Thermal mass flow sensor

A thermal mass flow sensor comprising:

• a housing comprising a first sensor region and a second sensor region;
• a first thin film temperature sensor is formed at said first sensor regions;
• a second thin film temperature sensor formed at said second sensor region and mounted at a first angle to said first thin film temperature sensor;
• a heating element arranged to heat said first temperature sensor;
• and
• a controller operably connected to said first temperature sensor, said second temperature sensor and said heating element, said controller controlling a power level to said heating element to maintain a temperature difference between said first temperature sensor and said second temperature sensor,
• wherein said first angle is from about 12 degrees to 70 degrees.

A thermal mass flow sensor comprising:

• a housing comprising a first sensor region and a second sensor region;
• a first thin film temperature sensor comprising an RTD formed at said first sensor region;
• a second thin film temperature sensor formed at said second sensor region;
• a heating element arranged to heat said first temperature sensor;
• a controller operably connected to said first temperature sensor, said second temperature sensor and said heating element, said controller controlling a power level to said heating element to maintain a temperature difference between said first temperature sensor and said second temperature sensor;
• and
• a mast connected to said housing and a mounting plate connected to said mast.

A thermal mass flow sensor comprising:

• a housing comprising a first sensor region and a second sensor region;
• a first thin film temperature sensor comprising an RTD formed at said first sensor region;
• a second thin film temperature sensor formed at said second sensor region;
• a heating element arranged to heat said first temperature sensor;
• a controller operably connected to said first temperature sensor, said second temperature sensor and said heating element said controller controlling a power level to said heating element to maintain a temperature difference between said first temperature sensor and said second temperature sensor;
• and
• a thermal choke between said first temperature sensor and said housing.

A flow sensing element for use in a thermal mass flow sensor comprising:

• a substrate;
• a planar RTD supported by said substrate and having a periphery;
• and
• a planar heating element comprising a strip of resistive material surrounding said RTD.

A method of measuring mass flow comprising the steps of:

• providing a first planar temperature sensor and a second planar temperature sensor;
• mounting a planar heating element along the first planar temperature sensor;
• mounting the first planar temperature sensor in a mass flow passageway defining a mass flow direction at a first angle to the mass flow direction;
• mounting the second planar temperature sensor in the mass flow passageway at a second angle to the mass flow direction such that said first sensor is not parallel to said second sensor;
• maintaining a predetermined temperature difference between the first temperature sensor and the second temperature sensor;
• and
• determining a mass flow from an amount of power required to maintain the predetermined temperature difference.

A thermal mass flow sensor comprising:

• a housing comprising a first support region and a second support region;
• a first substrate at the first support region and a second substrate at the second support region, said first substrate being mounted at an angle of about 12 to 70 degrees to said second substrate;
• a first planar temperature sensor formed on said first substrate;
• a second planar temperature sensor formed on said second substrate;
• a heating element arranged to heat said first temperature sensor;
• and
• a controller operably connected to said first temperature sensor, said second temperature sensor and said heating element, said controller controlling a power level to said heating element to maintain a temperature difference between said first temperature sensor and said second temperature sensor.

A method of measuring mass flow comprising the steps of:

• providing a first thin film RTD and a second thin film RTD;
• forming a thin film heating element around the first thin film RTD;
• mounting the first thin film RTD in a mass flow passageway defining a mass flow direction at a first angle to the mass flow direction;
• mounting the second thin film RTD in the mass flow passageway at a second angle to the mass flow direction;
• maintaining a predetermined temperature difference between the first RTD and second RTD;
• and
• determining a mass flow from an amount of power required to maintain the predetermined temperature difference.