Abstract: A thermal flow sensor is constructed in such a manner that the longitudinal axis of a thermal resistance element is positioned so as to face wires of a rectification net at an angle ranging from 10.degree. to 80.degree.. The surface of the thermal resistance element onto which the openings between the wires of the rectification net would be projected remains substantially the same, regardless of changes in attachment positions of the thermal resistance and the rectification net. Even when the thermal resistance element is arranged close to the rectification net, unevenness in characteristics between the components can be reduced.

Abstract: In a heat-sensitive flow sensor including a bridge circuit composed of a heat-sensitive resistor formed on a substrate provided within a fluid flow passage and a plurality of resistors and a control circuit for controlling current supplied to the heat-sensitive resistor to maintain the bridge circuit in a thermally balanced condition, a flow rate being detected from the thermal balance condition of the bridge circuit, current supply leads and a base portion of the substrate are buried in a heat insulating support member supported by a base. Preferably, lead terminals of the heat-sensitive resistor formed on the base portion are also buried in the heat insulating support member.

Abstract: A thermal flow sensor has a heat-sensitive resistor which is disposed at a predetermined angle relative to the line of stream of a fluid, and which has its heat-sensitive portion disposed on the surface portion of a substrate which is positioned downstream in the direction in which the fluid flows. Since the heat-sensitive resistor is already disposed at a predetermined angle relative to the line of stream of the fluid, this permits only slight influence on, hence, variation in detection characteristic to be caused by deviation in the disposition angle. Since the heat-sensitive portion is disposed on a surface portion positioned downstream in the direction of fluid flow, this restrains dust contained in air from directly depositing on the heat-sensitive portion, hence, from causing variation in detection characteristic.

Abstract: A thermal flow sensor has a housing through the inside of which a fluid is allowed to flow, and a supporting pipe passage disposed within and substantially in the center of the housing. A plurality of thermosensitive resistors are supported on the outer periphery of the supporting pipe passage and are disposed within substantially the same plane normal to the flow of the fluid. A fluid temperature sensor is provided within the supporting pipe passage. The flow rate can be detected correctly even when the flow rate of the fluid varies within that same plane, since the sensor is adapted to detect the average flow rate.

Abstract: A thermal flow sensor has a housing through the inside of which a fluid is allowed to flow, and a supporting substrate disposed within and substantially in the center of the housing. A flat-plate shaped thermosensitive resistor and a fluid temperature sensor are provided on the supporting substrate. The thermosensitive resistor is disposed on the supporting substrate by being supported by a plurality of slender supporting members which support end portions of the resistor in such a manner as to provide narrow portions of a heat transferring path. The sensor detects flow rate with a good sensibility, while preventing any reduction in high levels of measuring sensibility and responsibility that are possessed by a small thermosensitive resistor.

Abstract: A thermal flow sensor constructed by a temperature control circuit which includes a bridge circuit consisting of a thermoresistor arranged in a fluid passageway and a plurality of resistors, and a correction circuit for correcting the output of the control circuit in accordance with a gradient of a flow rate detecting characteristic is described. The correction circuit includes a subtracting circuit for subtracting a predetermined value from an output of the control circuit, a voltage dividing circuit for dividing an output of the subtracting circuit and an arithmetic operating circuit for performing either an addition or a substraction between outputs of the dividing circuit and the control circuit.

Abstract: A hot wire type flow sensor having a cylindrical housing to be placed in a fluid passage, a plurality of hot wire supporters mounted on the inner surface of the housing, a hot wire stretched between the supporters, and a control circuit connected to the hot wire to output a signal in proportion to a flow rate of fluid. The inner surface of the housing at the upstream side of the hot wire is so formed that the flow of the fluid is concentrated at the central part of the hot wire.