Thermally-sensitive type flow meter having a high accuracy

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.

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.