Thermal flowmeter for detecting rate and direction of fluid flow

A flowmeter for detecting a rate and a direction of a fluid flow comprising:

• a substrate;
• a heating resistor formed on the substrate;
• a flow rate detection resistive element formed on the substrate so that the flow rate detection resistive element is thermally affected by the heating resistor, the flow rate detection resistive element being arranged on only one of an upstream side and a downstream side of the heating resistor with respect to the fluid flow;
• a detection circuit coupled with the flow rate detection resistive element, the detection circuit detecting the rate and the direction of the fluid flow based on the temperature indicated by the flow rate detection resistive element;
• a fluid temperature detection resistive element formed on the substrate in a thermally isolated manner from the heating resistor;
• a heat temperature detection resistive element formed on the substrate, the heat temperature detection resistive element being formed apart from but adjacent to the heating resistor closer to the heating resister than the flow rate detection resistive element so as to detect the temperature of the heating resistor;
• and
• control circuit coupled with the fluid temperature detection resistive element, the heating resistor and the heat temperature detection resistive element, the control circuit controlling a current flowing through the heating resistor so that the temperature indicated by the heat temperature detection resistive element approaches a reference temperature determined based on the temperature indicated by the fluid temperature detection resistive element.

A method of detecting a rate and a direction of fluid flow, the method comprising:

• detecting a temperature of said fluid flow utilizing a fluid temperature detector;
• providing a heating resistor;
• detecting the rate and the direction of said fluid flow based on a temperature measured by a flow rate detector which is arranged on only one of an upstream side and a downstream of the heating resistor with reference to said fluid flow;
• detecting a temperature of said heating resistor utilizing a heat temperature detector which is apart from the heating resistor;
• and
• controlling the temperature of said heating resistor so that the temperature detected by said heat temperature detector approaches a reference temperature determined based on the temperature detected by said fluid temperature detector,
• wherein the temperature of said flow rate detector varies depending on the rate and the direction of said fluid flow.