Text-only reference. Published from the recorded official FAA General Chapter 12 PDF. Diagrams, photographs, and figure artwork are not reproduced here; use the official FAA PDF for those materials.
12-125 A F B NAND gate A (1) (0) (1) F B A F B Equivalent circuit NAND gate input/output 0 1 0 NAND gate input/output NAND gate truth table 0 1 0 1 0 1 A 0 1 0 1 B 0 1 f 1 0 OR gate input/output Truth table A f = A + B B A 0 1 0 1 B 0 1 f 0 1 Door unsafe Door warn Light on Cabin door not secured Baggage door secured+28 VDC Door unsafe Door warn Light off Cabin door secured Baggage door secured+28 VDC is plotted, the curve shown in Figure 12-273 results. This voltage is called an alternating voltage because of its reversal from positive to negative value, first in one direction and then in the other.
To use the voltage generated in the loop for producing a current flow in an external circuit, some means must be provided to connect the loop of wire in series with the external circuit. Such an electrical connection can be effected by opening the loop of wire and connecting its two ends to two metal rings, called slip rings, against which two metal or carbon brushes ride. The brushes are connected to the external circuit. By replacing the slip rings of the basic AC generator with two half cylinders, called a commutator, a basic DC generator is obtained. [Figure 12-274] In this illustration, the black side of the coil is connected to the black segment, and the white side of the coil to the white segment. The segments are insulated from each other. The two stationary brushes are placed on opposite sides of the commutator and are so mounted that each brush contacts each segment of the commutator as the latter revolves simultaneously with the loop. The rotating parts of a DC generator (coil and commutator) are called an armature.
The generation of an emf by the loop rotating in the magnetic field is the same for both AC and DC generators, but the action of the commutator produces a DC voltage. Generation of a DC Voltage manner, how a DC voltage is generated. This is accomplished by showing a single wire loop rotating through a series of positions within a magnetic field. Position A The loop starts in position A and is rotating clockwise. However, no lines of force are cut by the coil sides, which means that no emf is generated. The black brush is shown coming into contact with the black segment of the commutator, and the white brush is just coming into contact with the white segment.
12-126 X-NOR gate input/output Truth table A f = A + B 0f 0 0 B T0 T1 T2 T3 T4 1 A 0 1 B 0 1 0 1 f 1 0 1 0 A 1 0 T0 T1 T2 T3 T4 1 0 B 0 1 1 X-OR gate input/output Truth table A f 0 f 1 0 0 B T0 T1 T2 T3 T4 T5 1 A 0 1 B 0 1 0 1 f 0 1 0 A 1 0 0 T0 T1 T2 T3 T4 T4 1 0 B 0 0 1 1 NOR gate input/output NOR gate truth table 0 1 0 1 A 0 1 B 0 1 0 1 f 1 0 1 0 1 0 1 table. Position B In position B, the flux is now being cut at a maximum rate, which means that the induced emf is maximum. At this time, the black brush is contacting the black segment, and the white brush is contacting the white segment. The deflection of the meter is toward the right, indicating the polarity of the output voltage.
Position C At position C, the loop has completed 180° of rotation. Like position A, no flux lines are being cut and the output voltage is zero. The important condition to observe at position C is the action of the segments and brushes. The black brush at the 180° angle is contacting both black and white segments on one side of the commutator, and the white brush is contacting both segments on the other side of the commutator. After the 12-127 Typical integrated logic circuit 0.280" max 0.200" max 0.785" max 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 4Y 4A 4B GND 3A 3B 3Y 1Y 1A 1B VCC 2A 2B 2Y 14 13 12 11 10 9 8 1 2 3 4 5 6 7 Quad exclusive-OR circuit Input Output A 0 1 Y 0 1 0 B 0 1 0 1 1Q 2Q 2Q Enable Gnd 3Q 3Q 4Q 1Q 1D 2D Enable Vcc 3D 4D 4Q 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 DQ G Q QD Q G DQ G Q QD Q G D-register loop rotates slightly past the 180° point, the black brush is contacting only the white segment, and the white brush is contacting only the black segment.
Because of this switching of commutator elements, the black brush is always in contact with the coil side moving downward, and the white brush is always in contact with the coil side moving upward. Though the current actually reverses its direction in the loop in exactly the same way as in the AC generator, commutator action causes the current to flow always in the same direction through the external circuit or meter. Position D At position D, commutator action reverses the current in the external circuit, and the second half cycle has the same waveform as the first half cycle. The process of commutation is sometimes called rectification, since rectification is the converting of AC voltage to DC voltage.
The Neutral Plane At the instant that each brush is contacting two segments on the commutator [Figure 12-275A, C, and E], a direct short circuit is produced. If an emf were generated in the loop at this time, a high current would flow in the circuit, causing an arc and thus damaging the commutator. For this reason, the brushes must be placed in the exact position where the short occurs when the generated emf is zero. This position is called the neutral plane. If the brushes are installed properly, no sparking occurs between the brushes and the commutator. Sparking is an indication of improper brush placement, which is the main cause of improper commutation.
The voltage generated by the basic DC generator in for each revolution of the loop. This variation of DC voltage is called “ripple,” and may be reduced by using more loops, or coils, as shown in Figure 12-276A. As the number of loops is increased, the variation between maximum and minimum values of voltage is reduced [Figure 12-276B], and the output voltage of the generator approaches a steady DC value. In increased in direct proportion to the number of loops; that