100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
User Guide
Page 127
HA028910
Issue 13 Sep 16
4.3.11 FUNCTION (Cont.)
RELATIVE HUMIDITY
This determines the percentage relative humidity from wet and dry temperature and atmospheric pres-
sure inputs.
Standard temperature and pressure at sea level are defi ned as 1.01325 Bar, and 15˚C. Pressure varies
with height as indicated in table 4.3.11c. The standard psychrometric constant is 0.000666 (6.66 x 10
-4
).
The equation solved is:
Where:
RH = Percentage relative humidity
A
0
= 6.17204663 x 10
-3
A
1
= 4.28096024 x 10
-4
A
2
= 1.53342964 x 10
-5
A
3
= 2.40833685 x 10
-7
A
4
= 3.04249240 x 10
-9
A
5
= 2.65867713 x 10
-11
p = Psychrometric constant (0.000666)
AbsP = Pressure in Bar (absolute not gauge)
d = Dry bulb temperature in degrees Celsius
w = Wet bulb temperature in degrees Celsius
Table 4.3.11c
RH
!
A
0
#
wA
1
#
w
2
A
2
#
w
3
A
3
#
w
4
A4
#
w
5
A
5
"
p
$
AbsP d
"
w
.
/
0
1
A
0
#
dA
1
#
d
2
A
2
#
d
3
A
3
#
d
4
A
4
#
d
5
A
5
Figure 4.3.11q Relative humidity confi guration menu
Geometric height
(metres)
Pressure
(Bar)
1.04365
1.01325
0.983576
0.954612
0.926346
0.898762
0.845596
0.795014
-250
0
250
500
750
1000
1500
2000
Atmospheric pressure
versus
height
Function
Wet bulb temperature
Dry bulb temperature
Pressure
Psychrometric Constant
Maths Number
Value
Units
Units
Apply Discard
Relative Humidity
6.66E-4
Channel 1
1) Math 1
0.0000
Channel 2
Channel 3
Units