Vaisala SHM40 - Manual (Page 38)

USER'S GUIDE____________________________________________________________________
36 __________________________________________________________________ M211423EN-B
Quantities Explained
The table below describes the quantities measured by the HM40 indicator
with the HMP40S probe. All of the quantities are measured or calculated
when the HM40 is on, independent of what is currently displayed.
NOTE Relative humidity (RH) and temperature (T) are the most important
quantities for structural humidity measurement.
Table 5 Quantities Output by HM40S
Quantity Symbol Unit(s) Description
Relative
humidity
RH % Ratio of the partial pressure of
water vapor in the air to the
saturation vapor pressure of air
at the current temperature.
Dewpoint Td °C
°F Temperature at which the water
vapor in the air will condense into
water at the current pressure.
When the dewpoint is below 0 °C,
the HM40 outputs frostpoint (Tf)
instead of dewpoint.
Wet bulb
temperature Tw °C
°F
The minimum temperature that
can be reached by evaporative
cooling in the current conditions.
Absolute
humidity a g/m3
gr/ft3
Quantity of water in a cubic meter
(or cubic foot) of air.
Mixing ratio x g/kg
gr/lb Ratio of water vapor mass per
kilogram (or pound) of dry air.
Enthalpy h kJ/kg
btu/lb Sum of the internal energy of a
thermodynamic system.
Temperature T °C
°F Temperature in Celsius or
Fahrenheit scale.