Campbell CSAT3BH User manual

Revision: 01/2022
Copyright © 2020– 2022
Campbell Scientific, Inc.
Product Manual

Table of contents
1. Introduction 1
2. Precautions 1
3. Initial inspection 2
4. Overview 3
4.1 Features 4
4.2 Sensor components 4
4.2.1 Standard components 5
4.2.1.1 CSAT3H heater controller box 5
4.2.1.2 Temperature/relative humidity sensor and shield 5
4.2.1.3 CM250 leveling mounting kit 6
4.2.1.4 USB data cable 6
4.2.2 Optional components 7
4.2.2.1 Sonic environment option 7
4.2.2.2 Sonic carrying case 7
4.2.3 Common accessories 8
4.2.3.1 Power and communications cables 8
4.2.3.2 FW05 thermocouple 11
4.2.3.3 FWC-L cable 11
4.2.3.4 Thermocouple cover 12
4.2.3.5 Thermocouple cover backplate 12
4.2.3.6 FW/ENC thermocouple carrying case 12
4.2.4 Other accessories 12
4.2.4.1 Power/SDM splitter 13
4.2.4.2 CPI/RS-485 splitter 14
4.2.4.3 HUB-SDM8 15
4.2.4.4 SDM cable CABLE5CBL-L 16
4.2.4.5 HUB-CPI 16
4.2.4.6 CAT6 Ethernet cable 17
5. Specifications 17
5.1 Measurements 18
5.2 Communications 19
Table of contents - i

5.3 Power requirements 20
5.4 Physical description 21
5.4.1 Sonic anemometer dimensions 21
5.4.2 CSAT3H heater controller box dimensions 22
6. Installation 23
6.1 Introduction 23
6.2 Site considerations 23
6.3 Settings 24
6.3.1 Verify CSAT3BH settings 24
6.3.2 Set up the data logger and CSAT3H heater controller 29
6.4 Mounting 31
6.4.1 Mount the CSAT3BH 31
6.4.2 Mount CSAT3H 33
6.4.3 Mount the temperature/relative humidity probe 34
6.5 Orientation 34
6.5.1 Sonic azimuth 34
6.6 Leveling 36
6.7 Installing additional fast-response sensors 38
6.7.1 Fine-wire thermocouple 38
6.7.2 Other gas analyzers 39
6.8 Wiring 39
6.8.1 Grounding to earth 39
6.8.2 Controller box connections 42
6.8.3 CSAT3H heater controller connections 43
6.9 Communications 44
6.9.1 SDM communications 46
6.10 Multiple CSAT3BH configurations 49
6.10.1 CPI communications 52
6.10.2 RS-485 communications 58
6.10.3 USB 59
6.11 Confirm CSAT3BH factory settings 60
7. Operation 61
7.1 Theory of operation for wind and sonic temperature measurements 61
7.1.1 Algorithm Version 5 62
7.1.2 Effects of crosswind on the speed of sound 62
7.1.3 Sonic transducer shadow correction 63
Table of contents - ii

7.2 Theory of heater controller operation 64
7.3 Operating modes 65
7.3.1 Measurement trigger 66
7.3.2 Data filter 67
7.3.3 CSAT3BH sonic data output 68
7.3.4 Operating mode recommendations 71
7.4 Synchronization with other sensors 71
7.5 Data logger programming using SDM or CPI 73
7.5.1 CSAT3B() 73
7.5.2 CSAT3BMonitor() 75
7.5.3 Diagnostic word 76
7.5.4 SDMTrigger() 77
7.6 Programming 78
7.7 Data logger and CSAT3H heater controller box programs 78
7.8 CSAT3H heater controller output 78
8. Maintenance and troubleshooting 82
8.1 General maintenance 82
8.2 Sonic wicks 83
8.3 Desiccant 85
8.4 Calibration 86
8.4.1 Test for wind offset 86
8.5 Troubleshooting 88
8.5.1 Troubleshooting CSAT3H heater controller box issues 89
8.5.2 Sending an OS to the CSAT3H heater controller box 89
8.5.3 Sending an OS to the CSAT3BH 90
8.6 Returning the CSAT3BH 90
9. References 91
Appendix A. CSAT3BH orientation 92
A.1 Determining true north and sensor orientation 92
A.2 Online magnetic declination calculator 93
Appendix B. CSAT3BH measurement theory 95
B.1 Theory of operation 95
B.1.1 Wind speed 95
B.1.2 Temperature 96
Table of contents - iii

B.2 References 97
Table of contents - iv

1. Introduction
The CSAT3BH is a heated version of the CSAT3B 3-D sonic anemometer with integrated
electronics. This instrument measures sonic temperature and wind speed in three dimensions.
The ultrasonic transducers, chassis, and strut can be heated to keep ice from accumulating on the
instrument. This new heating feature gives the CSAT3BH an advantage over traditional
anemometers and sonic anemometers because data loss will be significantly reduced in areas
that experience frozen precipitation. The CSAT3BH features variable power for the heating
elements by only delivering power to the heaters when needed, as opposed to the common
method of providing two-way heating (on or off). Further, real-time data flags are generated
when the heaters are turned on, which is critical to post-processing the data.
The CSAT3BH can measure average horizontal wind speed and direction, or turbulent
fluctuations of horizontal and vertical wind, and sonic temperature. Further, momentum flux and
sensible heat flux can be calculated from the turbulent wind and sonic temperature fluctuations.
Latent and sensible heat flux and gas fluxes may be determined by computing the covariance
between vertical wind measured by the CSAT3BH and scalar quantities measured by other
appropriate sensors.
Before attempting to use or install the CSAT3BH, please review:
lPrecautions (p. 1)
lInitial inspection (p. 2)
2. Precautions
lREAD AND UNDERSTAND the Safety section at the back of this manual.
lCAUTION
oVoltage input must be within a range of 22 to 32VDC for the CSAT3H heater
controller and 9.5 to 32VDC into the power connector on the CSAT3BH electronics.
oThe CSAT3BH head should be handled by holding the block at the back of the
sensor. Handling it by the arms or transducers could cause geometric deformation,
which degrades the measurements.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 1

oThe transducer faces are fragile. Avoid scratching or rubbing the surface of the
transducer.
oGrounding the CSAT3BH is critical. Proper grounding to earth will ensure maximum
electrostatic discharge (ESD) and lightning protection and improve measurement
accuracy. The data logger, CSAT3H heater controller enclosure, and CSAT3BH
electronics should all be grounded to the same grounding rod.
oDuring winter, remove wicks from the transducers to prevent ice from melting and
collecting on the wicks, which could lead to re-freezing and ice buildup.
oAvoid opening the heater controller box because of unprotected electronics that are
vulnerable to ESD damage.
lIMPORTANT
oInstall USB drivers and Device Configuration Utility before attaching the sensor to a
computer.
3. Initial inspection
Upon receipt of the CSAT3BH, inspect the packaging and contents for damage. File any damage
claims with the shipping company. Contact Campbell Scientific to facilitate repair or replacement.
Immediately check package contents against shipping documentation. Thoroughly check all
packaging material for product that may be trapped inside. Contact Campbell Scientific about
any discrepancies. Model numbers are found on each product. On cables, the model number is
often found at the connection end of the cable. Check that correct lengths of cables are received.
The CSAT3BH ships with:
lTemp/RH sensor with radiation shield
lCSAT3BH replacement desiccant
lCSAT3BH foam case set
lCSAT3H heater controller box
lCM250 leveling mounting kit
lUSB data cable
CSAT3BH Three-Dimensional Heated Sonic Anemometer 2

Cables for the CSAT3BH, although not included in the standard package, are specified at the time
of order and are shipped with the CSAT3BH:
lCSAT3HCBL3-L
lRS-485 cable (either CSAT3HCBL1-L or CSAT3HCBL2)
lEither CSAT3BCBL1-L or CSAT3BCBL2-L and CSAT3BCBL3-L
4. Overview
The CSAT3BH is an ultrasonic anemometer for measuring sonic temperature and wind speed in
three dimensions. It is often used for studies of turbulence and flux measurements, where
turbulent fluctuations of wind speed and sonic temperature must be measured at high
frequencies (at 10Hz, for example).
From the turbulent wind fluctuations, momentum flux can be calculated. The covariance of
vertical wind and sonic temperature yields sonic sensible heat flux. By finding the covariance
between vertical wind and scalar measurements made by other fast-response sensors, such as
fine-wire thermocouples or gas analyzers, other fluxes can be calculated. For example, sensible
and latent heat fluxes, carbon dioxide flux, and other trace gas fluxes can all be measured by
combining the CSAT3BH with other sensors.
The CSAT3BH can communicate measurements using SDM (Synchronous Device for
Measurements), USB, RS-485, and CPI (CAN Peripheral Interface) communications. For optimal
synchronization with other fast-response sensors for applications such as eddy covariance,
Campbell Scientific recommends using SDM or CPI communications with an appropriate
Campbell Scientific data logger.
The CSAT3BH is a heated version of the CSAT3B, with the same measurement specifications.
Developed for use in cold environments that typically experience ice buildup on sensors, the
CSAT3BH is designed to prevent ice from accumulating on the sensor in order to avoid
prolonged periods of data loss.
The CSAT3BH is paired with a temperature and relative humidity probe that is used to determine
when the heaters need to be operating. The information from the temperature and relative
humidity probe is processed within the CSAT3H heater controller box, dictating operation of the
heaters. Additionally, temperature measurements are made throughout the body of the sonic
anemometer to determine the temperature change of the sensor as a result of the heaters. This
information is delivered to the controller box as well.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 3

4.1 Features
The CSAT3BH offers the following key features:
lIntegrated electronics provide easy mounting of a single piece of hardware
lIntegrated inclinometer
lHigh-precision measurements ideal for turbulence and eddy-covariance studies
lAn improved design with a thin, aerodynamic support strut close to the ends of the sensor
arms, creating greater rigidity and improved accuracy of sonic temperature
lSupport of data logger sampling at any frequency between 1 and 100 Hz
lCPI communications for more robust and higher bandwidth measurements
lMultiple communication options, including SDM, CPI, USB, and RS-485
lInternal temperature and humidity measurements with easily replaced desiccant
lVersion 5 algorithm for calculating data outputs; combines the signal sensitivity of version
3 with the rain performance of version 4
lOptions to filter high frequencies for applications requiring analysis of non-aliased spectra
lTwo controlled heating zones that automatically provide enough heat to keep the sensor
free of ice in areas that matter most
oArms and strut
oTransducer fingers
lDiagnostics to determine heat activity to allow for Quality Assurance/Quality Control of
data as well as reports of how much power is used to control the heaters
lCSAT3BH body temperature measurements from thermistors near the transducers, strut,
and arms to help track the heater performance
lStreamlined heater integration to preserve sonic aerodynamics and ensure proper
operation
4.2 Sensor components
The CSAT3BH consists of several components. Some components come standard with every
CSAT3BH; others are accessories that must be ordered separately. Some common accessories,
such as cables, are required to operate a CSAT3BH.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 4

4.2.1 Standard components
Standard components are items that are included or shipped with the CSAT3BH. The following
sections describe these items.
4.2.1.1 CSAT3H heater controller box
The CSAT3H heater controller box collects temperature and relative humidity data from the
temp/RH probe (see Temperature/relative humidity sensor and shield (p. 5)) as well as body
temperature measurements from the sonic anemometer. These measurements are used for
determining when the heaters are turned on or off, as well as how much power should be
supplied to the heaters to prevent ice accumulation and to prevent damage to the instrument
from overheating, in the case of a fault. The CSAT3H heater controller box is shown in FIGURE 4-1
(p. 5). Connectors at the bottom of the CSAT3H heater controller box are shown in FIGURE 6-12
(p. 41) and described in Controller box connections (p. 42).
FIGURE 4-1. CSAT3H heater controller box
4.2.1.2 Temperature/relative humidity sensor and shield
A temperature and relative humidity sensor (shown in FIGURE 4-2 (p. 6)) with a 6-plate gill
radiation shield comes with the CSAT3BH. This sensor provides important temperature and
relative humidity data that is used within the heating algorithm to determine when the heaters
are turned on or off. This sensor should be mounted in such a way that it is level with the sonic
CSAT3BH Three-Dimensional Heated Sonic Anemometer 5

anemometer but doesn’t interfere with the flow into the measurement path. A U-bolt, 1/2-in
screws, and washers come with the temp/RH probe for mounting the radiation shield containing
the sensor.
FIGURE 4-2. Temperature/relative humidity sensor and shield, with mounting hardware
4.2.1.3 CM250 leveling mounting kit
The CM250 leveling mounting kit is shipped with the CSAT3BH and comes with an adapter
(FIGURE 4-3 (p. 6)) that facilitates mounting a CSAT3BH at the end of a 3.33cm (1.31in) OD
crossarm or pipe. The kit includes a captive 3/8-in bolt that screws into the bottom of the
CSAT3BH block, and a 3/16-in Allen wrench to tighten the adapter on the pipe.
FIGURE 4-3. CM250 mount
4.2.1.4 USB data cable
The USB data cable is a 5m (16ft) USB cable (FIGURE 4-4 (p. 7)) included with the CSAT3BH. One
end has a standard type-A pin connector to connect to a computer, and the opposite end has a
mini-B pin connector, which connects to the USB port on either the back of the CSAT3BH block
or the bottom of the CSAT3H heater controller box. The mini-B pin connector is rated to Ingress
Protection 68 (IP68) to exclude fine dust and water. When connected with the cable, Device
CSAT3BH Three-Dimensional Heated Sonic Anemometer 6

Configuration Utility allows the user to view or set settings, send a new operating system to the
CSAT3BH, or view real-time measurements. It is also possible to use this cable to collect data with
a computer in unprompted USB mode. Communications (p. 44) provides additional information.
FIGURE 4-4. USB data cable
4.2.2 Optional components
4.2.2.1 Sonic environment option
If the CSAT3BH will be located in harsh environments, such as marine or heavily fertilized
locations, coated transducers can be purchased as an option to help prevent corrosion.
4.2.2.2 Sonic carrying case
A large, hard plastic Pelican™ carrying case is available for the CSAT3BH. It is watertight and
highly durable. This case is recommended for transporting and storing the CSAT3BH. It includes a
set of foam inserts that hold the CSAT3BH in a protected position while providing space for
additional components.
If the sonic carrying case option is not selected, the CSAT3BH will be shipped in a large
cardboard box. The same set of foam inserts used in the sonic carrying case is used in the
cardboard box to securely hold the CSAT3BH.
NOTE:
With the cardboard box shipment option, keeping the foam inserts and box is highly
recommended. When returning a CSAT3BH for factory recalibration or repair, it is important
to ship the unit with the foam inserts provided from the factory.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 7

4.2.3 Common accessories
Common accessories for the CSAT3BH include cables as well as other equipment to make
sensible heat flux measurements. A fine-wire thermocouple is an example of an additional sensor
often used with a CSAT3BH. Descriptions of cables and other common accessories are described
in greater detail in the following sections.
4.2.3.1 Power and communications cables
Cables required for the CSAT3BH to function must be ordered with the CSAT3BH. Cables are
required for both the anemometer itself and the CSAT3H controller box.
The anemometer requires a communication cable that transfers the data to the data logger.
Communication can either be made via SDM or CPI. If using SDM, an additional power cable is
not required because power can be transferred.
The CSAT3H heater controller box supplies power to the heaters and communicates with the
main data logger that is used to collect the wind and sonic temperature data from the
anemometer. Therefore, a power cable going from the 22 to 32VDC power supply to the
CSAT3H controller box is needed. An RS-485 cable that can establish a communication channel
between the controller and main data logger or computer is also required.
Campbell Scientific uses a system for naming cables that provides details of a cable and some
information about its use.
lThe “–L” in a cable model name is an option that denotes a user-specified length of cable in
feet.
lThe “–PT” is a cable option that specifies one end of the cable to have pigtail wires for
wiring to a power source, data logger terminals, or a wiring bus. The other end has an M16
connector for connecting to the corresponding port at the back of the CSAT3BH block.
lThe “–MC” option designates an M16 connector on both ends of the cable and is used to
daisy-chain several CSAT3BH instruments together in series.
NOTE:
Daisy-chaining requires ordering a splitter (see Power/SDM splitter (p. 13) and
CPI/RS-485 splitter (p. 14)) for each CSAT3BH in series except the terminal one. While
looking similar, two different splitters are required when daisy-chaining for Power/SDM
or for CPI. What differentiates the splitters is the number of pin channels they have,
making it impossible to use the incorrect splitter with a cable. The Power/SDM splitter
has six pin connectors, and the CPI/RS-485 splitter has eight.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 8

lThe “–RJ” option has an RJ-45 connector on one end for connecting directly to the CPI port
on a data logger such as the CR6 or to a CPI port on the HUB-CPI if a network of several CPI
devices is being installed in a star topology. The other end of the cable has an M16
connector for connecting to the CSAT3BH block.
The following paragraphs outline the types of cables needed for a specific communications
mode. For information on maximum cable lengths, refer to the specifications in Communications
(p. 44).
Power/SDM cable (CSAT3BCBL1)
To use SDM communications to collect data from a CSAT3BH with a data logger, the
CSAT3BCBL1-L-PT or CSAT3BCBL1-L-MC should be ordered. FIGURE 4-5 (p. 9) shows the two
versions. This cable transmits both power and SDM communication signals.
NOTE:
To collect data through another means (such as CPI, RS-485, or USB), the CSAT3BCBL1
Power/SDM cable may still be used to provide power to the CSAT3BH, in which case the SDM
wires should be left unwired to any ports on the data logger.
FIGURE 4-5. Options for CSAT3BCBL1 Power/SDM cable
Power cable (CSAT3BCBL2)
To use CPI, RS-485, or USB communications to collect data from a CSAT3BH, the
CSAT3BCBL2-L-PT or CSAT3BCBL2-L-MC should be ordered to provide power to the sensor. A
second cable to transmit the communications is also required (for example, a CSAT3BCBL3
CPI/RS-485 cable for CPI or RS-485, or a USB data cable).
For installations with long cable lengths, the CSAT3BCBL2 is preferred over the CSAT3BCBL1 for
providing power due to the heavier gauge wires that reduce voltage drop over long distances.
Allowed length is 1 to 550 feet. Although the maximum cable length is 550 feet, users requiring a
cable length of 401 to 550 feet should use a 24V power supply.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 9

FIGURE 4-6. Options for CSAT3BCBL2 power cable
CPI/RS-485 cable (CSAT3BCBL3)
To use CPI or RS-485 communications to collect data from a CSAT3B, the CSAT3BCBL3-L-PT,
CSAT3BCBL3-L-RJ, or CSAT3BCBL3-L-MC, should be ordered along with a cable to provide
power to the sensor (for example, either the CSAT3BCBL1 or CSAT3BCBL2).
FIGURE 4-7. Options for cabling CPI or RS-485 communications
CSAT3H heater controller RS-485 TX/RX cable (CSAT3HCBL1-L)
Important heater diagnostic information is collected by the CSAT3H heater controller box. To
transfer this information from the controller box to the main data logger for storage, a
CSAT3HCBL1-L cable should be ordered. One end of the cable is a 3-pin IP67 military connector
that connects to the CSAT3H heater controller box; the other end is a pigtail with brown, white,
and black wires that connects to the main data logger. Allowed lengths of this cable are between
1 and 300 ft.
CSAT3H heater controller RS-485 RX cable (CSAT3HCBL2)
If the sonic anemometer is using a computer or a data acquisition system other than a Campbell
Scientific data logger to collect data from the CSAT3H heater controller box, then a CSAT3HCBL2
CSAT3BH Three-Dimensional Heated Sonic Anemometer 10

should be ordered to connect the CSAT3H heater controller box to the other data acquisition
system. One end of the cable is a 3-pin IP67 military connector that connects to the controller
box; the other end is a pigtail with brown, white, and black wires that connects to the computer.
This cable comes at a set length of 15 ft.
CSAT3H heater controller power cable (CSAT3HCBL3-L)
A CSAT3HCBL3-L must be ordered to provide 24VDC power to the CSAT3H heater controller
box. This cable is ordered to a specified length ranging from 1 to 30 feet. The cable has a 2-pin
IP67 military connector on the end that connects to the controller box, and a red- and black-
wired pigtail that connects to the 24VDC power supply. Because the length of this cable has a
shorter maximum length than the CSAT3HCBL1-L, it is recommended that the CSAT3H controller
box be located close to the 24VDC power supply.
4.2.3.2 FW05 thermocouple
The FW05 is a Type E thermocouple with a 0.0127mm (0.0005in) diameter (FIGURE 4-8 (p. 11)).
The thermocouple measures atmospheric temperature fluctuations and may be used with the
CSAT3BH to directly calculate sensible heat flux. Larger size fine-wire thermocouples, such as the
FW1 and FW3, which are more robust but have slower response times, may also be used with the
CSAT3BH.
FIGURE 4-8. FW05 thermocouple
NOTE:
Users requiring fine-wire thermocouples for atmospheric temperature measurements should
consider their data logger choice. The CR6 data logger is not optimal for taking fine-wire
thermocouple measurements. For help in choosing the best data logger when fine-wire
thermocouples are required, contact Campbell Scientific.
4.2.3.3 FWC-L cable
The FWC-L is a cable with connector that is compatible with the connector on a FW05, FW1, or
FW3 fine-wire thermocouple. The other end of the cable has pigtail wires to wire to a pair of
CSAT3BH Three-Dimensional Heated Sonic Anemometer 11

differential voltage terminals on a data logger. The -L denotes the length of cable in feet, which
can be designated at the time of ordering.
4.2.3.4 Thermocouple cover
The thermocouple (TC) cover is a white, metal thermocouple cover that is placed over the
connectors of the FW05 and the FWC-L cable. It is used to mount the connectors to the side of
the CSAT3BH block. It also minimizes temperature gradients across the connectors.
4.2.3.5 Thermocouple cover backplate
The CSAT3BH fine-wire thermocouple cover backplate attaches to the CSAT3BH block and is
used to cover the back side of the TC cover.
NOTE:
The backplate is required for the CSAT3BH but not for other Campbell Scientific sonic
anemometers. In previous models, the back side of the TC cover is covered by the sensor
block.
4.2.3.6 FW/ENC thermocouple carrying case
The FW/ENC is a small case (FIGURE 4-9 (p. 12)) that is used for storing up to four fine-wire
thermocouples. Due to the fragile nature of the FW05 thermocouple, it should always be stored
in an FW/ENC when not in use. Ordering at least a set of four FW05 thermocouples for every
CSAT3BH is recommended, as the FW05 will break during normal wear and tear in the field.
FIGURE 4-9. FW/ENC for storing fragile thermocouples
4.2.4 Other accessories
The other accessories available for the CSAT3BH are used when combining multiple CSAT3BH
units into a network of sensors, the data from which is collected by a single data logger.
Networks of CSAT3BHs using SDM or CPI communications may be configured in one of three
different configurations:
CSAT3BH Three-Dimensional Heated Sonic Anemometer 12

lIn a series using a daisy-chain topology
lIn parallel using a star topology
lIn a combination of daisy-chain and star topologies
When designing an SDM or CPI network, careful attention should be given to not exceed a total
network cable length that will excessively attenuate the sensor signals. The exact total length will
depend on factors such as sample rate and topology, but in general the maximum cable lengths
(given in Communications (p. 44)) for each communication type and data rate should be
followed.
Because CPI communications can support longer network cable lengths, it is generally
recommended as the communication method for sensor networks. For more detailed
information on network topologies and limits on cable lengths for CPI networks, see the white
paper titled Designing Physical Network Layouts for the CPI Bus, available at
www.campbellsci.com .
4.2.4.1 Power/SDM splitter
The Power/SDM splitter, shown in FIGURE 4-10 (p. 13), has three 6-pin M16 connectors. This
splitter allows for connection at the Power/SDM port on the back of the CSAT3BH block to two
CSAT3BCBL1 or CSAT3BCBL2 cables. The splitter is IP68 rated, meaning it is dustproof and
watertight. It is used for daisy-chaining multiple CSAT3BHs in series. A Power/SDM splitter is
required for each CSAT3BH in the daisy chain (regardless of communication method used),
except for the terminal one.
FIGURE 4-10. CSAT3BH Power/SDM splitter (showing pin configuration)
CSAT3BH Three-Dimensional Heated Sonic Anemometer 13

4.2.4.2 CPI/RS-485 splitter
The CPI/RS-485 splitter, shown in FIGURE 4-11 (p. 14), has three 8-pin M16 connectors. This
splitter allows for connection at the CPI/RS-485 port on the back of the CSAT3BH block to two
CSAT3BCBL3 cables. The splitter is IP68 rated. It is used for daisy-chaining multiple CSAT3BHs in
series that use CPI or RS-485 communications. A splitter is required for each CSAT3BH in the
daisy chain, except for the terminal one. For a daisy chain of CSAT3BHs using SDM
communications, the CPI/RS-485 splitter is not needed; in this case, only the Power/SDM splitter
(see Power/SDM splitter (p. 13)) is needed.
NOTE:
The Power/SDM and CPI/RS-485 splitters look similar; however, they differ in number of pins
and are not interchangeable.
FIGURE 4-11. CSAT3BH CPI/RS-485 splitter (showing pin configuration)
Transient voltage drop is commonly caused by the large series inductance introduced by long
power cables, multiple CSAT3BHs connected by splitters, or a combination. Because the
measurements are synchronized, multiple CSAT3BHs connected to the same power cable each
draws a pulse of current at the same moment. This has a cumulative effect on the voltage drop. If
the voltage drop is sufficiently large, then the low-voltage detection circuit inside the CSAT3BH
sensor can be tripped, which forces the device to reset. A power cable compensation plug for the
CSAT3BH (FIGURE 4-12 (p. 15)) is needed if voltage drop creates problems. The plug is
compatible with all CSAT3BHs. The plug should be placed on the final Power/SDM splitter in the
CSAT3BH daisy chain, farthest from the power supply.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 14

FIGURE 4-12. CSAT3BH power cable compensation plug
The primary indicator of low voltage is in the diagnostic flags returned by the CSAT3BH to the
data logger. Flag number 32 (0x0020) indicates detection of a low-voltage condition. If the
instrument returns flag 32, first measure the power source voltage and ensure that its DC value
meets specifications. If that value is appropriate, the voltage at the far end of the cable should be
checked. This must be tested under load so a splitter at the end of the cable will be required to
measure the terminal voltage. These two tests will eliminate the DC voltage as the source of the
problem. Any DC voltage below 12 V at the sensor would be suspect for susceptibility to droop.
In larger systems, even DC voltages of 13 to 15V can still experience enough droop to trigger the
detection under the right conditions. Power systems of 24V are very unlikely to experience
enough droop to observe this problem. If the DC case checks out but the flag is still observed,
then the system would probably benefit from the addition of a power compensation plug
(FIGURE 4-12 (p. 15)).
4.2.4.3 HUB-SDM8
The HUB-SDM8 (shown in FIGURE 4-13 (p. 16)) allows up to six SDM devices (typically, one data
logger and multiple SDM sensors) to be connected in parallel. In the case of the CSAT3BH, up to
five CSAT3BHs, or CSAT3BH daisy chains using CSAT3BCBL1 cables, may be connected to the
HUB-SDM8. In cases where multiple CSAT3BHs are installed some distance from the data logger,
the HUB-SDM8 can be placed near the CSAT3BHs with a single SDM cable extended from the
hub to the data logger. This decreases the total network cable length, which limits signal
attenuation.
The HUB-SDM8 has eight terminal strips and features spring-loaded guillotine terminals for easy
wiring. It comes in a watertight enclosure and includes a U-bolt for mounting to a vertical pipe or
mast. An SDM cable (CABLE5CBL-L; see SDM cable CABLE5CBL-L (p. 16)) should be ordered to
connect the HUB-SDM8 to a data logger and a power supply.
CSAT3BH Three-Dimensional Heated Sonic Anemometer 15