Campbell EE181 User manual

Revision: 10/2021
Copyright © 2016 – 2021
Campbell Scientific, Inc.

Table of contents
1. Introduction 1
2. Precautions 1
3. Initial inspection 1
4. QuickStart 2
5. Overview 4
6. Specifications 5
6.1 Temperature measurement 5
6.2 Relative humidity measurement 6
7. Installation 7
7.1 Wiring to data logger 7
7.2 Data logger programming 7
7.2.1 VoltSE() instruction 8
7.3 Mounting 8
7.3.1 Shield installation 10
7.3.1.1 Installation in a RAD10E 10-plate shield 11
7.3.1.2 Installation in a 41003-5 10-plate shield 11
7.3.2 Mount the shield 11
8. Operation 12
8.1 Measurement 12
8.2 Low power operation 12
8.3 Long cable lengths 12
8.4 Absolute humidity 13
8.4.1 Measurement below 0 °C 14
9. Troubleshooting and maintenance 14
9.1 Troubleshooting 15
9.2 Maintenance 15
Table of contents - i

10. Attributions and References 16
Appendix A. Importing Short Cut code into CRBasic Editor 17
Appendix B. Example programs 18
Table of contents - ii

1. Introduction
The EE181 is a rugged, accurate temperature and relative humidity probe that is ideal for long-
term, unattended applications in all climates. The probe uses an E+E Elektronik® capacitive RH
element with a proprietary coating to measure relative humidity and a 1000Ω PRT to measure
temperature. For optimum results, the EE181 should be recalibrated annually.
For Edlog data logger support, contact Campbell Scientific.
2. Precautions
lREAD AND UNDERSTAND the Safety section at the back of this manual.
lCare should be taken when opening the shipping package to not damage or cut the cable
jacket. If damage to the cable is suspected, contact Campbell Scientific.
lAlthough the EE181 is rugged, it should be handled as a precision scientific instrument.
lDo not touch the sensor element.
lSantoprene® rubber, which composes the black outer jacket of the cable, will support
combustion in air. It is used because of its resistance to temperature extremes, moisture,
and UV degradation. It is rated as slow burning when tested according to U.L. 94 H.B. and
passes FMVSS302. However, local fire codes may preclude its use inside buildings.
3. Initial inspection
lUpon receipt of the EE181, inspect the packaging and contents for damage. File damage
claims with the shipping company.
lThe model number and cable length are printed on a label at the connection end of the
cable. Check this information against the shipping documents to ensure the expected
product and cable length were received.
EE181 Temperature and Relative Humidity Probe 1

4. QuickStart
A video that describes data logger programming using Short Cut is available at:
www.campbellsci.com/videos/cr1000x-data logger-getting-started-program-part-3 .Short
Cut is an easy way to program your data logger to measure the sensor and assign data logger
wiring terminals. Short Cut is available as a download on www.campbellsci.com . It is included
in installations of LoggerNet,RTDAQ, and PC400.
Use the following procedure to get started.
1. Open Short Cut and click Create New Program.
2. Double-click the data logger model.
3. In the Available Sensors and Devices box, type EE181 or locate the sensor in the Sensors >
Meteorological >Relative Humidity & Temperature >EE181 Temperature and Relative
Humidity Sensor folder. Double-click either EE181 (constant power) or EE181 (panel
switched power); the panel switched power option uses less current but requires a scan
rate that is greater than 5 seconds. Data defaults to degree Celsius. This can be changed by
clicking the Deg C box and selecting Deg F, for degrees Fahrenheit, or Kfor Kelvin.
EE181 Temperature and Relative Humidity Probe 2

4. Click the Wiring tab to see how the sensor is to be wired to the data logger. Click OK after
wiring the sensor.
5. Repeat steps three and four for other sensors.
6. In Output Setup, type the scan rate, meaningful table names, and Data Output Storage
Interval.
NOTE:
The EE181 has a two second settling time after power up; therefore, the scan rate must
be greater than two seconds when using the panel switched power option.
EE181 Temperature and Relative Humidity Probe 3

7. Select the measurement and its associated output option.
8. Click Finish and save the program. Send the program to the data logger if the data logger
is connected to the computer.
9. If the sensor is connected to the data logger, check the output of the sensor in the data
display in LoggerNet,RTDAQ, or PC400 to make sure it is making reasonable
measurements.
5. Overview
The EE181 is a digital probe with linear voltage outputs for temperature and humidity. Its voltage
signals are measured with two single-ended inputs on the data logger.
Campbell Scientific recommends 12 V power when used with our data loggers. When minimizing
power use is important, power can be switched on and off for the measurement, provided there
is a two-second warm-up delay. Switching power avoids constant current flow through data
logger ground, which can affect the accuracy of low-level single-ended voltage measurements.
The EE181 uses a metal mesh filter with excellent response, protection against dust, and no water
absorption.
Features:
lWell-suited for long-term, unattended applications
lAccurate and rugged
lCompatible with the following CRBasic data loggers: CR6, CR1000X, CR800series,
CR300series, CR3000, CR1000
EE181 Temperature and Relative Humidity Probe 4

6. Specifications
Operating temperature: –40 to 60 °C
Storage temperature: –40 to 80 °C
Probe length: 160 mm (6.3 in), 172 mm (6.77 in) including connector
Probe diameter: 21 mm (0.83 in)
Weight with 5 m cable: 290 g (10.2 oz)
Housing: Plastic material / IP65
Filter: 30 µm pore size, stainless steel mesh
Power consumption: <1.2 mA at 12 V
Supply voltage (using Campbell
Scientific cable): 7 to 30 VDC (12 VDC recommended)
Start-up time: 2 s typical
Maximum cable length: 300 m (1000 ft) with 12 V power
Analog outputs
Offset at 0 V: ±3 mV (maximum)
Deviation from digital signal: < ±1 mV (0.1 °C, 0.1% RH)
Compliance: View the EU Declaration of Conformity at
www.campbellsci.com/ee181-l
6.1 Temperature measurement
Sensor: Pt1000 Class A
Measurement range: –40 to 60 °C
Output signal range: 0 to 1.0 V
Accuracy at 23 °C: ±0.2 °C
Long term stability: <0.1 °C/year
EE181 Temperature and Relative Humidity Probe 5

Sensor time constant [63% step
change (1 m/s air flow at sensor)]
Standard PE filter: ≤22 s
Optional Teflon filter: ≤30 s
Accuracy over measurement range:
6.2 Relative humidity measurement
Sensor: HC101
Measurement range: 0 to 100% non-condensing
Output signal range: 0 to 1.0 VDC
Accuracy*
(including hysteresis, non-linearity
and repeatability, traceable to
international standards,
administrated by NIST, PTB, BEV)
–15 to 40 °C: ≤90% RH ± (1.3 + 0.003 • RH reading) % RH
–15 to 40 °C: >90% RH ± 2.3% RH
–25 to 60 °C: ± (1.4 + 0.01 • RH reading) % RH
–40 to 60 °C: ± (1.5 + 0.015 • RH reading) % RH
Typical long-term stability: <1% RH per year
Sensor time constant [63% of a 35
to 80% RH step change (1 m/s air
flow at sensor)]
Standard PE filter: ≤22 s
Optional Teflon filter: ≤30 s
EE181 Temperature and Relative Humidity Probe 6

* The accuracy statement includes the uncertainty of the factory calibration with an enhancement factor k=2 (2-
times standard deviation).
The accuracy was calculated in accordance with EA-4/02 and with regard to GUM (Guide to the Expression of
Uncertainty in Measurement).
7. Installation
If you are programming your data logger with Short Cut, skip Wiring to data logger (p. 7) and
Data logger programming (p. 7). Short Cut does this work for you. See QuickStart (p. 2) for a
Short Cut tutorial.
7.1 Wiring to data logger
Connections to Campbell Scientific data loggers for measuring humidity and temperature using
two single-ended analog inputs are given in Table 7-1 (p. 7). See Long cable lengths (p. 12) for a
discussion on errors caused by long cable lengths.
Table 7-1: Wire color, function, and data logger connection for single-ended measurement
Wire color Wire function Data logger connection terminal
Yellow Temperature signal Uconfigured for single-ended analog input1,
SE (single-ended, analog-voltage input)
Blue Relative humidity signal Uconfigured for single-ended analog input,
SE
Black Signal reference ⏚(analog ground)
Clear Shield ⏚
Red Power 12V or SW12V
1Uterminals are automatically configured by the measurement instruction.
7.2 Data logger programming
Short Cut is the best source for up-to-date programming code for Campbell Scientific data
loggers. If your data acquisition requirements are simple, you can probably create and maintain a
data logger program exclusively with Short Cut. If your data acquisition needs are more complex,
the files that Short Cut creates are a great source for programming code to start a new program
or add to an existing custom program.
EE181 Temperature and Relative Humidity Probe 7

NOTE:
Short Cut cannot edit programs after they are imported and edited in CRBasic Editor.
AShort Cut tutorial is available in QuickStart (p. 2). If you wish to import Short Cut code into
CRBasic Editor to create or add to a customized program, follow the procedure in Importing
Short Cut code into CRBasic Editor (p. 17). Programming basics for CRBasic data loggers are
provided in the following sections. Complete program examples for select data loggers can be
found in Example programs (p. 18).
Measure the EE181 with the VoltSE() measurement instruction as described in the following
section.
For a discussion on errors caused by long cable lengths, see Long cable lengths (p. 12).
7.2.1 VoltSE() instruction
When cable lengths are shorter than 6.1 meters or when power is switched, use the VoltSE()
measurement instruction to measure the temperature and relative humidity. The EE181 output
scale is 0 to 1000 millivolts for the temperature range of –40 to 60°C and for the relative humidity
range of 0 to 100%.
VoltSE(Dest, Reps, Range, SEChan, MeasOff, SettlingTime, Integ/FNotch, Mult, Offset)
Variations:
lTemperature reported as °C – set Mult to 0.1 and Offset to –40
lTemperature reported as °F – set Mult to .18 and Offset to –40
lHumidity reported as a percent – set Mult to 0.1 and Offset to 0
lHumidity reported as a fraction – set Mult to 0.001 and Offset to 0
NOTE:
When the probe is connected to a CS110 Electric Field Meter, the probe is measured by the
CS110 internal CR1000 data logger module using VoltSE() instructions. Relative humidity
and temperature signals are measured on single-ended terminals 1 and 2, respectively.
250µs integration should be used in the VoltSE() instructions.
7.3 Mounting
Sensors should be located over an open level area at least 9m (EPA) in diameter. The surface
should be covered by short grass or the natural earth surface where grass does not grow.
Sensors should be located at a distance of at least four times the height of any nearby
EE181 Temperature and Relative Humidity Probe 8

obstruction, and at least 30m (EPA) from large, paved areas. Sensors should be protected from
thermal radiation, and adequately ventilated.
Standard measurement heights:
1.5 m (AASC)
1.25 to 2.0 m (WMO)
2.0 m (EPA)
See Attributions and References (p. 16) for a list of references that discuss temperature and
relative humidity sensors.
When used in the field, the EE181 must be housed in a radiation shield such as the RAD10E
naturally aspirated shields.
The white color of these shields reflects solar radiation, and the louvered construction allows air
to pass freely through, thereby keeping the probe at or near ambient temperature. The RAD10E
uses a double-louvered design that offers improved sensor protection from insect intrusion and
driving rain and snow. In addition, the RAD10E shield has lower self-heating in bright sunlight
combined with higher temperatures (>24°C (75°F)) and low wind speeds (<2m/s (4.5mph)),
giving a better measurement.
The RAD10E radiation shield attaches to a crossarm, mast, or user-supplied pipe with a 2.5 to
5.3cm (1.0 to 2.1in) outer diameter. See FIGURE 7-2 (p. 12) for an example of shield mounting.
The optimal location for the EE181 sensor tip inside a multi-plate shield is approximately 1/3 to 1/2
of the way down from the top shield plate. With a ten-plate shield, the tip of the EE181 should be
located around three to four plates down from the top of the shield. See FIGURE 7-1 (p. 10).
EE181 Temperature and Relative Humidity Probe 9

FIGURE 7-1. EE181 sensor placement in a RAD10E multi-plate shield
Tools required:
l1/2 inch open-end wrench
lsmall screwdriver provided with data logger
lUV-resistant cable ties
lsmall pair of diagonal-cutting pliers
lAdjustable wrench with a minimum 1-7/8 inch jaw size
Attach the probe to the cable by aligning the keyed connectors, pushing the connectors
together, and finger tightening the knurled ring.
CAUTION:
Only finger tighten the knurled ring. Using a wrench may damage the connector.
7.3.1 Shield installation
Campbell Scientific recommends the EE181 with the MetSpec RAD10E multi-plate radiation shield
due to shield performance in bright sunlight and low wind speeds as well as over snow or
reflective surfaces. The EE181 will work with the RM Young 10-plate shield but requires an adapter
to accommodate sensor girth.
EE181 Temperature and Relative Humidity Probe 10

NOTE:
Do not mount the shield or route the sensor cable into the enclosure until after the EE181 is
installed inside the shield.
7.3.1.1 Installation in a RAD10E 10-plate shield
1. Loosen the nut on the entry gland at the bottom of the shield.
2. Insert sensor into the bottom of the multi-plate shield. Situate the gland so it’s 1.25 to
2.5cm (0.5 to 1in) above the sensor connector. See FIGURE 7-1 (p. 10).
3. Using an adjustable wrench, tighten down the nut on the gland until the sensor is held
firmly in place. Do not overtighten.
7.3.1.2 Installation in a 41003-5 10-plate shield
1. Slide the adapter over the sensor body and situate the adapter so it’s 1.25 to 2.5cm (0.5 to
1in) above the sensor connector.
2. Insert sensor and adapter into the bottom of the multi-plate shield.
3. Hold the collar and sensor and finish threading the collar into the shield by hand. Tighten
the collar around the probe until it firmly grips the body of the probe. Use an adjustable
wrench if necessary, but do not overtighten the collar.
7.3.2 Mount the shield
1. Attach the radiation shield to the tripod mast, crossarm, or tower leg using the supplied
U-bolt. See FIGURE 7-2 (p. 12) for an example of shield mounting.
2. Route the cable to the data logger, and secure the cable to the mounting structure using
cable ties.
CAUTION:
Failure to secure the cable can lead to breakage of the wires due to fatigue caused by
blowing back and forth in the wind.
EE181 Temperature and Relative Humidity Probe 11

FIGURE 7-2. EE181 and RAD10E solar radiation shield on a tripod mast
8. Operation
8.1 Measurement
The probe uses E+E Elektronik coated HC101 capacitive sensor to measure RH and a 1000Ω PRT
to measure temperature. Campbell Scientific data loggers measure the analog voltage outputs of
the EE181 Temperature and Relative Humidity Probe with the VoltSE() measurement
instruction.
8.2 Low power operation
The EE181 draws less than 1.2mA powered from 12V. The EE181 can be continuously powered
from the 12V terminal, or power can be switched with the SW12V terminal to conserve battery life.
When power is switched, a two-second warm-up period is required. This is programmed with the
Delay() instruction, using 0 for the delay option.
8.3 Long cable lengths
Long cable lengths cause errors in the measured temperature and relative humidity. The
approximate error in temperature and relative humidity is 0.31°C and 0.31% per 100 feet of cable
length, respectively.
EE181 Temperature and Relative Humidity Probe 12

When long cable lengths are required and the above errors in temperature and relative humidity
are unacceptable, use the HMP155A temperature and relative humidity probe instead.
Understanding the following details are not required for the general operation of the EE181 with
Campbell Scientific data loggers. The signal reference and the power ground (black) are the
same wire in the EE181. When the EE181 temperature and relative humidity are measured, both
the signal reference and power ground are connected to ground at the data logger. The signal
reference/power ground wire serves as the return path for 12V. There will be a voltage drop
along this wire because the wire has resistance. The EE181 draws approximately 1.2mA (worst
case) when it is powered. The wire used in the EE181 has resistance of 25.67Ω/1000 feet. Using
Ohm’s law, the voltage drop (Vd), along the signal reference/power ground wire, is given by Eq. 1
(p. 13).
Eq. 1
This voltage drop will raise the apparent temperature and relative humidity because the
difference between the signal and signal reference at the data logger has increased by Vd.
8.4 Absolute humidity
The EE181 measures relative humidity. Relative humidity is defined by the following equation:
Eq. 2
where RH is the relative humidity, e is the vapor pressure in kPa, and esis the saturation vapor
pressure in kPa. The vapor pressure, e, is an absolute measure of the amount of water vapor in
the air and is related to the dewpoint temperature. The saturation vapor pressure is the
maximum amount of water vapor that air can hold at a given air temperature. The relationship
between dewpoint and vapor pressure, and air temperature and saturation vapor pressure are
given by Goff and Gratch (1946), Lowe (1977), and Weiss (1977). Relative humidity is relative to
saturation above water, even below freezing point. This is why these sensors should not measure
100% RH below zero degrees C, as described in Measurement below 0 °C (p. 14).
When the air temperature increases, so does the saturation vapor pressure. Conversely, a
decrease in air temperature causes a corresponding decrease in saturation vapor pressure. It
follows then from Eq. 2 (p. 13) that a change in air temperature will change the relative humidity,
without causing a change absolute humidity.
EE181 Temperature and Relative Humidity Probe 13

For example, for an air temperature of 20°C and a vapor pressure of 1.17kPa, the saturation
vapor pressure is 2.34kPa and the relative humidity is 50%. If the air temperature is increased by
5°C and no moisture is added or removed from the air, the saturation vapor pressure increases
to 3.17kPa and the relative humidity decreases to 36.9%. After the increase in air temperature,
the air can hold more water vapor. However, the actual amount of water vapor in the air has not
changed. Thus, the amount of water vapor in the air, relative to saturation, has decreased.
Because of the inverse relationship between relative humidity and air temperature, finding the
mean relative humidity is meaningless. A more useful quantity is the mean vapor pressure. The
mean vapor pressure can be computed online by the data logger (see CRBasic Example 2 (p. 19)).
8.4.1 Measurement below 0 °C
The EE181 provides a humidity reading that is referenced to the saturated water vapor pressure
above liquid water, even at temperatures below 0°C, where ice might form. This is the common
way to express relative humidity and is as defined by the World Meteorological Organization. If
an RH value is required referenced to ice, the EE181 readings will need to be corrected.
One consequence of using water as the reference is that the maximum humidity that will
normally be output by the sensor for temperatures below freezing is as follows:
100% RH at 0 °C 82% RH at –20 °C
95% RH at –5 °C 78% RH at –25 °C
91% RH at –10 °C 75% RH at –30 °C
87% RH at –15 °C
In practical terms this means that, for instance, at –20°C the air is effectively fully saturated when
the sensor outputs 82% RH.
9. Troubleshooting and
maintenance
NOTE:
All factory repairs and recalibrations require a returned materials authorization (RMA) and
completion of the “Declaration of Hazardous Material and Decontamination” form. Refer to
the Assistance page at the end of this manual for more information.
EE181 Temperature and Relative Humidity Probe 14

9.1 Troubleshooting
Symptom: Relative Humidity is reported as –9999, NAN, –40°C, or 0%
1. Check that the sensor is wired to the correct analog input terminals as specified by the
measurement instructions.
2. Verify the range code for the single-ended measurement instruction is correct for the data
logger type.
3. Verify the red power wire is correctly wired to the 12V or SW12V terminal. The terminal the
wire is connected to will depend on the data logger program.
Connect the red wire to a 12V terminal to constantly power the sensor for troubleshooting
purposes. With the red wire connected to 12V, a voltmeter can be used to check the output
voltage for temperature and relative humidity on the yellow and blue wires respectively
(temperature °C = mV•0.14– 40.0; relative humidity %=mV•0.1).
Symptom: Incorrect temperature or relative humidity
1. Verify the multiplier and offset parameters are correct for the desired units (VoltSE()
instruction (p. 8)).
9.2 Maintenance
The EE181 probe requires minimal maintenance, but dust, debris, and salts on the filter cap will
degrade sensor performance. Check the metal mesh filter on the end of the sensor for debris. If
dirt or salt is engrained into the filter, it should be cleaned with distilled water or replaced. For
particularly stubborn contamination, swish the entire probe tip in isopropyl alcohol (rubbing
alcohol) and rinse off with distilled water. Make sure the filter is connected firmly with your
fingers — do not over tighten.
Check the radiation shield monthly to make sure it is free from dust and debris. To clean the
shield, remove the sensor from the shield. Dismount the shield. Brush all loose dirt off. If more
effort is needed, use warm, soapy water and a soft cloth or brush to thoroughly clean the shield.
Allow the shield to dry before remounting.
Replace filters that cannot be successfully cleaned. To replace the filter, unscrew the filter from
the probe and pull it straight away, being careful not to bend or damage the sensors. Before
putting on the replacement filter, check the alignment of the sensors with the probe, and if
necessary, carefully correct the alignment before installing the filter.
EE181 Temperature and Relative Humidity Probe 15

A coating of salt (mostly NaCl) may build up on the radiation shield, sensor, filter and even the
sensor element. A buildup of salt on the filter or sensors will delay or destroy the response to
atmospheric humidity.
Long-term exposure of the relative humidity sensor to certain chemicals and gases may affect
the characteristics of the sensor and shorten its life. The resistance of the sensor depends
strongly on the temperature and humidity conditions and the length of the pollutant influence.
The sensor should be calibrated annually. Please refer to the Limited warranty and Assistance
sections at the end of the manual for more information.
10. Attributions and References
E+E Elektronik® is a registered trademark of E+E Elektronik Ges.m.b.H.
Santoprene®is a registered trademark of Exxon Mobile Corporation.
AASC, 1985: The State Climatologist (1985) Publication of the American Association of State
Climatologists: Heights and Exposure Standards for Sensors on Automated Weather Stations,
v. 9, No. 4 October, 1985. (www.stateclimate.org/publications/state-climatologist/NOAA-
NCY-SCBOOKS-SC77097/00000029.pdf)
EPA, 2000: Meteorological Monitoring Guidance for Regulatory Modeling Applications, EPA-
454/R-99-005. Office of Air Quality Planning and Standards, Research Triangle Park, North
Carolina 27711.
EPA, 2008: Quality Assurance Handbook for Air Pollution Measurement Systems, Vol. IV,
Meteorological Measurements, Ver. 2.0, EPA-454/B-08-002 (revised 2008). Office of Air
Quality Planning and Standards, Research Triangle Park, NC 27711.
Goff, J. A. and S. Gratch, 1946: Low-pressure properties of water from -160° to 212°F, Trans. Amer.
Soc. Heat. Vent. Eng.,51, 125-164.
Lowe, P. R., 1977: An approximating polynomial for the computation of saturation vapor 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.
WMO, 2008. Guide to Meteorological Instruments and Methods of Observation. World
Meteorological Organization No. 8, 7th edition, Geneva, Switzerland.
EE181 Temperature and Relative Humidity Probe 16

Appendix A. Importing Short
Cut code into CRBasic Editor
Short Cut creates a .DEF file that contains wiring information and a program file that can be
imported into the CRBasic Editor. By default, these files reside in the C:\campbellsci\SCWin folder.
Import Short Cut program file and wiring information into CRBasic Editor:
1. Create the Short Cut program. After saving the Short Cut program, click the Advanced tab
then the CRBasic Editor button. A program file with a generic name will open in CRBasic.
Provide a meaningful name and save the CRBasic program. This program can now be
edited for additional refinement.
NOTE:
Once the file is edited with CRBasic Editor,Short Cut can no longer be used to edit the
program it created.
2. To add the Short Cut wiring information into the new CRBasic program, open the .DEF file
located in the C:\campbellsci\SCWin folder, and copy the wiring information, which is at
the beginning of the .DEF file.
3. Go into the CRBasic program and paste the wiring information into it.
4. In the CRBasic program, highlight the wiring information, right-click, and select Comment
Block. This adds an apostrophe (') to the beginning of each of the highlighted lines, which
instructs the data logger compiler to ignore those lines when compiling. The Comment
Block feature is demonstrated at about 5:10 in the CRBasic | Features video .
EE181 Temperature and Relative Humidity Probe 17