Abstract: A fuel metering control system for an internal combustion engine having a plurality of cylinders. The system includes an air/fuel ratio sensor and engine operating condition detecting means for detecting engine operating conditions such as engine speed and engine load. The basic quantity of fuel injection is determined by retrieving mapped data according to the detected parameters. A plurality of controllers are provided all using outputs of the air/fuel ratio sensor. The controllers are configured to receive the sensor outputs through filters having different cutout frequency so as to avoid control interference therebetween.

Abstract: A method for measuring electron density n.sub.p of a plasma in a plasma reaction chamber for semiconductor fabrication processes is capable of an accurate measurement without time-drifting of measuring values and metal contamination to semiconductor wafers. The method comprises injecting electrons in the plasma to generate a plasma oscillation, getting a plasma oscillation frequency .omega..sub.p by antenna and frequency analyzer, and easily computing n.sub.p by a well-known formula using the value of .omega..sub.p. A plasma generating apparatus for semiconductor fabrication processes is capable of keeping the electron density in a plasma reaction chamber constant. The apparatus comprises feed-back circuits for feeding back a deviation signal of the computed (n.sub.p) from a presetting value to an RF oscillator or a gas control unit so as to control RF power or pressure of a source gas, respectively.