Second, if there is a surface or part that needs to be monitored, consider how easy it will be able to access that surface. Surface and Ambient temperatures can vary dramatically due to factors such as direct sun, shade, and even the shape and mass of the structure. ![]() Measuring surface temperature is critically important since it is the substrate temperature that determines whether or not moisture will form on the surface. Some dew point meters, such as the PosiTector DPM will be able to calculate Delta as well. Generally, the surface, air, and wet bulb temperatures relative humidity and dew point temperature can be measured or calculated. There are four key decisions when selecting a dew point meter:įirst, it is important to identify the environmental parameters that need to be monitored. Which Dew Point Meter is right for my application? Surface temperature probes (sensors) allow the users to calculate and display the important delta value-the difference between the surface and dew point temperatures. Some meters calculate dew point only, but the more practical instruments include a surface temperature probe. Modern dew point meters such as the PosiTector DPM can immediately calculate dew point by measuring surface temperature and relative humidity using precision temperature and humidity sensors. While this technique worked well in a laboratory environment, it was less effective for the steel structure painting industry due to their bulk, fragility, and cost. As the air is cooled, dew would form on the mirror, blocking the light, and indicating that the air has reached the dew point. Sling psychrometers are limited since they are subject to interpolation errors, cannot be used for continuous monitoring, and do not offer memory storage.Ĭhilled mirror hygrometers measure dew point using a chilled mirror, light beam, and light detector. Traditionally, dew point was calculated using a sling psychrometer and complex look-up tables or psychometric slide-rule calculators. To ensure optimal performance of the coating system, ISO 8502-4 and SSPC guidelines recommend that the surface temperature must be a minimum of 5☏ or 3☌ above the dew point during the 3 critical phases of painting-surface preparation, coating application, and the cure cycle. Undiscovered condensation on freshly blasted steel may result in flash rusting and premature coating failure if a thin, invisible film of moisture is trapped between the coating and the substrate. Dew point is a function of air temperature and relative humidity and is described as the temperature to which a volume of air must be cooled in order to reach saturation. The multipurpose PosiTector DPM Dew Point Meter is ideal for continuous measurement of air temperature, surface temperature, and percent relative humidity.ĭew point (dewpoint) is the temperature at which moisture will begin to form on a surface. Multifunctional dew point meters have the ability to take immediate and continuous readings of all relevant environmental parameters that are less subject to operator interpretation and measurement errors, as well as calculation and rounding errors associated with the use of lookup tables. From there, the results were compared to those obtained from a surface temperature thermometer.Ĭonvenient, modern electronic dew point meters have simplified humidity and temperature measurements negating the need for complex lookup tables or slide rule calculators. After the appropriate amount of time, both bulbs are measured and the results are converted to humidity measurements using psychometric tables, graphs, or slide rules. Sling psychrometers are whirled rapidly for 90 seconds causing the liquid water to evaporate and for the wet bulb to read lower than the dry bulb. ![]() Sling psychrometers consist of two thermometers called dry bulb and wet bulb with the latter being covered in a wet sock (wick) saturated with water. Traditionally, relative humidity (RH) was calculated using the wet and dry bulb temperature measurements taken from a sling psychrometer (whirling hygrometer). High relative humidity can retard the rate of solvent evaporation. Relative Humidity is the amount of moisture in the air expressed as a percent of overall volume.
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