Model HMP45C Temperature and
Relative Humidity Probe
(1)
General Description
The HMP45C Temperature and Relative Humidity probe contains a Platinum
Resistance Temperature detector (PRT) and a Vaisala HUMICAP
®
180
capacitive relative humidity sensor.
The -L option on the model HMP45C Temperature and Relative Humidity
probe (HMP45C-L) indicates that the cable length is user specified. This
manual refers to the sensor as the HMP45C.
The HMP45C can be powered continuously or the power may be switched to
conserve battery life. The HMP45C consumes less than 4 milliamperes current
at 12 volts. Approximately 0.15 seconds is required for the sensor to warm up
after power is switched on. At measurement rates slower than once per
second, the overall power consumption (datalogger and sensors) may be
reduced by switching power to the HMP45C. Most current Campbell
Scientific dataloggers have a built-in switched 12 volts that can be used to
control power.
The CR9000, CR510, CR500, CR7, CR10 and 21X dataloggers do not have a
built-in switched 12 volts. Users with these dataloggers can power the sensor
continuously or purchase the model SW12V to switch power.
Lead length for the HMP45C is specified when the sensor is ordered. Table 1-1
gives the recommended lead length for mounting the sensor at the top of
the tripod/tower with a 2 foot crossarm. Lead length can be 2 feet shorter
when the sensor is mounted to the tripod mast / tower leg without a crossarm.
The HMP45C ships with:
(1) Adjustment Screwdriver from mfg
(1) Calibration Sheet
(1) Instruction Manual
1
TABLE 1-1. Recommended Lead Lengths
CM6
CM10
CM110
CM115
CM120
UT10
UT20
UT30
11’
14’
14’
19’
24’
14’
24’
37’
