Abstract: A conductivity sensor (16) and control circuit (18) for determining the conductivity of a fluid is provided. Conductivity sensor (16) is formed of a first annular electrode (24) spaced apart from a second annular electrode (26) having a tubular portion (28) therebetween. The first annular electrode (24) and the second annular electrode (26) are coupled to a control circuit (18). The control circuit (18) preferably includes a square wave generating circuit (40), a current-to-voltage converter circuit (42) coupled to one of the electrodes, a buffer circuit (44) coupled to the other one of the electrodes, a synchronous detector circuit (46). The synchronous detector circuit (46) is operated using the square wave from square wave generator circuit (40). By oscillating between a negative and positive gain, a constant direct current output corresponding to the conductivity of the fluid between the first annular electrode and second annular electrode is provided.

Abstract: An apparatus (1) for measuring the amount of air entrained in the fluid of a power steering pump. The apparatus includes a fluid conduit (3) having a connector (4) adapted to connect to a power steering pump (2) with the fluid conduit (3) in fluid communication with the internal fluid cavity (5) of the power steering pump (2). A pressure gauge (6) is operatively connected to the fluid conduit (3) for determining the pressure in the power steering pump (2), and a meter (7) is operatively connected to the fluid conduit (3) for measuring the rate at which mass is removed from the power steering pump (2). The apparatus further includes a vacuum pump (8) operatively connected with the fluid conduit (3) for drawing air out of the power steering pump (2).

Abstract: A method and apparatus for controlling air/fuel ratio of an internal combustion engine at a desired level of richness or leanness utilizes an existing air flow sensor for sensing air flow into the engine and generating a corresponding air flow signal. A signal multiplier multiplies the air flow signal by a constant to generate a modified air flow signal corresponding to the desired level of richness or leanness. A control signal is then generated for controlling the air/fuel ratio to the desired level.