• Hygrometer



ISO 8502-4, BS 7079-B4

  • Rugged design
  • High / Low Limits
  • Delta T Temperature: TΔ is pre-set at >3ºC (>5ºF), the industry norm

The Elcometer 309 digital Delta T Hygrometer provides a simple and fast measurement of Delta T temperature and relative humidity.

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.



T99921192 Protective Carry Case / Pouch
T99921325 USB Cable
T99916063 Wrist Strap
TCAL-309F Optional Full Calibration Certificate
G309----1 Elcometer 309 Delta T Hygrometer
Temperature Range (Air & Surface) -20 to +80ºC (-4 to +176ºF)
Relative Humidity (RH) Range 0 to 100%RH (Default upper limit 75%, user adjustable)
Resolution 0.1ºC / 0.1%
Power Supply 2 x AA 1.5V Batteries or via USB Cable
Battery Life Greater than 40 hours (Backlight off)
Dimensions 180 x 75 x 35mm (7 x 3 x 1.4”)
Weight 300g (10.6oz)
Certificate available Certificate of Calibration: issued for Fixed Calibration equipment and shows readings and traceability
Packing List Elcometer 309 Delta T Hygrometer, wrist strap, 2 x AA batteries, protective pouch with belt clip, RH probe calibration certificate and operating instructions