# US 5,703,288 A · Thermally-sensitive type flow meter having a high accuracy > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,703,288 A - Document ID: US5703288A - Status: Granted - Kind: A - Application number: 08/682,162 - Filed: 1996-07-17 - Granted: 1997-12-30 - Earliest claimed: 1995-07-19 - Assignees: Ricoh Company, Ltd.; Ricoh Elemex Corporation; Ricoh Seiki Company, Ltd. - Inventors: Hiroyuki Horiguchi; Yoshinobu Nakayama - Web page: https://patentgrep.com/patent/US5703288A ## CPC - G01F 1/698: Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters - G01F 1/6845: {Micromachined devices} - G01F 1/699: by control of a separate heating or cooling element - G01P 5/12: using variation of resistance of a heated conductor - G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) ## 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 ### Claim 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. ### Claim 2 (depends on 1) The flow meter as claimed in claim 1, wherein said first and second bridges extend perpendicular to the direction of flow. ### Claim 3 (depends on 1) 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. ### Claim 4 (depends on 1) 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. ### Claim 5 (depends on 1) 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. ### Claim 6 (depends on 1) 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. ### Claim 7 (depends on 1) The flow meter as claimed in claim 1, wherein said first bridge and said second bridge are formed over separate depressions. ### Claim 8 (depends on 1) 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. ### Claim 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. ### Claim 10 (depends on 9) The flow meter as claimed in claim 9, wherein said first and second bridges extend perpendicular to the direction of flow. ### Claim 11 (depends on 9) 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. ### Claim 12 (depends on 9) 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. ### Claim 13 (depends on 9) 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. ### Claim 14 (depends on 9) 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. ### Claim 15 (depends on 9) The flow meter as claimed in claim 9, wherein said first bridge and said second bridge are formed over separate depressions. ### Claim 16 (depends on 9) 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. ### Claim 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. ### Claim 18 (depends on 17) 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. ### Claim 19 (depends on 17) 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. ### Claim 20 (depends on 17) 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. ### Claim 21 (depends on 17) The flow meter as claimed in claim 17, wherein said first bridge and said second bridge are formed over separate depressions. ### Claim 22 (depends on 17) 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.