Temperature and Measurement Overview

Temperature Conversions

• Celsius to Fahrenheit: $(x0C imes rac{9}{5}) + 32$

• Fahrenheit to Celsius: $(x0F - 32) imes rac{5}{9}$

• Celsius to Kelvin: $K = C + 273$

• Key Temperatures: 0°C/32°F (freezes), 100°C/212°F (boils), -273°C (absolute zero)

Psychrometry

• Dry Bulb Temperature (DBT): Air temperature measured by a thermometer shielded from direct radiation.

• Wet Bulb Temperature (WBT): Lowest temperature air can be cooled by evaporation; indicates moisture content.

• Dew Point Temperature (DPT): Temperature at which air becomes saturated and condensation occurs.

• Relation: DBT and WBT are used to derive Relative Humidity (RH) and DPT.

Dew Point Temperature Characteristics

• DPT indicates condensation into visible moisture (clouds, fog).

• At RH of 100%, $DBT = WBT = DPT$

Measuring Temperature

• Types of Thermometers:

  • Liquid in Glass: Expansion of mercury/alcohol measures temperature.

  • Liquid in Metal: Pressure increase from liquid expansion measures temperature.

  • Thermocouple: Voltage generated from joint heating of two metals.

  • Bimetallic: Expansion of two bonded metals indicates temperature change.

  • Platinum: Resistance change in platinum wire measures temperature.

  • Thermistors: Change in resistance reflects temperature variations.

Recording Instruments

• Thermograph: Records temperature changes over time.

• Hygrograph: Records humidity changes over time.

Stevenson Screen

• Measures and houses instruments for DBT, WBT, and relative humidity.

• Instruments: Thermograph, Hygrograph, Barometer.

• Designed to shield instruments from solar radiation, giving accurate outdoor temperature readings (OAT).