Campbell HMP45C212 User manual

MODEL HMP45C212 TEMPERATURE
AND RELATIVE HUMIDITY PROBE
INSTRUCTION MANUAL
PRELIMINARY: 31/03/00
COPYRIGHT © 2000 CAMPBELL SCIENTIFIC (CANADA) CORPORATION

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WARRANTY AND ASSISTANCE
The HMP45C212 TEMPERATURE AND RELATIVE HUMIDITY PROBE is warranted by
CAMPBELL SCIENTIFIC (CANADA) CORP. (“CSC”) 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. CSC's obligation under this warranty is limited to
repairing or replacing (at CSC's option) defective products. The customer shall assume all
costs of removing, reinstalling, and shipping defective products to CSC. CSC will return
such products by surface carrier prepaid. This warranty shall not apply to any CSC
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. CSC is not liable
for special, indirect, incidental, or consequential damages.
Products may not be returned without prior authorization. To obtain a Return Merchandise
Authorization (RMA), contact CAMPBELL SCIENTIFIC (CANADA) CORP., at (780) 454-
2505. An RMA number will be issued in order to facilitate Repair Personnel in identifying
an instrument upon arrival. Please write this number clearly on the outside of the shipping
container. Include description of symptoms and all pertinent details.
CAMPBELL SCIENTIFIC (CANADA) CORP. does not accept collect calls.
Non-warranty products returned for repair should be accompanied by a purchase order to
cover repair costs.

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MODEL HMP45C212
TEMPERATURE AND RELATIVE HUMIDITY PROBE
1. GENERAL
The Model HMP45C212 probe contains a Vaisala
capacitive relative humidity sensor and a YSI
44212 thermistor as per attached documentation in
Appendix A. The probe is designed to be housed
in the 41002-2 12 Plate Gill Radiation Shield, or
equivalent; a ten foot lead length is standard.
Longer lead lengths are available up to 1000 feet.
Voltage drop in the longer lead lengths will lower
the RH reading by approximately 0.6% RH per 100
feet of cable. Do not extend lead lengths by adding
wire to the pigtail (connection) end or measurement
errors will result.
2. ACCURACY – TEMPERATURE SENSOR
Refer to Appendix A for details regarding the YSI
44212 thermistor.
3. RH SENSOR – SPECIFICATIONS
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: 0.15 seconds
Sensor: HUMICAP® 180
Relative Humidity Measurement Range:
0 to 100% non-condensing
RH Output Signal Range: 0.008 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: ±0.05% RH/°C
Typical Long Term Stability:
Better than 1% RH per year
Response Time (at 20°C, 90% response):
15 seconds with membrane filter
4. INSTALLATION
The HMP45C212 must be housed inside a radiation
shield when used in the field. The 41002 Radiation
Shield (Figure 1) mounts to a CM6/CM10 tripod or UT10
tower. The UT018 mounting arm and UT12VA Radiation
Shield mount to a UT30 tower (Figure 2).
A lead length of 6 feet allows the HMP45C212 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.
NOTE: Do not connect the power control lead and
the temperature excitation to the same excitation
channel. The power control will slow the response of
the excitation and result in temperature errors.

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FIGURE 1. HMP45C212 and 41002 Radiation Shield on a CM6/CM10 Tripod Mast or UT10 Tower leg
FIGURE 2. HMP45C212 with UT018 Mounting Bracket and Crossarm and
UT12VA Radiation Shield Mounted on a UT30 Tower
Red (+12V) Datalogger +12V
Yellow (Power Control) Control Port
Purple (RH Power GND) Ground (G or )
Clear (Shield GND) Ground (G or )
Green (RH Signal) Single Ended Input
Black (Temp. Excitation) Switched Excitation
Orange (Temp. Signal) Single Ended Input
White (Temp. GND) Analog Ground ( AG or )
FIGURE 3. HMP45C212 Probe Datalogger Connection

HMP45C212 TEMPERATURE AND RH PROBE
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TABLE 1. Datalogger Connections for Single-Ended Measurements
Description Colour 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
Power Control Yellow Control Port Control Port Control Port
Power Red 12 V 12 V 12 V
Power Ground Purple AG
Shield Clear G
Temperature Excitation Black Switched Excitation Switched Excitation Switched Excitation
5. WIRING
Connections to the datalogger for the HMP45C212
are shown in Figure 3 and Table 1. The probe
requires two single ended analog measurements,
the green (RH) and the orange (temp.) leads can
be inserted into either HI or LO inputs.
The black thermistor excitation lead connects to
any excitation channel. The yellow lead is used to
control switching 12 volts to the relative humidity
sensor and is connected to a control port. The
number of HMP45C212 probes per excitation
channel is physically limited by the number of lead
wires that can be inserted into a single excitation
terminal (approximately 10).
The white lead connects to Analog ground.
Analog ground, labelled “AG” on the CR10X, is the
same as Ground (G) for the 21X and CR7. The
clear lead is the shield which connects to Ground
(G) on the datalogger.
6. PROGRAMMING
Program Instruction 4 is used to measure the
temperature.
Program Instruction 4 sets an excitation voltage to
the thermistor bridge then makes a single ended
voltage measurement. The thermistor portion of
the probe has a linear millivolt output over the –50
to +50 Celsius range. A multiplier of 0.07154 and
an offset of –72.789 provides output of
temperature in Celsius.
The HMP45C212 output scale is 0 to 1000
millivolts for the relative humidity range of 0 to
100%. On the RH measurement, use a multiplier
of 0.1 for percent and a multiplier of 0.001 for
fraction output. The RH measurement does not
require an offset.
Example 1. Sample CR10(X) Program Using Single-Ended Measurement Instructions
;Measure the HMP45C212 temperature.
;
01: P 4 Excite, Delay, Volt (SE)
1: 1 Rep
2: 5 2500 mV Slow Range ; CR510 (2500mV); CR23X, 21X, CR7 (5000mV)
3: 3 IN Chan ; Orange Wire (SE3)
4: 1 EX Chan
5: 0 Delay
6: 2500 mV Excitation
7: 1 Loc [Air Temp.]
8: .07154 Mult ; Degrees Celsius
9: -72.789 Offset ; Degrees Celsius
;Turn the HMP45C212 RH circuitry on.
;
02: Do (P86)
1: 41 Set Port 1 High ; Yellow wire (C1)

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;Pause 150 mSec, before making measurements, so the
;probe can stabilize on true readings.
;
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 HMP45C212 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)
4: 2 Loc [ RH_pct ]
5: .1 Mult ; mult 0.1 for percent RH, mult 0.001 for fraction
6: 0 Offset
;Turn the HMP45C212 off.
;
05: Do (P86)
1: 51 Set Port 1 Low ; Yellow wire (C1)
7. MAINTENANCE
The HMP45C212 Probe requires minimal maintenance.
Check monthly to make sure the radiation shield is free
from debris. The black screen on the sensor’s end
should also be checked.
When installed in close proximity to the ocean or other
bodies of salt water (e.g., Great Salt Lake), a coating of
salt (mostly NaCl) may build up on the radiation shield,
sensor, filter and even the chip. NaCl has an affinity for
water. The humidity over a saturated NaCl solution is
75%. A buildup of salt on the filter or chip will delay or
destroy the response to atmospheric humidity.
The filter can be rinsed gently in distilled water. If
necessary, the chip can be removed and rinsed as well.
Do not scratch the chip while cleaning.
Long term exposure of the HUMICAP® relative humidity
sensor to certain chemicals and gases may affect the
characteristics of the sensor and shorten its life. Table 2
lists the maximum ambient concentrations, of some
chemicals, that the HUMICAP® can be exposed to.
Detailed information on allowed concentrations can be
requested from Campbell Scientific representatives.
Table 2. Chemical Tolerances of HMP45C212
Chemical Concentration (PPM)
Organic solvents 1,000 to 10,000
Aggressive Chemicals
(e.g. SO2, H2SO4,
H2S, HCL, CL2, etc.)
1 to 10
Weak Acids 100 to 1,000
Bases 10,000 to 100,000
Recalibrate the HMP45C212 annually. Obtain an
RMA number before returning the HMP45C212 to
Campbell Scientific for recalibration.
8. REFERENCES
Goff, J.A. and S. Gratch, 1946: Low-pressure
properties of water from -160° to 212°F, Trans.
Amer. Soc. Heat. Vent. Eng., 51, 126-164.
Lowe, P.R., 1977: An approximating polynomial
for the computation of saturation vapour
pressure, J. Appl. Meteor., 16, 100-103.
Weiss, A., 1977: Algorithms for the calculation of
moist air properties on a hand calculator, Amer.
Soc. Ag. Eng., 20, 1133-1136.