Patent ID: 7487674
Filing Date: 2009-02-10
Classification: G01F

Abstract:
1. A thermal flow sensor in which a bridge circuit is composed of a temperature detection element arranged in the vicinity of at least one heating element, a fluid temperature detection element, and a plurality of resistors; said heating element and said fluid temperature detection element are arranged in fluid, and said fluid temperature detection element is arranged at a location free from the influence of heat from said heating element; and a flow rate of said fluid is detected by using the fact that an amount of heat transmitted from said heating element to said fluid in a state where said heating element is always held at a control temperature higher by a predetermined value than the temperature of said fluid detected by said fluid temperature detection element depends on the flow rate of said fluid; said thermal flow sensor comprising: an amplifier section that amplifies a voltage across opposite ends of at least one of said plurality of resistors; a current control section that is controlled based on an output voltage of said amplifier section; and an output terminal that is connected to one end of said heating element, which is controlled to be energized through said current control section, for outputting a detection result corresponding to the flow rate of said fluid; wherein said amplifier section comprises an amplifier part that amplifies an input signal to said amplifier section, and an amplification factor control part that controls an amplification factor of said amplifier part; said amplification factor control part changes the amplification factor of said amplifier part by means of an electric signal so that the temperature of said heating element is adjusted to said control temperature.