Campbell Scientific HMP35C Temperature and RH Sensor - Manual (Page 6)

HMP35C TEMPERATURE AND RH PROBE
4
4. WIRING
Connections to Campbell Scientific dataloggers
are given in Table 3. The probe is measured by
two single-ended input channels, one for
temperature and one for relative humidity. A
single excitation channel is used for the
temperature measurement.
The number of HMP35C probes that can be
excited by one excitation channel is physically
limited by the number of lead wires that can be
inserted into a single excitation terminal
(approximately 6).
5. EXAMPLE PROGRAMS
This section is for users who write their own
datalogger programs. A datalogger program to
measure this sensor can be created using
Campbell Scientific’s Short Cut Program Builder
software. You do not need to read this section to
use Short Cut.
The temperature is measured using a single-
ended analog measurement and an excitation
channel (Instruction 11). The relative humidity is
measured using a single-ended analog
measurement (Instruction 1). Tables 4 and 5
provide calibration information for temperature
and relative humidity.
CAUTION: Do no turn the HMP35C on
before measuring the thermistor. Doing so
will induce a transient signal spike on the
thermistor leads that will result in an
erroneous temperature measurement.
Always measure the HMP35C temperature
first.
TABLE 4. Calibration for Temperature
Units Multiplier
(degrees mV
-1
)
Offset
(degrees)
Celsius 1 0
Fahrenheit 1.8 32
TABLE 5. Calibration for Relative Humidity
Units Multiplier
(% mV
-1
)
Offset
(%)
Percent 0.1 0
Fraction 0.001 0
TABLE 6. Wiring for Example 1
Description Color CR10(X)
Temperature Orange SE 3 (2H)
Relative Humidity Green SE 4 (2L)
Temperature Signal Reference White AG
Temperature Excitation Black E1
Power Control Yellow C1
Power Red 12 V
RH Signal, Power, & Control Reference Purple AG
Shield Clear G
Example 1. Sample CR10(X) Program measuring HMP35C
Temperature and Relative Humidity
;Measure the HMP35C temperature.
;
01: Temp (107) (P11)
1: 1 Reps
2: 3 SE Channel ;Orange wire (SE 3), White wire (AG)
3: 1 Excite all reps w/E1 ;Black wire (EX 1)
4: 1 Loc [ T_C ]
5: 1 Mult ;See Table 4 for alternate multipliers
6: 0 Offset ;See Table 4 for alternate offsets
;Turn the HMP35C on.
;
02: Do (P86)
1: 41 Set Port 1 High ;Yellow wire (C1)