Vortex flow sensor

• US 6,351,999 B1
• Filed: 06/22/1999
• Issued: 03/05/2002
• Est. Priority Date: 06/25/1998
• Status: Expired due to Fees

• Current Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Original Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Inventors: Maul, Joachim, Ohle, Frank
• Primary Examiner(s): Noori, Max
• Assistant Examiner(s): Mack, Corey D.
• Application Number:
  US09/337,996
• Time in Patent Office: 987 Days
• Field of Search: 738/612.2, 356/351, 356/345, 356/491, 356/517
• US Class Current: 73/861.22
• CPC Class Codes: G01F 1/3209 using Karman vortices
• CPC Class Codes: G01F 1/325 Means for detecting quantities used as proxy variables for swirl
• CPC Class Codes: G01F 1/661 using light
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods

Abstract

This sensor for measuring the flow velocity and/or the flow rate of a fluid provides an optical sensor system which is also suitable for use at temperatures higher than 400° C., does not come into contact with the fluid, and requires less space than conventional optical sensor systems. The sensor comprises a tube (1) through which the fluid flows in a first direction and which has a wall (11) in which a first window (2) and a second window (3) of optical, schlieren-free, high-temperature glass are set fluid-tight and pressure-tight at points lying opposite each other along a first tube diameter. A bluff body (4) is disposed along a second tube diameter and fixed in the tube for generating Kármán vortices, whose frequency f is proportional to the flow velocity u. The second diameter is up-stream of, and perpendicular to, the first. A laser differential interferometer (6, 6′) has a transmitting unit (61, 61′) mounted outside the tube in front of the first window and fixed thereto and comprises optical components, which follow one another in the direction to the first window: a laser (21, 31), a lens system (22, 32), a first polarization filter (23), a first Wollaston prism (24, 34), and a first lens (25, 35). A receiving unit (62, 62′) is mounted outside the tube in front of the second window and fixed thereto and comprises the optical components, which fellow one another in a direction away from the second window: a second lens (26, 36), a second Wollaston prism (27, 37), a second polarization filter (28), and a PIN diode (29, 39).

Claims

1. A vortex flow sensor for measuring at least one of the flow velocity and the volumetric flow rate of a fluid, said vortex sensor comprising;

a measuring tube;

through which the fluid flows in a first direction and which has a wall in which a first window and a second window of optical, schlieren-free, high temperature glass are set fluid tight and pressure tight at points lying opposite each other along a first diameter of the measuring tube;

a bluff body disposed along a second diameter of the measuring tube and fixed in the measuring tube for generating Ká

rmá

n vortices in the fluid, whose frequency is proportional to the flow velocity, said second diameter lying upstream of, and being essentially perpendicular to, the first diameter; and

a laser differential interferometer having a transmitting unit mounted outside the measuring tube in front of the first window and fixed to at least one of the first window and the measuring tube, said transmitting unit comprising the following optical components, which follow one another in the direction to the first window;

a laser, a lens system, a first polarization filter, a first Wollaston prism, and a first lens, and a receiving unit mounted outside the measuring tube in front of the second window and fixed to at least one of the second window and the measuring tube, said receiving unit comprising the following optical components, which follow one another in a direction away from the second window;

a second lens, a second Wollaston prism, a second polarization filter, and a PIN diode.

3. A vortex flow sensor as claimed in claim 1 wherein the first and second lenses are achromats.

2. A vortex flow sensor for measuring at least one of the flow velocity and the volumetric flow rate of a fluid, said vortex sensor comprising;

a measuring tube through which the fluid flows in a first direction and which has a wall in which a first window and a second window of optical, schlieren-free, high temperature glass are set fluid tight and pressure tight at points lying opposite each other along a first diameter of the measuring tube;

a bluff body disposed along a second diameter of the measuring tube and fixed in the measuring tube for generating Ká

rmá

n vortices in the fluid, whose frequency is proportional to the flow velocity, said second diameter lying upstream of, and being essentially perpendicular to, the first diameter; and

a laser differential interferometer having a transmitting unit mounted outside the measuring tube in front of the first of the front window and fixed to at least one of the first window and the measuring tube, said transmitting unit comprising the following optical components, which follow one another in the direction to the first window;

a laser emitting polarized light, a lens system, a first Wollaston prism, a first lens, and a receiving unit mounted outside the measuring tube in front of the second window and fixed to at least one of the second window and the measuring tube, said receiving unit comprising the following optical components, which follow one another in a direction away from the second window;

a second lens, a second Wollaston prism, a polarization filter, and a PIN diode.

4. A vortex flow sensor as claimed in claim 2 wherein the first and second lenses are achromats.