As the pressure of a system increases, the dew point temperature will rise and approach saturation. How does pressure affect dew point measurement?Ī. Only changes in pressure or the actual amount of water vapour present will affect the dewpoint. It is important to remember that dewpoint is independent of the ambient temperature. It is a common misconception that changes in temperature will affect the dewpoint. If the system temperature is at or below the dewpoint temperature in a closed system, the dew point will change because the water vapour is removed from the air. Dewpoint will not change as the system temperature changes below the saturation point. Does the dew point change when the system temperature changes?Ī. Some dewpoint sensors are highly sensitive to contamination in dirty process air causing frequent calibration and sensor maintenance. In some cases, dewpoint sensors can take several hours to settle where RH sensors may take only a few minutes. Dewpoint sensor reaction time is usually slower than relative humidity sensor reaction time. Dewpoint measurement technology is usually more expensive and more accurate than relative humidity measurement technology at low dewpoints. What are the pros and cons of measuring dew point versus relative humidity?Ī. The dewpoint changes with pressure which can create condensation in the compressed air system. Dewpoint is also ideal for compressed air systems because condensation is a concern as the air is compressed in the system. Most direct dewpoint measurement technologies are more suited to measuring very low amounts of moisture compared to relative humidity measurement technology. Dewpoint can be equated to the absolute amount of water vapour present as long as the air pressure remains constant. Dewpoint is also an ideal measurement for very dry conditions (<10% relative humidity). The alarm point for condensation, for example, can be set at a difference of 10 degrees between ambient temperature and dewpoint. It is fairly common to measure the difference between ambient temperature and the dew point temperature. Dewpoint is an ideal measurement when your goal is to avoid condensation or to know when condensation is about to occur. When should I choose dew point as the parameter I measure?Ī. The greater the difference between air temperature and dewpoint, the lower is the relative humidity. When the air temperature is equal to the dew point temperature, the air is at the saturation point and the relative humidity is 100%. Condensed water will appear as dew on a surface and may also appear as a cloud or fog suspended in the air. If the air temperature is equal to or below the dewpoint, water condensation will occur meaning water vapour will tranform from the vapour state into the liquid state. Dew point temperature is the temperature at which water vapour in any gas at constant pressure begins to condense into liquid water at the same rate as it evaporates.
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