Campbell Scientific BlackGlobe Temperature Sensor for Heat Stress - Manual (Page 16)

BlackGlobe Temperature Sensor for Heat Stress
7.2.6 Mean Site Barometric Pressure Calculation (SP_kPa)
The wet-bulb instruction needs mean barometric pressure which is closely
related to elevation of the site. U.S. Standard Atmosphere and dry air were
assumed when Equation 6 was derived (Wallace & Hobbes, 1977).
⎪⎭
⎪
⎬
⎫
⎪⎩
⎪
⎨
⎧
⎟
⎠
⎞
⎜
⎝
⎛ −
− − =
25328 . 5
69231 . 44307
1 1 325 . 101 325 . 101
E
SP
kPa
(6)
The value of SP
kPa
is in kilopascals and the site elevation, E, is in meters.
Use Equation 7 to convert feet to meters.
( )
( )
ft/m
ft E
m E
281 . 3
= (7)
The value for SP
kPa
must be put into the datalogger program.
7.3 Programming
7.3.1 Example CR1000 Program
The example includes measurements of the BlackGlobe temperature, and the
calculation of wet-bulb temperature and wet-bulb globe temperature.
Measurements of air temperature and relative humidity are supplied by an
HC2S3 in this example. Calculations for dewpoint, wet-bulb, and wet-bulb
globe temperature are also included.
'CR1000 Series Datalogger
'Program: BlackGlobe.CR1
'Declare constants
'Mean site barometric pressure at 1357.58 meters.
'CHANGE THIS VALUE TO MATCH YOUR ELEVATION.
Const SP_kPa = 86.04377
'Declare Public Variables
'Datalogger variables.
Public PnlTempC 'Datalogger panel temperature
Units PnlTempC=Deg C
Public Batt_Volt 'Datalogger battery voltage
Units Batt_Volt=VDC
'BlackGlobe variables.
Public BGTemp_C 'BlackGlobe temperature
Units BGTemp_C=Deg C
'Rotronic HC2S3 variables.
Public AirTempC 'Air temperature
Units AirTempC=Deg C
Public AirRH 'Humidity
Units AirRH=%
'Calculated variables.
Public DewPnt_C 'Dewpoint temperature
Public WetBlb_C 'Wet-bulb temperature
Public WBGT_C 'Wet-bulb globe (HUMIDEX) temperature
Dim SVP_kPa
Dim VP_kPa
10