Flowmeter with radial vibrational mode for ultrasonic waves

• US 4,601,210 A
• Filed: 05/01/1984
• Issued: 07/22/1986
• Est. Priority Date: 05/01/1984
• Status: Expired due to Fees

• Current Assignee: Manqing Technology Limited
• Original Assignee: Manqing Technology Limited
• Inventors: Brown, Alvin E.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US06/605,868
• Time in Patent Office: 812 Days
• Field of Search: 73/861.18, 73/861.27, 73/861.28, 73/597, 310/336, 310/326, 310/327, 310/333
• US Class Current: 73/861.27
• CPC Class Codes: B06B 1/0618 of piezo- and non-piezoelectric elements, e.g. 'Tonpilz'
• CPC Class Codes: G01F 1/66 by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters

Abstract

An ultrasonic flowmeter of the upstream-downstream type having piezoelectric crystals operated in the radial mode, as well as the compression mode, or primarily the radial mode. If both modes are used, one of the two may be selected in order to optimize the received signal. Selection would depend upon the molecular weight and temperature of the viscous fluid in the flowmeter. The selected frequency would be below the relaxation frequency of the flowing material. Radial mode oscillations are achieved by mass loading members adhered to either side of the crystal, thereby creating acoustic impedances which dampen the compressional mode, but enhance the radial mode of vibration. The mass loading member rearward of the crystal is significantly larger than the forward member so that most of the energy to be transmitted is directed in a forward direction. The forward end of the crystal is mounted in a tubular housing which is inserted into a pipe opening into a larger pipe where fluid flow occurs.

Claims

1. A method of operating an ultrasonic flowmeter for viscous fluids comprising,

transmitting and receiving ultrasonic acoustic waves generated by a piezoelectric crystal in upstream-downstream transducers of an ultrasonic flowmeter, said crystal having a radial vibrational mode,

enhancing radial mode vibration while damping compressional mode vibration, and

determining flow rate from said acoustic waves of radial vibrational mode.

2. The method of claim 1 further defined by controlling the temperature of said viscous fluid such that the relaxation frequency of the viscous fluid exceeds the frequency of said acoustic waves.

3. A method of operating an ultrasonic flowmeter for viscous fluids comprising,

transmitting ultrasonic waves having a pair of spaced-apart frequencies generated by piezoelectric crystals in upstream-downstream transducers of an ultrasonic flowmeter, said flowmeter having flow of a viscous fluid, where one of said two spaced-apart frequencies is compression mode vibration in the piezoelectric crystal and the other frequency is radial mode vibration, at least one frequency being below the relaxation frequency of the viscous fluid,

suppressing said compression mode vibration,

receiving selected ultrasonic waves with a piezoelectric crystal in upstream-downstream transducers of said flowmeter, the selected upstream-downstream ultrasonic waves having a frequency being below the relaxation frequency of the viscous fluid corresponding to the radial vibration mode, and

determining flow rate from said received selected frequency.

4. The method of claim 3 wherein said two spaced-apart frequencies are generated from the same crystal.

5. The method of claim 3 wherein both of said frequencies are below the relaxation frequency of the viscous fluid.

6. The method of claim 5 further defined by filtering one of said frequencies.

7. A transducer for an ultrasonic flowmeter of the upstream-downstream type comprising,

a hollow tubular housing closed at a first end, the housing having a central lengthwise axis, and

a piezoelectric crystal having opposed major sides, with first and second acoustic impedance loading members joined to said opposed major sides of the crystal forming a sandwich, wherein one of said loading members has a thickness of approximately one-half of a wavelength of said radial mode vibration and the other of said loading members has a thickness of approximately one-quarter of the same wavelength, the loading members having dimensions forcing radial mode vibration from the crystal, said sandwich disposed against said first end, with the major sides of the crystal disposed generally perpendicular to the axis of the housing.

8. An ultrasonic flowmeter comprising,

a pair of transducers in an upstream-downstream configuration transverse to a pipe carrying a viscous fluid, each transducer having a hollow tubular housing closed at a first end, the housing having a central lengthwise axis, and a piezoelectric crystal having opposed major sides, with first and second acoustic impedance loading members joined to said opposed major sides of the crystal forming a sandwich, the loading members having dimensions enhancing radial mode vibration from the crystal while suppressing compressional mode vibration, the radial mode having a substantially lower frequency than the compressional mode, said sandwich disposed against said first end, with the major sides of the crystal disposed generally perpendicular to the axis of the housing, whereby low frequency radial mode vibration is a measurement frequency.

9. An ultrasonic flowmeter comprising,

a pair of transducers in an upstream-downstream configuration transverse to a pipe carrying a viscous fluid, each transducer having a hollow tubular housing closed at a first end, the housing having a central lengthwise axis, and a piezoelectric crystal having opposed major sides, with first and second acoustic impedance loading members joined to said opposed major sides of the crystal forming a sandwich, the loading members having dimensions enhancing radial mode vibration from the crystal while suppressing compressional mode vibration, the radial mode having a substantially lower frequency than the compressional mode, said sandwich disposed against said first end, with the major sides of the crystal disposed generally perpendicular to the axis of the housing, the pipe having heating coil means surround ing the pipe for raising the temperature of the viscous fluid for acoustic energy transfer between the transducers.