When hearing terms like humidity and relative humidity, people often think about the weather. This is because water vapor has an impact on how humans perceive comfort; both high humidity and low humidity can make people feel uncomfortable. You might already be aware that amount of water vapor present in air can impact how a medical device performs. Understanding how water vapor affects analysis is key when designing medical equipment.
What’s the Difference Between Humidity, Relative Humidity, & Dew Point?
Simply put, humidity is the amount of water vapor that is present in the air. Environmental conditions like temperature and pressure affect humidity. For instance, the warmer the air, the higher the amount of water vapor it can hold.
Relative humidity is the percentage of water vapor in the air compared to the maximum amount of water vapor air can hold at the given environmental condition. So, if the relative humidity is 50 percent, that means the air at that temperature and pressure could hold twice as much water vapor as it currently does. If the air were heated (keeping pressure constant), the relative humidity would go down.
Dew point is the atmospheric temperature below which water droplets condense and dew forms. Relative humidity is 100% when ambient temperature is the same as dew point. During the spring and summer, you’ll often hear weather forecasters talk about dew point. An easy way to understand dew point is to think about a spring day when the dew point is 50 degrees Fahrenheit. During the day, the sun keeps the air warmed to about 60 degrees Fahrenheit. At night the air cools. When the temperature reaches 50 degrees Fahrenheit, the air is saturated. When it falls below 50 degrees Fahrenheit, the water vapor condenses to form dew, or liquid water, on the lawn and other surfaces. As the morning sun reheats the air, the dew is reabsorbed into the air and the lawn dries.
What Measurement is Best When Designing Medical Devices?
Dew point is preferred over relative humidity when developing a design. This is because relative humidity fluctuates with temperature whereas dew point is an absolute measurement. For example, if a breath sample passes through a heated tube and is warmed up, the relative humidity changes, but the actual amount of water vapor in the air remains the same. If dew point is used to measure the breath sample, it remains the same, even as temperatures fluctuate.
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