DeFelsko PosiTector DPM v.1.2 - Manual (Page 5)

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Td - The dew point temperature is a function of air tempera-
ture and the relative humidity (see ISO 8502-4 Annex A). It is
the temperature to which a volume of air must be cooled in
order to reach saturation.
Ts - A surface temperature thermocouple is located on the tip
of the probe. It is spring loaded and designed to quickly self-
align on a surface. Press it firmly against a surface and allow
a few seconds for the value to stabilize. Wet the surface for a
faster response.
D
- is the surface minus dew point temperature (Ts - Td ).
This value is important in judging the risk of condensation, or
dew, forming on a surface. For example, ISO 8502-4 recom-
mends that, unless otherwise agreed, the temperature of a
steel surface generally should be at least 3°C (5°F) above the
dew point when paints are applied.
The button cycles through these 5 values. For conven-
ience, all 5 values are displayed at once, but one is always
enlarged for easy viewing. Press to enlarge the other val-
ues one at a time.
The button operates two different HOLD features to
enable closer examination of the relationship between values.
Press once to "freeze" the display. The instrument will
measure one more time, then hold all values.
Press and hold to activate the automatic hold feature. Let
go of the button when the instrument begins to beep and
blink. Now touch the surface temperature probe to the sur-
face and wait. When the surface temperature has stabilized,
the LED will stay lit and the values will hold on the LCD.
Press and hold again to repeat or press and release to
exit.
This automatic hold feature takes the guesswork out of meas-
uring surface temperature. It is also useful in situations where
it is difficult to view the LCD during measurement.