时间：2011-03-11 23:11来源：蓝天飞行翻译 作者：admin 点击：次
|
capacitance afterfiring (reciprocating engines). The continuation of the spark across the gap in a shielded spark plug after the fuel-air mixture in the cylinder is ignited. Capacitance afterfiring is caused by the return of electrical energy stored in the capacitance of the shielded ignition leads. Capacitance afterfiring is eliminated by installing a resistor inside the spark plug. capacitance box. A piece of electrical test equipment made up of a number of capacitors and selector switches. Any amount of capacitance needed in a circuit can be selected on the switches and the capacitance box inserted into the circuit where the capacitance is needed. capacitance bridge. A piece of precision electrical test equipment used to measure capacitance. The bridge measures the capacitance of an unknown capacitor by comparing its capacitive reactance with that produced by a known value of capacitance. capacitance-type fuel quantity indicating system. A type of fuel quantity indicating system that shows the amount of fuel in the tanks of an aircraft. The sending units (probes) inside the fuel tank are cylindrical capacitors made of two concentric metal tubes. These probes, connected in parallel, reach across the tank from top to bottom. When the tank is full of fuel, the fuel acts as the dielectric, but when the tank is empty, air is the dielectric. The capacitance of a capacitor is directly proportional to the dielectric constant (k) of the material between its plates. Air has a k of one, and the fuel has a k of approximately two, depending upon its temperature and thus its density. The system contains an automatic balancing capacitance bridge and an indicator. The bridge measures the capacitance of the tank probes, which varies directly with the amount of fuel in the tanks. The capacitance is converted into terms of pounds of fuel in the tanks, and this is shown on the indicator. capacitive coupling (electronic circuit). A method of joining stages of electronic circuits with capacitors. Capacitors isolate the stages with regard to DC, but allow them to operate at the same AC potential. capacitive feedback (electronic circuit). A process in which part of the energy in the output of an electronic circuit is fed back to the input through a capacitor. capacitive load (electrical circuit). An electrical load that produces more capacitive reactance than inductive reactance in the circuit. Current leads the voltage in a capacitive load. capacitive reactance. Opposition to the flow of alternating current caused by capacitance in the circuit. Capacitive reactance, whose symbol is XC, is measured in ohms and is determined by the capacitance in the circuit and the frequency of the AC. The formula for capacitive reactance is: XC = 1 / (2π f C) XC = Capacitive reactance in ohms 2π = A constant, 6.28 f = Frequency of the AC in hertz C = Capacitance in farads capacitive time constant. The amount of time, measured in seconds, needed for the voltage across a capacitor to rise to 63.2% of the source voltage. The time constant is determined by the resistance and the capacitance of the circuit. |
