Campbell HMP45C Guide de l'utilisateur télécharger pdf (Page 21)

User Guide

in the air has not changed. Thus, the amount of water vapour in the air, relative

to saturation, has decreased.

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 vapour pressure. The mean vapour pressure can be

computed on-line by the datalogger (Example 3).

Table 8. Wiring for Vapour Pressure Examples

Description Colou

CR1000 CR10(X)

Temperature White SE 2 (1L) SE 3 (2H)

Relative Humidity Green SE 1 (1H) SE 4 (2L)

Signal Reference Blue AG

Jumper from

SW12V Control

N/A C1

Powe

Red SW12 V SW12 V

Power Ground Black AG

Shield Clear G

NOTE: These wire colours differ from HMP45C probes supplied in the USA.

CR1000 Program that Computes Vapour Pressure and Saturation Vapour Pressure

'CR1000 program that calculates Vapour 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,_50Hz,0.1,-40.0)

VoltSE(RH,1,mV2500,1,0,0,_50Hz,0.1,0)

SW12 (0)

If RH>100 And RH<108 Then RH=100

'Calculate Vapour Pressure

'Convert RH percent to RH Fraction

RH_Frac = RH * 0.01

'Calculate Saturation Vapour Pressure

SatVP(e_Sat, AirTC)

'Compute Vapour Pressure, RH must be a fraction

e_kPa = e_Sat * RH_Frac

CallTable(Temp_RH)

NextScan

EndProg

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 27 28

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Campbell HMP45C Guide de l'utilisateur Page 21

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