Campbell Scientific 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

act information is for US and International customers residing in countries

cont
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
serves your country. To obtain a Returned Materials Authorization (RMA),
contact CAMPBELL SCIENTIFIC, INC., phone [phone]. After an
applications engineer determines the nature of the problem, an RMA number
will be issued. Please write this number clearly on the outside of the shipping
container. CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____
815 W
Logan, Ut

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

est 1800 North

ah 84321-1784

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)

−40

−30

−20

−10

0 to +50 0.20

TABLE 2. Polynomial Error

Temperature

Range(°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

Temperature

Tolerance (±°C)

0.40

0.40

0.32

0.25

Error (°C)

1

HMP35C TEMPERATURE AND RH PROBE

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

2

HMP35C TEMPERATURE AND RH PROBE

FIGURE 3. HMP35C with UT018 Mounting Bracket and Crossarm and

UT12VA Radiation Shield Mounted on a UT30 Tower

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

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

White AG

Reference

Temperature

Black Excitation Channel Excitation Channel Excitation Channel

Excitation

Power Control Yellow Control Port Control Port Control Port

Power Red 12 V 12 V 12 V

RH Signal, Power, &

Purple AG

Control Reference

Shield Clear G

3