Coriolis Mass Flow Sensor

Abstract

A Coriolis mass flow sensor uses a multiple-loops form of sensing tube and combined it with a middle post. The resulted sensing tube has high swing stiffness and low twist stiffness and this increases the sensitivity of the sensor tremendously.

Claims

1. A Coriolis mass flow sensor comprising: a sensor base (1), a sensor PCB (2) and a sensing tube assembly (3).

2. The Coriolis mass flow sensor according to claim 1, wherein the sensor PCB (2) is bolted to the sensor base (1).

3. The Coriolis mass flow sensor according to claim 1, wherein the tube of sensing tube assembly (3) is formed as one integral piece which can be divided as a measuring loop (6), and two transition loops (7 and 8).

4. The sensing tube assembly (3) according to claim 3, wherein the measuring loop (6) consists of two vertical inlet beams (9 and 10), and three horizontal beams (11, 12 and 13).

5. The sensing tube assembly (3) according to claim 3, wherein the transition loop 7 consists of one vertical inlet beam (14), one vertical mounting beam (16) and one horizontal transition beam (15).

6. The sensing tube assembly (3) according to claim 3, wherein the transition loop 8 consists of one vertical outlet beam (17), one vertical mounting beam (19) and one horizontal transition beam (18).

7. The Coriolis mass flow sensor according to claim 1, wherein the sensing tube assembly (3) has a middle post (20).

8. The sensing tube assembly (3) according to claim 3, wherein the mounting beams (16, 19) are bound to the post (20) by brazing or other means.

9. The sensing tube assembly (3) according to claim 3, wherein the low end of the inlet beam (14) is fixed to the sensor base (1) airtightly by laser welding or brazing, where the fluid will flow in.

10. The sensing tube assembly (3) according to claim 3, wherein the low end of the outlet beam (14) is fixed to the sensor base (1) airtightly by laser welding or brazing, where the fluid will flow out.

11. The sensing tube assembly (3) according to claim 3, wherein the post (20) has a step at its low end, the end part is thinner than its main part, and the end part is inserted to a bore on the sensor base (1) and fixed by brazing or other means.

12. The sensing tube assembly (3) according to claim 3, wherein the post (20) has a slot at its top, in which the horizontal beam 11 is held and fixed by brazing or other means.

13. The sensing tube assembly (3) according to claim 3, wherein the post (20) has a flat surface at one side of its top, on which the permanent magnet disk (21) is attached by adhesive or other means.

14. The Coriolis mass flow sensor according to claim 1, wherein an excitation coil (6) mounted on the sensor PCB (2) will interact with the magnetic disk (21) on the sensing tube assembly (3) to make the sensing tube assembly (3) do swing vibration and produce Coriolis force.

15. The Coriolis mass flow sensor according to claim 1, wherein two optical sensors (4, 5) mounted on the sensor PCB (2) will monitor the motion of the sensing tube assembly (3).

16. The Coriolis mass flow sensor according to claim 1, wherein the circuit of the sensor PCB (2) will treat the signals obtained from the optical sensors (4, 5) to get the phase angle difference information between the beams (9 and 10), the treated signals will be calibrated to the mass flow rate of the fluid flowing through the sensor tube assembly (3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a sketch showing the principle of the Coriolis sensor.

[0041] FIG. 2 is a chart showing the phase angle of the swing motion and the twist motion.

[0042] FIG. 3 is a sketch showing the relationship of the relative, reference and absolute amplitude vectors.

[0043] FIG. 4 is a sketch showing the relationship of the relative, reference and absolute amplitude vectors when the phase delay angle is ignored.

[0044] FIG. 5 is a perspective view of the mass flow sensor of this invention.

[0045] FIG. 6 is a perspective view of the sensing tube assembly.

[0046] FIGS. 7A and 7B are section views at different planes of the Coriolis sensor of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] FIG. 5 is a perspective view of one of the embodiments of the Coriolis mass flow sensor of this invention. Sensor consists of sensor base 1, sensor PCB 2 and sensing tube assembly 3. Sensor base 1 has four counterbores to be used for mounting the sensor to either a flowmeter or a flow controller. It is preferred to be made of 316L. Sensor PCB 2 is mounted to base 1 from the back (not shown). On sensor PCB 2, two optical sensors 4 and 5, an excitation coil 6 are mounted. FIG. 6 is a perspective view of sensing tube assembly 3. It basically has three parts: a measuring tube, a middle post and a magnetic disk. To make the description easier, we name the measuring tube into different parts: measuring loop 6 and transition loops 7 and 8. Measuring loop 6 consists of two vertical beams 9 and 10, top horizontal transition beam 11 and bottom horizontal beams 12 and 13. Transition loop 6 consists of inlet beam 14, horizontal transition beam 15 and vertical mounting beam 16. Transition loop 7 consists of outlet beam 17, horizontal transition beam 18 and vertical mounting beam 19. Although there is no need to distinguish the difference between the inlet leg and the outlet leg for a Coriolis sensor, but if there is a thermal sensor installed in the inlet of the flowmeter or flow controller, it will make it necessary to do so. Post 20 is in the middle of sensing tube assembly 3. The lower part of post 20 are brazed together with mounting beams 16 and 19. On the top end of post 20, there is a fork shaped slot to host horizontal beam 11. There is also a flat surface on the top end of post 20 on which magnetic disk 21 is attached by adhesive. The low end of post 20 has a step. The diameter of the end part is thinner than the main body. This portion will be inserted into a bore on sensor base 1 and they will be brazed together. Sensing tube assembly 3 has two offset planes: inlet leg 14 and outlet leg 17 are located on one plane, we call it installation plane; measuring loop 6, post 20, mounting beams 16 and 19 are located on another plane, we call it measuring plane. The distance between these two parallel planes is around 2-3 mm. Transition beams 15 and 18 are crossing these two planes. Measuring tube is bent by one piece of tube. All the corners are with a fillet to facilitate the bending. The material of sensing tube assembly 3 is 316L for most of fluids and Hastelloy for some special fluids, and the ID and the OD of it are 0.406 and 0.508 mm for this embodiment, respectively. The material of post 20 is 316L or equivalent and its diameter is around 1 mm for this embodiment. The width and height of measuring loop 6 are 43.5 and 45 mm, respectively. Although increasing them will increase the sensitivity, but this is limited by the size of the sensor. The bottom ends of inlet leg 14 and outlet leg 17 will be welded or brazed airtightly to sensor base 1.

[0048] FIG. 7A and FIG. 7B are section views of the sensor. FIG. 7A is sectioned at the measuring plane and FIG. 7B is sectioned at the installation plane.

[0049] FIG. 7A shows that how post 20 is secured to sensor base 1 by brazing.

[0050] In the detail view of FIG. 7B, it can be seen that how inlet leg 14 and outlet leg 17 are secured to sensor base 1. They are laser-welded airtightly at 21. This jointing can be done with brazing if the application allows this.

[0051] The circuit will provide a sinusoidal current to excitation coil 6, which is concentrically installed with magnetic disk 21 and 1-3 mm apart, this will make sensing tube assembly 3 do a sinusoidal back and forth swing vibration. As mentioned before, to maintain a stable swing vibration, the excitation frequency of coil 6 is set as the same as the swing resonant frequency of sensing tube assembly 3, otherwise, either the power consumption is too much or the amplitude is too small to be measured.

[0052] When the sensing tube assembly 3 makes swing motion, and a fluid flows through the tube, the Coriolis force will be produced on vertical beams 9 and 10 of the measuring loop 6. There will be no Coriolis force on either top beam 11 or bottom beams 12 and 13. The Coriolis forces on vertical beam 9 and 10 change direction and magnitude periodically. These two forces will form an ever-changing torque twisting sensing tube assembly 3 periodically.

[0053] The measurement is implemented by optical sensors 4 and 5 mounted on PCB 2. The two arms of sensors 4 and 5 surround vertical beams 9 and 10 without contacting them. Light will emit from emitters 22 on the inner arms of the sensors and be received by receivers 23 on the outer arms of the sensors. The light will be partially blocked by vertical beams 9 and 10 of sensing tube assembly 3. The sensing elements of receivers 23 will output voltage signals to the circuit and they will be treated to obtain the phase angle difference between beam 9 and beam 10, and they will be in turn calibrated corresponding to the mass flow rate.

[0054] Due to the construction and supporting, the sensing tube assembly 3 has large resistance to swing motion and small resistance to twist motion. Table 1 shows some comparisons between the U-shaped tube Coriolis sensor and this invention.

TABLE-US-00001 TABLE 1 U-shaped Tube this invention Swing motion resonant  121.63  243.82 frequency (Hz) Twist motion resonant  272.20  297.68 frequency (Hz) [00028]${\omega }_{\theta }\left(\frac{\mathrm{rad}}{\sec }\right)$  763.84 1531.19 [00029]${\omega }_{\varnothing }\left(\frac{\mathrm{rad}}{\sec }\right)$ 1709.42 1869.43 [00030]$k_{\theta }\left(\frac{N.Math.\mathrm{mm}}{\mathrm{rad}}\right)$   42.75  576.92 [00031]$k_{\varnothing }\left(\frac{N.Math.\mathrm{mm}}{\mathrm{rad}}\right)$   86.38   90.97 Phase angle difference    0.67    3.08 2φ (degree)

[0055] The data in Table 1 is based on 1000 [g/h] flow rate. The dimensions for the U-shaped tube: W=43.5 mm, H=54 mm; the section sizes of U-shaped tube are the same as those in this invention. We can notice that from the table that this invention has a high swing motion stiffness and a low twist motion stiffness; this is shown on the difference between k.sub.θ and k.sub.Ø and between ω.sub.θ and ω.sub.Ø. Because of these characteristics, and from Eq. (34), the phase angle difference for this invention is almost 5 times of that of the U-shaped tube.