Thermally-sensitive type flow meter having a high accuracy

• US 5,703,288 A
• Filed: 07/17/1996
• Issued: 12/30/1997
• Est. Priority Date: 07/19/1995
• Status: Expired due to Fees

• Current Assignee: Ricoh Elemex Corporation (Ricoh Company Limited)
• Original Assignee: Ricoh Company Limited, Ricoh Elemex Corporation (Ricoh Company Limited), Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Inventors: Nakayama, Yoshinobu, Horiguchi, Hiroyuki
• Primary Examiner(s): Dombroske, George M.
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US08/682,162
• Time in Patent Office: 531 Days
• Field of Search: 73/204.26, 73/204.22, 73/204.14
• US Class Current: 73/204.26
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/698 Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
• CPC Class Codes: G01F 1/699 by control of a separate heating or cooling element
• CPC Class Codes: G01P 5/12 using variation of resistance of a heated conductor

Abstract

A thermally-sensitive type flow meter measures a flow rate with a high accuracy by eliminating a noise generated in a source voltage. The flow meter includes a sensor chip comprising a substrate carrying sensing elements. First and second resistors are provided on first and second bridges formed over a depression formed on the substrate. The first bridge is positioned on an upstream side and the second bridge is positioned on a downstream side. The first and second resistors generate a heat by the same voltage source. First and second temperature measuring resistors are provided adjacent to the first and second resistors, respectively, to measure a temperature of the first and second resistors. Third and fourth temperature measuring resistors are provided for measuring the temperature of the fluid. A temperature control unit, including the first, second, third and fourth temperature measuring resistors, controls a temperature of each of the first and second resistors to be constant. A flow rate of the fluid is determined based on a voltage difference between a first voltage applied to the first resistor and a second voltage applied to the second resistor.

Claims

1. A thermally-sensitive type flow meter for measuring a flow rate of a fluid, said flow meter including a sensor chip comprising a substrate carrying sensing elements, said flow meter comprising:

first and second bridges formed over a depression formed on said substrate, said first and second bridges being arranged along the direction of flow so that said first bridge is positioned on an upstream side and said second bridge is positioned on a downstream side;

first and second resistors for generating a heat, said first and second resistors provided on the respective one of said first and second bridges, said first and second resistors being heated by the same voltage source;

first and second temperature measuring resistors provided adjacent to the respective one of said first and second resistors;

third and fourth temperature measuring resistors for measuring a temperature of the fluid, said third and fourth temperature measuring resistors being located at positions not influenced by a temperature of said first and second resistors;

a temperature control unit, including said first, second, third and fourth temperature measuring resistors, for controlling a temperature of each of said first and second resistors to be constant; and

a flow rate determining unit for determining a flow rate of the fluid flowing around said first and second bridges, a determination being made based on a voltage difference between a first voltage and a second voltage, said first voltage being measured across said first resistor, said second voltage being measured across said second resistor.

2. The flow meter as claimed in claim 1, wherein said first and second bridges extend perpendicular to the direction of flow.

3. The flow meter as claimed in claim 1, wherein said first bridge extends perpendicular to the direction of flow and said second bridge extends parallel to the direction of flow.

4. The flow meter as claimed in claim 1, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first bridge extending in a direction 55 degrees inclined with respect to the <

100>

axis.

5. The flow meter as claimed in claim 1, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first bridge extending in a direction parallel to the <

100>

axis.

6. The flow meter as claimed in claim 1, further comprising a flow direction determining unit for determining a direction of flow based on whether said voltage difference is a positive value or a negative value.

7. The flow meter as claimed in claim 1, wherein said first bridge and said second bridge are formed over separate depressions.

8. The flow meter as claimed in claim 1, wherein said third and fourth temperature measuring resistors are provided on a bridge formed over a depression formed on said substrate.

9. A thermally-sensitive type flow meter for measuring a flow rate of a fluid, said flow meter including a sensor chip comprising a substrate carrying sensing elements, said flow meter comprising:

first and second bridges formed over a depression formed on said substrate, said first and second bridges being arranged along the direction of flow so that said first bridge is positioned on an upstream side and said second bridge is positioned on a downstream side;

first and second resistors for generating a heat, said first and second resistors provided on the respective one of said first and second bridges, said first and second resistors being heated by the same voltage source;

first and second temperature measuring resistors for measuring a temperature of the fluid, said first and second temperature measuring resistors being located at positions not influenced by a temperature of said first and second resistors;

a temperature control unit, including said first and second resistors and said first and second temperature measuring resistors, for controlling a temperature of each of said first and second resistors to be constant; and

a flow rate determining unit for determining a flow rate of the fluid flowing around said first and second bridges, a determination being made based on a voltage difference between a first voltage and a second voltage, said first voltage being measured across said first resistor, said second voltage being measured across said second resistor.

10. The flow meter as claimed in claim 9, wherein said first and second bridges extend perpendicular to the direction of flow.

11. The flow meter as claimed in claim 9, wherein said first bridge extends perpendicular to the direction of flow and said second bridge extends parallel to the direction of flow.

12. The flow meter as claimed in claim 9, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first bridge extending in a direction 55 degrees inclined with respect to the <

100>

axis.

13. The flow meter as claimed in claim 9, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first bridge extending in a direction parallel to the <

100>

axis.

14. The flow meter as claimed in claim 9, further comprising a flow direction determining unit for determining a direction of flow based on whether said voltage difference is a positive value or a negative value.

15. The flow meter as claimed in claim 9, wherein said first bridge and said second bridge are formed over separate depressions.

16. The flow meter as claimed in claim 9, wherein said first and second temperature measuring resistors are provided on a bridge formed over a depression formed on said substrate.

17. A thermally-sensitive type flow meter for measuring a flow rate of a fluid, said flow meter including a sensor chip comprising a substrate carrying sensing elements, said flow meter comprising:

first and second bridges formed over a depression formed on said substrate, said first and second bridges being arranged along the direction of flow so that said first bridge is positioned on an upstream side and said second bridge is positioned on a downstream side;

a third bridge provided between said first and second bridges, said third bridge being parallel to the direction of flow;

first, second and third resistors for generating a heat, said first, second and third resistors provided on the respective one of said first, second and third bridges, said first, second and third resistor being heated by the same voltage source;

first and second temperature measuring resistors for measuring a temperature of the fluid, said first and second temperature measuring resistors being located at positions not influenced by a temperature of said first and second resistors;

a temperature control unit, including said first and second resistors and said first and second temperature measuring resistors, for controlling a temperature of each of said first and second resistors to be constant; and

a flow rate determining unit for determining a flow rate of the fluid flowing around said first, second and third bridges, a determination being made based on a voltage difference between a first voltage and a second voltage, said first voltage being measured across one of said first resistor and said second resistor, said second voltage being measured across said third resistor.

18. The flow meter as claimed in claim 17, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first and second bridges extending in a direction 55 degrees inclined with respect to the <

100>

axis.

19. The flow meter as claimed in claim 17, wherein said substrate is comprised of a semiconductor substrate having a (110) plane and a <

100>

axis, said depression being formed on a surface corresponding to the (110) plane, said first and second bridges extending in a direction parallel to the <

100>

axis.

20. The flow meter as claimed in claim 17, further comprising a flow direction determining unit for determining a direction of flow based on whether said voltage difference is a positive value or a negative value.

21. The flow meter as claimed in claim 17, wherein said first bridge and said second bridge are formed over separate depressions.

22. The flow meter as claimed in claim 17, wherein said first temperature measuring resistor is provided on a fourth bridge formed over said depression and said second temperature measuring resistor is provided on a fifth bridge formed over said depression, said fifth bridge being located at a position opposite to said fourth bridge with respect to said first, second and third bridges.