Delta T (TΔ) is the difference between the surface temperature (Ts) and the dewpoint temperature (Td). When TΔ is less than 3ºC (5ºF) painting should not occur.

Relative Humidity (RH) - expressed as a percentage, RH is the ratio of the amount of water vapour actually held by the air compared to the maximum amount of water vapour the air could hold at a given temperature.  Typical maximum RH values specified by paint manufacturers are between 75% and 85%.

The Elcometer 309 Delta T Hygrometer key features include:

• Rugged design: Suitable for use in extreme environments the Elcometer 309 digital hygrometer is dustproof and waterproof with fully sealed sensors.
• High / Low Limits: Displayed on screen graphically as either (?) or (X) with flashing Red or Green LED’s to indicate pass or fail.
  • Delta T Temperature: TΔ is pre-set at >3ºC (>5ºF), the industry norm.
  • Relative Humidity: User definable upper limit can be set for RH.
• Measurement Hold / Release function: With a single button press readings are frozen on the screen.  These can then be recorded before, simply pressing the button again to unfreeze the screen and then take further readings as necessary.
• Backlight: Provides clearly lit information – ideal in dark or confined spaces.