JPS6336246Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Field of Application] The present invention relates to an improvement of a capacitive sensor that detects various information such as liquid level using a variable capacitive transducer. [Prior art] A variable capacitance converter (hereinafter simply referred to as a converter), which is a type of capacitor that converts a physical quantity or a chemical quantity into a capacitance, is used to When trying to detect from outside the container that the level has reached a certain level in a non-contact manner, conventionally, as shown in FIG.
Two electrodes 11 and 12 constituting the transducer are mounted facing each other at appropriate positions on the outer wall surface of the converter, and a capacitance change detection circuit 15 detects changes in the interelectrode capacitance as the liquid level of the chemical solution 14 falls. It is done by doing. The change in capacitance of the converter as the liquid level drops is schematically shown by the solid line 20 in Figure 2, and the capacitance reaches its maximum when the space between the electrodes is filled with the chemical solution, C _nax , Minimum when replaced by air
It becomes C _nio . Therefore, if the detection threshold level of the capacitance change detection circuit 15 is set slightly higher than the minimum value C _nio as shown by the straight line 21 in the figure, the solid line 20
In addition to the case shown in Figure 2, even if the type of chemical liquid 14 changes and its dielectric constant ε changes, resulting in a change in capacitance as shown, for example, in broken lines 22 and 23 in Figure 2, level detection can be performed correctly at the same detection threshold level. be able to. [Problem that the invention attempts to solve] However, the minimum value of interelectrode capacitance C _nio
changes depending on changes in measurement environmental conditions such as the type of container and temperature changes, so if the detection threshold level is set too low, the minimum value C _nio will be larger than the threshold level and the detection may not work. be. Therefore, in the past, the threshold level was newly set every time the intravenous fluid container was changed, which had the disadvantage that the device was very cumbersome to handle. In addition, as the capacitance change detection circuit 15 for detecting a change in capacitance, circuits that employ the AC capacitance bridge method or the LC resonance method are generally known, but the former has a complicated configuration, and the latter Since a stable oscillator and a detection circuit are required, both devices have the disadvantage of becoming large and expensive. Therefore, a relatively simple capacitance change detection circuit has been proposed in which an oscillation circuit is configured using the capacitance of the converter as a feedback capacitor, and capacitance changes are detected based on changes in the oscillation output. Since it is difficult to control the oscillation output according to Therefore, when applying this type of device to detect the liquid level of an intravenous drip container, if the electrodes are attached to the container body as shown in Figure 1, the electrode spacing is too wide and the capacitance change is small, so for example, There was a problem in that a thin tube with a small diameter communicating with the drip container had to be provided and a converter had to be attached to the tube. [Means for Solving the Problems] The present invention improves on these conventional drawbacks by providing one pulse generation circuit, branching the output of the pulse generation circuit into multiple parts, and each having a separate capacitance. a variable delay circuit including a variable capacitance converter as a component and delaying and outputting the pulses of the pulse generating circuit by an amount corresponding to the capacitance value of the capacitance variable converter; and a phase discrimination circuit that discriminates phase differences between pulses output from a plurality of series of variable delay circuits and outputs measurement information, and the variable delay circuit uses the capacitance variable converter as an integrating capacitor. The integration circuit and the output of the integration circuit are
The phase discrimination circuit includes an edge clock D which uses the output pulses of the variable delay circuit as data input and clock input.
An object of the present invention is to provide a capacitance type sensor characterized by including a flip-flop, a low-pass filter to which the output of the flip-flop is applied, and a binarization circuit that binarizes the output of the low-pass filter. This will be explained in detail below. FIG. 3 is a block diagram showing the basic configuration of the present invention, in which 30 is a pulse generation circuit, 31, 32
3 is a converter, 33 and 34 are variable delay circuits, 35 is a phase discrimination circuit, 36 is an output terminal, and 37 and 38 are delay adjustment circuits. As shown in the figure, the capacitive sensor of the present invention includes a pulse generation circuit 30 and separate converters 3 and 3.
1 and 32 as components, and their converters 31 and 32
The pulse generation circuit 3
A plurality of variable delay circuits 33 and 34 delay and output a zero output pulse, and the phase difference between the pulse signals output from the plurality of variable delay circuits 33 and 34 is discriminated and measurement information is sent to an output terminal 36. It is composed of a phase discrimination circuit 35 that outputs. The plurality of transducers 31 and 32 are configured to perform measurement purposes under the measurement environment so that physical and chemical changes to be measured are converted into relative changes in the capacitance of both transducers 31 and 32. They are arranged in a certain positional relationship according to the Since the variable delay circuits 33 and 34 have a delay amount depending on the capacitance of each converter 31 and 32, each variable delay circuit 3
The input pulses to the converters 3 and 34 are delayed by an amount corresponding to the capacitance of the converters 31 and 32 and output. Therefore, the variable delay circuits 33, 3
If the phase difference between the output pulses 4 and 4 is detected by the phase discrimination circuit 35, a relative change in the capacitance of the converters 31 and 32 can be detected, thereby making it possible to detect physical and chemical changes. It is. That is, the capacitive sensor of the present invention first converts the physical and chemical change to be measured into a relative change in the capacitance of the transducers 31 and 32, and then converts this into a pulse phase difference, that is, a time difference. It detects various types of information by converting it to
There is no need to reset the detection threshold level for each measurement unit. In addition, since capacitance changes are detected by converting them into time differences, highly accurate detection is possible.Furthermore, the oscillation accuracy of the pulse generation circuit 30 has no effect on detection accuracy, and therefore an inexpensive oscillation circuit is used. In addition, since the phase difference detection of the pulses can be realized with an inexpensive circuit, the device can be made smaller and less expensive. The transducers 31 and 32 include a variable electrode spacing type in which the electrode spacing changes in response to physical changes, an area variable type in which the electrode facing area changes in response to physical changes, and a variable electrode type in which the electrode spacing changes in response to physical changes, and converters in which the electrode spacing changes in response to physical changes. Any type of dielectric constant variation type that changes the dielectric constant of the interelectrode material can be adopted. The variable delay circuits 33 and 34 are, for example, R-C integration circuits, L-C
It is constructed by combining a known delay circuit such as an integrating circuit or a low-pass filter in which the capacitor is replaced with a converter, and a conventionally known binarization circuit such as a Schmitt circuit. Further, the phase discrimination circuit 35 is
It may have any configuration as long as it can detect the phase difference between pulses, and its output form may be either analog or digital. Note that the delay adjustment circuits 37 and 38 in FIG.
is for offset adjustment which delays the output pulse of the variable delay circuit 33 by an arbitrary amount and outputs the delayed pulse, and is composed of, for example, a one-shot multivibrator. In the illustrated example, each variable delay circuit 33,
34, but it is also possible to omit one of them. Also, the offset adjustment may be performed at other locations other than the above, such as the variable delay circuit 3.
You may also do this with 3 or 34. Additionally, remote offset adjustment can be accomplished by precision digital delay adjustment using a combination of clock pulses, presettable counters, gates, flip-flops, and the like. [Embodiment] Fig. 4 is an electrical circuit diagram of an embodiment in which the present invention is applied to an intravenous liquid level detection sensor, in which the same reference numerals as in Fig. 3 indicate the same parts, 40 is an inverted Schmitt circuit, 41 ~43 is a forward-rotating Schmitt circuit, 4
4, 45 are capacitors, 46 to 52 are resistors, 53
is a variable resistor, 54 is a delay adjustment circuit, 55 is an edge-clocked D-type flip-flop, C, D, Q,
Q is its clock input terminal, data input terminal, output terminal, and inverted output terminal, 56 and 57 are transistors, and 58 is a light emitting diode. Incidentally, it is also possible to use inverted types of Schmitt circuits 41 to 43. In the figure, a Schmitt circuit 40, a capacitor 44, and a resistor 46 are connected to a square wave pulse generation circuit 3.
0, and the pulses generated here are sent to the variable delay circuit 3 via a variable resistor 53 for offset adjustment.
3 and 34. The variable delay circuit 33 is composed of an integrating circuit consisting of a resistor 47 and a converter 31, and a Schmitt circuit 41, and delays the pulse from the pulse generating circuit 30 by an amount corresponding to the capacitance of the converter 31 and converts it to D. It is input to the data input terminal D of the flip-flop 55. Further, a variable delay circuit 34 is constituted by an integrating circuit consisting of a resistor 48 and a converter 32, and a Schmitt circuit 42, in which a pulse from the pulse generating circuit 30 is delayed by an amount corresponding to the capacitance of the converter 32. and is input to the clock input terminal C of the D-type flip-flop 55. In the case of non-contact liquid level detection, the transducers 31 and 32 are of a dielectric constant variable type, for example, as shown in FIG.
1 and 62 are attached to one side of the electrode support member 63 as shown in the figure, the electrode 61 and the ground electrode 60 constitute one converter 31, and the electrode 62 and the ground electrode 6
0 and the other converter 32 is used. In order to ensure good adhesion of the electrodes 60 to 63 to the container, the electrodes 60 to 63 are made of a flexible electrode material such as a thin metal film, conductive rubber, or conductive vinyl, and electrode supports are also used. The member 63 is also preferably made of a material with good cushioning properties, such as polyurethane foam. The transducers 31 and 32 having such a structure are attached to the drip liquid container, for example, as shown in FIG. 32, the electrodes 60 to 62 are brought into close contact with the side wall of the drip container 66 using, for example, a plate spring-shaped electrode holding fitting 65. Note that the electrode holding fitting 65 is a gripper 6 that holds the cap 67 of the container 66.
It is attached to one end of the sensor 8 so as to be movable in the vertical direction, allowing one-touch mounting of the sensor and free adjustment of the sensor mounting position. Furthermore, the D-type flip-flop 5 in FIG.
Reference numeral 5 constitutes a phase discrimination circuit 35, which sets the data at the data input terminal D at the timing of the rise of the pulse applied to the clock terminal C, outputs the set output to the Q terminal, and outputs its inverted output to the terminal. The following table is a truth table for the D-type flip-flop 55.

[Effect of idea]

As can be seen from the above explanation, the capacitive sensor of the present invention includes separate converters as components, and outputs the delayed input pulse by an amount corresponding to the capacitance value of the converter. Multiple variable delay circuits are provided to convert the physical and chemical changes to be measured into relative changes in the capacitance of multiple transducers, which are then converted into phase differences between pulses. death,
This phase difference is detected by a phase discrimination circuit to detect various information, and unnecessary fluctuations such as temperature changes cancel each other out, so it is necessary to reset the detection threshold level for each measurement unit. There isn't. Further, since capacitance changes are detected by converting them into time differences, it is possible to detect minute capacitance changes, and since the structure is simple, there is an advantage that the sensor can be made smaller and less expensive. Therefore, if the present invention is applied to a sensor for detecting the level of an intravenous liquid, it will be very effective.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of a conventional capacitive sensor, Fig. 2 is an explanatory diagram of its operation, Fig. 3 is a block diagram showing the basic configuration of the present invention, and Fig. 4 is an illustration of the present invention as an infusion solution. An electrical circuit diagram of an embodiment applied to a liquid level detection sensor, FIG. 5 is an external view showing an embodiment of the converter, FIG. 6 is an explanatory diagram of how to install the converter, and FIGS. 7 and 8 are Diagram 4 showing an example of signal waveforms at each part when the illustrated circuit is operated, 9th
Figures 1 and 10 are explanatory diagrams of the structure of a sensor for detecting the eccentricity of a coated wire. 40-43... Schmitt circuit, 44, 45...
. . . Capacitors, 46 to 52 . . . Resistors, 53 . . . Variable resistors, 54 .

Claims (1)

[Scope of utility model registration request] One pulse generation circuit, and the output of the pulse generation circuit is branched into a plurality of parts, each of which includes a separate variable capacitance converter as a component, and the amount of which corresponds to the value of the capacitance of the variable capacitance converter. A variable delay circuit comprising a plurality of series that delays and outputs the pulses of the pulse generation circuit; and a phase discrimination circuit that outputs measurement information by discriminating the phase difference between the pulses output from the variable delay circuits of the plurality of series. The plural series of variable delay circuits each include an integrating circuit using the variable capacitance converter as an integrating capacitor, and a binarization circuit that binarizes the output of the integrating circuit, The phase discrimination circuit includes an edge-clocked D-type flip-flop which receives output pulses from the plurality of series of variable delay circuits as data input and clock input, a low-pass filter to which the output of the flip-flop is applied, and binarizes the output of the low-pass filter. A capacitance type sensor comprising a binarization circuit.