Campbell HygroVUE 5 User manual

Revision: 11/2022
Copyright © 2019– 2022
Campbell Scientific, Inc.

Table of contents
1. Introduction 1
2. Precautions 1
3. Initial inspection 1
4. QuickStart 2
5. Overview 5
6. Specifications 5
6.1 Temperature measurement 6
6.2 Relative humidity measurement 6
7. Installation 7
7.1 Wiring to data logger 7
7.2 Data logger programming 8
7.3 CRBasic programming 8
7.4 Siting 9
7.4.1 Installation in a RAD06 radiation shield 10
7.4.2 Mount the shield 11
8. Operation 12
8.1 Sensor measurement 12
8.2 Measurements in programs with fast scan rates 14
8.3 Long cables 14
8.4 Power conservation 15
8.5 Measuring multiple SDI-12 sensors 15
9. Troubleshooting and maintenance 15
9.1 Troubleshooting 16
9.2 Maintenance 16
9.3 Calibration 17
9.4 Sensor element replacement 17
Table of Contents - i

10. Attributions and references 19
Appendix A. Importing Short Cut code into CRBasic Editor 21
Appendix B. CRBasic example program 22
Appendix C. Environmental performance 24
C.1 Exposure to pollutants 24
C.2 Operating range of the RH element 24
C.3 Measurement below 0 °C 25
Appendix D. SDI-12 sensor support 26
D.1 SDI-12 command basics 26
D.1.1 Acknowledge active command (a!) 27
D.1.2 Send identification command (al!) 27
D.1.3 Start verification command (aV!) 28
D.1.4 Address query command (?!) 28
D.1.5 Change address command (aAb!) 28
D.1.6 Start measurement commands (aM!) 29
D.1.7 Start concurrent measurement commands (aC!) 29
D.1.8 Start measurement commands with cyclic redundancy check (aMC! and aCC!) 31
D.1.9 Stopping a measurement command 31
D.1.10 Send data command (aD0! … aD9!) 31
D.1.11 Continuous measurement command (aR0! … aR9!) 32
D.2 References 32
D.3 SDI-12 transparent mode 32
D.3.1 Changing an SDI-12 address 33
Appendix E. Sensor element calibration 36
Table of Contents - ii

1. Introduction
The HygroVUE™5 Temperature and Relative Humidity Sensor is designed for general
meteorological and environmental applications. It is the entry level sensor in the HygroVUE line
of Relative Humidity and Temperature sensors. The HygroVUE sensors feature a low
maintenance design with a highly stable and accurate replaceable RH chip that will lower the
total cost of deployment throughout a network. The HygroVUE 5 uses the SDI-12
communications protocol to communicate with any SDI-12 recorder, simplifying wiring and
programming.
2. Precautions
lREAD AND UNDERSTAND the Safety section at the back of this manual.
lWhen opening the shipping package, do not damage or cut the cable jacket. If damage to
the cable is suspected, consult with a Campbell Scientific support engineer.
lAlthough rugged, the HygroVUE 5 should be handled as a precision scientific instrument.
3. Initial inspection
lCheck the packaging and contents of the shipment. If damage occurred during transport,
immediately file a claim with the carrier. Contact Campbell Scientific to facilitate repair or
replacement.
lCheck model information against the shipping documents to ensure the expected products
and the correct lengths of cable are received. Model numbers are found on each product.
On cables and cabled items, the model number is usually found at the connection end of
the cable. Report any shortages immediately to Campbell Scientific.
HygroVUE™5 Temperature and Relative Humidity Sensor 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.
The following procedure also shows using Short Cut to program the sensor.
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 HygroVUE5 or locate the sensor in the
Sensors >Meteorological >Relative Humidity & Temperature folder. Double-click
HygroVUE5/HygroVUE10 Temperature & Relative Humidity Sensor. Temperature units
default to degrees Celsius. This can be changed by clicking the Deg C box and selecting
Deg F, for degrees Fahrenheit, or Kfor Kelvin. SDI-12 Address defaults to 0. Enter the
correct SDI-12 Address for the HygroVUE 5 if it has been changed from the factory-set
default value.
HygroVUE™5 Temperature and Relative Humidity Sensor 2

4. Click the Wiring tab to see how the sensor is to be wired to the data logger. The default
control terminal for SDI-12 is C1. To change to another terminal, click the terminal name
and select another terminal. Click OK after wiring the sensor.
5. Repeat steps three and four for other sensors you want to measure. Click Next.
6. In Output Setup, type the scan rate (5 seconds or longer), meaningful table names, and the
Data Output Storage Interval. Click Next.
NOTE:
Making measurements from the HygroVUE 5 more frequently than 5 seconds can result
in small additional errors due to self-heating of the element. If the main scan rate needs
to be faster than this, please read Sensor measurement (p. 12) and Measurements in
programs with fast scan rates (p. 14) about alternate programming techniques.
HygroVUE™5 Temperature and Relative Humidity Sensor 3

7. Select the measurement and its associated output option.
8. Click Finish and save the program. Send the program just created 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.
HygroVUE™5 Temperature and Relative Humidity Sensor 4

5. Overview
The HygroVUE 5 sensor uses a single-chip element that incorporates both a temperature and an
RH sensor. Each element is individually calibrated with the calibration corrections stored on the
chip. The element is easily changed in the field, reducing downtime and calibration costs.
Electronics within the HygroVUE 5 control the measurement made by the sensor element, apply
temperature and linearization corrections to the readings, and present the data via SDI-12 to a
data logger.
A stainless steel mesh filter minimizes the effects of dust and dirt on the sensor while allowing air
exchange around the sensor element and reducing the chances of condensation remaining
inside the filter cap. A small PTFE membrane filter is bonded to the surface of the element which
prevents any finer dust or mold from directly influencing the measurement.
The sensor housing is designed to withstand permanent exposure to weather and to fit into a
range of radiation shields, including compact shields.
6. Specifications
Compatibility: Fully SDI-12 V1.3-compliant digital output (verified with an SDI-12
Verifier (www.sdi-12-verifier.com ).
Compatible with SDI-12 V1.4 recorders including Campbell
Scientific CR6, CR3000, CR1000X, CR800-series, CR300-series, and
CR1000 data loggers
Sensor element: Sensirion SHT35 derivative
Calibration traceability: NIST and NPL standards. See Sensor element calibration (p. 36)
for details of calibration traceability.
Supply voltage: 7 to 28 VDC
Current consumption: 50 µA quiescent, typical
0.6 mA during 0.5 s measurement typical
Warm-up time: Sensor normally powered all the time, if power is switched allow
1.8 s for sensor power-up.
Diameter: 12.5 mm (0.49 in) at sensor tip, maximum 16 mm (0.63 in) at the
cable end
HygroVUE™5 Temperature and Relative Humidity Sensor 5

Length: 115 mm (4.52 in), sensor only, without cable
Housing material: White PET-P
Housing classification: IP67 (electronics housing)
Sensor protection: Outer glass-filled polypropylene cap fitted with a stainless steel
mesh dust filter with nominal pore size of <30 µm. The sensor
element is fitted with a PTFE protective film with a filtration
efficiency of >99.99% for particles of 200 nm or larger size.
EMC compliance: Tested and conforms to IEC61326:2013
Calibration: The sensor element is individually calibrated during manufacture.
Compliance documents: View at www.campbellsci.com/hygrovue5
6.1 Temperature measurement
Operating range: –40 to 70 °C
Accuracy*: ±0.4 °C (–40 to 70 °C)
±0.3 °C (20 to 60 °C)
Long term drift: <±0.03 °C/year
Reported resolution: 0.001 °C
Repeatability**: 0.04 °C
Response time: 130 s (63% response time in air moving at 1 m/s)
Units: Degrees Celsius
*The accuracy figures quoted are relative to factory standards.
**Values are 3 standard deviations of 25 measurements at constant temperature.
6.2 Relative humidity measurement
Operating range: 0 to 100% RH
Accuracy (at 25°C)*: ±1.8% (0 to 80% RH)
±3% (80 to 100% RH)
Temperature dependence: < ±1% RH (–40 to 60 °C)
Short term hysteresis: < ±1% RH
Long-term stability: ±0.5% per year (drift in clean air conditions)
HygroVUE™5 Temperature and Relative Humidity Sensor 6

Reported resolution: 0.001% RH
Repeatability**: 0.05% RH
Response time with filter: 8 s (63% response time in air moving at 1 m/s @ 25 °C)
Environmental performance: See Environmental performance (p. 24)
*The accuracy figures quoted are relative to factory standards.
**Values are 3 standard deviations of 25 measurements at constant humidity.
7. Installation
If you are programming your data logger with Short Cut, skip Wiring to data logger (p. 7) and
Data logger programming (p. 8). Short Cut does this work for you. See QuickStart (p. 2) for a
Short Cut tutorial.
7.1 Wiring to data logger
The sensor is fitted with a tough, polyurethane sheathed cable. This has three conductors plus a
shield wire. The wiring of the sensor is shown in Table 7-1 (p. 7).
Table 7-1: Wire color, pin, function, and data logger connection
Pin Wire color Wire function Data logger connection terminal
1 Brown Power 12V
2 White SDI-12 Cterminal or Uterminal
configured for SDI-121
3 Black Power ground G
Clear Shield G
1Uterminals are automatically configured by the measurement instruction.
To use more than one sensor per data logger, either connect the different sensors to different
terminals on the data logger or change the SDI-12 addresses of the sensors and wire them to the
same terminal. Using the SDI-12 address reduces the use of terminals on the data logger and
allows sensors to be connected in a daisy-chain fashion that can minimize cable runs in some
applications. (See Long cables [p. 14] for limits on the total cable length.)
For the CR6 and CR1000X, triggering conflicts may occur when a companion terminal is used for
a triggering instruction such as TimerInput(),PulseCount(), or WaitDigTrig(). For
HygroVUE™5 Temperature and Relative Humidity Sensor 7

example, if the HygroVUE 5 is connected to C3 on a CR1000X, C4 cannot be used in the
TimerInput(),PulseCount(), or WaitDigTrig() instructions.
The SDI-12 address of the HygroVUE 5 can be set two ways:
lby sending the required commands to the sensors via an SDI-12 recorder/data logger that
allows talk through to the sensor.
lby loading a program into the recorder that sends the required commands.
See SDI-12 sensor support (p. 26) for detailed instructions.
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.
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. 21). Programming basics for CRBasic data loggers are
provided in the following section. A complete program example can be found in CRBasic
example program (p. 22).
NOTE:
Making measurements from the HygroVUE 5 more frequently than every 5 seconds can result
in small additional errors due to self-heating of the element. If the main scan rate needs to be
faster than this please read Sensor measurement (p. 12) and Measurements in programs with
fast scan rates (p. 14) about alternate programming techniques.
7.3 CRBasic programming
A complete program example can be found in CRBasic example program (p. 22).
The SDI12Recorder() instruction is used to measure a HygroVUE 5 configured for SDI-12
measurements. The SDI12Recorder() instruction sends a request to the sensor to make a
measurement and then retrieves the measurement from the sensor. See Sensor measurement (p.
12) for more information.
HygroVUE™5 Temperature and Relative Humidity Sensor 8

For most data loggers, the SDI12Recorder() instruction has the following syntax:
SDI12Recorder(Destination, SDIPort, SDIAddress, “SDICommand”, Multiplier, Offset,
FillNAN, WaitonTimeout)
Valid values for the SDIAddress are 0 through 9, a through z, and A through Z; alphabetical
characters need to be enclosed in quotes (for example, “A”). Also enclose the SDICommand in
quotes as shown. The Destination parameter must be an array. The required number of
values in the array depends on the command; see Table 8-1 (p. 13).
FillNAN and WaitonTimeout are optional parameters (refer to CRBasic Help for more
information).
7.4 Siting
The general EPA guidance for standard meteorological stations is to locate the sensor over an
open, level area at least 9 m (29.5 ft) 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 obstruction and at least 30 m (98.4 ft) (EPA) from
large, paved areas. Sensors should be protected from thermal radiation and adequately
ventilated. Protect the filter at the top of the sensor from exposure to liquid water.
NOTE:
The connector at the base of the removable sensing element is susceptible to corrosion in
locations where salt spray or corrosive gases are present. To protect the connector and avoid
corrosion, Campbell Scientific recommends applying a small amount of high-vacuum grease
around the pins of the connector. That type of grease is designed to have low levels of
volatiles and to not outgas.
The sensor should be installed at a standard measurement height which varies depending on the
guides being used:
l1.5 m (4.92 ft) (AASC)
l1.25 to 2.0 m (4.1 to 6.5 ft) (WMO)
l2.0 m (6.5 ft) (EPA)
See Attributions and references (p. 19) for a list of references that discuss temperature and
relative humidity sensors.
When used in the field, the HygroVUE 5 must be housed in a radiation shield. Typically, the
RAD06 unventilated or the TS100SS fan-aspirated solar radiation shield is used.
HygroVUE™5 Temperature and Relative Humidity Sensor 9

The white color of these shields reflects solar radiation, and the louvered construction allows air
to pass freely through, thereby keeping the sensor at or near ambient temperature. The RAD06
uses a double-louvered design that offers improved sensor protection from insect intrusion and
driving rain and snow. In addition, compared to shields of a similar appearance, the RAD shields
have lower self-heating in bright sunlight combined with low wind speeds giving a better
measurement.
The Apogee Instruments aspirated TS100SS shield can also be used where minimal solar errors
and a fast speed of response is desired. A special adapter is available to allow the HygroVUE 5 to
fit within the shield. Please refer for the documentation for that shield for further installation
instructions.
Each of these solar radiation shields attaches to a crossarm, mast, or user-supplied pipe with a 2.5
to 5.3 cm (1.0 to 2.1 inch) outer diameter.
Tools required for installing a radiation shield to a tripod or tower include:
ladjustable wrench (to suit 12 mm (1/2 in) nuts)
lsmall screwdriver provided with data logger
lsmall Phillips screwdriver
lUV-resistant cable ties
lsmall pair of diagonal-cutting pliers
ladjustable wrench with a minimum 50 mm (2 in) jaw size.
7.4.1 Installation in a RAD06 radiation shield
1. Loosen the nut on the entry gland at the bottom of the shield.
2. Insert the sensor into the gland. See Figure 7-1 (p. 11). The sensor should be pushed into the
shield all the way, so only the hexagonal parts of the white cable gland at the end of the
probe are just outside the hole in the large gray nut.
3. First tighten the nut on the gland by hand until the sensor is held firmly in place. Ensure the
gland tightens on larger round section of the white body of the sensor, not on the nut of
the cable gland. Then use the large adjustable wrench to further tighten the gland by 1/2 to
1 turn. Do not overtighten the nut as you risk damaging the sensor body and also making
service of the sensor more difficult in the future.
HygroVUE™5 Temperature and Relative Humidity Sensor 10

Figure 7-1. HygroVUE 5 detail of insertion in a RAD06 shield
7.4.2 Mount the shield
1. Attach the radiation shield to the tripod mast, crossarm, or tower leg using the supplied
U-bolt or band clamp. 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.
HygroVUE™5 Temperature and Relative Humidity Sensor 11

Figure 7-2. HygroVUE 5 installed in a RAD06 radiation shield on a pole
8. Operation
8.1 Sensor measurement 12
8.2 Measurements in programs with fast scan rates 14
8.3 Long cables 14
8.4 Power conservation 15
8.5 Measuring multiple SDI-12 sensors 15
8.1 Sensor measurement
The CRBasic instruction, SDI12Recorder(), measures the HygroVUE 5 sensor using the Start
Measurement (M!), Concurrent Measurement (C!), or Continuous Measurement (R!)
commands. The SDI-12 commands relevant to making measurements are shown in Table 8-1 (p.
13). SDI-12 sensor support (p. 26) describes all the SDI-12 commands that are supported.
Additional SDI-12 information is available at www.sdi-12.org .
HygroVUE™5 Temperature and Relative Humidity Sensor 12

Table 8-1: HygroVUE 5 SDI-12 measurement commands
SDI-12 Command
(a is the address) Values returned
aM!,aC!,aR0!,aMC!,aCC!,aR0C! Temperature (°C), relative humidity (%)
aM1!,aR1!,aMC1!,aRC1! Dewpoint (°C) of the air
aM3!,aR3!,aMC3!,aRC3! Temperature (°C), relative humidity (%),
dewpoint (°C), and vapor pressure (kPa)
When entering the command in a CRBasic program, the address and command are entered as
separate parameters. The SDI-12 command is entered as a string, excluding the address but
including the terminator character (for example “M!”).
When a measurement is initiated with the M! or C! commands, the sensor responds with the
maximum time delay until the measurements are available and the number of values to be
returned. The delay is 1 second for this sensor. For the M! commands, Campbell Scientific data
loggers interpret the response and automatically send one or more D! commands after the
sensor indicates data is ready and writes it to the result variables. The whole measurement
normally delays the data logger by about 400milliseconds with the standard M! command.
The C! command differs in that the data logger does not wait after sending the command and
continues with other instructions in the program. It automatically collects the data the next time
the SDIRecorder() instruction runs in the next scan. This allows measurements for several
different sensors to be triggered and made concurrently but the measurements seen in the data
logger are effectively one scan period old. For the HygroVUE 5 this instruction is rarely used
because the instruction takes longer to execute than the M! or R! commands.
The R! command switches the sensor to automatically make measurements every 10 seconds,
based on the sensor internal clock. Note this command must be entered as R0 (a single R alone is
invalid). For the data logger this instruction usually takes less than 220 milliseconds to execute so
this causes the least delay to program execution. However, for programs which operate with
scans longer than 10 seconds the power consumption by the sensor will be higher when using
this mode of operation. The automatic measurement mode and its consequent power
consumption can only be canceled by powering down the sensor to reset it.
With the standard commands (M!,C!, and R0!) the sensor returns two values: temperature (°C)
and relative humidity as a percentage (0 to 100). The sensor also supports some additional
variants of the measurement commands; see Table 8-1 (p. 13).
Dewpoint and vapor pressure are calculated using formulas from:
Alduchov, O. A., and R. E. Eskridge, 1996: Improved Magnus form approximation of saturation
vapour pressure. J. Appl Meteor., 35, 601-609.
HygroVUE™5 Temperature and Relative Humidity Sensor 13

These optional outputs are provided mainly for non-Campbell data logger applications.
Campbell data loggers have built in functions to calculate these derived variables and making the
calculations in the data logger will be quicker and take less power as it takes the sensor much
longer to perform the calculations required than the data logger.
The HygroVUE 5 also supports the MC!,CC!, and RC! instructions, which are the same as the M!,
C!, and R! instructions, but a cyclic redundancy check (CRC) is added that validates the data. Use
of the checksum option is only normally necessary for long cable runs.
The factory-set SDI-12 address for the HygroVUE 5 is 0. See Change address command (aAb!) (p.
28) for instructions on changing the SDI-12 address through the data logger. SDI-12 sensor
support (p. 26) all give full details of the additional commands and details of the SDI-12 protocol.
8.2 Measurements in programs with fast
scan rates
Calling the SDI12Recorder() instruction in a SlowSequence() allows the SDI-12
instruction to run as a background process, causing minimum interference to other
measurements in the data logger. Code and measurements that need to run at higher speeds
can run in the main scan.
8.3 Long cables
Digital data transfer eliminates offset and noise errors due to cable lengths. However, digital
communications can break down when cables are too long, resulting in either no response from
the sensor or corrupted readings. The original SDI-12 standard specifies the maximum total cable
length of 60 meters (200 ft). Low power SDI-12 sensors such as the HygroVUE 5 have been used
with longer cables up to 300 m (1000 ft). This model of sensor is normally only supplied with
cables up to 10 m in length. If the cable is to be extended, follow these guidelines:
lUse low capacitance, low resistance, screened cable (as fitted by Campbell Scientific) to
reach distances of several hundred meters.
lEnsure that the power ground cable has low resistance and is connected to the same
ground reference as the data logger control ports.
lBe aware that “daisy-chaining” or connecting sensors in parallel to the same SDI-12 port
reduces the total cable length roughly in proportion to the number of sensors connected.
For example, while it may be possible to use one cable run of 300 m (1000 ft) to a single
sensor, the cable length would be limited to around 100 m (300 ft) per sensor if three
sensors are connected to one port.
HygroVUE™5 Temperature and Relative Humidity Sensor 14

8.4 Power conservation
The HygroVUE 5 draws less than 100µA (50µA typical) of current between measurements. In
most applications this is insignificant compared to the data logger and other power draws, so the
sensor can be permanently powered.
In very low-power applications, battery power can be conserved by turning the 12V supply to the
HygroVUE 5 on just before the measurement (allowing a warm-up time of at least 1.8s) and then
turning it off afterwards. If available, the switched-12V output of the data logger can be used.
8.5 Measuring multiple SDI-12 sensors
Up to ten HygroVUE 5s or a combination of other SDI-12 sensors can be connected to a single
data logger terminal. Each SDI-12 device must have a unique SDI-12 address between 0-9, A-Z,
or a-z. See Change address command (aAb!) (p. 28) to change the HygroVUE 5 SDI-12 address
from its default address of 0.
9. Troubleshooting and
maintenance
NOTE:
All factory repairs and recalibrations require a returned material authorization (RMA) and
completion of the “Statement of Product Cleanliness and Decontamination” form. Refer to
the Assistance page at the end of this manual for more information.
HygroVUE™5 Temperature and Relative Humidity Sensor 15

9.1 Troubleshooting
Table 9-1: Symptoms, possible causes and solutions
Symptom Possible cause Solution
Temperature is reported as
–9999 or NAN, and relative
humidity is reported as 0or
as an unchanging value.
This indicates a problem
with the SDI-12
communications with the
sensor.
Recheck the sensor wiring.
Check the voltage to the sensor is 12V
with a digital voltage meter.
Verify the sensor SDI-12 address
matches the address entered for the
SDI12Recorder() instruction.
Inaccurate temperature or
relative humidity is
reported.
Inadequate delay after
power-up (only applicable
if using SW12)
The sensor element has
been contaminated
Electrical interference
Verify the program is allowing a
power-up time of at least 1.8s.
Clean the sensor tip with distilled
water or replace it.
Check that the sensor is not installed
too close to a radio transmitter or cell
phone.
Temperature and relative
humidity read –99.999
This indicates a fault with
the sensor element itself or
communication between
the sensor element and the
electronics in the sensor
body.
Check the sensor element is properly
plugged in, with the correct
orientation.
Check for water being present under
the sensor element connector and
that there is no corrosion of the
sensor pins or the socket.
Swap the element for another one.
9.2 Maintenance
The HygroVUE 5 sensor requires minimal maintenance, but dust, debris, and salts on the filter
cap will degrade sensor performance. Check the white filter on the end of the sensor for debris. If
dirt or salt is ingrained in the filter, clean with distilled water or replace it. Make sure the filter is
screwed onto the sensor 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, first remove the sensor. Dismount the shield. Brush all loose dirt off. If more effort is
HygroVUE™5 Temperature and Relative Humidity Sensor 16

needed, use warm, soapy water and a soft cloth or brush to thoroughly clean the shield. Allow
the shield to dry before remounting.
CAUTION:
The HygroVUE 5 sensor body is sealed and filled with a potting compound to totally protect
the electronics from any water ingress. This means there are no serviceable parts within the
sensor body.
9.3 Calibration
The life of the sensor element is primarily limited by drift of the humidity sensor and your own
acceptance of the errors incurred. Typical drift is less than 1% per year when used in cleaner
environments but can be higher than this in polluted air. Because it can be difficult to know what
the sensor has been exposed to and because the element is relatively inexpensive, Campbell
Scientific recommends replacing the sensor element annually. Replacing the element effectively
brings the sensor back to a factory calibration state both for temperature and relative humidity.
If you wish to check an old element’s calibration you can measure its performance by plugging it
into another sensor body in your calibration laboratory.
NOTE:
We cannot guarantee the accuracy of measurements if the sensor element is not changed
every year.
9.4 Sensor element replacement
Campbell Scientific offers a replacement temperature/RH element and cap for the HygroVUE5.
The replacement element is only available from Campbell Scientific. It includes a small circuit
board that is coated to ensure longer life at high humidity. A single row of four gold pins inserts
into one side of an eight-way socket at the end of the sensor.
The replacement element must be correctly installed for the sensor to work properly. Follow
these steps to correctly replace the element:
1. Wash your hands to avoid getting dirt or grease on the element. If possible, use cotton
gloves and handle the element by the edges of the small circuit board. Avoid touching the
square white filter on the surface of the small, black component on top of the circuit board.
HygroVUE™5 Temperature and Relative Humidity Sensor 17