Campbell Scientific HMP45C Temperature and RH Probe User Manual
Page 17
Model HMP45C Temperature and Relative Humidity Probe
Because of the inverse relationship between relative humidity and air
temperature, finding the mean relative humidity is meaningless. A more useful
quantity is the mean vapor pressure. The mean vapor pressure can be
computed on-line by the datalogger as shown in the following examples.
TABLE 7-1. Wiring for Vapor Pressure Examples
Color Description CR1000
CR10(X)
Yellow
Temperature
SE 2 (1L)
SE 3 (2H)
Blue
Relative Humidity SE 1 (1H)
SE 4 (2L)
White Signal
Reference
AG
Jumper
from
SW12V Control
C1
Red Power SW12V
SW12
V
Black Power
Ground
AG
Clear Shield
G
CR1000 Program that Computes Vapor Pressure and Saturation Vapor Pressure
'CR1000 program that calculates Vapor Pressure
Public AirTC
Public RH
Public RH_Frac, e_Sat, e_kPa
DataTable(Temp_RH,True,-1)
DataInterval(0,60,Min,0)
Average(1,AirTC,IEEE4,0)
Sample(1,RH,IEEE4)
Sample(1,e_kPa,IEEE4)
EndTable
BeginProg
Scan(1,Sec,1,0)
'HMP45C Temperature & Relative Humidity Sensor measurements AirTC and RH:
SW12
(1
)
Delay(0,150,mSec)
VoltSE(AirTC,1,mV2500,2,0,0,_60Hz,0.1,-40.0)
VoltSE(RH,1,mV2500,1,0,0,_60Hz,0.1,0)
SW12
(0)
If RH>100 And RH<108 Then RH=100
'Calculate
Vapor
Pressure
'Convert RH percent to RH Fraction
RH_Frac = RH * 0.01
'Calculate Saturation Vapor Pressure
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