Patent ID: 7926343

Claim:
A flow rate measuring device comprising: a main body portion extending into a main channel and having a circuit mount portion therein; a bypass channel that is formed at an extension side of the circuit mount portion of the main body portion and through which a part of measurement target fluid flowing through the main channel flows; a flow rate detecting element that is disposed in the bypass channel and has a detecting portion mounted on the surface thereof; and a control circuit that is mounted in the circuit mount portion and drives the flow rate detecting element to process a signal from the flow rate detecting element, wherein the bypass channel has a flow-in port that faces the upstream side of a flow direction of mainstream of the measurement target fluid and is opened along a plane vertical to the flow direction of the mainstream of the main body portion, a flow-out port that is parallel to the flow direction of the mainstream of the main body portion and is opened along a plane vertical direction to the extension direction of the main body portion, and one or more bending portion at the upstream side of the position at which the flow rate detecting element is disposed, wherein a ratio (L/H) of a width H of a channel in which the flow rate detecting element is disposed, the width H being set in a direction parallel to the flow rate detecting element, and a distance L of the channel in a direction parallel to the flow direction of the mainstream from the inner corner portion of the bending portion at the upstream side of the flow rate detecting element to the upstream end portion of the detecting portion is set in the range from 0 to 0.7, and wherein a ratio D/H of the width H of the channel in which the flow rate detecting element is disposed, the width H being set in a direction parallel to the flow rate detecting element, and a distance D of the channel in which the flow rate detecting element is disposed, the distance D being set in a direction vertical to the flow direction of the mainstream from side wall surface of the circuit mount portion side to the center of the detecting portion, is set in the range from 0.22 to 0.33.