The Elcometer 309 Delta T Hygrometer (part number G309) provides a simple and fast measurement of Delta T temperature and relative humidity, the two climatic parameters that most directly determine whether a surface is fit to paint.

Delta T is the difference between the surface temperature and the dewpoint temperature. When that difference is too small, moisture is likely to condense on the surface, and applying a coating in those conditions can cause it to fail. The Elcometer 309 Delta T Hygrometer pre-sets the Delta T limit at greater than 3 degrees C (greater than 5 degrees F), the industry norm, and lets the user define an upper limit for relative humidity, which defaults to 75% and is adjustable. Paint manufacturers typically specify maximum RH values between 75% and 85%. High and low limits are shown graphically on screen as a tick or a cross, with flashing red or green LEDs giving an immediate pass or fail.

The Elcometer 309 Delta T Hygrometer reads air and surface temperature from -20 to +80 degrees C and relative humidity from 0% to 100% RH to an accuracy of plus or minus 3%, with a resolution of 0.1 degrees C and 0.1%. A hold and release function freezes readings on screen for recording, and a backlight aids use in dark or confined spaces. The dustproof and waterproof body of the Elcometer 309 Delta T Hygrometer, with fully sealed sensors, suits extreme environments. It runs from two AA batteries or USB, with battery life over 40 hours, measures 180 x 75 x 35mm and weighs 300g.

The Elcometer 309 Delta T Hygrometer can be used in accordance with ISO 8502-4 and BS 7079-B4, the standards covering surface condensation and dewpoint assessment before coating. The Elcometer 309 Delta T Hygrometer is used by coatings inspectors in protective coating, marine and industrial painting work, and is supplied by BAMR, South Africa's authorised Elcometer distributor.