CN209979027U

CN209979027U - Liquid level sensor

Info

Publication number: CN209979027U
Application number: CN201921178281.4U
Authority: CN
Inventors: 泰克·布·杨; 赵奎文; 刁月鹏
Original assignee: Cryofocus Medtech Shanghai Co Ltd
Current assignee: Cryofocus Medtech Shanghai Co Ltd
Priority date: 2019-07-25
Filing date: 2019-07-25
Publication date: 2020-01-21
Anticipated expiration: 2029-07-25

Abstract

The present invention relates to a liquid level sensor, comprising a floating unit assembly including a floating unit and a plurality of conductive finger elements in electrical communication with each other, a position marker bar assembly including a plurality of annular conductive units, an insulating unit and a non-conductive conduit disposed in the inner cavities of the conductive and insulating units, the conductive and insulating units being coaxial, the conductive and insulating units being alternately arranged along a common axis thereof, the floating unit assembly being in mechanical engagement with the position marker bar assembly, the floating unit assembly being in constant electrical communication with at least two of the conductive units at any position of the position marker bar assembly to provide position feedback information to a monitoring system, the monitoring system detecting the position of the floating unit assembly corresponding to the position of the conductive unit, to determine the level of the reservoir.

Description

Liquid level sensor

Technical Field

The present application relates to the field of liquid level sensors, and more particularly, to a liquid level sensor operating in a low temperature environment.

Background

Cryogenic level sensors are typically custom made for a particular application and a particular gas. Not all known sensors are suitable for all cryogenic gases and all applications. Liquid level sensors are classified into two types, point sensors and continuous sensors. Point sensors include various types of thermal sensors, capacitive sensors, optical sensors, acoustic sensors, and vibrating blade sensors. These types of sensors require multiple sensors to be placed along different heights of the reservoir. To monitor small incremental changes in liquid level, the use of point sensors is very expensive and impractical. In addition, most point sensors cannot achieve high-precision detection due to their inherent characteristics and external induced conditions, such as evaporation of liquid refrigerant, water content inside refrigerant, influence of refrigerant flow, and the like. For example, the thermal sensor type works on the principle of detecting a large difference in resistance between liquid and vapor due to a temperature difference between the liquid and vapor. However, in the liquid reservoir, the liquid refrigerant is evaporated continuously, the temperature difference is not significant near the boundary of the gas-liquid separation, and the sensor cannot clearly detect the separation of the gas-liquid two layers. A significant temperature difference can only be detected when the sensor is far from the separation boundary. On the other hand, the optical sensor can be applied to liquid nitrogen, but cannot be applied to liquid hydrogen because of its light-transmitting property. Capacitive sensors, acoustic sensors and vibrating blade sensors are difficult to produce due to the high production costs.

Continuous sensors include various types of direct weight, differential pressure measurement, capacitance, acoustic, radioactive radiation, and radio frequency cavities. Such sensors are bulky, have low reliability and high cost and are difficult to implement. For example, the direct weight class requires a weighing device to be placed under the reservoir for detecting weight changes due to liquid level changes. It requires the scale and reservoir to be secured together to prevent relative movement thereof, which results in a bulky device. The reliability of most continuous sensors is greatly affected by moisture or ice deposition on the sensor surface. To make such sensors robust, such as radioactive emission sensors, costly and highly specialized to implement.

Therefore, there is a need for a level sensor that overcomes the above-mentioned disadvantages, and that can operate in a manner similar to a point sensor, while having good incremental level detection performance that approximates a continuous sensor.

Disclosure of Invention

In order to overcome the above-mentioned deficiencies, it is an object of the present invention to provide a reliable point level sensor having a performance close to that of a continuous sensor, and which is easy to implement directly, small, low cost, and suitable for all liquid refrigerants.

The purpose of the utility model is realized through the following technical scheme:

a liquid level sensor comprises a floating unit assembly, a position marker post assembly and a monitoring system: said floating unit assembly including a floating unit and a plurality of conductive finger elements disposed on said floating unit in electrical communication with each other, said position post assembly including a plurality of annular conductive units, a plurality of annular insulating units and a non-conductive conduit disposed within the interior cavities of said conductive and insulating units to provide alignment and structural support for said conductive and insulating units, said conductive and insulating units being coaxial and said conductive and insulating units being alternately arranged along a common axis thereof, wherein said floating unit assembly is in mechanical engagement with said position post assembly, said floating unit assembly maintaining constant electrical communication with at least two of said conductive units at any position of said position post assembly to provide position feedback information to said monitoring system, the monitoring system detects a position of the floating unit assembly corresponding to a position of the conductive unit to determine a level of the reservoir.

The purpose of the utility model can be further realized through the following technical scheme:

in one embodiment, each of the conductive elements in the position post assembly is electrically connected to a position wire routed along the lumen of the non-conductive conduit and connected at one end to a monitoring system through a top opening of the non-conductive conduit and at the other end to the conductive element through an opening provided in the non-conductive conduit. In a preferred embodiment, a plurality of the position lines constitute a position cable bundle.

In a preferred embodiment, the opening provided in the non-conductive conduit is a side groove formed along a length direction of the non-conductive conduit.

In a preferred embodiment, the conductive elements in the position post assembly are electrically isolated from each other by the insulating element. The position post assembly is a static unit that is generally flush with the height of the reservoir. One end of the position marker post assembly is connected to the top of the reservoir and the other end extends to near the bottom of the reservoir. The floating unit assembly has two moving directions, upward or downward. It can only move along the same axis throughout the length of the position post assembly and is constrained from extending beyond the ends of the position post assembly. The buoyancy forces lift the floating unit assembly upwards and gravity pulls it downwards. As the floating unit assembly moves up and down, its position is fed back to the monitoring system. The monitoring system receives the feedback information in the form of electrical signals and then determines the corresponding liquid level.

In a preferred embodiment, each of said conductive elements forms an open loop circuit with said monitoring system before said conductive element is in contact with said floating element assembly and forms a closed loop circuit with said monitoring system after said conductive element is in contact with said floating element assembly.

In one embodiment, the floating cell assembly has at least two of the conductive finger elements in electrical communication with each other and with the conductive cell.

In one embodiment, the floating cell assembly further comprises a conductive cylinder providing direct electrical communication between the conductive finger elements and intimately bonded to the floating cell and the conductive finger elements.

In one embodiment, the level sensor establishes a closed loop circuit of continuous electrical connections from the monitoring system to a first of the conductive elements, to the floating element assembly, to a second of the conductive elements, and back to the monitoring system to effect level monitoring.

In one embodiment, the level sensitivity of the level sensor and the required buoyancy volume are determined prior to determining the level.

In a preferred embodiment, each of the conductive elements has an equal height, and the level sensitivity is set to be one-half of the height of the conductive element to twice the height of the conductive element. Preferably, the level sensitivity is one half of the height of the conductive element.

In a preferred embodiment, the required buoyancy volume is one half to three quarters of the height of the floating unit.

In one embodiment, a spring and a stopper are mounted at both ends of the non-conductive conduit, respectively. The spring allows relative movement of the different materials due to thermal changes. The stop means limits the range of travel of the floating unit assembly. The floating unit assembly moves along the length of the position pole assembly defined by the top stop and the bottom stop. The floating unit assembly is in electrical communication with the at least two conductive units at all times at any position of the cylindrical position post assembly. When the conductive cells are in contact with the floating cell assembly, a closed loop circuit is formed between the conductive cells. Once the closed loop circuit is formed, the monitoring system detects the position of the floating cell assembly corresponding to the position of the conductive cell and then determines the level of the liquid within the reservoir.

In a preferred embodiment, an adapter member is installed at the top end of the non-conductive pipe, and a locking unit is installed at the bottom end of the non-conductive pipe.

In a preferred embodiment, the height of the conductive element is less than 20% of the total length between the top and bottom stops. In a preferred embodiment, the height of the conductive element is less than 10% of the maximum travel of the floating element assembly.

Compared with the prior art, the utility model discloses a level sensor's advantage as follows:

1. cryogenic liquids need to be preserved to adiabatic dewar container, and current mainstream level gauge needs to pass through the dewar container and installs, and it is comparatively difficult to realize sealed installation. The utility model discloses a level sensor can directly put into the dewar container in, does not need special installation requirement, realizes simply.

2. If the liquid phase drainage tube and the related measuring instrument are normally and directly exposed in the air, if the liquid phase drainage tube and the related measuring instrument are used for measuring the liquid level of the low-temperature fluid, the low-temperature fluid can quickly absorb heat, boil and gasify when flowing out of the heat-insulating Dewar container and entering the liquid phase drainage tube, so that the phenomenon of obvious coexistence of boiling gas and liquid in the tube is caused, and accurate reading is difficult. In addition, vaporization of the cryogenic fluid results in a large consumption of cryogenic fluid. The utility model discloses a level sensor need not be with cryogenic fluid to adiabatic dewar container external drainage, can avoid the liquid level measurement error that cryogenic fluid boiling phase transition arouses, avoids measuring the cryogenic fluid consumption that arouses simultaneously.

3. The special liquid level meter for part of the low-temperature fluid realizes liquid level monitoring by adopting a complex photoelectric module or an electromagnetic module, and has a complex structure and higher realization cost.

4. The liquid level sensor of the utility model adopts standard parts or slightly improved parts, so that the design is realized directly with low cost. The liquid level sensor of the present invention is more compact in structure, making it applicable to all types of refrigerants as further described below. Including a standard conductive finger element with spring-like characteristics. The purpose of the conductive finger element is to provide a positive contact force with the conductive element. This will ensure that electrical communication between the floating cell assembly and the position post assembly is not disturbed. The contact force between the conductive finger elements and the conductive units is optimized to reduce the resistance caused by friction. During descent, the drag force is overcome by the weight of the floating unit assembly. During ascent, the buoyancy force generated by the volume of the first floating unit overcomes the friction force and its own weight. The level sensor can be assembled using existing standard parts and is therefore very cost effective.

Drawings

Fig. 1 is a schematic diagram of the general structure of the liquid level sensor of the present invention.

Fig. 2 is a schematic structural diagram of the position marker post assembly of the present invention.

Fig. 3 is a partial cross-sectional view of a level sensor of the present invention, wherein the floating unit is located between two conductive units.

Fig. 4 is a partial cross-sectional view of a level sensor of the present invention, wherein the floating unit is in contact with three conductive elements, an upper conductive element and two lower conductive elements.

Fig. 5 is a partial cross-sectional view of a level sensor of the present invention, wherein the floating unit is in contact with two conductive units.

Fig. 6 is a partial cross-sectional view of a level sensor of the present invention, wherein the floating unit is in contact with three conductive elements, two upper conductive elements and one lower conductive element.

Fig. 7 is a schematic diagram of the floating unit assembly of the present invention located at the bottom of the level sensor.

Fig. 8 is a cross-sectional view of the floating unit assembly of the present invention positioned at the bottom of the level sensor.

Fig. 9 is a schematic diagram of the floating unit assembly of the present invention positioned on top of a level sensor.

Fig. 10 is a cross-sectional view of the floating unit assembly of the present invention positioned on top of a level sensor.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail with reference to the accompanying drawings and examples.

As shown in fig. 1 and 2, the present invention provides a liquid level sensor 100, which comprises a floating unit assembly 11, a position marker post assembly 50 and a monitoring system (not shown): said floating unit assembly 11 comprising a floating unit 1 and a plurality of conductive finger elements disposed on said floating unit 1 in electrical communication with each other, said position post assembly 50 comprising a plurality of annular conductive units 3, a plurality of annular insulating units 5, and a non-conductive conduit 15, said non-conductive conduit 15 being disposed within the lumens of said conductive units 3 and said insulating units 5 to provide alignment and structural support for said conductive units 3 and said insulating units 5, said conductive units 3 and said insulating units 5 being coaxial, said conductive units 3 and said insulating units 5 being alternately arranged together along their common axis, said floating unit assembly 11 being in mechanical engagement with said position post assembly 50, said floating unit assembly 11 being in constant electrical communication with at least two of said conductive units 3 at any position of said position post assembly 50, thereby providing position feedback information to the monitoring system which detects the position of the floating unit assembly 11 corresponding to the position of the conductive unit 3 to determine the level of the reservoir.

The floating unit 1 is light in weight and large in volume. This volume creates the buoyancy required to lift the floating unit assembly 11 upwards as the liquid level below rises. The volume of the floating unit 1 depends on the particular application. This principle applies to all types of liquid refrigerants.

Each of the conductive elements 3 in the position post assembly 50 is electrically connected to a position wire 35A, the position wire 35A running along the lumen of the non-conductive conduit 15 and having one end connected to a monitoring system through the top opening of the non-conductive conduit 15 for electrical communication with the monitoring system and the other end connected to the conductive element 3 through an opening provided in the non-conductive conduit 15. In one embodiment, the opening provided in the non-conductive conduit 15 is a side groove formed along the length of the non-conductive conduit 15. In a preferred embodiment, a plurality of the position lines 35A constitute a position cable bundle 35. The floating unit assemblies 11 are in electrical communication with the position pole assemblies 50, and their communication signals are fed back to a monitoring system (not shown) via the position cable harness 35.

The conductive elements 3 in the position post assembly 50 are electrically isolated from each other by the insulating elements 5. In one embodiment, the insulation unit 5 is an insulation sheet. The position post assembly 50 is a static unit that is generally flush with the height of the reservoir. The position post assembly 50 has one end connected to the top of the reservoir and the other end extending to near the bottom of the reservoir. The floating unit assembly 11 has two directions of movement, up or down. It can only move along the same axis throughout the length of the position post assembly 50 and is constrained from extending beyond the ends of the position post assembly 50. The buoyancy forces lift the floating unit assembly 11 upwards and gravity pulls it downwards. In one embodiment, each conductive element 3 forms an open loop circuit with the monitoring system before the conductive element 3 contacts the floating element assembly 11, and each conductive element 3 forms a closed loop circuit with the monitoring system after the conductive element 3 contacts the floating element assembly 11. In one embodiment, the floating unit assembly 11 has at least two of the conductive finger elements in electrical communication with each other and with the conductive unit 3. As the floating unit assembly 11 moves up and down, its position is fed back to the monitoring system. The monitoring system receives the feedback information in the form of electrical signals and then determines the corresponding liquid level.

Fig. 3 shows a partial cross-sectional view of the liquid level sensor 100, wherein the floating cell assembly 11 is in electrical contact with two conductive cells 3. The floating cell assembly 11 includes two

conductive finger elements

23 and 33, a conductive cylinder 25, and a floating cell 1. The conductive cylinders 25 provide direct electrical communication between the conductive finger elements and are in intimate contact with the floating unit 1 and the

conductive finger elements

23 and 33. The

conductive finger elements

23 and 33 are in electrical contact with at least two conductive elements 3 at all times at any location along the length of the fluid level sensor 100. As the floating unit assembly 11 moves along the length of the fluid level sensor 100, the conductive elements 3 in contact with the conductive finger elements are also in electrical communication with each other, thereby forming a closed loop circuit. The position line 35A connects the conductive element 3 to the monitoring system. A closed loop circuit of continuous electrical connections is established from the monitoring system to the first conductive element 3, to the floating element assembly 11, to the second conductive element 3, and back to the monitoring system. Once a closed loop circuit is established between at least two conductive elements 3, the liquid level can be determined.

As shown in fig. 1, a spring and a stopper are respectively installed at both ends of the non-conductive pipe 15. The spring allows relative movement of the different materials due to thermal changes. The stop means limits the range of travel of the floating unit assembly 11. The floating unit assembly 11 moves along the length of the position pole assembly 50 as defined by the top and bottom stops. An adaptor member 13 is mounted on the top end of the non-conductive pipe 15, and a locking unit 19 is mounted on the bottom end of the non-conductive pipe 15. In one embodiment, at the top end of the level sensor 100, the top spring 7 and top retainer 9 are mounted on a non-conductive conduit 15 with an axis parallel to the axis of the non-conductive conduit 15. An adapter member 13 is secured to the end of the non-conductive conduit 15 to provide a stop for the top stop 9. The position cable bundle 35 exits the top opening of the adapter section 13 and is then connected to a monitoring system. The adapter part 13 is connected to the reservoir. At the bottom end of the level sensor 100, a bottom spring 17 and a bottom stopper 21 are mounted on the non-conductive conduit 15. A locking unit 19 is fixed to the bottom end of the non-conductive conduit 15 and provides a stop for a bottom stop 21. The floating unit assembly is in electrical communication with the at least two conductive units at all times at any position of the cylindrical position post assembly. When the conductive cells are in contact with the floating cell assembly, a closed loop circuit is formed between the conductive cells. Once the closed loop circuit is formed, the monitoring system detects the position of the floating cell assembly corresponding to the position of the conductive cell and then determines the level of the liquid within the reservoir. As shown in fig. 2, the position wires 35A exiting from the adapter part 13 are bundled together to form a position cable bundle 35.

To determine the liquid level, the level sensitivity of the level sensor 100 and the required buoyancy volume need to be determined prior to determining the liquid level. The object of the present invention is to design a level sensor with a level sensitivity that is highly correlated with the conductive element 3. The design of the specific use sensor is made according to the height of the conductive elements 3, in one embodiment, the height of each conductive element 3 is equal, and the liquid level sensitivity is set to be in the range of one half of the height of the conductive element 3 to twice the height of the conductive element 3. In a preferred embodiment, the liquid level sensitivity may be set to twice the height of the conductive element, or may be set to one-half the height of the conductive element.

To determine the required buoyancy volume, the floating unit assembly 11 is designed to have a low drag between the conductive finger elements and the conductive unit 3. The total mass of the floating unit assembly 11 is optimized to be greater than 100% of the total drag force generated by the conductive finger elements contacting the conductive unit and less than 125% of the total drag force. The net weight of the floating unit assembly 11 being greater than the drag force enables the floating unit assembly 11 to descend as the liquid level decreases. On the other hand, it is not only necessary to optimize the size of the floating unit 1 to be compact, but also to have sufficient volume to provide adequate buoyancy. The buoyancy required to lift the weight of the floating unit assembly 11 should be greater than 100% of the total drag force. The object of the invention is that the required buoyancy volume should account for approximately one half to three quarters of the height of the floating unit 1. Preferably, the required buoyancy level is three quarters of the height of the floating unit. The buoyancy volume refers to the height of the floating unit submerged below the liquid level.

Based on the preferred embodiment, the sensitivity of the liquid level sensor 100 is one half of the height of the conductive unit 3 and the buoyancy volume is three quarters of the height of the floating unit 1, the liquid level shown in fig. 3 can be determined as one half of the height of the conductive unit 3 at the top. The determined liquid level is only applicable to the design shown in fig. 3, with only two conductive units over the length of the conductive finger units 23 and the conductive finger elements 33. Changing the height of the conductive element 3 requires re-evaluation of the parameters involved to determine the correct level.

The accuracy of the level sensor is affected by the height of the conductive element 3. Reducing the height of the conductive unit 3 allows for detection of smaller liquid level changes, improving the sensitivity of the liquid level sensor. In a preferred embodiment, the height of the conductive element 3 in the present application is less than 20% of the total length between the top stopper 9 and the bottom stopper 21. In a preferred embodiment, the height of the conductive element 3 is less than 10% of the maximum travel of the floating element assembly 11.

As shown in fig. 4, when the floating unit assembly 11 moves downward and comes into contact with the third conductive unit 3, the liquid level is at the top of the conductive unit 3 in the middle. As shown in fig. 5, when the floating unit assembly 11 is further moved downward by a distance within a precision range, the liquid level does not change. As shown in fig. 6, the floating unit assembly 11 is moved beyond the accuracy range where the liquid level is at a half height of the conductive unit 3 located in the middle, and where the liquid level is changed. The liquid level is then changed according to the cycle described above. The present application describes one particular embodiment of the relative height of the conductive elements 3 and the distance between the conductive finger elements 23 and the conductive finger elements 33. Furthermore, the height of the conductive elements 3 can be reduced and the distance between the conductive finger elements can be increased to increase the incremental accuracy reading capability of the level sensor.

As shown in fig. 7 to 10, the floating unit assembly 11 is located at the most extreme positions, i.e., the full level position and the empty level position. In the empty level position, the floating unit assembly 11 is on the bottom stop 21. Located above the bottom stop 21 is a bottom spring 17. In the full level position, the floating unit assembly 11 is pressed below the top stop 9. Below the top stop 9 is a top spring 7. The spring enables relative movement of the components between the top retainer 9 and the bottom retainer 21, primarily due to the different thermal effects of expansion and contraction of the different materials at extreme temperatures. The utility model discloses a be located two springs at level sensor both ends respectively. In addition, a longer displacement spring may be used and placed at one end of the level sensor.

The adapter part 13 shown in fig. 10 has a top opening through which all positions of the cable bundle 35 can be passed. The adapter part 13 contains a position line seal 37 which serves as a pressure seal. The position wire 35A is welded to the conductive element 3 through a side groove opening 39 in the inner wall of the non-conductive conduit 15 and then sealed by a position wire seal 37. All the position wires 35A are bundled together to form a position cable bundle 35, and the position cable bundle 35 comes out of the opening of the adapter part 13. Position cable harness 35 is connected to a monitoring system that monitors electrical communication between conductive elements 3 to determine the position of floating cell assembly 11 and thus the liquid level within the reservoir.

The utility model discloses a level sensor relies on buoyancy to promote the unit subassembly that floats that will trail the liquid level change. The position information is fed back electrically to the monitoring system to determine the liquid level. The utility model discloses a standard engineering spare part, existing standard part include conductive element, insulating unit, the unit that floats, touch and indicate component, electric wire etc.. The parts are all suitable for low-temperature environment, so that the design is easy to realize at low cost, and the floating technology is suitable for various types of refrigerants. The design includes direct mechanical mechanisms, components and simple wire connections, is compact, and can be customized to suit different liquids and different application areas.

The foregoing has described in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the teachings of this invention without undue experimentation. Therefore, the technical solutions that can be obtained by a person skilled in the art through logic analysis, reasoning or limited experiments based on the prior art according to the concepts of the present invention should be within the scope of protection defined by the claims.

Claims

1. A liquid level sensor is characterized by comprising a floating unit component, a position marker post component and a monitoring system,

the floating cell assembly includes a floating cell and a plurality of electrically conductive finger elements disposed on the floating cell in electrical communication with each other,

said position marker post assembly comprising a plurality of annular conductive elements, a plurality of annular insulating elements, and a non-conductive conduit disposed within the lumens of said conductive elements and said insulating elements to provide alignment and structural support for said conductive elements and said insulating elements, said conductive elements and said insulating elements being coaxial, said conductive elements and said insulating elements being alternately arranged along a common axis thereof,

wherein the floating unit assembly is in mechanical engagement with the position pole assembly, the floating unit assembly being in constant electrical communication with at least two of the conductive units at any position of the position pole assembly to provide position feedback information to the monitoring system, the monitoring system sensing the position of the floating unit assembly corresponding to the position of the conductive units to determine the level of the reservoir.

2. The fluid level sensor of claim 1, wherein each of said conductive elements in said position post assembly is electrically connected to a position wire routed along the lumen of said non-conductive conduit and having one end connected to a monitoring system through the top opening of said non-conductive conduit and the other end connected to said conductive element through an opening provided in said non-conductive conduit.

3. The fluid level sensor of claim 2, wherein the conductive elements in the position post assembly are electrically isolated from each other by the insulating element.

4. The fluid level sensor of claim 2, wherein each of said conductive elements forms an open loop circuit with said monitoring system before said conductive element contacts said floating element assembly and forms a closed loop circuit with said monitoring system after said conductive element contacts said floating element assembly.

5. The fluid level sensor of claim 1, wherein the floating unit assembly has at least two of the conductive finger elements, the conductive finger elements being in electrical communication with each other and the conductive finger elements being in electrical communication with the conductive unit.

6. The fluid level sensor of claim 5, wherein the floating cell assembly further comprises a conductive cylinder providing direct electrical communication between the conductive finger elements and being in intimate engagement with the floating cell and the conductive finger elements.

7. The fluid level sensor of claim 1, wherein the fluid level sensor establishes a closed loop circuit of continuous electrical connections from the monitoring system to a first one of the conductive elements, to the floating element assembly, to a second one of the conductive elements, and back to the monitoring system to enable fluid level monitoring.

8. The fluid level sensor of claim 1, wherein each of the conductive elements is of equal height, and the fluid level sensitivity is set to be one-half the height of the conductive element to twice the height of the conductive element.

9. The fluid level sensor of claim 8, wherein the fluid level sensitivity is one-half of the height of the conductive element.

10. The fluid level sensor of claim 1, wherein an adapter member is mounted at a top end of the non-conductive conduit and a locking unit is mounted at a bottom end of the non-conductive conduit.