CN216695176U - Liquid level measurement sensor based on interdigital capacitor - Google Patents

Abstract

The utility model discloses a liquid level measuring sensor based on interdigital capacitors, which comprises an insulating shell, and interdigital capacitors and a capacitor detection circuit which are respectively arranged in the insulating shell, wherein the number of the interdigital capacitors is multiple, the multiple interdigital capacitors are distributed in the insulating shell in a sectional mode, the multiple interdigital capacitors are connected to the capacitor detection circuit through interdigital capacitor leads, the capacitor detection circuit is led out to the outside of the sensor through a power supply and a communication bus, and two ends of the insulating shell are sealed. The utility model has convenient wiring, is beneficial to sealing, improves the consistency of products and reduces the cost.

Description

A Liquid Level Measurement Sensor Based on Interdigital Capacitance

technical field

The utility model relates to the technical field of liquid level (solid material level) and water content measurement, in particular to a liquid level measurement sensor based on interdigital capacitance.

Background technique

Capacitive liquid level sensor is a kind of variable dielectric capacitor that uses the change of the measured medium surface to cause the capacitance change. Such sensors are generally installed vertically in the container under test. The capacitive liquid level sensor has the advantages of large dynamic range, fast response speed, small zero drift, simple structure and strong adaptability.

Capacitive sensors Liquid level sensors generally have two types: parallel plate type and coaxial capacitive type. Its structure is shown in Figure 1, including parallel plate type and coaxial capacitive type. As shown in Figures 1a and 1b, the most commonly used is the coaxial capacitive sensor, which generally uses two coaxial inner and outer metal tubes with different diameters. The two pole plates that constitute the capacitor should maintain a certain gap between the two metal tubes. The change of the liquid level interface causes the linear change of the capacitance value, and the liquid level of the liquid level can be calculated according to the capacitance value.

Since a single capacitor cannot resolve the multi-phase interface, it is limited in the measurement of the multi-phase interface. For example, the oil extracted from the oil field is a three-phase mixture of oil, gas and water, and the extraction process is also accompanied by the presence of sediment. Usually, from the top of the tank to the bottom of the tank, the order is crude oil, oil-water emulsion, water, and sludge layer. In the process of oil exploitation, multi-phase liquid level measurement is required in various links such as transfer tanks, sedimentation tanks, crude oil dehydrators, electric dehydrators, buffer tanks, storage and transportation tanks, etc. The water content of crude oil and crude oil production in the process provide data.

The measurement of multi-phase interface mainly adopts segmented capacitive sensor. The segmented capacitive sensor can distinguish each capacitance in a certain layer according to the value of each capacitance, and then calculate and distinguish the multi-phase interface. Segmented capacitive sensors have high measurement accuracy, low cost, and are the most widely studied.

There are mainly three types of commonly used arrangement of segmented capacitor electrodes, as shown in Figure 2. Figure 2a shows a symmetrical bipolar plate segmented capacitor structure. The two polar plates of each capacitor are symmetrical and have the same parameters. Figure 2b shows a segmented capacitor structure with a common electrode. Figure 2c shows a unipolar segmented capacitor structure. This solution uses the container wall as the common electrode of the segmented capacitor and can only be used in metal containers.

For some longer containers, more segment capacitors are often required. For example, in the process of crude oil gathering and transportation, the height of some tanks is usually more than 10 meters. In order to improve the accuracy of liquid level measurement as much as possible, the measurement scheme of segmented capacitance measurement is adopted. The number of capacitors is generally dozens, and may even be as many as hundreds. . At present, the main problems faced by several segmented capacitance measurement schemes based on Figure 2 are as follows:

The capacitance measurement circuit is generally placed outside the tank. A large number of leads are drawn out to the measurement circuit, which brings difficulties to the installation and maintenance of the measurement system. The capacitor leads are long, the parasitic capacitance value is large, and the lengths of different capacitor leads are different, which brings great inconvenience to measurement and data processing.

The sensors in Fig. 2a) and Fig. 2b) have many electrodes and lead wires, which brings great difficulties to the sealing and processing of the sensor.

Figure 2 c) Because the unipolar scheme is adopted, it is easy to seal, but the container wall needs to be used as the electrode of the capacitor, and the measurement accuracy is poor, and it can only be used for metal containers. This type of sensor has two disadvantages:

First, the shape of the tank and the position of the sensor will affect the sensor parameters, so the sensor parameters of this structure need to be calibrated on site, which brings inconvenience to installation and debugging.

Second, due to the large diameter of the storage tank and the use of the tank body as the electrode, the accuracy of the sensor is affected, and accurate measurement cannot be achieved if the inner wall of the tank is made of non-metallic materials.

The change of the internal degree of the container easily affects the dielectric constant of the liquid and the medium in the capacitive sensor, resulting in a large temperature drift and affecting the measurement accuracy.

In the measurement process of relatively dirty liquids such as crude oil, if PTFE material is not used, the surface of the segmented capacitive sensor is easy to hang oil, which will cause the capacitance value to gradually shift and affect the measurement accuracy. PTFE has good anti-stick properties, and as an insulating material, it can better solve the problem of oil hanging. However, almost all glues cannot firmly bond PTFE, which brings sealing problems to segmented capacitive sensors based on PTFE materials.

Utility model content

Aiming at the defects of the prior art, the utility model provides a liquid level measuring sensor and a liquid level measuring method based on interdigital capacitance, which is convenient for wiring, facilitates sealing, improves product consistency and reduces costs.

In order to solve the technical problem, the technical solution adopted by the present utility model is: a liquid level measurement sensor based on interdigital capacitance, comprising an insulating shell, an interdigital capacitor and a capacitance detection circuit respectively arranged in the insulating shell, and the interdigital capacitance is The number of capacitors is multiple, and the multiple interdigitated capacitors are distributed in segments in the insulating housing. The multiple interdigitated capacitors are connected to the capacitance detection circuit through the interdigitated capacitor leads, and the capacitance detection circuit is led to the outside of the sensor through the power supply and the communication bus. Both ends of the insulating housing are sealed.

Further, the insulating shell is an insulating circular tube, the two electrodes of the interdigital capacitor are processed by a flexible circuit board, and the interdigital capacitor is closely attached to the inner wall of the insulating circular tube.

Further, the material of the insulating housing is polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, perfluoroethylene propylene copolymer or ethylene-tetrafluoroethylene copolymer.

Further, the thickness of the flexible circuit board is more than 0.1 mm.

Further, when the number of interdigital capacitors is greater than the set value, multiple capacitance detection circuits are required, and the multiple capacitance detection circuits are cascaded together and connected to the same power supply and communication bus.

Further, both ends of the insulating housing are sealed by insulating joints, or one end of the insulating housing is sealed by insulating joints, and the other end is sealed by welding.

Beneficial effects of the utility model: The utility model adopts a segmented sensor structure, the two electrodes of each capacitor are sealed in the same insulating shell, and the capacitance detection circuit is also arranged in the insulating shell, so that the interdigital capacitance and capacitance detection The circuit wiring is convenient. The circular tube insulating shell is very beneficial to sealing, which greatly reduces the sealing cost of this type of sensor and improves the reliability of the sensor. Using FPC to process interdigital capacitors, FPC interdigital capacitors rely on their own elasticity to stick to the inner wall of the circular tube insulating shell. The FPC interdigital capacitor measures the dielectric constant outside the tube through an insulated circular tube, and calculates the liquid interface accordingly. FPC interdigital capacitors can be processed in batches, and have good consistency, which can improve product consistency and lower cost.

Description of drawings

1 is a schematic structural diagram of an existing capacitive sensor;

2 is a schematic structural diagram of an existing segmented capacitive liquid level sensor;

FIG. 3 is a schematic structural diagram of an interdigital capacitor;

4 is a schematic structural diagram of the liquid level measurement sensor described in Embodiment 1;

5 is a schematic top view of the liquid level measurement sensor according to Embodiment 1;

In the figure: 1. Power and communication bus, 2. Upper sealing connector, 3. Insulating round tube, 4. Interdigital capacitor, 5. Lower sealing connector, 6. Interdigital electrode, 7. Capacitance detection circuit, 8. Fork Refers to capacitor electrode leads.

Detailed ways

The present utility model will be further described below in conjunction with the accompanying drawings and specific embodiments.

Example 1

This embodiment discloses a liquid level measurement sensor based on an interdigital capacitor. The interdigital capacitor is processed by a flexible circuit board (Flexible Printed Circuit, FPC). The basic structure of the interdigital capacitor is shown in FIG. 3 . The two electrodes of the capacitor are formed by wires. Because different substances have different dielectric constants, the change of the substance (usually liquid or solid powder) on the surface of the interdigital electrode will cause the change of the capacitance value of the interdigital capacitor. According to the change of the capacitance value It can calculate the moisture content of sand, cement or other solid or liquid. It can also be used to calculate the liquid level of solid powder or liquid. The insulating shell is generally made of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxy Vinyl ether copolymer (PFA), perfluoroethylene propylene copolymer (FEP) or ethylene-tetrafluoroethylene copolymer (ETFE) processing, other insulating materials can also be used. FPC interdigital capacitors rely on their own elasticity to adhere to the insulation The inner wall of the circular tube. The FPC interdigital capacitor measures the dielectric constant outside the tube through the insulated circular tube, and calculates the liquid interface accordingly.

As shown in FIGS. 4 and 5 , the liquid level measurement sensor in this embodiment includes an insulating housing, an interdigital capacitor 4 and a capacitance detection circuit 7 respectively disposed in the insulating housing. The number of the interdigital capacitors 4 is multiple. The interdigital capacitors 4 are distributed in sections in the insulating housing, and the plurality of interdigital capacitors 4 are connected to the capacitance detection circuit 7 through the interdigital capacitor electrode leads 8. The capacitance detection circuit 7 is led to the outside of the sensor through the power supply and the communication bus 1, and the insulation Both ends of the housing are sealed.

In this embodiment, the insulating shell is an insulating circular tube 3 , the two electrodes of the interdigital capacitor 4 are processed by a flexible circuit board, and the interdigital capacitor 4 is closely attached to the inner wall of the insulating circular tube 3 .

In order to ensure sufficient elasticity, the thickness of the flexible circuit board is above 0.1mm.

If the container with the measured liquid level is high (or long), more segmented capacitors are required, and when the number of interdigital capacitors is greater than the set value, multiple capacitance detection circuits 7 are required, and multiple capacitance detection circuits 7 are cascaded together and connected to the same power and communication bus 1.

In this embodiment, the two ends of the insulating round tube 3 are sealed by the upper insulating joint 2 and the lower insulating joint 5 respectively. In other embodiments, if the material allows, one end of the insulating round tube 3 is sealed by the insulating joint, and the other end is sealed by welding .

The above descriptions are only the basic principles and preferred embodiments of the present invention, and improvements and replacements made by those skilled in the art according to the present invention belong to the protection scope of the present invention.

Claims (6)

1. a liquid level measuring sensor based on interdigital capacitance, it is characterized in that: comprise insulating housing, the interdigital capacitance and capacitance detection circuit that are respectively arranged in the insulating housing, the quantity of interdigital capacitance is a plurality of, a plurality of forks The finger capacitors are distributed in sections in the insulating shell. Multiple interdigital capacitors are connected to the capacitance detection circuit through the interdigitated capacitor leads. The capacitance detection circuit is led out of the sensor through the power supply and the communication bus. Both ends of the insulating shell are sealed. 2. The liquid level measuring sensor based on interdigital capacitance according to claim 1, characterized in that: the insulating shell is an insulating circular tube, the two electrodes of the interdigital capacitor are processed by a flexible circuit board, and the interdigital capacitor is closely attached on the inner wall of the insulated circular tube. 3. The liquid level measuring sensor based on interdigital capacitance according to claim 1, wherein the insulating shell is made of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, Fluoroethylene propylene copolymer or ethylene-tetrafluoroethylene copolymer. 4 . The liquid level measurement sensor based on interdigital capacitance according to claim 2 , wherein the thickness of the flexible circuit board is more than 0.1 mm. 5 . 5. The liquid level measuring sensor based on interdigital capacitance according to claim 1, characterized in that: when the number of interdigital capacitances is greater than the set value, a plurality of capacitance detection circuits are required, and a plurality of capacitance detection circuits are cascaded together, and connected to the same power and communication bus. 6 . The liquid level measuring sensor based on interdigital capacitance according to claim 1 , wherein both ends of the insulating housing are sealed by insulating joints, or one end of the insulating housing is sealed by insulating joints, and the other end is sealed by welding. 7 .

Images