JP2005274158A - Electrostatic capacity type liquid sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic capacity type liquid sensor prevented from erroneous operation by widening a detection range of a semiconductive substance. <P>SOLUTION: An insulating film 31 is formed to the inner peripheral surface becoming a contact surface coming into contact with a coating solution is formed to a ring-shaped detection electrode 30 by PFA coating. The inner peripheral surface is exposed to the inside of a pipe part 22 through which the coating solution 12 passes. Therefore, the resistance value between the detection electrode 30 and the pipe part 22 being an earth electrode increases to become almost infinite and the detection circuit in a circuit part 25 detects the coating solution 12 only by a change in electrostatic capacity between the detection electrode 30 and the pipe part 22 being the earth electrode in spite of the resistance value. Further, since the detection circuit becomes almost infinite in resistance value, even if the change in electrostatic capacity is small, the semiconductive substance can be detected. Accordingly, a range capable of detecting the semiconductive substance is widened and the arroneous operation of an electrostatic capacity type liquid sensor is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitive liquid sensor that detects a liquid to be detected based on a change in capacitance between a detection electrode and a ground electrode due to a relative dielectric constant of the liquid to be detected and outputs a detection signal.

  In factories and plants, it is important to detect and measure substances, and various detection sensors are used. For example, a capacitance type level sensor is used to detect liquid in a tank or piping.

  Such a capacitance type level sensor utilizes the fact that the capacitance between the detection electrode and the ground electrode changes due to the relative dielectric constant of the liquid when the liquid as the detection object contacts the detection electrode. The liquid is detected (see, for example, Patent Document 1). In such a capacitance type level sensor, a detection circuit constituted by a resonance circuit or the like is connected to the detection electrode, and when the detected object comes into contact with the detection electrode, the detection electrode is grounded by the relative permittivity of the detected object. Detection is performed by utilizing the fact that the capacitance between the electrodes changes and the resonance circuit resonates. In other words, when the level of the object to be detected increases and the contact surface with the detection electrode increases, the capacitance increases and the resonance circuit reaches the operating point, causing resonance and a rapid increase in response current. Is used to detect that the detected object has reached a predetermined level.

  In the above-described capacitance type level sensor, the detected object is detected only by a change in the capacitance value between the detection electrode and the ground electrode due to the relative dielectric constant of the detected object. However, there is a known method for performing detection in consideration of not only the change in capacitance value but also the influence of the conductivity of the object to be detected (see, for example, Patent Document 2). Below, the detection method of the to-be-detected object in the electrostatic capacitance type level sensor of patent document 2 is demonstrated.

  FIG. 5 is a graph showing the relationship between the resistance value of the detection circuit (reciprocal of conductivity) and the capacitance in the capacitance type level sensor, and is called a GC characteristic. The horizontal axis indicates the resistance value, and the vertical axis indicates the capacitance value. When the object to be detected has an ideal insulating property, even if the object to be detected contacts the electrode, there is almost no change in the resistance value, and only the capacitance due to the relative dielectric constant of the object to be detected changes. If the change in the capacitance is greater than or equal to a predetermined threshold, the resonance operation of the resonance circuit enters the ON region, and the detection circuit outputs a detection signal indicating that the detected object has reached a predetermined level.

  Further, when a conductive object to be detected adheres to the detection electrode, the electrical conductivity increases (resistance value decreases), causing a malfunction. However, even in this case, if the GC characteristic works, the resistance value between the detection electrode and the ground electrode is, for example, 10 kΩ, and the adhesion capacitance is 2 pF, the resonance operation does not enter the ON region, and the OFF region And no malfunction occurs. On the other hand, when the object to be detected reaches the detection electrode, the increase in electrostatic capacity is much larger than the adhesion capacity 2 pF, so that it correctly enters the ON region and outputs a detection signal.

  Furthermore, in addition to the factor due to the detected object adhering to the detection electrode, when the detected object is a semiconductive substance, it does not match the GC characteristic, which causes a malfunction. In other words, even if a semiconductive object to be detected comes into contact with the detection electrode, it does not enter the ON region because the increase in capacitance is too small for the decrease in the resistance value between the detection electrode and the ground electrode. Instead, the malfunction remains in the OFF region. In order to avoid such inconvenience due to the material properties, a resistance (for example, 4.8 kΩ) is inserted between the detection electrode and the ground electrode to force the GC characteristic to act. Here, the resistance value is not changed by the object to be detected due to the insertion of the resistor, but the sensitivity is considerably lowered, so a capacitor (for example, 15 pF) is connected in parallel to the insertion resistor. Then, when the object to be detected reaches the detection electrode, the shortage of the increase in the capacitance is compensated by the parallel capacitor. In other words, even when the detected object reaches the detection electrode, even when the capacitance is relatively small, the ON region is correctly entered and the detection signal is output. That is, if a resistor or capacitor is added to create another circuit (called a Z-type amplifier) to weaken the function of the GC characteristic, the conductive object is attached to the detection electrode. Although the detection accuracy is reduced by this, it is possible to detect a semiconductive substance that does not match the normal (standard amplifier) GC characteristic.

Japanese Patent Laid-Open No. 7-190838 JP 2002-195867 A

  However, although the function of the GC characteristic is weakened by the Z-type amplifier, it corresponds to the detection of the semiconductive material, but even if the Z-type amplifier is used, the stable region is small and it corresponds to all the semiconductive materials. There was a problem that I could not. For this reason, it has been necessary to widen the detectable range for the semiconductive material to prevent malfunction.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a capacitive liquid sensor in which a detectable range for a semiconductive substance is expanded to prevent malfunction.

  In order to solve the above problems, the capacitive liquid sensor of the present invention detects a liquid to be detected based on a change in capacitance between the detection electrode and the ground electrode due to the relative dielectric constant of the liquid to be detected. In the capacitive liquid sensor that outputs a detection signal, an insulator is provided on the contact surface of the detection electrode that contacts the liquid to be detected.

  Further, the insulator is provided by coating the contact surface with PFA.

  In the capacitance type liquid sensor of the present invention, since the insulator is provided on the contact surface of the detection electrode that contacts the liquid to be detected, the resistance value between the detection electrode and the ground electrode increases. For this reason, the range which can detect a semiconductive liquid spreads, a malfunction is prevented, and a semiconductive substance can be detected reliably. For this reason, it is possible to reliably detect semi-conductive to insulating liquid, so if it is semi-conductive to insulating liquid, all liquids can be handled with one capacitive liquid sensor. can do.

  In addition, since the insulator is provided with PFA coating on the contact surface, it is not easily corroded by the liquid to be detected. For this reason, since the resistance value of the detection electrode does not change, malfunction of the capacitive liquid sensor can be prevented.

  FIG. 1 is a schematic view of a coating facility. The coating facility 10 connects the coating device 11, a tank 13 for storing the coating solution 12 supplied to the coating device 11, the coating device 11 and the tank 13, and the coating solution 12 in the tank 13 is applied to the coating device 11. The pipe 14 to be supplied to the pipe 14, the electrostatic capacity type liquid sensor 15 for detecting the coating liquid 12 in the pipe 14, and the detection signal output from the electrostatic capacity type liquid sensor 15 are acquired, and based on this detection signal And a controller 16 for controlling the coating apparatus 11. The pipe 14 is provided with a pump 17, and the pump 17 sends the coating solution 12 from the tank 13 to the coating device 11. Further, the capacitive liquid sensor 15 is connected between the flange portions 14 a and 14 b of the pipe 14. In this embodiment, the case where the capacitance type liquid sensor 15 of the present invention is provided in the pipe 14 for supplying the coating liquid 12 to the coating apparatus 11 will be described. anything is fine.

  Next, the configuration of the capacitive liquid sensor 15 will be described. This capacitive liquid sensor 15 is a simplified function of the capacitive level sensor, and detects only the presence or absence of liquid in the pipe 14, not the liquid level detection. FIG. 2 is a longitudinal sectional view showing the configuration of the capacitive liquid sensor 15. The capacitive liquid sensor 15 includes two flange portions 20a and 20b provided at both ends, a pipe portion 22 provided between the flange portions 20a and 20b, and a detection portion provided at the center of the pipe portion 22. 23 and a circuit unit 25 connected to the detection unit 23 via the connection unit 24. The flange portions 20 a and 20 b are attached to the flange portions 14 a and 14 b and connected to the pipe 14. For this reason, the coating liquid 12 flowing in the pipe 14 flows into the pipe portion 22 from the left side in the drawing and flows out from the right side. The pipe portion 22 is made of a conductive metal, is grounded, and functions as a ground electrode.

  The detection unit 23 is provided with a ring-shaped detection electrode 30 made of stainless steel (SUS304), and is arranged in the pipe portion 22 so as to expose the inner peripheral surface. This inner peripheral surface is a contact surface that comes into contact with the coating liquid 12 that is the liquid to be detected. As shown in FIG. 3, the contact surface (inner peripheral surface) of the detection electrode 30 is provided with an insulating film 31 that is an insulator by a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) coating. Yes. The thickness of the insulating film 31 is uniform, and the thickness is preferably about 500 μm, although it varies depending on the type of the liquid to be detected. The thickness of the insulating film 31 is not limited to this, and the design may be changed as appropriate depending on the type of the liquid to be detected. The detection electrode 30 is made of stainless steel (SUS304). However, the detection electrode 30 is not limited to this and may be any metal having conductivity.

  In addition, two insulating rings 32 and 33 are arranged in the detection unit 23 so as to cover both side surfaces of the detection electrode 30. The insulating rings 32 and 33 are insulators formed of a fluororesin such as PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer). The insulating rings 32 and 33 allow the detection electrode 30 and the pipe portion 22 to be connected to each other. Are electrically isolated. The insulating rings 32 and 33 are formed with O-ring grooves 32a, 32b, 33a and 33b on the inner surface on the detection electrode 30 side and the outer surface on the pipe portion 22 side, and the O-ring 34 is inserted. Yes. The O-ring 34 prevents the coating liquid 12 in the pipe part 22 from leaking outside the pipe part 22.

  Further, the insulating film 31 and the insulating rings 32 and 33 are not limited to fluororesins such as PFA, but may have any heat resistance, chemical resistance, and insulation. Since the insulating film 31 is formed of a material having heat resistance and chemical resistance, it is difficult to be corroded by the coating liquid 12 that is a liquid to be detected. For this reason, the resistance value of the detection electrode 30 does not change, and the malfunction of the capacitive liquid sensor 15 can be prevented.

  Moreover, the detection electrode 30 is connected to the connection part 35a of the conductor rod 35 formed with the metal which has electroconductivity. The conductor bar 35 is inserted through the connection portion 24 and connected to the circuit portion 25. Similar to the detection electrode 30, the conductor bar 35 is insulated from the pipe portion 22.

  The circuit unit 25 includes a detection circuit therein, and the detection circuit is connected to the above-described conductor rod 35 and the pipe unit 22 that is a ground electrode. The detection circuit includes a resonance circuit, and outputs a detection signal based on the operation of the resonance circuit due to a change in capacitance between the detection electrode 30 and the pipe portion 22 that is the ground electrode. That is, the detection circuit outputs an ON signal when the resonance circuit reaches the operating point and performs a resonance operation, and outputs an OFF signal when the resonance circuit does not reach the operating point and does not resonate. . For this reason, the electrostatic capacitance type liquid sensor 15 detects the presence or absence of the coating liquid 12 in the pipe portion 22, and outputs an ON signal to the controller 16 when the coating liquid 12 is in contact with the detection electrode 30. When the coating liquid 12 is not in contact with the detection electrode 30, an OFF signal is output to the controller 16.

  Next, the operation of the capacitive liquid sensor 15 having the above configuration will be described. In the description of this operation, three kinds of semiconductive coating liquids used in the PS plate production line, that is, the coating liquids A, B, and C shown in the table of FIG. 4 are used as the coating liquid 12. The case will be described in comparison with the operation when a conventional capacitance type level sensor (capacitance type liquid sensor having a bare electrode in which an insulating film is not formed on the contact surface of the detection electrode) is used. In addition, as a conventional capacitance type liquid sensor, a commercially available DS-P2 pipeline type level sensor manufactured by Yamamoto Electric Industry Co., Ltd. was used. FIG. 5 is a graph showing GC characteristics of the standard amplifier and the Z-type amplifier.

  When the coating liquid A is stored in the tank 13, the coating liquid A is supplied from the tank 13 to the coating apparatus 11, and the coating liquid A in the pipe portion 22 contacts the detection electrode 30. When the detection electrode 30 is a bare electrode, the capacitance is 27.4 pF, the resistance value is 23.4 kΩ, and the ON region is output. Therefore, an ON signal is output from the conventional capacitance type liquid sensor to the controller 16. For this reason, the coating liquid A can be detected without malfunction even with a conventional capacitive liquid sensor.

  Further, when the capacitance type liquid sensor 15 of the present invention having the insulating film 31 formed on the contact surface of the detection electrode 30 is used, the capacitance is 17.3 pF and the resistance value is 1000 kΩ, which becomes the ON region. Then, an ON signal is output from the capacitive liquid sensor 15 to the controller 16. For this reason, the coating liquid A can be detected by the capacitive liquid sensor 15 without malfunction.

  Next, when the coating liquid B is stored in the tank 13, the coating liquid B is supplied from the tank 13 to the coating apparatus 11, and the coating liquid B in the pipe portion 22 contacts the detection electrode 30. When the detection electrode 30 is a bare electrode, the capacitance is 22.84 pF, the resistance value is 3.1 kΩ, and both the standard amplifier and the Z-type amplifier are in the OFF region. 16, an OFF signal is output. For this reason, even if the coating liquid B contacts the detection electrode 30, the coating liquid B cannot be detected by the conventional capacitive liquid sensor.

  On the other hand, when the capacitance type liquid sensor 15 of the present invention in which the insulating film 31 is formed on the contact surface of the detection electrode 30 is used, the capacitance is 18.9 pF and the resistance value is infinite. Since the ON region is entered, an ON signal is output from the capacitive liquid sensor 15 to the controller 16. For this reason, the coating liquid B can be reliably detected by the capacitive liquid sensor 15.

  Next, when the coating liquid C is stored in the tank 13, the coating liquid C is supplied from the tank 13 to the coating device 11, and the coating liquid C in the pipe portion 22 contacts the detection electrode 30. As shown in FIG. 5, since the coating liquid C has physical properties outside the sensor measurement area, when the detection electrode 30 is a bare electrode, both the capacitance and the resistance value cannot be measured. For this reason, the coating liquid C cannot be detected by the conventional capacitive liquid sensor.

  On the other hand, when the capacitance type liquid sensor 15 of the present invention in which the insulating film 31 is formed on the contact surface of the detection electrode 30 is used, the capacitance is 19.0 pF and the resistance value is infinite. Since the ON region is entered, an ON signal is output from the capacitive liquid sensor 15 to the controller 16. For this reason, the coating liquid C can be reliably detected by the capacitance type detection liquid sensor 15.

  As described above, since the insulating film 31 is formed on the inner peripheral surface of the detection electrode 30, that is, the contact surface in contact with the liquid to be detected, the resistance value between the detection electrode 30 and the pipe portion 22 that is the ground electrode is reduced. It increases and becomes almost infinite. Therefore, the detection circuit in the circuit unit 25 detects an object to be detected only by a change in capacitance between the detection electrode 30 and the pipe unit 22 that is the ground electrode, regardless of the resistance value. Further, since the resistance value of the detection circuit is almost infinite, it is possible to detect the semiconductive liquid even if the change in the capacitance is small as shown in the graph of the GC characteristic in FIG. In addition, the range in which the semiconductive substance can be detected is expanded, and the semiconductive substance can be reliably detected by the capacitive liquid sensor 15.

  In addition, since the insulating film 31 is formed on the contact surface of the detection electrode 30, the detection accuracy of the conductive object to be detected decreases due to adhesion to the detection electrode. Can be reliably detected. For this reason, if it is a semiconductive to insulating liquid, it can respond to all the liquids with one capacitive liquid sensor.

  In the present embodiment, the capacitive liquid sensor has been described so as to detect the liquid in the pipe. However, the present invention is not limited to this. For example, the liquid stored in the tank is detected. May be.

  In the present embodiment, the capacitive liquid sensor has been described so as to detect the presence or absence of the liquid to be detected. However, the present invention is not limited to this, and the capacitance that continuously detects the level of the liquid to be detected. The present invention can be applied to a type level sensor.

It is the schematic which shows a coating equipment. It is a longitudinal cross-sectional view which shows the structure of an electrostatic capacitance type liquid sensor. It is sectional drawing which shows the structure of a detection electrode and an insulating ring. It is a table | surface which shows the electrostatic capacitance between a detection electrode and a ground electrode with respect to each liquid, and resistance value. It is a graph which shows the GC characteristic of the detection circuit of an electrostatic capacitance type liquid sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Application equipment 12 Application liquid 15 Capacitance type liquid sensor 22 Pipe part 23 Detection part 25 Circuit part 30 Detection electrode 31 Insulation film 32, 33 Insulation ring

Claims (2)

In a capacitive liquid sensor that detects a liquid to be detected and outputs a detection signal based on a change in capacitance between the detection electrode and the ground electrode due to the relative permittivity of the liquid to be detected.
An electrostatic capacity type liquid sensor, wherein an insulator is provided on a contact surface of the detection electrode that contacts the liquid to be detected.   2. The capacitive liquid sensor according to claim 1, wherein the insulator is provided by coating the contact surface with PFA.

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