Out of product sensors can include a housing having a first surface and defining a flow channel. A circuit board can be coupled to the first surface of the housing and support a thermistor bridge. The thermistor bridge can be arranged so that some thermistors are in a first sensing area and other thermistors are in a second sensing area. The housing can be configured such that thermal resistance between the flow channel and the first sensing area is lower than thermal resistance between the flow channel and the second sensing area, and/or fluid flowing in the flow channel is directed more toward the first sensing area than the second sensing area. Liquid in the flow channel can affect thermal behavior of thermistors in the first and second sensing area differently and can be used to determine whether liquid is flowing through the sensor.

A thermal type flowmeter that can accurately perform flow rate determination at high speed and high precision even at low flow rate includes a sensor portion conducting heating and temperature detection of a fluid contact portion in contact with a fluid flowing in a flow path, and a control portion controlling heating and temperature detection conducted by the sensor portion. The control portion measures the temperature rise time until the temperature of the fluid contact portion reaches an upper limit set temperature when heating the fluid contact portion and the temperature drop time until the temperature of the fluid contact portion reaches a lower limit set temperature when stopping heating the fluid contact portion, and based on the temperature rise time and the temperature drop time, converts a determined flow velocity into a flow rate value so as to perform flow rate determination.

Various methods, apparatuses, and systems for sensing a flow of fluid are provided. The apparatus includes, but not limited to: a membrane structure defining a heated area; a heating structure disposed over the membrane structure and configured to heat the heated area, where the heating structure has a centerline; a first thermopile including a plurality of first thermocouples disposed upstream of the centerline, where at least a portion of the plurality of first thermocouples are disposed over the membrane structure and at least one junction of the plurality of first thermocouples has rounded corners; and a second thermopile including a plurality of second thermocouples disposed downstream of the centerline, where at least a portion of the plurality of second thermocouples are disposed over the membrane structure and at least one junction of the plurality of second thermocouples has rounded corners.

A fluid flow measuring apparatus and method can be configured to measure fluid flow in a conduit when the conduit is located in the fluid flow measuring apparatus. The apparatus can include a housing including a throughway configured to accept the conduit through which fluid flows, and a thermal source (either cooling or heating source) located in the housing and adjacent the throughway. A plurality of sensors can be positioned adjacent the throughway and spaced from the thermal source in upstream and downstream directions such that the thermal source is located between the sensors which are symmetrically located about the thermal source. A controller can be connected to sensors and configured to calculate flow rate of the fluid passing through the conduit, wherein flow rate calculation is dependent on the symmetrical relationship between the sensors about the thermal source.

A fluid flow measuring apparatus and method can be configured to measure fluid flow in a conduit when the conduit is located in the fluid flow measuring apparatus. The apparatus can include a housing including a throughway configured to accept the conduit through which fluid flows, and a thermal source (either cooling or heating source) located in the housing and adjacent the throughway. A plurality of sensors can be positioned adjacent the throughway and spaced from the thermal source in upstream and downstream directions such that the thermal source is located between the sensors which are symmetrically located about the thermal source. A controller can be connected to sensors and configured to calculate flow rate of the fluid passing through the conduit, wherein flow rate calculation is dependent on the symmetrical relationship between the sensors about the thermal source.