TPT March 2011

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94 March 2011 ›
Inspection, Testing & Q uality Control
AIR has the capacity to hold a certain
amount of moisture as vapour, depending
on the temperature. Relative humidity is
the proportion of moisture in the air at a
given temperature, as a percentage of the
maximum amount that can be held by the
air at that temperature. As air cools, the
capacity to hold moisture is reduced and the
relative humidity in the air will increase until
the moisture starts to condense out of the
air on to surrounding cold surfaces.
The dewpoint is the temperature at
which condensation occurs for air with a
given relative humidity. If the air can be
cooled to the dewpoint then the moisture will
condense out of the air. More importantly if
there is a cold surface at or below the
dewpoint temperature the moisture will
condense on that surface as a thin film of
water molecules.
When applying paint it is vital that the
substrate is not only clean but also dry
in order to achieve the service life of the
coating system. The rule of thumb used
in the protective coatings industry is that
the surface temperature must be at least
3°C above the dewpoint temperature for
the surface to be free of moisture from the
surrounding air.
The monitoring of climatic conditions
should not be limited to determining if it is
“OK to paint”; changes in temperatures and
humidity during the cure process can result
Why measure the climatic conditions?
in changes to the recoat time and/or defects
in the finished film.
The Elcometer 319 Digital Dewpoint
meter has been designed to determine if the
climatic conditions are appropriate to paint
and to monitor the climatic conditions during
the cure process.
These rugged Dewpoint meters
quickly and accurately measure relative
humidity (RH %), air temperature (Ta) and
surface temperature (Ts) and calculates
the dewpoint temperature (Td) and the
difference between the surface temperature
and the dewpoint temperature (ΔT). Each
gauge also calculates the equivalent
wet and dry bulb temperatures from the
measured values for the convenience of
some coating inspection regimes.
The new Elcometer 319 Dewpoint Meter
has many features to make its use quick,
simple and accurate, including Bluetooth®
wireless communication.
Available in two models (Standard &
Top) the Elcometer 319 can be used as a
hand held gauge to measure the climatic
conditions or as a stand-alone data logger
to monitor conditions over an extended
period of time, during the coating cure
process for example.
The gauge can be held in place on a
steel surface for the logging process using
magnets attached to the back of the gauge.
When used as a data logger the gauge has
an external magnetic surface temperature
probe to monitor continuously.
TheElcometer 319 is operated using easy
to use menus, allowing the user to quickly set
up features such as warning limits, backlight
brightness, measurement units, etc, and
review statistics and measurement records.
Standard versions have a rolling memory
of the last 10 readings; Top versions come
with a memory capacity for up to 25,000
records in up to 999 separate batches and
the Elcometer 319 Top is also supplied with
ElcoMaster™ Software allowing users to
not only download data from their gauge for
instant report generation, but also provides
users with a remote Watchguard™ facility
which allows remote data monitoring of up
to 42 gauges on the PC.
The Elcometer 139 Digital Dewpoint meter
gauge is ideal for determining if it is safe to
paint when substrates are cool and relative
humidity is high and there is a risk that
water vapour is condensing from the air on
to the cool surface that is to be painted. The
Elcometer 319 can also be used as a data
logger for monitoring the climatic conditions
regularly over a long period of time, during
the cure of a coating for example.
Elcometer Ltd – UK
Fax: +44 161 371 6010
Email:
Website:
The Elcometer 139 Digital Dewpoint meter gauge