2.3.1 Classes of Temperature Sensors

Sensors used for monitoring ambient temperature include: 

• wire bobbins

• thermocouples

• thermistors

Platinum resistance temperature detectors (RTD) are among the more popular sensors used in ambient monitoring; these sensors provide accurate measurements and maintain a stable calibration over a wide temperature range. The RTD operates on the basis of the resistance changes of certain metals, usually platinum or copper, as a function of temperature. These two metals are the most commonly used because they show a fairly linear increase of resistance with rising temperature [5].

Three wire" and "four wire" RTDs are commonly used to compensate for lead resistance errors. A second type of resistance change thermometer is the thermistor, which is made from a mixture of metallic oxides fused together. The thermistor generally gives a larger resistance change with temperature than the RTD. Because the relation between resistance and temperature for a thermistor is non-linear, systems generally are esigned to use a combination of two or more thermistors and fixed resistors to produce a nearly linear response over a specific temperature range [5, 8].

Thermoelectric sensors work on the principle of a temperature dependent electrical current flow between two dissimilar metals. Such sensors, called thermocouples, have some special handling requirements for installation in order to avoid induction currents from nearby AC sources, which can cause errors in measurement [5]. Thermocouples are also susceptible to spurious voltages caused by moisture. For these reasons, their usefulness for routine field measurements is limited.

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