The Elcometer 309 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 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%.

 

Features of the Elcometer 309 Delta T Hygrometer

• Rugged design: Suitable for use in extreme environments the Elcometer 309 is dustproof and waterproof with fully sealed sensors.
• High / Low Limits: Displayed on screen graphically as a tick or x with flashing Red or Green LEDs to indicate pass or fail.
• Delta T temperature: Delta T 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.

The Elcometer 309 Delta T Hygrometer can be used in accordance with:

• ISO 8502-4
• BS 7079-B4*

Standards not in bold have been superseded but are still recognised in some industries.

Elcometer 309 Delta T Hygrometer – Specifications

Part Number	Description	Certificate
G309—-1	Elcometer 309 Delta T Hygrometer	●
Operating Range	-20ºC to +80ºC
Air Temperature (TΔ)	-20ºC to +80ºC
Surface Temperature (TS)	-20ºC to +80ºC
Relative Humidity (RH) & Accuracy*	0% to 100% RH (±3%) (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
Weight	300g

* At 1m/s
● Basic Calibration Certificate supplied as standard.

Elcometer 309 Delta T Hygrometer – Data Sheet

Elcometer 309 Delta T Hygrometer Data Sheet

Elcometer 309 Delta T Hygrometer – Standards

The Elcometer 309 Delta T Hygrometer can be used in accordance with:

• ISO 8502-4
• BS 7079-B4*

Standards not in bold have been superseded but are still recognised in some industries.

Elcometer 309 Delta T Hygrometer – Accessories

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

Elcometer 309 Delta T Hygrometer – Video

If climatic conditions; such as surface temperature, air temperature, relative humidity, wet bulb temperature, dry bulb temperature, dewpoint temperature, and the Delta T; are wrong at the time of applying a coating, this could cause coating failure.

That’s why it’s vital to monitor a range of climatic parameters before and during the coating application process, to ensure your coating can have a successful service life.

So what climatic parameters do we measure, why do we measure them, and how?

Contents

0:00 – Introduction
0:50 – What climatic conditions do we measure?
1:48 – Why do we measure climatic conditions?
3:58 – How do we measure climatic conditions?
4:20 – How to use a Whirling Hygrometer / Sling Psychrometer
8:29 – Using a surface temperature thermometer
10:03 – Elcometer 319 Dewpoint Meter

The key climatic parameters include:

• Surface temperature (Ts), the temperature of the surface to be painted;
• Air temperature (Ta), the temperature of the air surrounding the surface to be painted;
• % Relative Humidity (RH), the amount of water vapour present in the air compared to the maximum possible, expressed as a percentage;
• Wet bulb temperature (Twb), the air temperature as read by a thermometer that’s covered in water-soaked fabric over which air is passed;
• Dry bulb temperature (Tdb), the temperature that is usually thought of as air temperature;
• Dewpoint (Td), the temperature at which moisture condenses on a surface, calculated from the air temperature and % Relative Humidity;
• And the Delta T (TΔ), the difference between the surface temperature (Ts) and the dewpoint temperature (Td).

While it’s important to monitor all of these parameters, special attention should be paid to surface temperature and relative humidity, as most paint data sheets will specify acceptable ranges of these parameters in which the paint can be applied.

However, by far the most important parameter of all is the Delta T, as it tells you the difference between the surface temperature and the dewpoint temperature. The smaller the difference, the more likely that moisture (or dew) will have condensed on the surface.

It is generally accepted within the industry that the Delta T should be at least 3°C or higher for the coating to be applied.

How do you actually measure and calculate the key climatic parameters? There are two main methods you can follow.

The traditional method requires multiple pieces of equipment to complete.

The first piece required is the whirling hygrometer, also known as a sling psychrometer, and it is used to measure the wet bulb and dry bulb temperatures. These temperatures are then used to work out the dewpoint and relative humidity. Elcometer provides two types of hygrometer, but they work in pretty much the same way.

Hygrometers consist of two liquid filled thermometers positioned side-by-side in a rotating body. One thermometer is covered with a fabric “sock” or “wick” connected to a reservoir (this measures your wet bulb temperature), while the other is uncovered (this measures your dry bulb temperature).

Once you have your results, typically conversion tables are then used to determine the relative humidity and dewpoint temperature, like the ones supplied with the Elcometer 116 Hygrometers. Alternatively, the Elcometer 114 Dewpoint Calculator provides a quick and easy way to determine these values, and we show you how it works in our Elcometer 114 video: https://youtu.be/HLbuapAnoqA

However you are still missing the all-important Delta T measurement, and to calculate this, you still need a surface temperature measurement – something a hygrometer can’t provide, meaning you’ll need a separate surface thermometer. Once you have your surface temperature, subtract your dewpoint temperature from it, and you have the Delta T.

However there is a quicker and simpler method, without sacrificing on accuracy.

The Elcometer 319 Dewpoint Meter is a digital gauge that can monitor and record all of the key climatic parameters simultaneously, telling you if conditions are suitable for painting. What’s more it can continuously monitor and log the conditions as you paint, and instantly alarm if one of the parameters falls outside of the specified range.