Figure 20. Wind speed and direction gages. 



The accuracy of the speed transmitter and indicator assemblies is ±1 knot 

 from 2- to 100-knot winds and ±2 knots for 100- to 200-knot winds at 20° to 

 25 Celsius. The wind-direction transmitter and indicator assemblies are ac- 

 curate to ±5° at an airspeed of 5 knots or greater for any horizontal direction 

 at 20° to 25° Celsius. 



The wind- direction transmitter assembly includes a direction transmitter 

 body and a spread-tail wind vane. The transmitter body consists of a 12-volt 

 (direct current) synchro transmitter coupled to the wind-vane shaft. The mo- 

 ment of inertia of the vane is approximately 583,000 gram-centimeters squared. 

 The synchro transmitting element gives a minimum resistance to the electrical 

 current when the vane is directed to due north and increases the resistance as 

 the vane turns away from north. Two potentiometers are used to determine which 

 direction the vane has turned with respect to north. 



The windspeed transmitter includes a windspeed transmitter body and a 

 cup rotor. A direct-current magneto is coupled to the cup rotor and provides 

 a voltage-versus revolution-per-minute ratio of 0.004007 with an electrical 

 load of 428.6 ohms. The terminal resistance of the magneto is 40 ohms ±1 ohm; 

 the moment of inertia of the cup rotor and magneto armature is 70,700 gram- 

 centimeters squared (maximum) . National Weather Service (1979) provides addi- 

 tional details on the wind measuring system. In late 1979, an analogue recorder 

 was installed to provide continuous records of the wind speed and direction. 



24 



