Movable low-disturbance riverway water quality accurate sampler

Abstract

The invention relates to the technical field of sampling devices, and discloses a movable low-disturbance riverway water quality accurate sampler, which comprises a sampling part, the sampling part comprises a sampling bottle, the top end of the sampling bottle is in threaded connection with a bottle cap fixedly connected with the lower end of a depth control part, and the outer side of the sampling bottle is sleeved with a protection part for buffering the water entry impact force of the sampling part. The protection part comprises positioning rings arranged up and down, the positioning rings are elastically connected through telescopic springs arranged in the middle, and floating plates are slidably connected to the outer portions of the positioning rings. The device is provided with the protection part, the protection part is arranged to be of a structure which deforms along with the change of the depth of the sampling part entering the river channel, when the sampling part just enters the river channel, the lower positioning ring in the opening state moves upwards under the action of water resistance, and the higher the depth of the sampling part entering the water body is, the closer the lower positioning ring is to the upper positioning ring; the stable downward movement of the sampling part is realized, and the impact force on the water body in the falling process of the sampling part is buffered.

Description

Technical Field

[0001] The present invention relates to the technical field of sampling devices, and in particular to a mobile low-disturbance river water quality precision sampler. Background Art

[0002] A water quality sampler is a device for collecting water quality samples. There are many defects in the water quality sampling and detection equipment in the prior art. The sampler produces severe impact and agitation when entering the water body because of its own inertia, high entry speed, irregular shape, and the density difference between water and air and the surface tension of the water body. The combined effect of these factors leads to the impact and agitation phenomenon.

[0003] The violent impact and agitation of the sampler will destroy the original stratified temperature structure inside the water body. For example, in some lakes or reservoirs, there is a thermocline, where the upper water temperature is higher and the lower water temperature is lower. If the sampler vigorously stirs the water body, the upper and lower layers of water will mix, which will cause the measured water temperature to not accurately reflect the temperature of the original water layer. This temperature change may affect the subsequent research on the thermal conditions of the water body and some temperature-dependent physical and chemical processes. At the same time, the impact and agitation will cause the sediments at the bottom of the water to re-suspend in the water, such as the silt accumulated at the bottom of the river. When the sampler stirs the water body, these silts will be lifted up, causing the turbidity of the water body to increase significantly, which will not only interfere with the measurement of indicators related to the clarity of the raw water. From the perspective of water quality analysis, violent impact and agitation will also change the distribution of dissolved oxygen in the water body. The oxygen-rich water on the surface and the relatively oxygen-deficient water in the deep layer will mix quickly, which may cause abnormal fluctuations in the dissolved oxygen content in the local area of ​​the water body. The impact and agitation phenomenon interferes with the accuracy of subsequent water sample testing, so that the test results cannot truly reflect the concentration and distribution of various substances in the water body under normal conditions. Summary of the invention

[0004] Technical issues solved

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a mobile low-disturbance river water quality precision sampler, which can effectively solve the problem that the sampling water area may be impacted and stirred during the entry and sampling process of the prior art sampler.

[0006] Technical Solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] The present invention provides a mobile low-disturbance river water quality precision sampler, comprising: a depth control unit;

[0009] The sampling part, the lower end of the depth control part is fixedly connected to the upper end of the sampling part, the sampling part includes a sampling bottle, the top of the sampling bottle is threadedly connected to a bottle cap fixedly connected to the lower end of the depth control part, the outer side of the sampling bottle is provided with a protective part for buffering the impact force of the sampling part entering the water, the protective part includes upper and lower positioning rings, the positioning rings are elastically connected by a telescopic spring arranged in the middle, and the outer side of the positioning ring is slidably connected to a floating plate;

[0010] Wherein, a suction member for controlling the position of the floating plate on the outer surface of the positioning ring is arranged on the surface of the positioning ring.

[0011] Furthermore, the upper positioning ring is fixedly connected to the upper part of the circumferential outer surface of the sampling bottle, and grooves are provided on the outer sides of the upper and lower positioning rings. A plurality of fixing grooves are evenly arranged on the inner sides of the grooves, and a fixing rod is slidably connected to the inner wall of the fixing groove, and a floating plate is fixedly connected to one end of the fixing rod away from the center of the positioning ring.

[0012] Furthermore, the protection part also includes an inclined wedge block 2 fixedly connected to the far end of the fixing rod near the center of the positioning ring, and the other side of the inclined wedge block 2 is elastically connected to an elastic member, and the inclined wedge block 2 and the elastic member are both located in a movable groove provided on the inner wall of the positioning ring, and a suction member is attached to the upper surface of the inclined wedge block 2.

[0013] Furthermore, the suction component of the upper positioning ring is located at the bottom, and the suction component of the lower positioning ring is located at the top. The suction components of the upper and lower positioning rings are symmetrically arranged, and the suction components enter each other's magnetic field space when the telescopic spring is compressed to the minimum size.

[0014] Furthermore, the suction part includes an inclined wedge block 1 that is in contact with the upper surface of the inclined wedge block 2. The top of the inclined wedge block 1 is fixedly connected to a positioning rod. A compression spring is sleeved on the outside of the positioning rod. The top of the compression spring is fixedly connected to a magnetic part. In the initial state, the lower surface of the magnetic part is flush with the upper surface of the positioning ring.

[0015] Furthermore, a sampling head is fixedly connected to the bottom end of the sampling bottle, a buffer is provided above the sampling head at a position at the bottom end of the inner cavity of the sampling bottle, a buffer groove is provided on the inner wall of the buffer, and a side notch is provided on the side of the buffer groove.

[0016] Furthermore, in the initial state, the lower surface of the positioning ring below is higher than the bottom end of the sampling head.

[0017] Beneficial Effects

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0019] The present invention is provided with a sampling bottle and a bottle cap, and the sampling head is set to be conical. The side that first contacts the water surface has a small diameter. The physical impact force generated when the device enters the water is small, and the water body displacement effect is weak. It can accurately sample in a detailed research scene, and the risk of physical damage to aquatic organisms is low, and the range of interference with their behavior is narrow. The top of the sampling bottle is threadedly connected with a bottle cap, and the sampling bottle and the bottle cap are detachably connected. After the sampling process is completed, the device can separate the sampling bottle and the bottle cap by rotating the bottle cap. The staff can fully clean the inner wall of the sampling bottle, and can also conduct a detailed inspection of each part to check whether there is damage, blockage or corrosion. For the parts with problems, they can be repaired or replaced separately without complicated operations on the entire cylindrical device, which helps to improve the maintenance efficiency of the equipment.

[0020] The present invention is provided with a buffer component, and the side groove performs a diversion operation on the water poured into the buffer groove. The poured water enters the side groove of the curved pipe section from the buffer groove of the straight pipe section. The liquid on the side of the side groove is subjected to the effect of centrifugal force and tends to be squeezed outward. On the inner side of the curved pipe, the flow of the liquid is hindered and the flow rate is reduced. At the same time, under the obstruction of the inner wall of the buffer component, the liquid directly poured into the inner wall of the buffer component will also be diverted through the side groove, so that the entity poured into the sampling bottle is smooth and slow during sampling, reducing the impact of the water flow on the internal components of the sampling bottle, and preventing impurities in the water flow, such as sand, pebbles, etc., from wearing the internal components of the sampler like abrasives at high flow rates.

[0021] The present invention is provided with a suction piece. In the initial state, the inclined wedge block 1 located at the bottom of the movable groove is tightly fitted with the upper surface of the inclined wedge block 2. The inclined wedge block 1 squeezes the inclined wedge block 2 through the action of the inclined wedge structure. The inclined wedge block 2 overcomes the elastic force of the elastic member due to the extrusion force, and drives the fixed rod to move in the direction away from the center of the positioning ring. The movement of the fixed rod drives the floating plate to move, and the floating plate moves out from the inner side of the groove. The cross-sectional area of ​​the structure surrounded by the positioning ring and the floating plate is larger than the cross-sectional area between the two when the floating plate is located on the inner side of the groove. The larger the cross-sectional area, the larger the contact surface with the water body. After the sampling head contacts the water surface, the positioning ring below also contacts the water surface, avoiding the impact caused by the entire sampling part falling on the water surface, avoiding the destruction of the original layered temperature structure inside the water body, and avoiding abnormal fluctuations in the dissolved oxygen content of the local water body. The interference of impact and stirring phenomena is reduced, so that the detection results can truly and accurately reflect the concentration and distribution of various substances in the water body under normal conditions.

[0022] The present invention is provided with a protection part, and the protection part is configured to be a structure that deforms as the depth of the sampling part entering the river channel changes. When the sampling part just enters the river channel, the lower positioning ring in an open state moves upward under the action of water resistance. As the depth of the sampling part entering the water body increases, the lower positioning ring is closer to the upper positioning ring, thereby achieving a smooth downward movement of the sampling part and buffering the impact force of the sampling part on the water body during the falling process. Then, after the two positioning rings are attracted to each other, the telescopic spring is no longer located on the outside of the positioning ring, but is embedded in the groove on the outside of the positioning ring. The reduction in the cross-sectional area of ​​the protection part reduces the resistance of the water body to the protection part, and the sampling part and the protection part can completely enter the interior of the river channel, thereby achieving the purpose of the sampling part smoothly entering the corresponding position of the river channel, and avoiding the situation where the sampling water area is impacted and stirred during the device entering the water. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a schematic diagram of the structure of the device according to an embodiment of the present invention after it has completely entered the river channel;

[0025] Figure 2 This is a schematic diagram of the initial state structure of the protection unit of an embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of the separation structure of the positioning ring and a single floating plate according to an embodiment of the present invention;

[0027] Figure 4 It is a schematic diagram of the separation structure of the positioning ring and a single suction member according to an embodiment of the present invention;

[0028] Figure 5 Schematic diagram of the cross-sectional structure of the sampling part of an embodiment of the present invention;

[0029] Figure 6 Schematic diagram of the cross-sectional structure of a buffer member according to an embodiment of the present invention.

[0030] The numbers in the figure represent respectively: 1. sampling part; 11. sampling bottle; 12. sampling head; 13. bottle cap; 14. buffer part; 141. buffer groove; 142. side notch; 2. protection part; 21. positioning ring; 211. fixing groove; 22. fixing rod; 23. floating plate; 25. telescopic spring; 26. suction part; 261. magnetic part; 262. compression spring; 263. fixing rod; 264. oblique wedge block 1; 27. oblique wedge block 2; 28. elastic part; 3. depth control part. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention will be further described below in conjunction with the embodiments.

[0033] Example:

[0034] See also Figure 1-Figure 6 , the present invention provides a technical solution: refer to Figure 1 The device comprises a sampling part 1, a protection part 2 and a depth control part 3. The outer surface of the sampling part 1 is provided with the protection part 2, and the top of the protection part 2 is fixedly connected with the depth control part 3. Figure 5 As shown, the sampling part 1 includes a sampling bottle 11 for storing the sampled water. The bottom of the sampling bottle 11 is fixedly connected with a sampling head 12. The sampling head 12 is set to be conical. The side that first contacts the water surface has a small diameter. When the device enters the water, the physical impact force generated is small, and the water displacement effect is weak. In the fine research scene, accurate sampling can be performed, and the risk of physical damage to aquatic organisms is low, and the range of interference with their behavior is narrow. The top of the sampling bottle 11 is threadedly connected with a bottle cap 13. The sampling bottle 11 and the bottle cap 13 are detachable. After the sampling process is completed, the sampling bottle 11 and the bottle cap 13 are separated by rotating the bottle cap 13. The staff can fully clean the inner wall of the sampling bottle 11, and can also conduct a detailed inspection of each part to check whether there is damage, blockage or corrosion. For the parts with problems, they can be repaired or replaced separately without complicated operations on the entire cylindrical device, which helps to improve the maintenance efficiency of the equipment.

[0035] like Figure 5 and Figure 6As shown, a buffer 14 is fixedly connected above the sampling head 12, and a buffer groove 141 is provided inside the buffer 14. After the sampling head 12 is turned on, the water in the corresponding area will enter the buffer groove 141 through the sampling head 12. A side notch 142 is provided on the side of the buffer groove 141. The side notch 142 performs a diversion operation on the water poured into the buffer groove 141. The poured water enters the side notch 142 of the curved pipe section from the buffer groove 141 of the straight pipe section, and the liquid is separated from the side of the side notch 142. Due to the effect of centrifugal force, there will be a tendency to squeeze outward. On the inside of the bend, the flow of liquid is hindered and the flow rate is reduced. At the same time, under the obstruction of the inner wall of the buffer 14, the liquid directly poured into the inner wall of the buffer 14 will also be diverted through the side groove 142, so that the entity poured into the sampling bottle 11 is smooth and slow during sampling, reducing the impact of the water flow on the internal components of the sampling bottle 11, and preventing impurities in the water flow, such as sand, pebbles, etc., from wearing out the internal components of the sampler like abrasives at high flow rates.

[0036] The setting of the sampling part 1 minimizes disturbance to the water body in the river during the water collection process. For example, the sampling head 12 adopts a slow suction design to avoid violent impact and agitation on the water body, and can maintain the original state of the water sample to the greatest extent, ensuring that the collected water quality data truly reflects the actual situation of the river. The low-disturbance sampling method reduces the interference and impact on aquatic organisms in the river, and will not damage the habitat and living state of aquatic organisms, which is of great significance for protecting the water ecological environment.

[0037] refer to Figure 1 and Figure 2 The outer surface of the sampling part 1 is covered with a protective part 2. The protective part 2 in the initial state is as follows: Figure 2 As shown in the figure, after the sampling part 1 completely enters the river water body, the structural state of the protection part 2 is as follows Figure 1 As shown, the protection part 2 includes two positioning rings 21 distributed in an upper and lower manner, the upper positioning ring 21 is fixedly connected to the upper outer surface of the protection part 2, and a plurality of suction members 26 are evenly arranged at the bottom end of the upper positioning ring 21, which are set to four here. In the initial state, the bottom end of the lower positioning ring 21 is slightly higher than the bottom end of the bottle cap 13, and another four suction members 26 magnetically connected to the four suction members 26 arranged at the bottom end of the upper positioning ring 21 are evenly arranged at the top end of the lower positioning ring 21, and a telescopic spring 25 is elastically connected between the upper positioning ring 21 and the lower positioning ring 21.

[0038] like Figure 2 and Figure 3As shown, a groove for storing the floating plate 23 in a contracted state is provided on the side of the positioning ring 21, and four fixing grooves 211 are evenly provided in the groove. A fixing rod 22 is slidably connected inside the fixing groove 211. The end of the fixing rod 22 away from the positioning ring 21 is fixedly connected to the floating plate 23. The floating plate 23 is set to a material with a density less than that of the positioning ring 21. In the initial state, the floating plate 23 is away from the fixing groove 211, and the cross-sectional area between the positioning ring 21 and the floating plate 23 is large. When the sampling part 1 enters the water body and contacts the positioning ring 21, the positioning ring 21 is pushed upward by the water surface tension, and the lower positioning ring 21 moves upward to squeeze the telescopic spring 25. The telescopic spring 25 is elastically deformed under the pressure, and the other end of the fixing rod 22 is fixedly connected to an inclined wedge block 27, and the other end of the inclined wedge block 27 is elastically connected to an elastic member 28.

[0039] like Figure 2 , Figure 3 and Figure 4 As shown, a circular groove is provided on the surface of the positioning ring 21, and an attraction member 26 is arranged on the inner side of the circular groove. The attraction member 26 includes a compression spring 262 elastically connected to the circular groove. The compression spring 262 is sleeved on the outer side of the positioning rod 263. A magnetic member 261 is fixedly connected to the top of the positioning rod 263. The two groups of magnetic members 261 arranged up and down enter each other's magnetic induction range when the telescopic spring 25 is compressed to the minimum. The magnetic members 261 are attracted to each other. An inclined wedge block 264 is fixedly connected to the bottom end of the magnetic member 261. The inclined wedge block 264 is located in a movable groove opened inside the positioning ring 21.

[0040] In the initial state, the inclined wedge block 1 264 at the bottom of the movable groove is tightly fitted with the upper surface of the inclined wedge block 27. The inclined wedge block 1 264 squeezes the inclined wedge block 27 through the action of the inclined wedge structure. The inclined wedge block 27 overcomes the elastic force of the elastic member 28 due to the squeezing force, and drives the fixed rod 22 to move in the direction away from the center of the positioning ring 21. The movement of the fixed rod 22 drives the floating plate 23 to move, and the floating plate 23 moves out from the inner side of the groove. The cross-sectional area of ​​the structure surrounded by the positioning ring 21 and the floating plate 23 is larger than the cross-sectional area between the two when the floating plate 23 is located inside the groove. The larger the cross-sectional area, the larger the contact surface with the water body. After the sampling head 12 contacts the water surface, the positioning ring 21 below also contacts the water surface, avoiding the impact caused by the entire sampling part 1 falling on the water surface, avoiding the destruction of the original layered temperature structure inside the water body, and avoiding abnormal fluctuations in the dissolved oxygen content of the local water body. Reduce the interference of impact and stirring phenomena, so that the detection results can truly and accurately reflect the concentration and distribution of various substances in the water body under normal conditions.

[0041] As the device is launched, the larger the cross-section of the object is, the greater the water resistance it may encounter during the entry into the water. The lower positioning ring 21 and the telescopic spring 25 move upward under the push of the reverse force of the water body, and the positioning ring 21 moves upward to squeeze the telescopic spring 25. As the device is launched, the squeezing of the telescopic spring 25 by the lower positioning ring 21 gradually increases until the telescopic spring 25 shrinks to the minimum size. At this time, the upper and lower magnetic parts 261 enter each other's magnetic field space, and the two magnetic parts 261 attract each other. The magnetic part 261 of the upper positioning ring 21 moves downward, and the magnetic part 261 of the lower positioning ring 21 moves downward. The magnetic piece 261 of the positioning ring 21 moves upward, and the magnetic piece 261 drives the positioning rod 263 to move. Under the action of the magnetic attraction force, the positioning rod 263 overcomes the elastic force of the compression spring 262 and quickly attracts each other. At the same time, the inclined wedge block 1 264 moves upward and no longer squeezes the inclined wedge block 27. The elastic deformation of the elastic piece 28 is restored. The elastic piece 28 drives the inclined wedge block 27 to move toward the center of the positioning ring 21. The movement of the inclined wedge block 27 drives the fixing rod 22 to move. The movement of the fixing rod 22 drives the floating plate 23 to move. The floating plate 23 moves until it is embedded in the inner side of the groove, thereby Figure 2 The protection part 2 of the state changes to Figure 1 The protective part 2 in the contracted state, the structural cross-sectional area between the positioning ring 21 and the floating plate 23 is reduced to the cross-sectional area of ​​the positioning ring 21 itself. At this time, the sampling part 1 almost completely enters the interior of the river water. After the cross-sectional area is reduced, the resistance of the water body is also reduced. The sampling part 1 as a whole, the protective part 2 in the contracted state and the depth control part 3 also gradually enter the interior of the water body, and the water sampling operation is started.

[0042] The protective part 2 is sleeved on the outside of the sampling part 1, and the protective part 2 is configured to be deformed as the depth of the sampling part 1 entering the river channel changes. When the sampling part 1 just enters the river channel, the lower positioning ring 21 in the open state moves upward under the action of the water resistance. As the sampling part 1 enters deeper into the water body, the lower positioning ring 21 is closer to the upper positioning ring 21, so that the sampling part 1 can move downward smoothly, and the impact force of the sampling part 1 on the water body during the falling process is buffered. Then, after the two positioning rings 21 are attracted to each other, the telescopic spring 25 is no longer located on the outside of the positioning ring 21, but is embedded in the groove on the outside of the positioning ring 21. The reduction in the cross-sectional area of ​​the protective part 2 reduces the resistance of the water body to the protective part 2, and the sampling part 1 and the protective part 2 can completely enter the interior of the river channel, so as to achieve the purpose of the sampling part 1 smoothly entering the corresponding position of the river channel, and avoid the situation where the sampling water area is impacted and stirred during the device entering the water.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mobile low-disturbance river water quality precision sampler, characterized in that: include: Depth control unit (3); The sampling part (1) has a lower end of the depth control part (3) fixedly connected to the upper end of the sampling part (1), the sampling part (1) comprising a sampling bottle (11), the top end of the sampling bottle (11) being threadedly connected to a bottle cap (13) fixedly connected to the lower end of the depth control part (3), the outer side of the sampling bottle (11) being sleeved with a protective part (2) for buffering the impact force of the sampling part (1) entering water, the protective part (2) comprising upper and lower positioning rings (21), the positioning rings (21) being elastically connected to each other via a telescopic spring (25) arranged in the middle, and the outer side of the positioning ring (21) being slidably connected to a floating plate (23); Wherein, a suction member (26) for controlling the position of the floating plate (23) on the outer surface of the positioning ring (21) is provided on the surface of the positioning ring (21).

2. The mobile low-disturbance river water quality precision sampler according to claim 1 is characterized by: The upper positioning ring (21) is fixedly connected to the upper part of the outer surface of the circumference of the sampling bottle (11), and the outer sides of the upper and lower positioning rings (21) are both provided with grooves, and a plurality of fixing grooves (211) are evenly arranged inside the grooves. The inner wall of the fixing groove (211) is slidably connected to a fixing rod (22), and the end of the fixing rod (22) away from the center of the positioning ring (21) is fixedly connected to a floating plate (23).

3. A mobile low-disturbance river water quality precision sampler according to claim 2, characterized in that: The protection part (2) further comprises a second inclined wedge block (27) fixedly connected to the distal end of the fixing rod (22) near the center of the positioning ring (21), the other side of the second inclined wedge block (27) being elastically connected to an elastic member (28), the second inclined wedge block (27) and the elastic member (28) being both located in a movable groove provided on the inner wall of the positioning ring (21), and a suction member (26) being attached to the upper surface of the second inclined wedge block (27).

4. The mobile low-disturbance river water quality precision sampler according to claim 3 is characterized by: The suction piece (26) of the upper positioning ring (21) is located at the bottom, and the suction piece (26) of the lower positioning ring (21) is located at the top. The suction pieces (26) of the upper and lower positioning rings (21) are symmetrically arranged, and the suction pieces (26) enter each other's magnetic field space when the telescopic spring (25) is compressed to the smallest size.

5. The mobile low-disturbance river water quality precision sampler according to claim 4 is characterized by: The suction member (26) comprises an inclined wedge block 1 (264) which is in contact with the upper surface of the inclined wedge block 2 (27); a positioning rod (263) is fixedly connected to the top of the inclined wedge block 1 (264); a compression spring (262) is sleeved on the outer side of the positioning rod (263); a magnetic member (261) is fixedly connected to the top of the compression spring (262); and in an initial state, the lower surface of the magnetic member (261) is flush with the upper surface of the positioning ring (21).

6. The mobile low-disturbance river water quality precision sampler according to claim 1 is characterized by: The bottom end of the sampling bottle (11) is fixedly connected to a sampling head (12); a buffer component (14) is arranged above the sampling head (12) at a position at the bottom end of the inner cavity of the sampling bottle (11); a buffer groove (141) is provided on the inner wall of the buffer component (14); and a side notch (142) is provided on the side of the buffer groove (141).

7. The mobile low-disturbance river water quality precision sampler according to claim 1 is characterized by: In the initial state, the lower surface of the positioning ring (21) is higher than the bottom end of the sampling head (12).

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