Flexible pressure sensor for monitoring mine air pressure and method of making same

Abstract

The present application relates to the technical field of mine ventilation, in particular to a flexible pressure sensor for monitoring mine air pressure and a preparation method thereof, which mainly solves the technical problems of low sensitivity, poor sealing performance and limited application range of the existing mine air pressure monitoring pressure sensor. The sensor comprises a phase change flexible tube, a first electrode flexible tube and a second electrode flexible tube, the inner cavity of the phase change flexible tube is filled with a solid-liquid phase change material and pre-buried with a heating wire, and the inner cavity wall of the two electrode flexible tubes is provided with a conductive coating and electrode leads are drawn out. The sensor produces stress concentration in the flexible tube at a small inner diameter and contact point through a double helix structure, significantly improves the capacitance change amount, and thus improves the detection sensitivity; the two end seals cooperate with the conductive coating of the inner wall to form a closed structure, which is suitable for the high humidity environment underground; the pre-buried heating wire controls the phase state of the solid-liquid phase change material, dynamically adjusts the sensitivity, so that the sensor can select the appropriate sensitivity according to the actual working conditions, and expand the application range.

Description

Technical Field

[0001] This invention relates to the field of mine ventilation technology, and in particular to a flexible pressure sensor for monitoring mine air pressure and its preparation method. Background Technology

[0002] Mine ventilation systems are critical facilities for safe underground production, continuously optimizing air quality in the work area and effectively diluting harmful media such as methane and dust. As the core power unit of the ventilation system, the operating conditions of ventilation fans directly affect the underground ventilation effect. Fluctuations in the air pressure at the fan outlet can accurately reflect potential malfunctions such as door seal failure, duct blockage, and fan efficiency degradation. Therefore, real-time monitoring of the fan outlet air pressure is an important means of mine safety management.

[0003] Currently, conventional rigid pressure sensors are commonly used for mine ventilation pressure monitoring. However, these sensors have several shortcomings in the complex underground environment: First, their detection sensitivity is relatively low, making it difficult to accurately detect subtle operational hazards. Second, the underground environment is characterized by high relative humidity and moisture. The simple sealing structure of these sensors results in weak waterproof and airtight performance, making them susceptible to interference from the humid environment over long-term use, which reduces their service life and detection stability. Third, the sensitivity of these sensors is fixed and cannot be flexibly adjusted according to the on-site installation environment and actual working conditions, thus limiting the applicability of the equipment.

[0004] Therefore, there is an urgent need to develop a mine ventilation pressure monitoring pressure sensor with high sensitivity, strong sealing, and adjustable sensitivity. Summary of the Invention

[0005] To overcome the technical defects of existing mine ventilation pressure monitoring pressure sensors, such as low sensitivity, poor sealing, and limited applicability, this invention proposes a flexible pressure sensor for monitoring mine ventilation pressure and its preparation method.

[0006] The present invention provides a flexible pressure sensor for monitoring mine ventilation pressure and a method for manufacturing the same, comprising:

[0007] A phase change flexible tube, both ends of which are sealed and the inner cavity is filled with a solid-liquid phase change material, wherein a heating wire is embedded in the solid-liquid phase change material, and both ends of the heating wire are led out from the same end of the phase change flexible tube.

[0008] The first electrode flexible tube is spirally wound around the periphery of the phase change flexible tube. Both ends of the first electrode flexible tube are sealed and the inner wall is provided with a first conductive coating. The first conductive coating is led out from one end of the first electrode flexible tube through a first electrode lead.

[0009] The second electrode flexible tube is spirally wound around the periphery of the phase change flexible tube and forms a double helix structure with the first electrode flexible tube. Both ends of the second electrode flexible tube are sealed and the inner wall is provided with a second conductive coating. The second conductive coating is led out from one end of the second electrode flexible tube through the second electrode lead wire.

[0010] Furthermore, both ends of the phase change flexible tube, the first electrode flexible tube, and the second electrode flexible tube are sealed with flexible polymer.

[0011] Furthermore, the inner diameter of the first electrode flexible tube is larger than the inner diameter of the phase change flexible tube, and the inner diameter of the second electrode flexible tube is larger than the inner diameter of the first electrode flexible tube.

[0012] Furthermore, the solid-liquid phase change material is one of polyethylene glycol, paraffin wax, n-octacosan, n-hexadecyl alcohol, or inorganic salt phase change gel.

[0013] Furthermore, both the first conductive coating and the second conductive coating are prepared by mixing conductive powder with a flexible substrate.

[0014] The present invention provides a method for fabricating a flexible pressure sensor for monitoring mine ventilation pressure, comprising the following steps:

[0015] S1. Structure preparation;

[0016] Seal one end of the phase change flexible tube, insert the heating wire into the preset position from the other end of the phase change flexible tube, then inject the solid-liquid phase change material, and finally seal the other end of the phase change flexible tube as a basic structure for later use.

[0017] One end of the first electrode flexible tube is sealed, and a first conductive coating is uniformly applied from the other end of the first electrode flexible tube to its inner wall. Then, one end of the first electrode lead is connected to the first conductive coating and the other end is led to the outside of the first electrode flexible tube. Finally, the other end of the first electrode flexible tube is sealed and used as the first electrode for later use.

[0018] One end of the second electrode flexible tube is sealed, and the second conductive coating is uniformly coated from the other end of the second electrode flexible tube to its inner wall. Then, one end of the second electrode lead is connected to the second conductive coating and the other end is led to the outside of the second electrode flexible tube. Finally, the other end of the second electrode flexible tube is sealed and used as the second electrode for later use.

[0019] S2. Electrode winding;

[0020] The first and second electrodes are wound around the periphery of the base structure to form a double helix structure.

[0021] Furthermore, in preparing the first and second electrodes, a solution is first prepared using conductive powder, a flexible substrate, and a flow modifier. Then, the solution is injected into the inner wall of the corresponding electrode flexible tube. Finally, the flow modifier is evaporated by baking and heating to form the corresponding conductive coating.

[0022] Furthermore, when sealing the phase change flexible tube, the first electrode flexible tube, and the second electrode flexible tube, a flexible polymer is inserted into the end of the corresponding flexible tube to complete the sealing.

[0023] Furthermore, the type of solid-liquid phase change material is selected based on the actual working conditions of the mine's air pressure monitoring, so that the prepared flexible pressure sensor has an appropriate sensitivity adjustment range.

[0024] Furthermore, the spacing of the electrode winding is determined according to the actual working conditions of the mine's wind pressure monitoring, so that the prepared flexible pressure sensor has an appropriate sensitivity adjustment range.

[0025] The technical solution provided by this invention has the following advantages compared with the prior art.

[0026] The flexible pressure sensor for monitoring mine ventilation pressure provided by this invention consists of a first electrode flexible tube and a second electrode flexible tube wound around the periphery of a phase change flexible tube to form a double helix structure. Under stress, the flexible tubes deform to different degrees at different locations, resulting in stress concentration at smaller inner diameters and contact points. This causes a significant increase in deformation in localized areas, leading to a larger capacitance change and thus improving the sensor's detection sensitivity. The two ends of the first and second electrode flexible tubes are sealed, and a conductive coating is applied to the inner wall of the flexible tubes to form a closed structure for effective waterproofing, adapting to the high humidity and moisture-laden underground environment. The inner cavity of the phase change flexible tube is filled with a solid-liquid phase change material and pre-embedded with a heating wire. By controlling the phase state of the solid-liquid phase change material through the heating wire, the stiffness of the phase change flexible tube is changed, thereby affecting the degree of deformation of the electrode flexible tubes and achieving dynamic adjustment of sensitivity. Ultimately, this allows the sensor to select an appropriate sensitivity based on the actual ventilation pressure conditions at the installation location, expanding its applicable range.

[0027] The method for preparing a flexible pressure sensor for monitoring mine ventilation pressure provided by the present invention can prepare the above-mentioned flexible pressure sensor and has the above-mentioned advantages. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of the flexible pressure sensor in an embodiment of the present invention;

[0031] Figure 2 This is a cross-sectional view of the phase change flexible tube in an embodiment of the present invention;

[0032] Figure 3 This is a cross-sectional view of the first electrode flexible tube in an embodiment of the present invention;

[0033] Figure 4 This is a cross-sectional view of the second electrode flexible tube in an embodiment of the present invention;

[0034] Figure 5 This diagram illustrates a comparison of the deformation of the flexible electrode tube at temperatures below and above the phase transition temperature, according to an embodiment of the present invention.

[0035] Figure 6 This diagram illustrates the variation of the relative distance between the two flexible electrode tubes with relative body force at temperatures below and above the phase transition temperature, according to an embodiment of the present invention.

[0036] Figure 7 This diagram shows the finite element deformation contour of the electrode flexible tube in an embodiment of the present invention when a relative body force of 0.05 is applied below the phase transition temperature.

[0037] Figure 8 The diagram shows the finite element deformation contour of the electrode flexible tube in an embodiment of the present invention when a relative body force of 0.05 is applied above the phase transition temperature.

[0038] Figure 9 This is a schematic diagram showing a comparison of flexible pressure sensors with different winding spacings in embodiments of the present invention.

[0039] In the figure: 1. Phase change flexible tube; 11. Solid-liquid phase change material; 12. Heating wire; 2. First electrode flexible tube; 21. First conductive coating; 22. First electrode lead; 3. Second electrode flexible tube; 31. Second conductive coating; 32. Second electrode lead; 4. Flexible polymer. Detailed Implementation

[0040] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0042] The following is combined Figures 1 to 9 Specific embodiments of the present invention will be described in detail below.

[0043] Reference Figures 1 to 4 This embodiment provides a flexible pressure sensor for monitoring mine ventilation pressure, including a phase change flexible tube 1, a first electrode flexible tube 2, and a second electrode flexible tube 3. Both ends of the phase change flexible tube 1 are sealed and the inner cavity is filled with a solid-liquid phase change material 11. A heating wire 12 is embedded in the solid-liquid phase change material 11, and both ends of the heating wire 12 are led out from the same end of the phase change flexible tube 1. The first electrode flexible tube 2 is spirally wound around the periphery of the phase change flexible tube 1. Both ends of the first electrode flexible tube 2 are sealed and the inner cavity wall is provided with a first conductive coating 21. The first conductive coating 21 is led out from one end of the first electrode flexible tube 2 through a first electrode lead 22. The second electrode flexible tube 3 is spirally wound around the periphery of the phase change flexible tube 1 and forms a double helix structure with the first electrode flexible tube 2. Both ends of the second electrode flexible tube 3 are sealed and the inner cavity wall is provided with a second conductive coating 31. The second conductive coating 31 is led out from one end of the second electrode flexible tube 3 through a second electrode lead 32.

[0044] Specifically, in this embodiment, both ends of the phase change flexible tube 1, the first electrode flexible tube 2, and the second electrode flexible tube 3 are sealed with flexible polymer 4. The type of flexible polymer 4 is not limited; for example, silicone or polyurethane. Using flexible polymer 4 for sealing provides better sealing performance and facilitates the extraction of structures such as the heating wire 12, the first electrode lead 22, and the second electrode lead 32, making operation more flexible. In other embodiments, rigid sealing plugs can also be used to seal both ends; alternatively, one end can be designed as an integrally molded sealing structure, while the other end is sealed with a sealing plug or flexible polymer 4.

[0045] Specifically, in this embodiment, the inner diameter of the first electrode flexible tube 2 is larger than the inner diameter of the phase change flexible tube 1, and the inner diameter of the second electrode flexible tube 3 is larger than the inner diameter of the first electrode flexible tube 2. The specific value of the inner diameter is not limited; for example, the inner diameter of the phase change flexible tube 1 is 0.6 mm, the inner diameter of the first electrode flexible tube 2 is 1 mm, and the inner diameter of the second electrode flexible tube 3 is 2 mm. By designing different inner diameters for each flexible tube, it is more conducive to generating uneven deformation, inducing a local stress concentration effect, and improving the sensor sensitivity. In other embodiments, the inner diameters of the three flexible tubes can also be designed to be the same.

[0046] Specifically, the solid-liquid phase change material 11 in this embodiment is one of polyethylene glycol, paraffin wax, n-octacosane, n-hexadecyl alcohol, or inorganic salt phase change gel. Polyethylene glycol can be used alone or in combination with conductive particles; the conductive particles are preferably PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate); the paraffin wax can be industrial paraffin wax or soft paraffin wax; the inorganic salt phase change gel is preferably calcium chloride hexahydrate (CaCl2·6H2O). Different solid-liquid phase change materials 11 can produce different stiffnesses in the phase change flexible tube 1, and the appropriate material can be selected according to the actual situation; however, regardless of the type of solid-liquid phase change material 11, it must have the property of "being solid below the phase change temperature and liquid above the phase change temperature". The foregoing only lists preferred solid-liquid phase change materials 11; in other embodiments, other types of solid-liquid phase change materials 11 can also be used, as long as they possess the aforementioned properties.

[0047] It should be noted that, referring to Figure 5 F represents wind pressure, d0 represents the relative distance between the two flexible electrode tubes when not subjected to wind pressure F, and d1 represents the relative distance between the two flexible electrode tubes after being subjected to wind pressure F. Below the phase transition temperature, the solid-liquid phase change material 11 exhibits a solid phase with a high modulus, making it less prone to deformation; while above the phase transition temperature, the solid-liquid phase change material 11 exhibits a liquid phase with a low modulus, making it more susceptible to deformation. (Refer to...) Figures 6 to 8 Under the same physical force, compared with the solid phase, the solid-liquid phase change material 11 in the liquid phase has a greater degree of deformation of the electrode flexible tube and a greater change in the distance between the upper and lower electrodes, thus enabling the sensor to obtain higher sensitivity.

[0048] Specifically, in this embodiment, both the first conductive coating 21 and the second conductive coating 31 are formed by mixing conductive powder with a flexible substrate. The type of conductive powder is not limited, but MBene (two-dimensional transition metal boride) powder is preferred; the type of flexible substrate is not limited, but Ecoflex (ultra-soft silicone rubber) is preferred. The mixing of conductive powder and flexible substrate can form a solution, which is more conducive to the coating operation of the conductive coating.

[0049] The working principle of the flexible pressure sensor used to monitor mine ventilation pressure in this embodiment is as follows.

[0050] In use, the flexible pressure sensor is fixed at the fan outlet or other locations where wind pressure needs to be monitored. The first electrode lead 22 and the second electrode lead 32 are connected to the positive and negative terminals of the LCR measuring instrument, respectively. One end of the heating wire 12 is connected to the constant pressure source U through the variable resistor R, and the other end of the heating wire 12 is grounded. When the wind pressure acts on the surface of the flexible pressure sensor, it forces the first electrode flexible tube 2 and the second electrode flexible tube 3 to deform, causing the capacitance value measured by the LCR measuring instrument to change. The slight fluctuation of the wind pressure can be inferred from the amount of change in the capacitance value.

[0051] The method for preparing a flexible pressure sensor for monitoring mine air pressure in this embodiment includes steps S1 and S2.

[0052] S1. Structure preparation: One end of the phase change flexible tube 1 is sealed, and the heating wire 12 is inserted into the preset position from the other end of the phase change flexible tube 1. Then, the solid-liquid phase change material 11 is injected, and finally the other end of the phase change flexible tube 1 is sealed as a basic structure for later use; One end of the first electrode flexible tube 2 is sealed, and the first conductive coating 21 is uniformly coated from the other end of the first electrode flexible tube 2 onto its inner wall. Then, one end of the first electrode lead 22 is connected to the first conductive coating 21 and the other end is led to the outside of the first electrode flexible tube 2. Finally, the other end of the first electrode flexible tube 2 is sealed as a first electrode for later use; One end of the second electrode flexible tube 3 is sealed, and the second conductive coating 31 is uniformly coated from the other end of the second electrode flexible tube 3 onto its inner wall. Then, one end of the second electrode lead 32 is connected to the second conductive coating 31 and the other end is led to the outside of the second electrode flexible tube 3. Finally, the other end of the second electrode flexible tube 3 is sealed as a second electrode for later use.

[0053] It is easy to understand that when injecting solid-liquid phase change material 11, the solid-liquid phase change material 11 should first be heated to a temperature higher than the phase change temperature and presented as a liquid phase. Then, the liquid solid-liquid phase change material 11 should be injected into the phase change flexible tube 1 using tools such as a syringe.

[0054] Specifically, in preparing the first and second electrodes, a solution is first prepared using conductive powder, a flexible substrate, and a flow modifier. This solution is then injected into the inner wall of the corresponding electrode's flexible tube. Finally, heating is used to evaporate the flow modifier, forming the corresponding conductive coating. The type of conductive powder is not limited, but MBene (two-dimensional transition metal boride) powder is preferred. The type of flexible substrate is not limited, but Ecoflex (ultra-soft silicone rubber) is preferred. The type of flow modifier is not limited, but toluene is preferred. The solution injection can be performed using tools such as syringes. Heating is performed using an oven, with the heating temperature determined based on the type of flow modifier. For example, for toluene, the preferred heating temperature is 50°C. The flow modifier enhances the solution's fluidity, making it easier to inject into the corresponding electrode's flexible tube and simplifying the operation. Simultaneously, heating removes the flow modifier from the solution, preventing any impact on the conductivity of the conductive coating.

[0055] It should be noted that the solution should be slowly injected along the inner wall of the flexible electrode tube until the inner wall of the flexible electrode tube (excluding the sealed ends) is completely coated.

[0056] Specifically, when sealing the phase change flexible tube 1, the first electrode flexible tube 2, and the second electrode flexible tube 3, a flexible polymer 4 is inserted into the end of the corresponding flexible tube to complete the sealing.

[0057] Specifically, the type of solid-liquid phase change material 11 is selected according to the actual working conditions of the mine's air pressure monitoring, so that the prepared flexible pressure sensor has an appropriate sensitivity adjustment range. Different types of solid-liquid phase change materials 11 can give the phase change flexible tube 1 different stiffnesses, so that when subjected to the same external force, the electrode flexible tube will produce different deformations, ultimately causing the sensor to exhibit different sensitivities.

[0058] S2. Electrode winding: The first electrode and the second electrode are wound around the periphery of the base structure to form a double helix structure.

[0059] Specifically, the spacing of the electrode winding is determined based on the actual working conditions of the mine's air pressure monitoring system, so that the fabricated flexible pressure sensor has a suitable sensitivity adjustment range. (Refer to...) Figure 9 Changing the winding spacing essentially alters the support density and deformation space of the flexible electrode tube, thereby changing the intensity of the local stress concentration effect and the efficiency of capacitance change: when the winding spacing is large, deformation mainly occurs locally, the equivalent electrode spacing changes rapidly, and the sensitivity is high; when the winding spacing is small, deformation becomes more uniform, the equivalent electrode spacing changes slowly, and the sensitivity is low.

[0060] It should be noted that the sensor sensitivity can be adjusted by the phase change of the solid-liquid phase change material 11, but it has a fixed range. By selecting different types of solid-liquid phase change materials 11 or changing the winding spacing, the sensitivity adjustment range can be redefined, thereby increasing the applicability of the sensor.

[0061] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A flexible pressure sensor for monitoring mine ventilation pressure, characterized in that, include: A phase change flexible tube (1) is sealed at both ends and its inner cavity is filled with a solid-liquid phase change material (11). A heating wire (12) is embedded in the solid-liquid phase change material (11), and the two ends of the heating wire (12) are led out from the same end of the phase change flexible tube (1). The first electrode flexible tube (2) is spirally wound around the periphery of the phase change flexible tube (1). Both ends of the first electrode flexible tube (2) are sealed and the inner wall is provided with a first conductive coating (21). The first conductive coating (21) is led out from one end of the first electrode flexible tube (2) through the first electrode lead (22). The second electrode flexible tube (3) is spirally wound around the periphery of the phase change flexible tube (1) and forms a double helix structure with the first electrode flexible tube (2). Both ends of the second electrode flexible tube (3) are sealed and the inner wall is provided with a second conductive coating (31). The second conductive coating (31) is led out from one end of the second electrode flexible tube (3) through the second electrode lead wire (32).

2. The flexible pressure sensor for monitoring mine ventilation pressure according to claim 1, characterized in that, Both ends of the phase change flexible tube (1), the first electrode flexible tube (2), and the second electrode flexible tube (3) are sealed with flexible polymer (4).

3. The flexible pressure sensor for monitoring mine ventilation pressure according to claim 1 or 2, characterized in that, The inner diameter of the first electrode flexible tube (2) is larger than the inner diameter of the phase change flexible tube (1), and the inner diameter of the second electrode flexible tube (3) is larger than the inner diameter of the first electrode flexible tube (2).

4. The flexible pressure sensor for monitoring mine ventilation pressure according to claim 1, characterized in that, The solid-liquid phase change material (11) is one of polyethylene glycol, paraffin, n-octacosane, n-hexadecyl alcohol or inorganic salt phase change gel.

5. The flexible pressure sensor for monitoring mine ventilation pressure according to claim 1, characterized in that, Both the first conductive coating (21) and the second conductive coating (31) are prepared by mixing conductive powder with a flexible substrate.

6. A method for preparing a flexible pressure sensor for monitoring mine ventilation pressure, characterized in that, Includes the following steps: S1. Structure preparation; Seal one end of the phase change flexible tube (1), insert the heating wire (12) into the preset position from the other end of the phase change flexible tube (1), then inject the solid-liquid phase change material (11), and finally seal the other end of the phase change flexible tube (1) as a basic structure for later use. Seal one end of the first electrode flexible tube (2), uniformly coat the inner wall of the first electrode flexible tube (2) from the other end of the first electrode flexible tube (2), then connect one end of the first electrode lead (22) to the first conductive coating (21) and lead the other end to the outside of the first electrode flexible tube (2), and finally seal the other end of the first electrode flexible tube (2) as the first electrode for later use. Seal one end of the second electrode flexible tube (3), uniformly coat the second conductive coating (31) from the other end of the second electrode flexible tube (3) to its inner wall, then connect one end of the second electrode lead (32) to the second conductive coating (31) and lead the other end to the outside of the second electrode flexible tube (3), and finally seal the other end of the second electrode flexible tube (3) as the second electrode for later use. S2. Electrode winding; The first and second electrodes are wound around the periphery of the base structure to form a double helix structure.

7. The method for preparing a flexible pressure sensor for monitoring mine ventilation pressure according to claim 6, characterized in that, When preparing the first and second electrodes, a solution is first prepared using conductive powder, a flexible substrate, and a flow modifier. Then, the solution is injected into the inner wall of the corresponding electrode flexible tube. Finally, the flow modifier is evaporated by baking and heating to form the corresponding conductive coating.

8. The method for preparing a flexible pressure sensor for monitoring mine ventilation pressure according to claim 6, characterized in that, When sealing the phase change flexible tube (1), the first electrode flexible tube (2) and the second electrode flexible tube (3), a flexible polymer (4) is inserted into the end of the corresponding flexible tube to complete the sealing.

9. A method for preparing a flexible pressure sensor for monitoring mine ventilation pressure according to any one of claims 6 to 8, characterized in that, The type of solid-liquid phase change material (11) is selected according to the actual working conditions of the mine wind pressure monitoring so that the prepared flexible pressure sensor has an appropriate sensitivity adjustment range.

10. A method for preparing a flexible pressure sensor for monitoring mine ventilation pressure according to any one of claims 6 to 8, characterized in that, The spacing of the electrode winding is determined based on the actual working conditions of the mine's wind pressure monitoring, so that the prepared flexible pressure sensor has an appropriate sensitivity adjustment range.

Images