Amprobe THWD-3 TH-3 Relative-Humidity-Temperature-Meters - Manual (Page 6)

4
Dew Point and Wet Bulb Temperature
(THWD-3 only) Operation
The Meter displays ambient temperature when first turned on. To
display dew point (DP) temperature, press
DP WB once. Press DP WB again
to switch to wet bulb (WB) temperature. Pressing DP WB a third time
returns the Meter to ambient temperature. The display indicates when
dew point and wet bulb temperatures are selected.
Auto Power Off
By default, when the meter is powered on, it is in the auto power
off mode. The meter will power itself off after 30 minutes if no key
operation is performed. To disable the auto power off feature, press
and hold the � button and then power on the meter, The auto
power off symbol will disappear to indicate that auto power off is
disabled.
Low Battery Condition
When the battery voltage is under proper operation requirement, the
�
symbol displays on the LCD and the battery needs to be replaced.
Wet Bulb Temperature Readings (TH-3)
Occasionally the Wet Bulb temperature is required. Use the following
procedure and your TH-3 to obtain the wet bulb temperature.
1. Determine RH% condition with the TH-3.
2. Determine temperature (dry-bulb) with the TH-3.
3. Locate dry bulb (DB) temperature line on the Psychrometric chart
(vertical line across the bottom of the chart).
4. Locate relative humidity (RH) line on the chart (curved line across
the chart).
5. Find the intersection of the DB and RH lines on the chart.
6. Draw a diagonal line, starting at your intersectioin point, until the
Wet Bulb (WB) point is determined. (The wet bulb temperature line
is at the outmost curve of the chart).
For example, locate the DB temperature of 78 °F on the Psychrometer
chart. Locate the RH conditions of 50% RH on the chart. Draw a
diagonal line up to the 65 °F WB point.