6
Read wet & dry bulb ther-
mometers; replace body in
8
Read % relative humidity
as indicated by arrow.
2Instruction 0012-9015
4
Pull body
from tube
until body
hangs
free.
5
Use tube
as handle;
whirl body
about 1-½
minutes.
7
Set thermometer readings on
upper two calculator scales.
A D G H I
B G H C F E
2
Fill psy-
chrometer
reservoir
with water.
Replace cap.
3
Be sure
wick covers
“wet” bulb
(the other
bulb is dry).
1
Remove
cap; im-
merse end
of body to
saturate
wick.
OPERATION
APPLICATION
MAINTENANCE
WICK (A) should be kept clean; when dirty,
cut off WICK below WET BULB THER-
MOMETER (D) and pull clean section out of
END CAP (B) and slide over bulb on WET
BULB THERMOMETER.
A WICK REPLACEMENT KIT may be pur-
chased separately (refer to parts list). One
or two extra WICKS may be kept in END
CAP and will help retain moisture longer.
Pack WICKS loosely to allow thorough water
saturation and ample water supply to the
WET BULB THERMOMETER.
THERMOMETERS (D) and (F) are re-
placeable by backing off SCREWS (G) and
loosening THERMOMETER CLIPS (H). To
separate BODY (C) and TUBE (E), drive
ROLL PIN (I) out of eye in PLUG AND
SWIVEL ASSEMBLY, which then may be
slid out back end of TUBE.
Wet-bulb temperatures should be read first
and as quickly as possible for highest ac-
curacy. Delay in reading may cause error. In
addition, the wick must be kept clean, satu-
rated with water, and whirled long enough
to stabilize temperatures.
The range of the psychrometer is from 10%
to 100% R.H., for dry-bulb temperatures of
30° to 100°F (–5° to 50°C).
In addition to the above instructions,
barometric pressure and other factors will
influence exact relative humidity determin-
ations to a very minor degree. For precise
work, use a psychrometric chart or set of
tables such as W.B. No. 235 “Psychrometric
Tables for Obtaining the Vapor Pressure,
Relative Humidity, and Temperature of Dew
Point,” which can be purchased from the
Superintendent of Documents, United States
Govern
ment Printing Office, Washington,
D.C. The accuracy of the Psychrometer,
however, is satisfactory for all except the
most exacting work.
3
Instruction 0012-9015
3. Holding TUBE, whirl body two to three
revolutions per second (120 to 180 RPM).
4. Continue whirling until temperatures
stabilize (1-½ minutes is usually ample).
5. Immediately read WET BULB THER-
MOMETER (D) and then DRY BULB
THERMOMETER (F). (See application
instructions.)
6. Set wet and dry bulb temperatures op-
posite each other on side rule type calcu-
lator scales, sliding BODY into TUBE as
required.
7. Read % R.H. (percent relative humidity)
indicated by arrowhead on lower scale.
Before Using:
WICK (A) should be thoroughly saturated
with water. Remove END CAP (B) and im-
merse PSYCHROMETER BODY (C) up to
mercury (or red spirit) reservoir on the ther-
mometers until WICK is thoroughly wetted.
Fill END CAP with water and replace; tighten
just enough to prevent leakage.
To Use:
1. Be sure WICK (A) is wet and covers mer–
cury (or red spirit) reservoir on WET BULB
THERMOMETER (D). Be sure reservoir
on other THERMOMETER (F) is dry.
2. Pull TUBE (E) clear of BODY so BODY
can swivel.
