Operating Principle:

The operating principle of a hair tension hygrometer is based on the hygroscopic properties of human or animal hair. As humidity changes, the hair expands or contracts, causing a mechanical mechanism to move, which is then translated into a measurement of relative humidity.

• Advantage: Provides continuous relative humidity readings.

• Disadvantage: Slow response time in extremely humid environments.

• Uncertainty: Errors when exposed to rapid changes in humidity.

Operating Principle:

A psychrometer measures relative humidity by comparing the readings of two thermometers, one with a dry bulb and the other with a wet bulb. Evaporation from the wet bulb causes cooling, and the extent of cooling depends on the moisture content of the air. By comparing the temperature readings from both bulbs, the relative humidity can be determined using psychrometric tables or equations. 

• Advantage: Easy for field and experimental use

• Disadvantage: It is fragile and requires careful handling

• Uncertainty: Operator slinging technique can bring a variability in results

Operating Principle:

A dew point meter uses a mirror surface that cools down until dew forms on it. The temperature at which the dew forms is measured, providing the dew point temperature.

• Advantage: Can accurately measure the moisture content of air directly of a variety of gases

• Disadvantage: Sensitive to environmental factors like contaminants in the air.

• Uncertainty: Errors when exposed to rapid changes in moisture content levels.