The environmental conditions during pre-treatment and application of a coating system are major factors affecting the long-term performance of coatings on steel structures. Dew Point Meters can be used to monitor environmental conditions before, during, and after painting. Ideal for surface preparation as required by ISO 8502-4, an electronic Dew Point Meter determines the likelihood of dew forming on structures which are being painted.
DeFelsko offers three types of meters to measure environmental conditions: dew point meters, wind speed sensors, and infrared thermometers.
Conforms to ISO 8502-4, BS 7079-B4, ASTM D3276, IMO PSPC, SSPC-PA7, US Navy NSI 009-32, and Navy NAVSEA 009-32
Depending on the model selected, PosiTector DPM Dew Point Meters measure and record climatic conditions including: relative humidity (%RH), air temperature, surface temperature, dew point temperature, the difference between surface and dew point temperatures (Delta), wind speed, and wet bulb temperature.
Available options:
Conforms to ISO 8502-4, BS 7079-B4, ASTM D3276, IMO PSPC, SSPC-PA7, US Navy NSI 009-32, and Navy NAVSEA 009-32.
The PosiTector DPM L and DPM L+ Dew Point Meter Loggers attach to steel structures to measure and record environmental parameters independently for up to 200 days (DPM L) or 600 days (DPM L+). Stored readings can be downloaded using the PosiTector App (iOS/Android).
Conforms to ISO 8502-4, BS 7079-B4, ASTM D3276, IMO PSPC, SSPC-PA7 and US Navy NSI009-32.
The PosiTector IRT non-contact Infrared Thermometer measures surface temperatures in areas where conventional sensors will not work including hard to reach areas, moving parts, freshly sprayed powder coating, and objects whose temperatures are above the range of direct contact sensors.
A Dew Point Meter measures and records climatic conditions including: relative humidity (%RH), air temperature, surface temperature, dew point temperature, the difference between surface and dew point temperatures (Delta), and wet bulb temperatures.
Environmental conditions are monitored and recorded using handheld, portable Dew Point Meters during surface preparation, application, and cure of paints and coatings. Doing so allows paint and coatings applicators to determine when optimal environmental conditions are met—greatly reducing the likelihood of costly reworks and premature failure of the coating or paint systems.
Read "Measuring Outdoor Climatic Conditions" for more information.
Relative Humidity is the amount of moisture in the air expressed as a percent of overall volume. High relative humidity can retard the rate of solvent evaporation.
Traditionally, relative humidity (RH) was calculated using the wet and dry bulb temperature measurements taken from a sling psychrometer (whirling hygrometer). 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. 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. 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. From there, the results were compared to those obtained from a surface temperature thermometer.
Convenient, modern electronic dew point meters have simplified humidity and temperature measurements negating the need for complex lookup tables or slide rule calculators. 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.
The multipurpose PosiTector DPM Dew Point Meter is ideal for continuous measurement of air temperature, surface temperature, and percent relative humidity.
Dew point (dewpoint) is the temperature at which moisture will begin to form on a surface. 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.
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. 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°F or 3°C above the dew point during the 3 critical phases of painting—surface preparation, coating application, and the cure cycle.
Traditionally, dew point was calculated using a sling psychrometer and complex look-up tables or psychometric slide-rule calculators. Sling psychrometers are limited since they are subject to interpolation errors, cannot be used for continuous monitoring, and do not offer memory storage.
Chilled mirror hygrometers measure dew point using a chilled mirror, light beam, and light detector. As the air is cooled, dew would form on the mirror, blocking the light, and indicating that the air has reached the dew point. 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.
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. Some meters calculate dew point only, but the more practical instruments include a surface temperature probe. Surface temperature probes (sensors) allow the users to calculate and display the important delta value—the difference between the surface and dew point temperatures.
There are four key decisions when selecting a dew point meter:
First, it is important to identify the environmental parameters that need to be monitored. Generally, the surface, air, and wet bulb temperatures; relative humidity; and dew point temperature can be measured or calculated. Some dew point meters, such as the PosiTector DPM will be able to calculate Delta as well. Measuring surface temperature is critically important since it is the substrate temperature that determines whether or not moisture will form on the 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.
Second, if there is a surface or part that needs to be monitored, consider how easy it will be able to access that surface. Will it be too hot for conventional surface temperature sensors? Out of reach? Dew point meters equipped with an infrared surface temperature sensor, such as the PosiTector DPM IR can accomplish this measurement while still measuring and calculating other parameters.
Third, do the environmental conditions need to be monitored over a period of time or would instantaneous measurements suffice? All PosiTector DPM models measure instantly and also feature Auto Log mode for continuous measurement. Advanced models feature an enhanced Auto Log mode that turns the instrument off between readings for up to 8 months of battery life. The PosiTector DPM L and PosiTector DPM L+ are specifically designed for autonomous monitoring. The PosiTector DPM L features battery life of up to 200 days while the PosiTector DPM L+ features battery life of up to 600 days. The PosiTector DPM L+ automatically sends readings directly to the cloud-based PosiSoft.net via WiFi allowing jobsite conditions to be remotely monitored from any location in the world.
Finally, are there memory and/or reporting requirements? All PosiTector DPM Standard models can store up to 2,500 datasets. All PosiTector DPM Advanced models can store up to 250,000 datasets or 1,000 batches. The PosiTector DPM L Dew Point Meter Logger can store up to 10,000 datasets (60,000 readings). Software solutions are available for viewing, analyzing, and reporting data.
Depending on which PosiTector DPM model is selected, a dataset can consist of five or more of the environmental parameters below.
Standard models feature storage of 2,500 datasets.
Advanced models can store up to 250,000 datasets.
The PosiTector DPM L can store up to 10,000 datasets.
RH — Relative Humidity: the amount of moisture in the air expressed as a percent of overall volume
Ta — Air Temperature: the temperature of the air
Ts — Surface Temperature: the temperature of a surface
V — Wind Velocity: the speed at which the air is moving (PosiTector DPM A only)
Td — Dew Point Temperature: the temperature at which moisture will begin to form on a surface
Ts–Td —Delta: the difference between surface and dew point temperatures
Tw — Wet Bulb Temperature
For more information on environmental parameters, read our "Measuring Environmental Conditions" article.
*Dependent on model
