Vibration sensor with calibration element and method of calibrating the oscillation behavior of two prongs

Abstract

The invention relates to a vibration sensor (10) having a housing (12), a mechanical oscillator (14) and a drive unit (20) for exciting the mechanical oscillator (14), wherein a first prong (16) and a second prong (18) are arranged on the mechanical oscillator (14), the drive unit (20) is fixed relative to the mechanical oscillator (14) by means of a yoke (22), the yoke (22) has at least one yoke cavity (32), a root (36) of at least one prong (16, 18) has a prong cavity (38), the yoke cavity (32) and the prong cavity (38) are aligned with one another, and a calibration element (40) is displaceably arranged in the yoke cavity (32) such that it can be at least partially arranged in the prong cavity (38). The invention also relates to a method for calibrating the oscillation behavior of two prongs (16, 18) of a vibration sensor (10).

Description

Technical Field

[0001] This invention relates to a vibration sensor with a calibration element. The invention also relates to a method for calibrating the oscillation characteristics of the two prongs of the vibration sensor. Background Technology

[0002] Field devices used to record and / or influence process variables are commonly used in process automation engineering. Examples of such field devices include fill level measuring devices, limit level measuring devices, and pressure measuring devices, which have sensors that record the corresponding process variables such as fill level, limit level, or pressure. These field devices are often connected to higher-level units, such as guidance or control systems. These higher-level units are used to control, visualize, and / or monitor the process. Field devices known in the prior art typically have a housing, sensors, and electronic units housed within the housing.

[0003] As an example of such a field device, a vibration sensor, known from the prior art as a vibration limit switch, is typically used. A vibration sensor generally has a mechanical oscillator (usually a diaphragm) that can be excited to oscillate by a drive unit, and forks arranged on the mechanical oscillator can be excited to oscillate by the oscillator. Depending on the degree to which the forks are covered by a filler material, and depending on the viscosity of the filler material, the forks oscillate with a characteristic frequency and amplitude; therefore, the mechanical oscillator also oscillates with a characteristic frequency and amplitude, which can be detected by the vibration sensor and converted into a measurement signal.

[0004] In a vibration sensor with two forks (fork-shaped vibration sensor), the two forks may not oscillate at the same frequency and amplitude (e.g., due to asymmetrical cast diaphragms, asymmetrical welded connections of the forks, or asymmetry of the drive unit).

[0005] However, in order to achieve smooth (symmetrical) oscillation of the fork teeth relative to the clamping of the diaphragm and reliable operation, it is necessary to adjust the resonant frequency and oscillation amplitude of the two fork teeth to make them the same.

[0006] To date, for this purpose, in particular, milling processes have been used to manipulate the rigidity of a fork tooth, in which material is removed from the fork tooth by milling until both forks oscillate at the same frequency and the same amplitude.

[0007] The disadvantage of this milling process is that it is time-consuming because machining generates friction and heat. In order to reliably measure the frequency as a calibrated quantity, a waiting time or additional cooling is required after milling. Furthermore, milling produces visible variations in the optically visible range on the fork teeth. Summary of the Invention

[0008] The basic objective of this invention is to provide a vibration sensor with two forks and a calibration method for the oscillation characteristics of the two forks, enabling simple calibration of the oscillation behavior of the two forks.

[0009] The vibration sensor according to the invention has a housing and a mechanical oscillator. Specifically, the mechanical oscillator is a diaphragm. A first fork and a second fork are arranged on the mechanical oscillator. These two forks are spaced apart from each other on the mechanical oscillator, and this is a fork-shaped vibration sensor. The vibration sensor has a drive unit for exciting the mechanical oscillator.

[0010] Here, the drive unit is connected to the housing via a yoke and is fixed relative to the mechanical oscillator by the yoke. The yoke refers to a component that extends laterally across the drive unit on the drive unit side opposite to the mechanical oscillator, and is used to connect the drive unit and to clamp it relative to the diaphragm. Specifically, the yoke is a separate component. Preferably, the yoke is cup-shaped and U-shaped in cross-section, and is supported on the mechanical oscillator by sidewalls. Specifically, the yoke is screwed onto the mechanical oscillator. The base surface of the yoke extends in the lateral direction of the vibration sensor. Specifically, the base surface has a central through-hole in which biasing bolts for connecting and clamping the drive unit relative to the mechanical oscillator are arranged.

[0011] Here, the yoke has at least one yoke cavity. Specifically, the yoke cavity extends along the entire height of the sidewall of the yoke. Additionally, at least one fork tooth has a fork tooth cavity at its root. In this case, the root is the portion of the fork tooth adjacent to the mechanical oscillator. Specifically, the root extends at most 30% of the length of the fork tooth, and preferably at most 20% or 10% of the length of the fork tooth. Specifically, the root may be thickened compared to the rest of the fork tooth's base. The at least one yoke cavity and the corresponding fork tooth cavity are aligned with each other. Specifically, an opening exists in the mechanical oscillator that allows a passage between the yoke cavity and the fork tooth cavity. A calibration element is displaceably arranged in the yoke cavity such that it can be at least partially arranged in the fork tooth cavity.

[0012] By arranging a calibration element that can be displaced through the yoke into the root of at least one fork tooth, the rigidity of the root of the at least one fork tooth is directly altered at the mechanical oscillator, thereby changing the oscillation frequency and amplitude of the fork tooth. The calibration element can be guided particularly well through the yoke or yoke cavity, and the calibration element can also be easily displaced through the yoke or yoke cavity. When calibration is not required, the calibration element can simply be placed in the yoke cavity or removed in a simple manner. In this case, the root is designed such that the insertion of the calibration element affects the rigidity of the entire fork tooth; that is, the root is constructed to have a smaller mass compared to the calibration element.

[0013] Another advantage over milling is that the position of the calibration bolt can be corrected, whereas the material removed by milling no longer allows for correction, or can only be compensated for by another milling process on the opposite fork teeth.

[0014] In practical implementations of the vibration sensor, the yoke cavity is constructed as a channel with internal threads. Specifically, the channel is formed by a hollow screw. The calibration element correspondingly has external threads. By screwing the calibration element into the yoke cavity, the position of the calibration element can be adjusted with particular precision. In particular, the calibration element has fine threads to enable particularly precise adjustment and positioning of the calibration element.

[0015] In particular, the at least one yoke cavity is formed by a hollow screw. Preferably, the hollow screw also serves to connect the yoke to the mechanical oscillator. This arrangement is particularly compact because the additional yoke cavity for arranging the calibration elements is formed within the connection portion of the yoke's conventional arrangement.

[0016] Specifically, if the yoke cavity has internal threads, the calibration element is correspondingly a threaded rod. The threaded rod can then be easily inserted into the hollow screw, and can be at least partially displaced from the yoke cavity into the fork cavity to calibrate the oscillation characteristics.

[0017] In another practical implementation, the fork cavity is formed as a blind hole. Specifically, the fork cavity extends only at the root of the fork, so that the fork remains unchanged in other respects and retains its mechanical integrity as much as possible. By using a blind hole only at the root, the displaceability of the calibration element is limited to the root of the fork. Additionally, the fork cavity can extend at an angle to the oscillation axis of the fork.

[0018] Alternatively, the tooth cavity can extend beyond the root of the tooth into the tooth's base. This expands the range of oscillation characteristics that can be adjusted using calibration elements, and also allows for the calibration of forks with very different oscillation characteristics.

[0019] The fork cavity can be threaded, and the calibration element can be screwed into the thread, thus securing the calibration element within the fork cavity. Alternatively, without threads, the calibration element can be tightly guided within the yoke cavity, or it can be glued to the yoke cavity. If the calibration element is constructed as a threaded rod, in the latter two cases, it can also be constructed without threads in the lower region.

[0020] In another practical configuration of the vibration sensor, the first and second forks each have a fork cavity at their roots, and correspondingly, a yoke cavity aligned with each fork cavity is formed in the yoke. Specifically, in this case, the yoke has two yoke cavities, each extending at the height of its sidewalls. Specifically, the two yoke cavities are formed by hollow screws for connecting the yoke to the mechanical oscillator. In this case, calibration elements can be arranged in one yoke cavity, or even in both yoke cavities, and the corresponding calibration elements can be introduced into the root of one (or both) fork as needed. Flexibility is increased because the oscillation characteristics of the two forks can be adjusted, as the desired oscillation frequency and amplitude can now be adjusted within a certain range, and both forks can be tuned to this range.

[0021] The present invention also relates to a method for calibrating the oscillation characteristics of two forks in a vibration sensor, specifically the resonant frequency and amplitude. In particular, this is a vibration sensor with a yoke and two forks as described above. The rigidity of the root of at least one fork is changed by inserting a calibration element through a yoke cavity into a fork cavity located at the root of the at least one fork and aligned with the yoke cavity. The oscillation characteristics of the fork change depending on the distance the calibration element is inserted into the fork.

[0022] For other advantages, please refer to the above explanation.

[0023] Specifically, the calibration element is screwed into the yoke cavity and the fork cavity. Therefore, the position of the calibration element can be adjusted with particular precision and in a controlled manner. Specifically, the yoke cavity is formed by a hollow screw, and the calibration element is a threaded rod inserted into and screwed into the hollow screw.

[0024] The position of the calibration element can be fixed after the oscillation characteristics have been calibrated. This can be done, for example, by pouring glue or threadlocker. In particular, glue can be applied before calibration and then allowed to cure. Attached Figure Description

[0025] Other practical implementation schemes are described below with reference to the accompanying drawings. In the accompanying drawings:

[0026] Figure 1 A schematic cross-sectional view shows a vibration sensor with two forks, a yoke, and a calibration element according to a first embodiment;

[0027] Figure 2 A schematic cross-sectional view of a vibration sensor with two forks, a yoke, and two calibration elements according to a second embodiment is shown, wherein the calibration elements are arranged in an initial position;

[0028] Figure 3 It shows according to Figure 2 A vibration sensor with two calibration elements, one of which is positioned at a second position offset from the initial position;

[0029] Figure 4 A graph showing the change in the frequency of the two fork teeth relative to the position of the calibration element is shown. Detailed Implementation

[0030] Figure 1 A fork-shaped vibration sensor 10 according to a first embodiment is shown. The vibration sensor 10 includes a housing 12 and a mechanical oscillator 14, which is a diaphragm in this example. A first fork tooth 16 and a second fork tooth 18 are arranged side by side on the mechanical oscillator 14.

[0031] A drive unit 20 for exciting the mechanical oscillator 14 is arranged in the housing 12. The drive unit 20 is connected to the mechanical oscillator 14 and is capable of causing the mechanical oscillator 14 to oscillate, and is also capable of detecting the oscillation of the mechanical oscillator 14.

[0032] Furthermore, a yoke 22 is arranged within the housing 12. The yoke 22 has a cup-shaped structure and is U-shaped when viewed in cross-section. The yoke 22 laterally surrounds the drive unit 20 and is located on the side opposite to the mechanical oscillator 14. The yoke 22 has circumferentially extending sidewalls 24 and a base surface 26 extending transversely in the axial direction (z-direction).

[0033] The drive unit 20 is held relative to the mechanical oscillator 14 via the yoke 22. For this purpose, the yoke 22 has a central through hole 28 through which bolts 30 or flat-head screws are guided to hold the drive unit 20 toward the mechanical oscillator 14.

[0034] Additionally, the yoke 22 has two yoke cavities 32 in the sidewall 24, which in this example extend across the entire height of the sidewall 24 to the mechanical oscillator 14. In this example, each yoke cavity 32 is formed by a hollow screw 34, which also serves to connect the yoke 22 to the mechanical oscillator 14. Here, the yoke cavities 32 extend through the mechanical oscillator 14. The hollow screws 34 have internal threads.

[0035] Fork tooth cavities 38 are formed in the root 36 of fork teeth 16 and 18, and each fork tooth cavity 38 is aligned with a yoke cavity 32. The fork tooth cavities 38 are formed as blind holes.

[0036] Here, in the first fork tooth 16 arranged on the left, a displaceable calibration element 40 is arranged in the yoke cavity 32 and the fork tooth cavity 38 aligned with the yoke cavity 32. Here, the calibration element 40 is a threaded rod.

[0037] The following is for reference Figure 2 , Figure 3 and Figure 4 Explain the calibration method for oscillation characteristics.

[0038] To illustrate other embodiments, the same reference numerals as those used in the first embodiment are used for the same or at least functionally identical components.

[0039] Figure 2 and Figure 3 A second embodiment of the vibration sensor 10 is shown. It is substantially the same as the first embodiment, except that a calibration element 40 is arranged in the yoke cavity 32 of the two forks 16, 18.

[0040] exist Figure 2 In this configuration, the two calibration elements 40 are located solely within the yoke cavity 32 and do not protrude beyond the mechanical oscillator 14 in the z-direction. The calibration elements 40 are arranged in their initial positions.

[0041] In contrast, Figure 3 In the middle, the right calibration element 40 in the right fork 18 moves further in the z-direction and now protrudes into the fork cavity 38 in the root 36 of the right fork 18. Therefore, the right calibration element 40 is screwed into the fork cavity 38 in the z-direction. The left calibration element 40 in the left fork 16 remains in contact with... Figure 2 Same location.

[0042] Figure 4 The occurrence of this phenomenon in the corresponding fork tooth 18 by moving or screwing in the calibration element 40 is clearly shown. Figure 4 In the diagram, the displacement “z” of calibration element 40 in the z direction is plotted on the x-axis. The resonant frequencies “f” of fork teeth 16 and 18 are plotted on the y-axis.

[0043] In this example, curve 42 (solid line) represents the resonant frequency of the first fork tooth 16, which is the left fork tooth in this example. In this example, curve 44 (dashed line) represents the resonant frequency of the second fork tooth 18 on the right.

[0044] It is easy to see that the resonant frequencies of the two forks 16 and 18 deviate from each other at z = 0. Given the same coverage (or no coverage), the first fork 16 on the left has a higher resonant frequency than the second fork 18 on the right.

[0045] To calibrate and tune the two resonant frequencies, such as Figure 3As shown, a calibration element 40, used to change the rigidity of the root 36 of the fork tooth 18, is screwed into the fork tooth 18. The further the calibration element is screwed in in the z-direction, the more consistent the resonant frequency of curve 44 is with the resonant frequency of the first fork tooth 16. The calibration element 40 is inserted into the second fork tooth 18 until the resonant frequency of the second fork tooth 18 is consistent with the resonant frequency of the first fork tooth 16.

[0046] List of reference numerals

[0047] 10 Vibration Sensors

[0048] 12. Shell

[0049] 14 Mechanical Oscillator (Diaphragm)

[0050] 16 First fork tooth

[0051] 18 Second fork tooth

[0052] 20 drive units

[0053] 22 Yoke

[0054] 24 Sidewalls

[0055] 26 Base plane

[0056] 28 through holes

[0057] 30 bolts

[0058] 32 Yoke cavity

[0059] 34 Hollow Screw

[0060] 36. Roots

[0061] 38 Fork-tooth cavity

[0062] 40 Calibration Elements

[0063] 42 Frequency curve

[0064] 44 Frequency curve

[0065] f Resonant frequency

[0066] z-axis direction

Claims

1. A vibration sensor having a housing (12), a mechanical oscillator (14), and a drive unit (20) for exciting said mechanical oscillator (14), wherein, A first fork tooth (16) and a second fork tooth (18) are arranged on the mechanical oscillator (14). The drive unit (20) is fixed relative to the mechanical oscillator (14) by a yoke (22). The drive unit (20) is disposed between the first fork tooth (16) and the second fork tooth (18). The yoke (22) has at least one yoke cavity (32) in its sidewall (24), wherein the at least one yoke cavity (32) extends across the entire height of the sidewall (24). 32) Formed by a hollow screw (34), wherein at least one yoke cavity (32) extends through the mechanical oscillator (14), the root (36) of at least one fork tooth (16, 18) has a fork tooth cavity (38), the yoke cavity (32) and the fork tooth cavity (38) are aligned with each other, and a calibration element (40) is displaceably arranged in the yoke cavity (32) such that it can be at least partially arranged in the fork tooth cavity (38) so that the resonant frequency of the first fork tooth (16) and the resonant frequency of the second fork tooth (18) are consistent.

2. The vibration sensor according to the preceding claim, Its features are, The yoke cavity (32) is configured as a channel with internal threads, and the calibration element (40) accordingly has external threads.

3. The vibration sensor according to claim 1 or 2, Its features are, The hollow screw (34) is also used to connect the yoke (22) to the mechanical oscillator (14).

4. The vibration sensor according to any one of the preceding claims, Its features are, The calibration element (40) is a threaded rod.

5. The vibration sensor according to any one of the preceding claims, Its features are, The fork cavity (38) is configured as a blind hole.

6. The vibration sensor according to any one of the preceding claims, Its features are, The fork cavity (38) has threads.

7. The vibration sensor according to the preceding claim, Its features are, The first fork tooth (16) and the second fork tooth (18) each have a fork tooth cavity (38) in their root (36), and correspondingly, a yoke cavity (32) aligned with the fork tooth cavity is formed in the yoke (22).

8. A method for calibrating the oscillation characteristics of two fork teeth (16, 18) of a vibration sensor (10), wherein, The rigidity of the root (36) of at least one of the forks (16, 18) is altered by inserting a calibration element (40) through the yoke cavity (32) into the fork cavity (38), and the resonant frequency of the first fork (16) is made to coincide with the resonant frequency of the second fork (18). The fork cavity is located in the root (36) of the at least one fork (16, 18) and aligned with the yoke cavity. The yoke cavity (32) is located in the sidewall (24) of the yoke (22) of the vibration sensor (10). At least one of the yoke cavities (32) extends across the entire height of the sidewall (24). At least one of the yoke cavities (32) is formed by a hollow screw (34). At least one of the yoke cavities (32) extends through the mechanical oscillator (14) of the vibration sensor (10).

9. The method according to the preceding claim, Its features are, The calibration element (40) is screwed into the yoke cavity (32) and the fork cavity (38).

10. The method according to claim 8 or 9, Its features are, After calibrating the oscillation characteristics, fix the position of the calibration element (40).

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