FIGURE 7-4. HMP60 and RAD06 Radiation Shield on a tripod mast
8. Operation
8.1 Measurement
The HMP60 Temperature and Relative Humidity Probe uses a Platinum Resistance Temperature
detector (PRT) and a Vaisala INTERCAP® capacitive relative humidity sensor.
8.2 Long cable lengths
Long cable lengths cause errors in the measured temperature and relative humidity. The
approximate error in temperature and relative humidity is 0.52 °C and 0.52% per 100 feet of cable
length, respectively.
When long cable lengths are required and the above errors in temperature and relative humidity
are unacceptable, use the EE181 or HMP155A temperature and relative humidity probe instead.
Understanding the following details are not required for the general operation of the HMP60
with Campbell Scientific data loggers. The signal reference and the power ground (black) are the
same wire in the HMP60. When the HMP60 temperature and relative humidity are measured,
both the signal reference and power ground are connected to ground at the data logger. The
signal reference/power ground wire serves as the return path for 12 V. There will be a voltage
drop along this wire because the wire has resistance. The HMP60 draws approximately 2 mA
(worst case) when it is powered. The wire used in the HMP60 has resistance of 26.2 Ω/1000 feet.
HMP60 Temperature and Relative Humidity Probe
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