Product Description
Technical Specification
Instruction Manual
Data Sheet

Elcometer 309 Delta T Hygrometer

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.
Elcometer 309 Digital Hygrometer
Elcometer 309 Delta T Hygrometer

Technical Specification

Part Number Description Certificate
G309----1 Elcometer 309 Delta T Hygrometer

Operating Range

-20ºC to +80ºC (-4 ºF to +176ºF)


Air Temperature (TΔ)

-20ºC to +80ºC (-4 ºF to +176ºF)


Surface Temperature (TS)

-20ºC to +80ºC (-4 ºF to +176ºF)


Relative Humidity (RH) & Accuracy*

0% to 100% RH (±3%) (Default upper limit 75%, user adjustable)


0.1ºC (0.1ºF) / 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)  
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  


BS 7079-B4, ISO 8502-4


* At 1m/s 

 Basic Calibration Certificate supplied as standard.


Part Number Description
T99921192 Protective Carry Case / Pouch
T99921325 USB Cable
T99916063 Wrist Strap
TCAL-309F Optional Full Calibration Certificate


Climatic Conditions

An Introduction to Climatic Testing

When it comes to applying a coating; whether in a shipyard, in a construction yard, or even in a warehouse; even if you have successfully controlled and monitored the surface cleanliness, surface profile, and both the wet and dry film thickness, if the climatic conditions are wrong at the time of application, this could cause the coating to fail – regardless of the success of the other parameters.

Click here to download the video script in English.