Campbell HMP35C User manual

INSTRUCTION MANUAL
Model HMP35C Temperature
and Relative Humidity Probe
Revision: 1/99
Copyright (c) 1990-1999
Campbell Scientific, Inc.

Warranty and Assistance
The HMP35C TEMPERATURE AND RELATIVE HUMIDITY PROBE
is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in
materials and workmanship under normal use and service for twelve (12)
months from date of shipment unless specified otherwise. Batteries have no
warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is
limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option)
defective products. The customer shall assume all costs of removing,
reinstalling, and shipping defective products to CAMPBELL SCIENTIFIC,
INC. CAMPBELL SCIENTIFIC, INC. will return such products by surface
carrier prepaid. This warranty shall not apply to any CAMPBELL
SCIENTIFIC, INC. products which have been subjected to modification,
misuse, neglect, accidents of nature, or shipping damage. This warranty is in
lieu of all other warranties, expressed or implied, including warranties of
merchantability or fitness for a particular purpose. CAMPBELL SCIENTIFIC,
INC. is not liable for special, indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. The following
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served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
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contact CAMPBELL SCIENTIFIC, INC., phone [phone]. After an
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CAMPBELL SCIENTIFIC, INC.
RMA#_____
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CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

1
MODEL HMP35C
TEMPERATURE AND RELATIVE HUMIDITY PROBE
1. GENERAL DESCRIPTION
The HMP35C Temperature and Relative
Humidity probe contains a thermistor for
measuring temperature and a Vaisala
capacitive polymer H chip for measuring relative
humidity.
The -L option on the model HMP35C
Temperature and Relative Humidity probe
(HMP35C-L) indicates that the cable length is
user specified. This manual refers to the
sensor as the HMP35C.
2. SPECIFICATIONS
Operating Temperature: -35°to +60°C
Storage Temperature: -40°to +80°C
Probe Length: 25.4 cm (10 in.)
Probe Body Diameter: 2.5 cm (1 in.)
Filter: 0.2 µm Teflon membrane
Filter Diameter: 1.9 cm (0.75 in.)
Power Consumption: < 4 mA
Supply Voltage (via CSI switching circuit):
7 to 35 VDC
Settling Time after power is switched on:
0.15 seconds
2.1 TEMPERATURE SENSOR
Sensor: thermistor (100 kΩ@ 25°C)
Temperature Measurement Range:
-35°to +55°C
Thermistor Interchangeability Error:
Typically < ±0.2°C over 0°to +60°C, ±0.4°C
@ -35°C
Polynomial Linearization Error:
< ±0.5°C over -35°to +50°C
2.1.1 Temperature Sensor Accuracy
The overall probe accuracy is a combination of
the thermistor's interchangeability specification,
the precision of the bridge resistors, and the
polynomial error. In a "worst case" all errors
add to an accuracy of ±0.4°C over the range of
-24°C to 48°C and ±0.9°C over the range of
-38°to 53°C. The major error component is the
interchangeability specification of the
thermistor, tabulated in Table 1. For the range
of 0°to 50°C the interchangeability error is
predominantly offset and can be determined
with a single point calibration. Compensation
can then be done with an offset entered in the
measurement instruction. The bridge resistors
are 0.1% tolerance with a 10 ppm temperature
coefficient. Polynomial errors are tabulated in
Table 2 and plotted in Figure 1.
TABLE 1. Thermistor Interchangeability
Temperature
(°C) Temperature Tolerance (±°C)
−40 0.40
−30 0.40
−20 0.32
−10 0.25
0 to +50 0.20
TABLE 2. Polynomial Error
Temperature
Range(°C) Error (°C)
−40 to +56 <±1.0°C
−38 to +53 <±0.5°C
−24 to +48 <±0.1°C
2.2 RELATIVE HUMIDITY SENSOR
Sensor: Vaisala capacitive polymer H chip
Relative Humidity Measurement Range:
0 to 100% non-condensing
RH Output Signal Range:
0.002 to 1 VDC
Accuracy at 20°C
±2% RH (0 to 90% Relative Humidity)
±3% RH (90 to 100% Relative Humidity)
Temperature Dependence of Relative Humidity
Measurement: ±0.04% RH/°C
Typical Long Term Stability:
Better than 1% RH per year
Response Time (at 20°C, 90% response to
steep change in humidity):
15 seconds with membrane filter

HMP35C TEMPERATURE AND RH PROBE
2
FIGURE 1. Error Produced by Polynomial Fit to Published Values
3. INSTALLATION
The HMP35C must be housed inside a radiation
shield when used in the field. The 41002
Radiation Shield (Figure 2) mounts to a
CM6/CM10 tripod or UT10 tower. The UT018
mounting arm and UT12VA Radiation Shield
mount to a UT30 tower (Figure 3).
A lead length of 6 feet allows the HMP35C to be
mounted at a 2 meter height on a CM6/CM10
tripod. Use a lead length of 9 feet for the UT10
tower or a UT30 tower respectively.
NOTE: The black outer jacket of the cable
is Santoprene® rubber. This compound was
chosen for its resistance to temperature
extremes, moisture, and UV degradation.
However, this jacket will support
combustion in air. It is rated as slow
burning when tested according to U.L. 94
H.B. and will pass FMVSS302. Local fire
codes may preclude its use inside buildings.
FIGURE 2. HMP35C and 41002 Radiation Shield on a
CM6/CM10 Tripod Mast or UT10 Tower Leg

HMP35C TEMPERATURE AND RH PROBE
3
FIGURE 3. HMP35C with UT018 Mounting Bracket and Crossarm and
UT12VA Radiation Shield Mounted on a UT30 Tower
FIGURE 4. HMP35C Probe to Datalogger Connections
TABLE 3. Datalogger Connections
Description Color CR10(X), CR500 CR23X 21X, CR7
Temperature Orange Single-Ended Input Single-Ended Input Single-Ended Input
Relative Humidity Green Single-Ended Input Single-Ended Input Single-Ended Input
Temperature Signal
Reference White AG
Temperature
Excitation Black Excitation Channel Excitation Channel Excitation Channel
Power Control Yellow Control Port Control Port Control Port
Power Red 12 V 12 V 12 V
RH Signal, Power, &
Control Reference Purple AG
Shield Clear G
Orange Temperature Signal
Green Relative Humidity Signal
White Temperature Signal Reference
Black Temperature Excitation
Yellow Power Control
Red Power
Purple RH Signal, Power, & Control Reference
Clear Shield

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)

HMP35C TEMPERATURE AND RH PROBE
5
;Pause 150 milliseconds, before making the measurement, so the
;probe can stabilize on the true relative humidity.
;
03: Excitation with Delay (P22)
1: 1 Ex Channel
2: 0 Delay W/Ex (units = 0.01 sec)
3: 15 Delay After Ex (units = 0.01 sec)
4: 0 mV Excitation
;Measure the HMP35C relative humidity.
;
04: Volt (SE) (P1)
1: 1 Reps
2: 5 2500 mV Slow Range
;CR500 (2500 mV); CR23X (1000 mV); 21X, CR7 (5000 mV)
3: 4 SE Channel ;Green wire (SE 4), Purple wire (AG)
4: 2 Loc [ RH_pct ]
5: 0.1 Mult
;See Table 5 for alternate multipliers
6: 0 Offset
;Turn the HMP35C off.
;
05: Do (P86)
1: 51 Set Port 1 Low
;Yellow wire (C1)
6. LONG LEAD LENGTHS
When long lead lengths are required, the
measurement settling time for the temperature
measurement must be increased. For
HMP35Cs with lead lengths greater than 300
feet, use the DC Half Bridge instruction
(Instruction 4) with a 20 millisecond delay to
measure the thermistor (Example 2).
Long lead lengths cause errors in the measured
relative humidity. The approximate error in
relative humidity is 0.6% RH per 100 feet of
cable length. When long lead lengths are
required and the above errors in relative
humidity are unacceptable, use the HMP45C
temperature and humidity probe.
TABLE 7. Wiring for Example 2
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

HMP35C TEMPERATURE AND RH PROBE
6
Example 2. Sample CR10(X) Program measuring HMP35C Temperature
using DC Half Bridge with Delay
;Measure the HMP35C thermistor.
;
01: Excite-Delay (SE) (P4)
1: 1 Reps
2: 2 7.5 mV Slow Range
;CR500 (7.5 mV); CR23X (10 mV); 21X, CR7 (15 mV)
3: 3 SE Channel ;Orange wire (SE 3), White wire (AG)
4: 1 Excite all reps w/Ex 1 ;Black wire (EX 1)
5: 2 Delay (units 0.01 sec)
6: 2000 mV Excitation
;CR500, CR23X (2000 mV); 21X, CR7 (4000 mV)
7: 1 Loc [ T_C ]
8: 0.4 Mult
;CR500, CR23X (0.4); 21X, CR7 (0.2)
9: 0 Offset
;Compute the temperature in degrees Celsius.
;
02: Polynomial (P55)
1: 1 Reps
2: 1 X Loc [ T_C ]
3: 1 F(X) Loc [ T_C ]
4: -53.46 C0
5: 90.807 C1
6: -83.257 C2
7: 52.283 C3
8: -16.723 C4
9: 2.211 C5
;Apply the temperature multiplier.
;
03: Z=X*F (P37)
1: 1 X Loc [ T_C ]
2: 1 F
;See Table 4 for alternate multipliers
3: 1 Z Loc [ T_C ]
;Apply the temperature offset.
;
04: Z=X+F (P34)
1: 1 X Loc [ T_C ]
2: 0 F
;See Table 4 for alternate offsets
3: 1 Z Loc [ T_C ]
;Turn the HMP35C on.
;
05: Do (P86)
1: 41 Set Port 1 High
;Yellow wire (C1)
;Pause 150 milliseconds, before making the measurement, so the
;probe can stabilize on the true relative humidity.
;
06: Excitation with Delay (P22)
1: 1 Ex Channel
2: 0 Delay W/Ex (units = 0.01 sec)
3: 15 Delay After Ex (units = 0.01 sec)
4: 0 mV Excitation

HMP35C TEMPERATURE AND RH PROBE
7
;Measure the HMP35C relative humidity.
;
07: Volt (SE) (P1)
1: 1 Reps
2: 5 2500 mV Slow Range
;CR500 (2500 mV); CR23X (1000 mV); 21X, CR7 (5000 mV)
3: 4 SE Channel ;Green wire (SE 4), Purple wire (AG)
4: 2 Loc [ RH_pct ]
5: 0.1 Mult
;See Table 5 for alternate multipliers
6: 0 Offset
;Turn the HMP35C off.
;
08: Do (P86)
1: 51 Set Port 1 Low
;Yellow wire (C1)
6.1 TEMPERATURE
Understanding the following details are not
required for the general operation of the
HMP35C with Campbell Scientific’s
dataloggers.
Whenever an analog input is switched into the
datalogger measurement circuitry prior to
making a measurement, a finite amount of time
is required for the signal to stabilize to its
correct value. The rate at which the signal
settles is determined by the input settling time
constant which is a function of both the source
resistance and input capacitance. Campbell
Scientific dataloggers allow a 450 µs settling
time before initiating the measurement. In most
applications, this settling time is adequate, but
additional wire capacitance associated with long
sensor leads can increase the settling time
constant so that measurement errors occur.
See Section 13 in the datalogger manuals for
more information.
6.2 RELATIVE HUMIDITY
Understanding the following details are not
required for the general operation of the
HMP35C with Campbell Scientific’s
dataloggers.
The relative humidity signal reference and the
power reference (black) are the same lead in
the HMP35C. When the measuring relative
humidity, both the signal and power references
are connected to ground at the datalogger. The
signal/power reference lead serves as the
return path for 12 V. There will be a voltage
drop along this lead because the wire itself has
resistance. The HMP35C draws approximately
4 mA when it is powered. The wire used in the
HMP35C (P/N 9721) has a resistance of 13.9
Ω/1000 feet. Using Ohm’s law, the voltage drop
(Vd), along the signal reference/power ground
lead, is given by Eq. (1).
VIR
d
=∗
=∗
=
mA ft
mV ft
4 139 1000
556 1000
.
.Ω(1)
This voltage drop will raise the apparent
temperature and relative humidity because the
difference between the signal and signal
reference, at the datalogger, has increased by
Vd. The approximate error in relative humidity is
0.6% RH per 100 feet of cable length.
7. ELECTRICALLY NOISY
ENVIRONMENTS
AC power lines can be the source of electrical
noise. If the datalogger is in an electronically
noisy environment, the HMP35C temperature
measurement should be made with the AC half
bridge instruction (Instruction 5) with the 60 Hz
rejection integration option on the CR10(X),
CR500, and CR23X. Use the slow integration on
the 21X and CR7.
Use the 60 Hz rejection integration option when
measuring the relative humidity with the single-
ended analog measurement on the CR10(X),
CR500, and CR23X. Use the slow integration on
the 21X and CR7.

HMP35C TEMPERATURE AND RH PROBE
8
TABLE 8. Wiring for Example 3
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 3. CR10(X) Program that Measures the HMP35C
in an Electrically Noisy Environment
;Measure the HMP35C thermistor.
;
01: AC Half Bridge (P5)
1: 1 Reps
2: 22 7.5 mV 60 Hz Rejection Range
;CR500 (7.5 mV); CR23X (10 mV)
;21X, CR7 (15 mV)
3: 3 SE Channel ;Orange wire (SE 3), White wire (AG)
4: 1 Excite all reps w/Ex 1 ;Black wire (EX 1)
5: 2000 mV Excitation ;CR500, CR23X (2000 mV); 21X, CR7 (4000 mV)
6: 1 Loc [ T_C ]
7: 800 Mult
8: 0 Offset
;Compute the temperature in degrees Celsius.
;
02: Polynomial (P55)
1: 1 Reps
2: 1 X Loc [ T_C ]
3: 1 F(X) Loc [ T_C ]
4: -53.46 C0
5: 90.807 C1
6: -83.257 C2
7: 52.283 C3
8: -16.723 C4
9: 2.211 C5
;Apply the temperature multiplier.
;
03: Z=X*F (P37)
1: 1 X Loc [ T_C ]
2: 1 F
;See Table 4 for alternate multipliers
3: 1 Z Loc [ T_C ]
;Apply the temperature offset.
;
04: Z=X+F (P34)
1: 1 X Loc [ T_C ]
2: 0 F
;See Table 4 for alternate offsets
3: 1 Z Loc [ T_C ]