Apparatus for measuring the mass of a flowing medium

An apparatus for measuring the mass of a flowing medium, such as the intake air mass to an internal combustion engine comprising:

• a tubular member having an inner surface which defines a flow cross section of the flowing medium,
• a mounting aperture,
• an insert element which is plugged into the mounting aperture and mounted to the tubular member,
• a probe ring mounted to the insert element and arranged within the flow cross section,
• a bridge circuit including at least two resistors supported within the probe ring so that they are exposed to the flowing medium, one of said resistors being embodied as a hot wire, a parameter of which is controlled in dependence on the mass of the flowing medium,
• a multiple contact plug connected to the tubular member which connects the bridge circuit to a source of D.C. voltage and from which the parameter control is detected,
• a terminal box mounted to the tubular member,
• a mounting board mounted within the terminal box to the insert element,
• an electrical control circuit mounted to the mounting board,
• a printed circuit board having minimal conductive paths,
• (i) the extent to which the controlled parameter of said one of said resistors is controlled being a measure of the mass of the flowing medium and
• (ii) the electrical control circuit being connected by the printed circuit board to the multiple contact plug and to the bridge circuit,
• (iii) the electrical control circuit comprising a hybrid switching circuit,
• a frame,
• (iv) the frame being arranged between the mounting board and the printed circuit board, and includes perforations which taper in the direction toward the printed circuit board, and
• (v) the bridge circuit, the hybrid switching circuit and the multiple contact plug each including contacts, said contacts extending through the perforations in said frame.