A psychrometer is an instrument used to measure relative humidity in the air. It consists of two thermometers: a dry-bulb thermometer and a wet-bulb thermometer. Here's how it works:
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Dry-Bulb Thermometer: This thermometer measures the ambient air temperature. It is exposed directly to the air.
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Wet-Bulb Thermometer: This thermometer has a cloth wick that is saturated with water, and it measures the temperature of the air after the water has evaporated. Evaporation causes a cooling effect, so the wet-bulb temperature will be lower than the dry-bulb temperature, particularly in drier conditions.
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Measurement Process:
- You first take the temperature reading from the dry-bulb thermometer.
- Then, you take the temperature reading from the wet-bulb thermometer after allowing time for evaporation to occur.
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Calculating Relative Humidity: The difference between the two temperatures (dry-bulb and wet-bulb) is used to determine the relative humidity. This is often done using a psychrometric chart or a mathematical formula. The greater the difference, the lower the humidity, because dry air allows more evaporation, leading to a lower wet-bulb temperature.
In summary, a psychrometer measures relative humidity by utilizing the cooling effect of evaporation on the wet-bulb thermometer compared to the temperature reading of the dry-bulb thermometer, and then calculating the humidity based on the temperature difference.
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