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 B.  The rotor has poles, or lobes, extending outward from its outer circumference. The stator has an equal number of lobes extending inward. The stator also has a coil around it, which is connected to a controlled source of dc power. When the stator coil is energized, the stator becomes an electromagnet. When the wheel is turning, the lobes on the rotor pass by the lobes on the stator, thus changing the distance between them. The change in distance causes a change in the magnetic field of the stator because of the variation of magnetic coupling (magnetic reluctance) between the stator and the rotor. This change in magnetic field generates in the stator coil an ac voltage which is superimposed on the controlled dc energizing voltage. The frequency of the generated voltage is directly proportional to the rotational speed of the wheel. This ac signal is fed into the antiskid control unit.
 C.  The transducer produces a sine wave having 150 pulses for one complete rotation of the wheel. The ac signal ranges from an output of 1.5 volts minimum at 150 Hz to an output of 3.0 volts minimum at 5000 Hz.
Antiskid Control Unit (Fig. 1)
_____________________
 A.  The antiskid control unit is located in the electrical/electronic equipment compartment. It contains all the circuits necessary for antiskid control and autobrake functions. The antiskid control unit contains printed circuits; two dual main wheel control circuits and built-in test circuits, a digital autobrake circuit and a multilayer interconnect circuit. Circuitry includes individual wheel control in normal antiskid mode. Alternate antiskid circuitry controls the wheels in pairs.
 B.  Built-in-test features incorporate continuous monitoring of antiskid valve and transducer circuits and their interfaces. The antiskid control unit front panel includes antiskid system fault isolation provision and an autobrake test capability in the form of test switches and lights to assist in trouble shooting the antiskid system.
Antiskid Control Valve (Fig. 2)
______________________
 A.  The antiskid control valve is an electrically controlled hydraulic valve which will reduce metered pressure supplied to the brakes when provided with a signal from the control unit. The amount of pressure reduction is proportional to the control current provided. Each control valve consists of an electrically controlled 1st-stage or servo valve, and a hydraulically controlled 2nd-stage spool valve. Each of the normal antiskid control valves operates independently of the other to control the brake on one wheel. An alternate antiskid control valve controls paired wheels of each main gear.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 6.  Air-Ground Sensors (Fig. 3)
__________________
 A.  Air-ground sensors are located in the right main gear wheel well and the nose gear torsion link to provide brake release signals to the antiskid control unit for touchdown protection during landing. Main gear sensing acts on inboard wheels and the nose gear sensing acts on outboard wheels.
 7.  Landing Gear Lever Up Switch
____________________________
 A.  The landing gear lever up switch is located in the lower nose section forward of the nose wheel well. It is a two pole switch actuated by a cam fastened to the landing gear lever control cable.
 (1)  
One pole of the switch disables the alternate antiskid portion of the antiskid system during the retraction cycle of the landing gear to allow positive braking action. Disabling prevents antiskid system from sensing a skid and signalling brake release.

 (2)  
The second pole opens the circuit which senses pressurization of the alternate brake system to prevent a false antiskid inoperative condition to be registered as landing gear is retracted.

TORQUE MOTOR BIAS SPRING PLATE
FEEDBACK
CHAMBER

CHECK VALVE
FILTER (2 PLACES) MAGNET
1ST STAGE VALVE
(FLAPPER)

FILTER
BIAS SPRING
2ND STAGE VALVE
PRESSURE BRAKE RETURN (SPOOL VALVE) Antiskid Control Valve Schematic
Figure 2
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