2.2.3 Wind Direction Transducers

Many kinds of simple commutator type transducers utilize brush contacts to divide the wind direction into eight or 16 compass point sectors. However, these transducers do notprovide adequate resolution to characterize transport for most air quality modeling applications.

A fairly common transducer for air quality modeling applications is a 360° potentiometer. The voltage across the potentiometer varies directly with the wind direction. A commonly used solution to the discontinuity that occurs across the small gap in a single potentiometer is to place a second potentiometer 180° out of phase with the first one [5]. In this case the voltage output corresponds to a 0° to 540° scale. This transducer utilizes a voltage discriminator to switch between the "upper" and "lower" potentiometers at appropriate places on the scale. This technique eliminates chart "painting" which occurs on strip chart recorders when the wind oscillates across north (i.e., between 0° and full scale). A disadvantage is that chart resolution is reduced by one third.

Another type of transducer being used is a wind direction resolver, which is a variable phase transformer where the phase change is a function of the shaft rotation angle. This system alleviates the maintenance problems associated with the friction caused by the wiper in a potentiometer; however, this type of transducer is more expensive and requires more complex signal conditioning circuity.

2. PRIMARY METEOROLOGICAL VARIABLES 
 2.1 Wind Speed
      2.1.1 Cup Anemometers
      2.1.2 Vane-oriented and Fixed-mount Propeller Anemometers 
      2.1.3 Wind Speed Transducers 
  2.2 Wind Direction 
      2.2.1 Wind Vanes  
      2.2.2 U-V and UVW Systems  
      2.2.3 Wind Direction Transducers 
      2.2.4 Standard Deviation and Turbulence Data  
  2.3 Temperature and Temperature Difference 
      2.3.1 Classes of Temperature Sensors  
      2.3.2 Response Characteristics  
      2.3.3 Temperature Difference 
      2.3.4 Sources of Error 
  2.4 Humidity  
      2.4.1 Humidity Variables  
      2.4.2 Types of Instrumentation  
  2.5 Precipitation 
  2.6 Pressure  
  2.7 Radiation  
  2.8 Recommendations