User guide

User Guide
5
1. Do not push the probe so far into the radiation shield
that the sensor tip touches the top of the shield.
2. Ensure that your last action before tightening the large
securing nut is not to withdraw the probe (i.e. do not pull
in a downwards direction). This will cause the sealing
membrane to also pull downwards and will form a well
around the sensor which may then trap water. The
sealing membrane must curve UPWARDS towards the
tip of the sensor to encourage any water to run away
from the sensor body – see Figure 2.
3. Do not over-tighten the nut, as it is possible to crush the
sensor if too much force is used.
4. Always use the cable ties provided to attach the cable to
the mounting arm to prevent cable movement in the
wind, which could cause the wire to break.
In dirty environments, clean the radiation shield every month.
4. Wiring
Connections to Campbell Scientific dataloggers are given in Tables 1 through 3.
The probe can be measured by two single-ended or differential analogue input
channels.
When measuring the HMP45C with single-ended
measurements, the blue and black leads must both be
connected to AG on the CR10(X) and CR500/CR510 or to
on the CR800/850, CR1000, CR5000, and CR23X.
Doing otherwise will connect the datalogger’s analogue and
power ground planes to each other, which in some cases
can cause offsets on low-level analogue measurements. To
avoid 4 mA flowing into analogue ground, switch the sensor
on/off for its own measurement.
Description Colour
Temperature Signal White
Relative Humidity Signal Green
Signal Reference Blue
Powe
r
Red
Power Ground Black
Screen/Shield Shield
NOTE: These wire colours differ from HMP45C probes supplied in the USA.
Figure 3. HMP45C Probe to Datalogger Connections
CAUTION
CAUTION