CS
120A
and CS125
Visibility and Present
Weather Sensors
Revision
Copyright ©
Campbell Scientific, Inc.
: 01/2021
2013 – 2021
About this manual
Some useful conversion factors:
Area: 1 in
Length: 1 in. (inch) = 25.4 mm
2
(square inch) = 645 mm2
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass:
Pressure: 1 psi (lb/in
Volume: 1 UK pint = 568.3 ml
1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
2
) = 68.95 mb
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: +44 (0) 1509 601141 Fax: +44 (0) 1509 270924
Email: support@campbellsci.co.uk
www.campbellsci.co.uk
Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. Introduction ................................................................. 1
1.1 General Safety........................................................................................... 2
1.2 Sensor Unit Safety .................................................................................... 2
1.3 Principle of operation ................................................................................ 3
1.4 Recommended Tools ................................................................................ 6
1.5 Quickstart .................................................................................................. 6
2. Measurement specification ........................................ 6
3. Technical specification ................................ .............. 7
3.1 Electrical specification .............................................................................. 7
3.2 Optical specification ................................................................................. 7
4. Communications specification .................................. 8
4.1 Communications electrical specifications ................................................. 8
4.2 Supported data rates and formats .............................................................. 8
5. Environmental specifications .................................... 9
6. Mechanical specifications .......................................... 9
6.1 Dimensions ............................................................................................... 9
6.2 Weights ................................................................................................... 10
6.3 Mounting................................................................................................. 10
7. Installation procedure .............................................. 10
7.1 Equipment grounding ............................................................................. 11
7.2 Mounting the sensor ................................ ................................ ................ 12
7.3 Optional Campbell Scientific Mount ...................................................... 14
8. Sensor internal connectors’ description ................ 17
8.1 Sensor recommended wiring using Campbell Scientific cables ............. 19
9. HygroVUE 5, HygroVUE 10 or CS215 T/RH Sensor
(CS125 only) ................................................................... 21
10. Functions of the internal switches ........................ 23
ii
11. Message Formats: A breakdown of the different
default outputs of the sensor –
Basic/Partial/Full ............................................... 24
11.1 Visibility only messages ....................................................................... 25
11.2 Messages with SYNOP Present Weather Codes (CS125 only) .............. 26
11.3 Messages with METAR Present Weather Codes (CS125 only) ............. 27
11.4 Messages with Generic SYNOP Present Weather Codes (CS125 only) 28
11.5 Example sensor message outputs .......................................................... 33
11.6 Custom message format ........................................................................ 34
12. Interface methods – Device Configuration
Utility/Command line/Menu .................................. 36
12.1 Configuring a PC for talking to the sensor ........................................... 37
13. Definition of the variables that can be set by
the user on the sensor ........................................ 37
14. Command line mode............................................... 39
14.1 The SET Command .............................................................................. 40
14.1.1 Example of a SET Command ................................................... 40
14.2 The SETNC Command ......................................................................... 41
14.2.1 Example of a SETNC Command .............................................. 41
14.3 The MSGSET Command ...................................................................... 41
14.4 The GET Command .............................................................................. 43
14.5 The MSGGET Command ..................................................................... 45
14.6 The POLL Command – Polling the sensor ........................................... 46
14.7 The ACCRES Command – Resetting the accumulation value ............. 47
15. Entering the sensor menu system ........................ 47
16. Calibrating the sensor ............................................ 53
16.1 Visibility calibration ............................................................................. 53
16.2 Dirty window zero calibration .............................................................. 57
16.3 Internal temperature check (CS125) ..................................................... 57
17. Performing an operating system update .............. 58
18. Cleaning .................................................................. 60
19. Lubricating the enclosure screws ......................... 61
20. Desiccant ................................................................. 61
Addendum .................................................................Add-1
iii
Appendices
A. Sensor Block Diagram ........................................... A-1
B. Example C code of the checksum CRC-16 ........... B-1
C. Present Weather Codes ........................................ C-1
D. A comparison of the two alternative visibility
calibrations ........................................................... D-1
Figures
1-1 Particles in the sample volume scatter light in all directions, including
into the detector ....................................................................................... 3
1-2 Signals from large, slow falling snowflakes and smaller, faster,
raindrops .................................................................................................. 4
1-3 Defining possible precipitation types based on wet bulb and dry
bulb temperatures ..................................................................................... 5
1-4 A typical size/speed map used by the CS125 present weather
algorithm ................................................................................................... 5
7-1 Airflow ................................................................................................... 11
7-2 Grounding boss ....................................................................................... 12
7-3 Mounting arrangement ........................................................................... 13
7-4 Mounting to a flat surface ....................................................................... 13
7-5 Use of band clamps ................................................................................ 14
7-6 Optical sensor mast ................................................................ ................. 15
7-7 Mounting footprint ................................................................................. 16
8-1 Connections ............................................................................................ 17
8-2 Communications and power connections ............................................... 19
8-3 Communications and power connector .................................................. 20
8-4 Configuration cable ................................................................................ 20
8-5 USB configuration cable ........................................................................ 20
9-1 Connection for the optional HygroVUE 5, HygroVUE 10 &
CS215 T/RH sensors .......................................................................... 22
10-1 Internal switches ................................................................................... 23
16-1 Calibration disk .................................................................................... 55
16-2 Mounting calibration disk ..................................................................... 56
17-1 Sensor DevConfig download instructions ............................................ 58
17-2 Sensor DevConfig screen when OS update is complete ....................... 59
Tables
10-1 Internal switch functions ..................................................................... 24
11-1 Summary of message IDs and descriptions ......................................... 30
11-2 Summary of system alarms and descriptions ....................................... 31
13-1 User definable settings and descriptions .............................................. 37
1
CS120A and CS125 Visibility and Present
Weather Sensors
1. Introduction
The CS120A is a visibility sensor. The CS125 additionally detects and reports
present weather in the form of SYNOP, METAR or NWS codes. The CS125 has
the same specification for visibility measurement as the CS120A. It is possible to
upgrade a CS120A to a CS125, please contact Campbell Scientific for more
details.
The sensors are infra-red forward scatter visibility and present weather sensors for
automatic weather stations including road, marine and airport based stations.
They both use the well-established forward scatter system for visibility
measurement, utilising a 42º scatter angle. The CS125 uses high speed sampling
to reduce missed events and improves response to other suddenly changing
conditions.
The CS125 has a temperature sensor mounted in the cross arm used as part of the
process for identifying precipitation.
When an optional CS215 or HygroVUE temperature and RH sensor is connected,
the CS125 can distinguish wet and dry obscuration (for example mist and haze)
and make more precise discrimination between liquid and frozen precipitation.
Dew heaters are provided to keep the sensor optics clear of condensation and more
powerful hood heaters to prevent the build up of snow or ice.
This sensor is certified for Aviation use by the German Meteorological Service,
Deutscher Wetterdienst (DWD) (see Section 1.3 regarding the settings).
CS120A and CS125 Visibility and Present Weather Sensors
2
1.1 General Safety
This manual provides important safety considerations for the installation,
operation and maintenance of the sensor. These safety considerations are
classified into three levels:
Warnings alert the installer or user to serious hazards.
Ignoring these warnings could result in injury or death
and/or irrevocable damage to the sensor unit.
Cautions warn of potential hazards. Ignoring these cautions
could result in the sensor being damaged and data being lost.
Notes highlight useful information in the installation, use and
maintenance of this product. These should be followed carefully in
order to gain the maximum benefit from the use of this product.
1.2 Sensor Unit Safety
The sensor has been checked for safety before leaving the factory and
contains no internally replaceable or modifiable parts.
Do not modify the sensor unit. Such modifications will
lead to damage of the unit and could expose users to
dangerous light levels and voltages.
In unusual failure modes and environmental conditions
the sensor hood could become hot. In normal operation
they will be at ambient temperature or slightly above.
Ensure that the correct voltage supply is provided to the
sensor.
WARNING
CAUTION
NOTE
WARNING
WARNING
CAUTION
Instruction Manual
3
1.3 Principle of operation
Figure 1-1. Particles in the sample volume scatter light in all directions,
including into the detector
The CS120A and CS125 comprise an emitter and detector aligned as in
Figure 1-1. The emitter produces a beam of near infra-red light pulsed at 1 kHz. A
detector has a field of view which overlaps the beam and is inclined at 42 degrees
to it. Light scattered by a particle (for example a fog droplet or particle of
precipitation) from the overlap or sample volume towards the detector is detected
by a photodiode and recorded as a signal. The size of the signal is therefore
proportional to the extinction of the emitted beam caused by scattering. The
scattering signal averaged over one second is used to calculate an extinction
coefficient or EXCO assuming the relationship between forward scatter and
EXCO is linear. Sixty one second averages are then themselves averaged to give a
one minute average EXCO. This is then converted to a value of Meteorological
Optical Range (MOR) using Koschmieder’s law:
MOR = 3/EXCO where MOR is in km and EXCO in units of km-1.
The CS125 calibration for visibility was derived by comparison with other high
grade, forward scatter sensors and has also been verified in a study by trained
meteorological observers. This is called the MOR calibration in this manual.
An alternative calibration, known as TMOR, is also available. This was derived
by following the ICAO procedure of calibrating the sensor against a
transmissometer. An empirical equation to convert from MOR to TMOR was
developed.
CS120A and CS125 Visibility and Present Weather Sensors
4
This non-linear equation results in significantly higher visibility readings at lower
visibilities below 5000 metres. Further details of the calibration and graphs
comparing the two calibration options are given in Appendix D.
The TMOR calibration should be used for aviation applications as it is considered
to give more representative visibility values for a plane landing and viewing
landing lights. Use of the TMOR calibration is obligatory for use of this sensor on
German airfields.
The CS125 can be switched between outputting data using the original MOR or
the alternative TMOR calibration by using a configuration switch (See Section
10). Sensors made from early December 2020 leave the factory with this switch
set to ON to make the sensor output values according to the TMOR calibration.
The CS125 is capable of identifying weather type in addition to measuring
visibility. It does this by analysing the amplitude and width of spikes in the APD
signal corresponding to particles of precipitation passing through the sample
volume. The amplitude of the signal is a guide to the size of the particle and the
width, because it represents the time taken for the particle to fall through the
sample volume, is proportional to the fall speed, see Figure 1-2.
Figure 1-2. Signals from large, slow falling snowflakes and smaller, faster,
raindrops
The CS125 also has a temperature sensor. These three parameters, fall speed, size
and temperature are used to identify the type of particle. If an additional external
temperature and relative humidity probe is connected then a wet-bulb temperature
can be calculated. This provides useful additional information identifying particles
more accurately especially, between liquid and frozen around 0°C.
Figure 1-3 shows how these temperatures are used to define possible precipitation
types around 0°C.
Instruction Manual
5
Figure 1-3. Defining possible precipitation types based on wet bulb and
dry bulb temperatures
The processing algorithm then works with several ‘maps’ such as Figure 1-4 to
identify each particle.
Figure 1-4. A typical size/speed map used by the CS125 present weather
algorithm
CS120A and CS125 Visibility and Present Weather Sensors
6
1.4 Recommended Tools
The following installation tools are recommended:
10 mm open spanner/wrench (for grounding boss, must be open ended)
13 mm spanner/wrench
19 mm open spanner/wrench (for cable glands, must be open ended)
2 mm flat screwdriver
Number 2 cross head screwdriver
1.5 Quickstart
The sensor is shipped set to the following default communication RS-232, 8N1,
38400 baud, a sensor ID = 0 and set to transmit default messages, full format,
visibility only for the CS120A, SYNOP present weather full format for the
CS125, at 1 minute intervals (see Section 11).
To start using the CS120A or CS125, first connect a DC supply matching the
specification in Section 3.1 to the red and black wires on the ‘D-connector’ (see
Figure 8-3) and connect to a PC communications port with a terminal emulator set
to RS-232, 38400 baud, 8N1. After a couple of minutes, data messages will be
received. Typing ‘open 0’ will access the menu structure, see Section 15.
2. Measurement specification
Minimum
Value
Nominal
Value
Maximum
Value
Visibility characteristics
Reported visibility (metric)
5 metres
-
75,000
metres
Reported visibility (imperial)
16 feet
-
46 miles
Visibility accuracy calibration
against factory calibration disk**
-
+/- 2%
-
Visibility accuracy up to 600 m
-
+/-8%
-
Visibility accuracy up to 10,000 m
-
+/-10%
-
Visibility accuracy up to 15,000 m
-
+/-15%
-
Visibility accuracy above 15,000 m
-
+/-20%
-
Precipitation characteristics, water equivalent (CS125 only)
Reported accumulation range
0 – 999.9 mm
Accumulation accuracy
+/-15%
Accumulation resolution
0.1 mm
Reported intensity range (up to *)
0 - 999.99 mm/hr
Intensity accuracy**
+/-15%
Intensity resolution
0.01 mm/hr
*The maximum intensity reported is dependent on the mixture of precipitation falling.
**Please refer to Section 1.3 regarding the calibration options for the sensor.
Instruction Manual
7
3. Technical specification
3.1 Electrical specification
Minimum
Value
Nominal
Value
Maximum
Value
Main power supply for DSP and dew heaters
Power supply, (DC only)
7V
12V
30V
(1)
Current consumption sampling
continuously with dew heaters ON and
RS-232 communications active
(2, 3)
(at 12V DC)
-
200 mA
248 mA
Current consumption sampling
continuously with dew heaters disabled
(at 12V DC)
-
110 mA
151 mA
Current consumption without any
sampling occurring and dew heaters
disabled (at 12V DC)
-
21 mA
30 mA
Hood heater power supply
Hood heater voltage (AC or DC)
-
24V
(3)
30V
(4)
Hood heater wattage (at 24V AC or
DC)
-
60W
(5)
-
User alarm outputs
User output high level (at 85ºC)
3.8V - -
User output high level (at 25ºC )
4.13V - -
User output low (All temperatures)
0.25V - 0.55V
User output current
- - 32 mA
(1) If a CS215 or HygroVUE probe is being used with a CS125 the supply voltage should not exceed
28V.
(2) The RS-232 communications interface will automatically turn itself off when not transmitting.
(3) If hood heaters are not being used ensure ‘Hood heater override’ (details in Section 13) is set to
off.
(4) It is recommended that the hood heaters are run at 24V AC/DC. It is possible to run the heaters at
any voltage below 24V but the heaters will generate proportionally less heat reducing their ability
to prevent ice build-up.
(5) Each hood takes 30W, 60W is the total for both hoods on the sensor together.
If a CS215 or HygroVUE probe is being used the supply
voltage should not exceed 28V.
3.2 Optical specification
Minimum
Value
Nominal
Value
Maximum
Value
Optical characteristics
LED centre wavelength
-
850 nm
-
LED spectral bandwidth
-
+/-35 nm
-
Pulse characteristics
CAUTION
CS120A and CS125 Visibility and Present Weather Sensors
8
Light pulse rate
-
1KHz
-
4. Communications specification
4.1 Communications electrical specifications
Minimum
Value
Nominal
Value
Maximum
Value
RS-232 Communications
(1)
RS-232 input threshold Low
0.8V
1.5V
-
RS-232 input threshold High
-
2.0V
2.4V
RS-232 input absolute maximum
-15V
-
+15V
RS-232 input resistance
12K
-
-
RS-232 output voltage low
- - 0.4V
RS-232 output voltage high (into
3K)
4.4V - -
RS-485 Communications
RS-485 input threshold voltage
-0.2V
-
+0.2V
RS-485 output (Unloaded)
- - 5V
RS-485 output (Load 50)
2V - -
Maximum voltage at any terminal
(2)
-7V
-
+7V
(1) The RS-232 communications interface will automatically turn itself off when not transmitting.
(2) The ground of the sensor and the ground of any RS-485 equipment cannot be further apart than
this voltage. The sensor ground (pin 1) on connector B, see page 18, can be connected to the
ground of the host equipment. This will reduce any parasitic currents.
4.2 Supported data rates and formats
Serial setting 8N1
Supported data rates
• 1200 bps
• 2400 bps
• 9600 bps
• 19200 bps
• 38400 bps - default
• 57600 bps
• 115200 bps
Supported formats
• RS-232 (Full duplex only), default
• RS-485 (Half duplex)
• 8 bit data bytes
• 1 stop bit
• Parity checking is not supported as most communication protocols used by
the CS125 have built in checksums as well as checks that communications
have been understood.
Instruction Manual
9
5. Environmental specifications
Minimum
Value
Nominal
Value
Maximum
Value
Sensor temperature ranges
Operating temperature
-25°C
-
+60°C
Extended operating temperature
-40°C
-
+70°C
(1)
Storage temperature
-40°C
-
+85°C
Sensor humidity ranges
Operating humidity range
0%
-
100%
Sensor heater thresholds
Dew heater Turn On
-
<35°C
-
Dew heater Turn Off
-
>40°C
-
Hood heater Turn On
-
<15°C
-
Hood heater Turn Off
-
>25°C
-
(1) Extended temperature ranges are only guaranteed if the sensor has been tested by Campbell
Scientific and verified within this temperature range. Some degradation of absolute accuracy can
be expected at the extremes of the extended ranges.
6. Mechanical specifications
6.1 Dimensions
CS120A and CS125 Visibility and Present Weather Sensors
10
6.2 Weights
Sensor weight: 3 Kg
Shipping weight: 6 Kg (including packing box)
6.3 Mounting
Sensor mounting: Bracket mounts on a vertical pole 32-52.5 mm diameter. The
mounting bracket has cut-outs for band clamps for larger
diameter masts.
7. Installation procedure
The sensor measures environmental variables and is designed to be located in
harsh weather conditions. However, there are a few considerations to take into
account if accurate and representative data from a site are to be obtained.
The descriptions in this section are not exhaustive. Please refer to
meteorological publications for further information on locating
weather instruments
The sensor should be sited in a position representative of local weather conditions
and not of a specific microclimate (unless the analysis of microclimate weather is
being sought).
The sensor has good resistance to background light but it is a good idea to avoid
locations where the transmitter is pointing at a light scattering or reflecting
surface. Ideally, the receiver should point north in the northern hemisphere or
south in the southern hemisphere but this is not critical. This is because it is more
important to make sure the receiver is not pointing towards any possible sources
or reflected light in its field of view, for instance nearby sensors or enclosures
mounted below it on a mast. Where those objects cannot be moved, pointing the
sensor away from North/South is acceptable. Failure to do this can result in the
sensor reporting a DC light saturation error when there is bright sunlight.
To give non-microclimatic measurements the sensor should be sited away from
possible physical obstructions that could affect the fall of precipitation. The sensor
should also be positioned away from sources of heat, electrical interference and in
such a position as to not have direct light on the sensor lenses. Whenever possible,
the sensor should be located away from windbreaks.
Several zones have been identified upwind and downwind of a windbreak in
which the airflow is unrepresentative of the general speed and direction. Eddies
are generated in the lee of the windbreak and air is displaced upwind of it. The
height and depth of these affected zones varies with the height and to some extent
the density of the obstacle.
Generally, a structure disturbs the airflow in an upwind direction for a distance of
about twice the height of the structure, and in a downwind direction for a distance
of about six times the height. The airflow is also affected to a vertical distance of
about twice the height of the structure. Ideally, therefore, the sensor should be
located outside this zone of influence in order to obtain representative values for
the region.
NOTE
Instruction Manual
11
Figure 7-1. Airflow
In order to reduce the service frequency with the unit, the sensor should be placed
away from sources of contamination, in the case of roadside monitoring; larger
mounting poles can be used. More regular maintenance will be required when the
instrument is placed in areas where contamination is unavoidable or where
measurements may be safety critical.
The WMO recommend a sample volume height of 1.5 m. However, for
applications such as aviation or road visibility other heights may be appropriate.
If operating a sensor indoors it is likely that there will be sources of
light and/or reflections that will create false readings and erratic
results.
If carrying out simple checks, blocking a lens or the sample volume
will simulate an INCREASE in visibility not a decrease.
7.1 Equipment grounding
The sensor must be properly grounded. It is sufficient to ground the mounting
bracket and if the sensor is connected to a grounded metal mast, and in electrical
contact with it, then this will be sufficient. Otherwise, the mounting bracket
should be earthed and a grounding boss is supplied to allow this.
A ground wire with a minimum cross section of 6 mm2 and maximum length of
5 m should be used.
The pole and foundations of a pole mounted installation will provide some basic
lightning protection and protection against radio frequency interference and
should also be correctly grounded.
NOTE
NOTE
CS120A and CS125 Visibility and Present Weather Sensors
12
Figure 7-2. Grounding boss
7.2 Mounting the sensor
A quick release pole mounting kit is supplied with the sensor.
If a power supply enclosure has been supplied with the sensor it can be mounted
on the pole, near its base using the brackets supplied with the enclosure.
Alternatively the power supply can be mounted elsewhere, e.g. on a wall at some
distance from the sensor. The power supply enclosure should be mounted away
from the sensor head to avoid wind flow disturbance or rain drops bouncing back
up into the sensor’s sensing volume.
Take care not to overtighten the nuts on the bolts, as it may
be possible to distort and/or damage the brackets or DSP
plate by doing so, and/or the nuts may seize up. Only tighten
the nuts to a degree necessary to hold the sensor firmly in
place.
Where the sensor is to be mounted onto another type of mast, please refer to the
manual for that mast for mounting details.
Ensure that the sensor is mounted according to the following
figure. Do not reposition, once fixings are tightened, by
forcing the arms of the unit as this can cause damage.
CAUTION
CAUTION
Instruction Manual
13
Do not remove the mounting plate as this will compromise
resistance to water ingress.
Figure 7-3. Mounting arrangement
If you need to mount the sensor to a flat surface, remove the plastic formers from
the mounting brackets and use the holes as shown in Figure 7-4.
If mounting to a flat surface ensure that there is no obstruction to
airflow through the sample volume.
Figure 7-4. Mounting to a flat surface
CAUTION
NOTE
CS120A and CS125 Visibility and Present Weather Sensors
14
Slots are provided to allow band clamps to be used with larger diameter masts, see
Figure 7-5.
Figure 7-5. Use of band clamps
7.3 Optional Campbell Scientific Mount
A Campbell Scientific ‘optical sensor mount’ is available. This will put the
sample volume at about 1.5 m in compliance with the WMO ‘Guide to
Meteorological Instruments and Methods of Observation’, 7th Edition, Section
9.3.4.
Instruction Manual
15
Figure 7-6. Optical sensor mast
If one is to be used, use the following installation instructions.
Install the mount on a concrete foundation. If one does not already exist then a
concrete foundation should be constructed at least 600 mm square and 600 mm
deep. Ensure the ground consistency is not too loose and will be able to support
the mount and concrete foundation.
CS120A and CS125 Visibility and Present Weather Sensors
16
Drill four 12 mm diameter holes using the mount base as a template or using the
following in Figure 7-7 to a depth of 77 mm.
Figure 7-7. Mounting footprint
Clean the holes of all debris.
Place washers and nuts on the ends of the wedge anchors supplied (to protect the
threads during installation).
Hammer the wedge anchors into the holes until the start of the threads are below
the surface.
Tighten the nuts until about 25 mm of thread protrudes above the surface.
Remove the washers and nuts from the protruding length screw. Then lower the
mount into place.
Finally secure the mount with the washers and nuts.
If the surface is not level and flat it may be necessary to add washers under the
base on one or more of the foundation screws.
Instruction Manual
17
8. Sensor internal connectors’ description
The sensor has four standard IP66 rated glands. The first gland is by default used
by the power/communications line. This comprises the 7-30 V for the main
electronics, and the serial communications wires. The sensor is supplied with 5 m
cable already connected.
The second gland is used for the 24 V feeds for the hood heaters fitted with a 5 m
cable.
Glands 3 and 4 are spare. If user alarms are connected they usually use gland 3
and if a CS215 or HygroVUE probe is fitted this usually uses gland 4.
If you need to run cables through the cable glands follow these guidelines. If a
torque wrench is available use a torque of 2.5 Nm (do not over tighten).
Otherwise tighten with fingers as tight as possible and then add a further ¾ turn
with a 19 mm spanner (do not over tighten).
The glands are suitable for cables between 5 and 9 mm diameter.
If the power cable is incorrectly wired to the sensor then
damage can be done to the unit.
10 m is the longest length of the cable type supplied
recommended. In particular, additional RS-485
communication should be twisted pair. Please contact
Campbell Scientific if you wish to use a longer length of cable.
Figure 8-1. Connections
CAUTION
CAUTION
CS120A and CS125 Visibility and Present Weather Sensors
18
Connector A - Five way connector
Pin number
Description
Notes
Pin 1
+ve supply
Main electronics +ve supply input
Pin 2
0V
Auxiliary Electronics 0V. Common with the main electronics 0V.
Pin 3
Hood low
This is for the hood heater power supply. If the hood heater supply is
DC it should be the negative connection and if it is AC it should be
the ‘neutral’ or ‘ground’ connection if there is one.
Pin 4
0V
Auxiliary Electronics 0V. Common with the main electronics 0V.
Pin 5
Hood high
This is for the hood heater power supply. If the hood heater supply is
DC it should be the positive connection.
To avoid damage to noise filters on the hood heater inputs if
the heater voltage is DC the –ve connection should be made
to pin 3 and the +ve to pin 5. If the heater voltage is AC with a
ground or neutral wire then this should be connected to pin 3.
Pin 3 should not be more than 5 volts from the main
electronics 0V.
Connector B - Three way connector
Pin number
Description
Notes
Pin 1
0V
0V connection for serial communications. This connection is
common with the main electronics 0V (Connector A, pin 2).
Pin 2
Receive
RS-232 receive line, RXD, B/D+ for RS-485 half duplex
Pin 3
Transmit
RS-232 transmit line, TXD, A/D− for RS-485 half duplex
It may be necessary to use a 120 ohm termination resistor to reduce signal
distortion when using RS-485 for cable runs over about 500 m and baud rates
above 38400. It should be connected between pins 2 and 3.
Connector C - Four way connector
Pin number
Description
Notes
Pin 1
0V
0V connection for user alarms. This connection is common with the
main electronics 0V (Connector A, Pin 2).
Pin 2
User 2
Output for user alarm 2
Pin 3
0V
0V connection for user alarms. This connection is common with the
main electronics 0V (Connector A, Pin 2).
Pin 4
User 1
Output for user alarm 1
CS125 only
Pin number
Description
Pin 1
+12V
Pin 2
SDI-12
Pin 3
0V
To use these connections it is necessary to either use the cable gland
taking the hood heater power or, if the hood heater is also required,
to use different cables to those supplied. Please contact Campbell
Scientific if you need any advice on choice of cable.
CAUTION
NOTE
Instruction Manual
19
8.1 Sensor recommended wiring using Campbell Scientific cables (this cable is supplied already connected as standard)
The sensor is provided pre-wired with a default 5 m power and communications
cable which is terminated at one end with a 9 pin D-connector (DB9). The
D-connector can be connected directly to a PC or to a datalogger such as the
Campbell Scientific CR1000 using a suitable interconnecting cable such as the
SC110. If another type of connection is required then the D-connector should be
removed.
Figure 8-2. Communications and power connections
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