MICRO-CORIOLIS MASS FLOW SENSOR WITH STRAIN MEASUREMENT DEVICES

Abstract

The invention relates to a micro-Coriolis mass flow sensor, comprising a Coriolis tube having a fixed inlet and a fixed outlet, being fixed in tube fixation means, excitation means for oscillating the Coriolis tube about an excitation axis, detection means (8) for detecting, in use, at least a measure for movements of part of the Coriolis tube, characterized by the detection means (8) comprising one or more strain measurement devices (9, 11) configured for resistive readout being arranged in or on the Coriolis tube.

Claims

1.-13. (canceled)

14. A Micro-Coriolis mass flow sensor (1) comprising a Coriolis tube (2) having a fixed inlet (3) and a fixed outlet (4), being fixed in tube fixation means (5), excitation means for oscillating the Coriolis tube about an excitation axis (6, 7), detection means (8) for detecting, in use, at least a measure for movements of part of the Coriolis tube, wherein the detection means (8) comprising one or more strain measurement devices (9) configured for resistive readout being arranged in or on the Coriolis tube.

15. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) are arranged in or on one or more freely suspended portions (10) of the Coriolis tube (2) for locally measuring strain of the Coriolis tube.

16. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) comprise one or more strain gauges (11).

17. The Micro-Coriolis mass flow sensor (1) according to claim 16, wherein the one or more strain gauges (11) have a length of 200-1000 μm.

18. The Micro-Coriolis mass flow sensor (1) according to claim 17, wherein the one or more strain gauges (11) have a length of 200-400 μm.

19. The Micro-Coriolis mass flow sensor (1) according to claim 16, wherein a width of the one or more strain gauges (11) amounts to 2-20 μm.

20. The Micro-Coriolis mass flow sensor (1) according to claim 19, wherein a width of the one or more strain gauges (11) amounts to 4-5 μm.

21. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) are arranged to locally coincide with an axial direction (12) of the Coriolis tube (2).

22. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) are arranged at an angle of 30-60° with respect to the excitation axis (6, 7).

23. The Micro-Coriolis mass flow sensor (1) according to claim 22, wherein the one or more strain measurement devices (9) are arranged at an angle of 40-50° with respect to the excitation axis (6, 7).

24. The Micro-Coriolis mass flow sensor (1) according to claim 23, wherein the one or more strain measurement devices (9) are arranged at an angle of 45° with respect to the excitation axis (6, 7).

25. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) are arranged at a distance from the tube fixation means (5).

26. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein the one or more strain measurement devices (9) are arranged adjacent to the tube fixation means (5).

27. The Micro-Coriolis mass flow sensor (1) according to claim 14, wherein, in rest, in the Coriolis tube (2) is arranged in a tube plane (13) and has a mirror plane (14), perpendicular to the tube plane, with the fixed inlet (3) and outlet (4) being symmetrically arranged with respect to the mirror plane, wherein a pair of strain measurement devices (9) is symmetrically arranged with respect to the mirror plane.

28. The Micro-Coriolis mass flow sensor (1) according to claim 27, wherein the Coriolis tube (2) has a rectangular or square loop shape, with perpendicular tube portions (15) extending perpendicular to the mirror plane (14), wherein the pair of strain measurement devices (9) is arranged in or on the perpendicular tube portions.

29. The Micro-Coriolis mass flow sensor (1) according to claim 27, wherein the Coriolis tube (2) has a rectangular or square loop shape, with parallel tube portions (16) extending parallel to the mirror plane (14), wherein the pair of strain measurement devices (9) is arranged in or on the parallel tube portions.

30. The Micro-Coriolis mass flow sensor (1) according to claim 28, wherein a strain measurement device (9) is located on a straight portion of the substantially rectangular Coriolis tube (2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be explained hereafter showing the operation of the micro-Coriolis mass flow sensor according to the present disclosure and with reference to the drawings. Therein:

[0042] FIGS. 1a-1d show the operation principle of a micro-Coriolis mass flow sensor according to the present disclosure;

[0043] FIG. 2 shows a SEM image of a sensor chip comprising a micro-Coriolis mass flow sensor according to the present disclosure, wherein the inset shows a close-up of one of the resistive strain gauges;

[0044] FIGS. 3a-3d show the principle of operation of the resistive readout of a micro-Coriolis mass flow sensor according to the present disclosure;

[0045] FIG. 4 shows the output of the resistive readout in relation to the applied flow; and

[0046] FIG. 5 shows a representation of the electronic readout circuit.

DETAILED DESCRIPTION

[0047] FIGS. 1-5 will be discussed in conjunction. FIGS. 1a-1d schematically show an exemplary embodiment of a micro-Coriolis mass flow sensor 1, comprising a Coriolis tube 2 with a channel loop having a substantially rectangular shape, i.e. a shape with edges or corners connected by straight tubes, wherein the edges or corners are preferably slightly rounded (see e.g. FIG. 2). The Coriolis tube 2 has a fixed inlet 3 and a fixed outlet 4, being fixed in tube fixation means 5. Excitation means (not shown) are provided for oscillating the Coriolis tube 2 about an excitation axis 7 in swing mode, as shown in FIGS. 1b and 1c, or around an excitation axis 6 in twist mode, as shown in FIGS. 1a and 1d. As shown in FIGS. 2 and 3, detection means 8 are provided for detecting, in use, at least a measure for movements of part of the Coriolis tube 2. The detection means 8 comprise one or more strain measurement devices 9 configured for resistive readout being arranged in or on the Coriolis tube 2.

[0048] The channel loop of the Coriolis tube 2 is brought into resonance at actuation angle θ.sub.T/θ.sub.S through Lorentz force F.sub.L, resulting from a magnetic field B and an AC current i. FIG. 1b shows that a mass flow ϕ.sub.m through the channel induces vibration in the detection mode through Coriolis force F.sub.Coriolis. The ratio between the two vibration mode amplitudes is a measure for the flow.

[0049] FIG. 2 shows a drawing after a SEM image of a sensor chip 17 comprising a micro-Coriolis mass flow sensor 1 according to the present disclosure. As shown in FIGS. 2 and 3a-3d, the one or more strain measurement devices 9 are arranged in or on one or more freely suspended portions 10 of the Coriolis tube 2 for locally measuring strain of the Coriolis tube 2. The one or more strain measurement devices 9 as shown comprise one or more strain gauges 11, for instance made of gold, platinum or another metal or silicon nitride. The one or more strain measurement devices 9 are arranged to locally coincide with an axial direction 12 of the Coriolis tube 2, although the one or more strain measurement devices 9 can also be placed at an angle with respect to the excitation axis, such as an angle of 45°. The “straight” and “angled” strain gauges 11 can be connected in series, such that Coriolis vibration can be measured, as well as actuation vibration. The combination of these measurements then leads to a ratio which provides information about the mass flow.

[0050] The strain gauges 11 reside on two freely suspended sections 10 sections of channel close to the fixed inlets/outlets 3, 4 at a distance from the tube fixation means 5. The strain gauges 11 may have an axial length of for instance 200-1000 μm, such as 200-400 μm. The width of the strain gauges 11 may advantageously amount to for instance 2-20 μm, such as 4-5 μm. In the exemplary embodiment as shown in FIG. 2 though, the strain gauge 11 has a width of 72 μm.

[0051] In rest, in the Coriolis tube 2 is arranged in a tube plane 13 and has a mirror plane 14 (FIG. 2), perpendicular to the tube plane 13 (FIG. 1c). The fixed inlet 3 and outlet 4 are symmetrically arranged with respect to the mirror plane 14. A pair of strain measurement devices 9 is symmetrically arranged with respect to the mirror plane 14.

[0052] As stated before, the Coriolis tube 2 may have a rectangular or square loop shape, with perpendicular tube portions 15 extending perpendicular to the mirror plane 14. The pair of strain measurement devices 9 can be arranged in or on the perpendicular tube portions 15, i.e. at opposite sides of the mirror plane 14.

[0053] The Coriolis tube 2 may also have parallel tube portions 16 extending parallel to the mirror plane 14, wherein the pair of strain measurement devices 9 is arranged in or on the parallel tube portions 16, again symmetrically arranged on opposite sides of the mirror plane 14. Therein, as stated before, in some situations it is conceivable to arrange the one or more strain measurement devices 9 close or adjacent to the tube fixation means 5, for instance near the fixed inlet 3 and fixed outlet 4, due to the strain being the largest there.

[0054] The fabrication process of the sensor chip 17 can for instance be based on the surface channel technology proposed in J. Groenesteijn et al., “A versatile technology platform for microfluidic handling systems, part I: fabrication and functionalization”, Microfluidics and Nanofluidics 2017, Volume 21, Issue 7.

[0055] FIGS. 3a-3d further elucidate the principle of operation of the resistive readout, wherein FIG. 3a shows the configuration of the strain gauges 11 in rest, FIG. 3b shows the configuration of the strain gauges 11 in the twist mode, wherein one strain gauge 11 is elongated, and the other is compressed. This results in opposite change in resistance. FIG. 3c shows the strain gauges 11 in the swing mode, wherein both strain gauges are elongated due to torsion of the channel or tube 2. This results in equal resistance change. FIG. 3d shows a combination of the two modes, which gives two resistance signals R.sub.1, R.sub.2 with a phase shift dependent on the mass flow rate.

[0056] FIG. 4 shows the output of the resistive readout in relation to the applied flow, for both excitation modes and at different excitation amplitudes. The error bars represent the standard deviation.

[0057] FIG. 5 shows a schematic representation of the electronic readout circuit 18. The resistance R.sub.1/2 of one strain gauge 11 is converted to a voltage via a 1 MHz carrier signal 19 and a reference resistor R.sub.ref. The 1 MHz carrier signal 19 is used to eliminate crosstalk from the actuation current. The carrier signal 19 is mixed out after which a lock-in amplifier 20 determines the magnitude and phase of the signal. Each strain gauge 11 is read out with a circuit such as depicted in FIG. 5. The phase difference between the two resulting signals R.sub.1, R.sub.2 is a measure for the flow.

Experimental Results

[0058] Multiple flow measurements have been carried out while actuating the sensor 1 and sensor chip 17 at various actuation angles θ.sub.T/θ.sub.S in the swing/twist mode respectively.

[0059] Nitrogen gas was fed through the sensor chip 17 at an input pressure of 7 bar. The mass flow rate was controlled by a mass flow controller at the outlet of the sensor chip 17.

[0060] FIG. 4 shows the resulting phase difference output of the resistive readout. There is an approximately linear relation between the output and mass flow. The sensitivity is approximately 0.5°/(g h.sup.−1) when actuating in the swing mode and approximately 0.9°/(g h.sup.−1) when actuating in the twist mode.

[0061] The results show that the resistive readout is more sensitive when actuating in the twist mode. This is to be expected, since the strain gauges were designed to be most sensitive to swing mode deformation, which is in this case the Coriolis mode. However, in the swing mode, better accuracy is obtained. This could be due to lower dependency on external vibrations. The readout shows great potential to become a better alternative to the prior art capacitive readout especially when one or more of the following improvements are implemented:

[0062] 1) Optimizing the design to increase sensitivity to a specific mode,

[0063] 2) Adding on-chip reference resistors to reduce drift, and/or

[0064] 3) Adding additional strain gauges 11 on the tube 2 to allow for a full Wheatstone bridge readout.

[0065] It should be clear that the description above is intended to illustrate the operation of preferred embodiments of the invention, and not to reduce the scope of protection of the invention. Starting from the above description, many embodiments will be conceivable to the skilled person within the inventive concept and scope of protection of the present invention.

LIST OF REFERENCE NUMERALS

[0066] 1. Micro-Coriolis mass flow sensor [0067] 2. Coriolis tube [0068] 3. Fixed inlet [0069] 4. Fixed outlet [0070] 5. Tube fixation means [0071] 6. Excitation axis (twist mode) [0072] 7. Excitation axis (swing mode) [0073] 8. Detection means [0074] 9. Strain measurement device [0075] 10. Freely suspended portion [0076] 11. Strain gauge [0077] 12. Axial direction of Coriolis tube [0078] 13. Tube plane [0079] 14. Mirror plane [0080] 15. Perpendicular tube portion [0081] 16. Parallel tube portion [0082] 17. Sensor chip [0083] 18. Electronic readout circuit [0084] 19. Carrier signal [0085] 20. Lock-in amplifier