Abstract: A mass flowmeter comprising heat sensitive coils mounted at an upstream position and a downstream position of a conduit through which a fluid flows. The heat sensitive coils have a resistance variable with the fluid temperature, and are each included in a constant temperature difference circuit. This circuit further includes an ambient temperature detecting resistor having approximately the same characteristics as the heat sensitive coils, and a temperature difference setting resistor having approximately zero temperature coefficient. These resistors are connected in series to the heat sensitive coil. The circuits are connected to a control unit which controls differences between temperatures of the heat sensitive coils and ambient temperature to be approximately the same as a value set by the temperature difference setting resistor. A mass flow rate of the fluid through the conduit being measured by detecting a difference in amounts of energy supplied to the heat sensitive coils.

Abstract: A mass gas flow sensor for measuring the mass flow rate of a gas through a passage, and a method of manufacture thereof. The sensor includes a substrate having a streamlined end surface which is to project upstream in the passage, upstream and downstream heating resistors formed on the substrate, protective films covering the resistors, and circuitry for applying current to the resistors so as to heat the resistors, the gas cooling the upstream resistor more than the downstream resistor. The circuitry also produces an electrical voltage responsive to differences in voltage across the upstream and downstream resistors, corresponding to the mass gas flow in the passage.