Vaisala DM500 - Manual (Page 44)

User's Guide ______________________________________________________________________
42 __________________________________________________________________ M210205EN-D
5. To achieve the optimum measuring results, clean the sensor and
determine the clean sensor value before the first measurements,
see page 65.
6. Start measurement by pressing START/STOP .
7. Wait until yellow led turns to green in the DMP501 dewpoint
sensing unit front panel. The symbol disappears from the
display and the error limit value appears on the upper right
corner of the display. The measuring cycle is now balanced.
You can follow the stabilization from the graphic trend.
Error limit value
↓
Measurement mode display
8. Droplet symbol 6 on the upper left corner of the display
indicates the presence of dew on the sensor.
If the condensation on the sensor freezes the droplet changes to a
snowflake symbol 7. If the sensor has both dew and frost on the
surface, both 6 and 7 symbols are displayed. The moment of
instability is indicated both by blinking 6 and 7 symbols as well as by
increased error limit value. The instability period usually lasts less
than 10 minutes until the condensation is frozen. Thus, the user need
not keep track of the moisture phase in order to obtain reliable
measurement results in the temperature range where either dew or
frost or both can exist on the sensor (typically 0 ºC...-30 ºC)
More About the Moisture Phases
67
The system detects the phase of the moisture on the sensor
automatically and uses this phase data when converting measured
sensor temperature to the user selected unit. For example, if the user
wishes to output dewpoint, not frostpoint, the system uses the
measured sensor temperature as dewpoint temperature as long as the
moisture phase remains liquid (6 symbol in the display). If the
dewpoint is low, the sensor may freeze. The system detects the
moment of freezing and thereafter considers the sensor temperature to
be the frostpoint temperature. This frostpoint temperature is