Campbell Scientific HMP45C Temperature and RH Probe - Manual (Page 14)

Model HMP45C Temperature and Relative Humidity Probe
Ω/1000 feet, or 13.9 Ω/1000 feet. Using Ohm’s law, the voltage drop (V
d
),
along the signal reference/power ground, is given by Eq. (1).
ft 1000 mV 6 . 55
ft 1000 9 . 13 mA 4
=
Ω ∗ =
∗ = R I
V
d
(1)
This voltage drop will raise the apparent temperature and relative humidity
because the difference between the signal and signal reference lead, at the
datalogger, has increased by V
d
. The approximate error in temperature and
relative humidity is 0.56 °C and 0.56% per 100 feet of cable length,
respectively.
TABLE 6-1. Wiring for
Differential Measurement Examples
Color Description CR1000 CR10(X)
Yellow Temperature 2H 2H
Jumper to 1L 2L 2L
Blue Relative Humidity 1H 1H
White Signal Reference 1L 1L
Jumper from SW12V
Control
C1
Red Power SW12 V SW12 V
Black Power Ground G G
Clear Shield G
CR1000 Program using Differential Measurement Instructions Using SW12V on Datalogger
'CR1000 program to measure HMP45C with differential measurements
Public AirTC
Public RH
DataTable(Temp_RH,True,-1)
DataInterval(0,60,Min,0)
Average(1,AirTC,IEEE4,0)
Sample(1,RH,IEEE4)
EndTable
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