Flow calibrator

• US 5,440,925 A
• Filed: 09/10/1993
• Issued: 08/15/1995
• Est. Priority Date: 05/20/1991
• Status: Expired due to Term

• Current Assignee: Mesa Laboratories Inc.
• Original Assignee: Computer Control Corporation (Core Solutions, Inc.)
• Inventors: Rumore, Frank C., Padden, Harvey F., Calvert, Scott R.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US08/119,808
• Time in Patent Office: 704 Days
• Field of Search: 73/3, 73/232, 73/239, 73/243, 73/247, 73/861.47, 73/861.54, 92/155, 92/170.1, 92/222, 92/248
• US Class Current: 73/253
• CPC Class Codes: G01F 1/90 with positive-displacement meter or turbine meter to determine the volume flow
• CPC Class Codes: G01F 25/11 using a seal ball or piston in a test loop
• CPC Class Codes: G01F 3/16 in stationary cylinders

Abstract

The invention relates to a high accuracy flowmeter for testing and calibrating flowmeters and the like, and more particularly to a positive displacement flowmeter which may include a cylinder (12), a piston (10) within the cylinder (12) which makes a clearance seal with the inside of the cylinder, an encoder (40) associated with the piston, and a control valve (V) for controlling the supply of a fluid flow (A1) to be measured. More generally, the flowmeter includes a channel for receiving a fluid flow so as to move the piston (10) within its enclosure (12); and a device (36, 38, 40) for detecting movement of the piston and generating electrical signals representative of the fluid flow to be measured. The movement of the piston is detected as a function of a known volume of the enclosure traversed by the piston, and a measured variable elapsed time over which the piston traverses the volume. Preferably, the flowmeter system includes a damping device (FIGS. 6A-6D) which may be mechanical, pneumatic, or fluidic. A memory device (e.g., 109) may be provided for supplying data representative of the capacity of the cell, and the fluid flow may be calculated (100) as a function of the cell capacity.

Claims

1. A gas flowmeter comprising in combination:

an enclosure;

a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure;

a channel for receiving a gas flow to be measured and directing said flow so as to move said piston within said enclosure; and

a movement detector for detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured;

wherein said piston and enclosure have respective interfacing portions which have substantially the same coefficient of thermal expansion;

wherein said portion of said piston contains graphite and said portion of said enclosure contains borosilicate glass.

2. A gas flowmeter comprising in combination:

an enclosure;

a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure;

a channel for receiving a gas flow to be measured and directing said flow so as to move said piston within said enclosure; and

a movement detector for detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured;

wherein said piston and enclosure have respective interfacing portions which have substantially the same coefficient of thermal expansion;

wherein said piston contains carbon lubricating material to reduce friction in the event of contact with said enclosure;

wherein said interfacing portion of said piston contains graphite and said interfacing portion of said enclosure contains borosilicate glass.

3. A method of measuring gas flow, comprising the step of:

providing an enclosure and a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure, said piston and enclosure having respective interfacing portions with substantially the same coefficient of thermal expansion;

channeling a received gas flow to be measure, and directing said flow so as to move said piston within said enclosure; and

detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured;

further comprising the step of making said portion of said piston containing graphite and making said portion of said enclosure containing borosilicate glass.

4. A gas flowmeter comprising in combination:

an enclosure;

a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure;

a channel for receiving a gas flow to be measured and directing said flow so as to move said piston within said enclosure; and

a movement detector for detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured;

wherein said piston and enclosure have respective interfacing portions which have substantially the same coefficient of thermal expansion;

wherein one of said portions contains carbon and the other of said portions contains glass.

5. A flowmeter as in claim 4, wherein said portion of said piston contains carbon and said portion of said enclosure contains glass.

6. A flowmeter as in claim 4, wherein said movement detector generates said electrical signals as a function of a known volume of said enclosure traversed by said piston and a measured variable elapsed time over which the piston traverses such volume.

7. A method of measuring gas flow, comprising the steps of:

providing an enclosure and a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure, said piston and enclosure having respective interfacing portions with substantially the same coefficient of thermal expansion;

channeling a received gas flow to be measured, and directing said flow so as to move said piston within said enclosure;

detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured; and

making one of said portions containing carbon and the other of said portions containing glass.

8. A method as in claim 7, wherein said portion of said piston contains carbon and said portion of said enclosure contains glass.

9. A method as in claim 7, comprising the step of generating said electrical signals as a function of a known volume of said enclosure traversed by said piston and a measured variable elapsed time over which the piston traverses such volume.

10. A method of measuring gas flow, comprising the steps of:

providing an enclosure and a piston movable within said enclosure, the piston having a surface which forms a clearance seal with a surface of said enclosure, said piston and enclosure having respective interfacing portions with substantially the same coefficient of thermal expansion;

channeling a received gas flow to be measured, and directing said flow so as to move said piston within said enclosure;

detecting movement of said piston and generating therefrom electrical signals representative of said gas flow to be measured;

providing said piston with carbon lubricating material to reduce friction in the event of contact with said enclosure; and

making said interfacing portion of said piston containing graphite and said interfacing portion of said enclosure containing borosilicate glass.