100/180MM DISTRIBUTED GRAPHIC RECORDER: USER GUIDE
HA029324
Issue 11 Oct 14
Page 117
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:
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
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
Table 4.3.11 c
Height versus atmospheric pressure
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
RH
A
0
wA
1
w
2
A
2
w
3
A
3
w
4
A
4
w
5
A
5
{p
AbsP(d
w)}
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
Summary of Contents for 6100
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