discharged to the _first potential (V ₁ ) through the fifth resistor 90. In this way, the first analog switch 88 and the second analog switch are set for the time determined by the length of the portion where the third detection electrode 54 is immersed in the liquid to be measured and the length of the portion outside the liquid to be measured. By alternately opening and closing 89 and charging / discharging the capacitor 92, an analog voltage representing the liquid level of the liquid to be measured is output to both ends of the capacitor 92.

Similarly to this, because at time t ₃ ~t ₄ and t ₈ ~t ₉ in FIG. 9, the third analog switch 93 is a fourth analog switch 94 in the "closed" is "open", The capacitor 97 is charged through the sixth resistor 95 from the _second potential (V ₂ ). 9, since the third analog switch 93 is “open” and the fourth analog switch 94 is “closed” at the times t _{0 to} t ₃ and t _{5 to} t ₈ in FIG. The discharged electric charge is discharged to the _first potential (V ₁ ) through the fifth resistor 95. In this way, the second capacitor 97 is charged for a time proportional to the difference between the capacitance measured by the first detection electrode 52 and the capacitance measured by the second detection electrode 53. In addition, by repeating the operation of discharging the charge charged in the second capacitor 97 for a time proportional to the capacitance measured by the first detection electrode 52, the liquid quality of the liquid to be measured is expressed. An analog voltage is output across the capacitor 97.

The voltage output to both ends of the capacitors 92 and 97 includes a ripple, but since this ripple is removed by the low-pass filters 91 and 96, the level of the liquid to be measured is measured after a lapse of a certain time after the power is turned on. a DC voltage (V _h ^D) a first voltage conversion circuit 98 that represent, so that the DC voltage representative of the liquid property of the test liquid (V _q ^D) is added to the second voltage conversion circuit 100.

  Next, the operation of the voltage conversion circuits 98 and 100 will be described with reference to FIGS. 10 (a), (b), (c), and (d).

FIG. 10A is a characteristic diagram showing the relationship between the liquid level of the liquid to be measured that intersects the third detection electrode 54 and the DC voltage (V _h ^D ). Here, the liquid level of the liquid to be measured is normalized by the total length of the third detection electrode 54 and expressed as 0 to 100%, and the DC voltage (V _h ^D ) is the second potential and the first potential. It is represented by 0 to 100%, normalized by the difference (V ₂ −V ₁ ).

FIG. 10B is a characteristic diagram showing the relationship between the quality of the liquid to be measured and the DC voltage (V _q ^D ). Here, the liquid quality of the liquid to be measured is normalized by an appropriate value and expressed as 0 to 100%, and the DC voltage (V _q ^D ) is the difference between the second potential and the first potential (V ₂ − It is represented by 0 to 100% normalized by V _1).

  FIG. 10C shows the liquid level of the liquid to be measured that intersects the third detection electrode 54 and the first voltage conversion circuit 98.

It is a characteristic view which shows the relationship. Where

Is represented by 0 to 100%, normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. FIG. 10C shows the liquid level of the liquid to be measured.

Is compressed to 10-40% and added to the first input of the switching circuit 99.

  FIG. 10 (d) shows the liquid quality of the liquid to be measured and the second voltage conversion circuit 100.

It is a characteristic view which shows the relationship. Where

Is represented by 0 to 100%, normalized by the difference (V ₂ −V ₁ ) between the second potential and the first potential. The liquid quality of the liquid to be measured is shown from FIG.

Is converted to 60-90% and added to the second input of the switching circuit 99.

  By converting the voltage in this way, the first voltage conversion circuit 98 representing the liquid level of the liquid to be measured is used.

And the second voltage conversion circuit 100 representing the liquid quality of the liquid to be measured.

It always takes a voltage value in a different range.

  Next, operations of the switching circuit 99, the waveform shaping / frequency dividing circuit 101, the pulse width modulation circuit 102, and the sawtooth generator 103 will be described with reference to FIG.

FIG. 11A shows an output signal of the sawtooth generator 103, and this output signal is applied to the waveform shaping / frequency dividing circuit 101 and the pulse width modulation circuit 102. In the waveform shaping / dividing circuit 101, the output signal is shaped into a rectangular pulse wave shown in FIG. 11 (b), and then divided into four, whereby the rectangular pulse wave shown in FIG. Output as. Then, as shown in FIG. 11 (d), the switching circuit 99 is connected to the first voltage conversion circuit 98 from the time when the control signal falls (t _p0 ).

The second potential (V ₂ ) is applied to the first input of the pulse width modulation circuit 102 from the rising _edge (t _p1 ) of the next control signal. Next, the switching circuit 99 starts the second voltage conversion circuit 100 from the time when the next control signal falls (t _p2 ).

The first potential (V ₁ ) is applied to the first input of the pulse width modulation circuit 102 from the time when the next control signal rises (t _p3 ). Thereafter, the same operation is repeated. The pulse width modulation circuit 102 performs pulse width modulation on the second input signal from the sawtooth generator 103 with the first input signal from the switching circuit 99, and converts the voltage signal as shown in FIG. Add to 77 control inputs. Thus, after outputting the voltage signal indicating the liquid level a predetermined number of times (eight times), outputting the voltage signal indicating the liquid quality a predetermined number of times (eight times) is repeated.

  The current switching circuit 77 outputs a large current of, for example, 14 mA when the voltage applied to the current switching circuit 77 is high, as in the case of the sensor device 20 in the embodiment of the present invention shown in FIG. When the voltage applied to the current switching circuit 77 is low, for example, a small current of 7 mA is output. As described above, in the sensor device according to another embodiment of the present invention, the output current of two levels of magnitude, switched by the current switching circuit 77, is output from the output terminal 71 as a digital signal representing the liquid level and liquid quality. It is something that can be done.

  A method for transmitting a digital signal representing a liquid level and a liquid quality from a sensor device according to another embodiment of the present invention to an ECU or the like of a vehicle located at a position away from the sensor device is shown in FIG. Similar methods to those described can be used.

  As is clear from the above description, the sensor device according to another embodiment of the present invention can always accurately correct the liquid level even if the dielectric constant or temperature of the liquid to be measured changes without providing a complicated arithmetic device. The signal indicating the liquid level and the signal indicating the liquid quality can be output, and the signal indicating the liquid level and the signal indicating the liquid quality can be output using only two power lines. Thus, it is possible to provide a sensor device that is easy to handle and has low manufacturing costs, particularly in a device having a long extension distance of an electric wire.

  The sensor device according to the present invention can output a signal that accurately represents the liquid level and a signal that represents the liquid quality even if the dielectric constant or temperature of the liquid to be measured changes without providing a complicated arithmetic device. The sensor that can output the signal indicating the liquid level and the signal indicating the liquid quality with only two lines of the power supply line, which is easy to handle and suppresses the manufacturing cost, particularly in a device having a long extension distance of the electric wire. The present invention has an effect that the device can be provided, and is particularly useful as a sensor device for detecting the level of engine oil or fuel in automobiles, construction machines and the like.

DESCRIPTION OF SYMBOLS 21 1st circuit 22 2nd circuit 26 1st voltage limiting circuit 27 2nd voltage limiting circuit 28 Switching circuit 30 Pulse width modulation circuit 33 Current switching circuit 51 Detection part 52 1st detection electrode 53 2nd detection Electrode 54 Third detection electrode 55 Fourth detection electrode 77 Current switching circuit 98 First voltage conversion circuit 99 Switching circuit 100 Second voltage conversion circuit 102 Pulse width modulation circuit

Claims (2)

A first circuit that converts a first physical quantity into a first DC voltage, a second circuit that converts a second physical quantity into a second DC voltage, and a voltage value of the first DC voltage as a first value A first voltage limiting circuit that limits the voltage value of the second DC voltage to a second range that does not overlap with the first range; A switching circuit for outputting each of the output voltages of the second voltage limiting circuit at a constant period, and a circuit for modulating the output voltage from the switching circuit to a pulse width on the output side of the switching circuit; A current switching circuit for switching the output current from the current source between two levels of large and small by a modulation signal modulated in width, and the output current of the two levels of large and small switched by the current switching circuit and the first physical quantity A digital value representing the physical quantity of 2 Sensor apparatus that superimposed on the power line as a signal. A first detection electrode which is always immersed in the liquid to be measured and which measures the capacitance between the electrodes without being affected by the dielectric constant of the liquid to be measured; and a first detection electrode which is always immersed in the liquid to be measured and A second detection electrode that measures the capacitance between the electrodes under the influence of the dielectric constant of the measurement liquid, a third detection electrode that measures the liquid level of the measurement liquid, and is always outside the measurement liquid The fourth detection electrode is provided in the detection unit, and the third detection electrode is charged for a time proportional to the length of the portion immersed in the liquid to be measured, and the third detection electrode is measured. A circuit that generates a first DC voltage proportional to the liquid level by repeating the operation of discharging the charged charge for a time proportional to the length of the portion outside the liquid, and the second The capacitance measured by the detection electrode and the measurement by the first detection electrode It is proportional to the liquid quality by repeating the operation of charging for a time proportional to the difference from the capacitance and discharging the charged charge for a time proportional to the capacitance measured by the first detection electrode. A first voltage limiting circuit for limiting the voltage value of the first DC voltage to a first range, and a voltage value of the second DC voltage. A second voltage limiting circuit for limiting to a second range that does not overlap with the first range, and a switching circuit for outputting each of the output voltages of the first and second voltage limiting circuits at a constant period, and On the output side of the switching circuit, a circuit that modulates the output voltage of the switching circuit to a pulse width, and a current switching circuit that switches the output current from the current source between two levels, large and small, by the modulation signal modulated to the pulse width; Set up The sensor apparatus that superimposes the power line the output current of the switched large and small levels in the current switching circuit as a digital signal representative of the liquid level and Ekishitsu.

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