Campbell Scientific PWS100 User Manual
PWS100
Present Weather Sensor
Revision: 3/12
Copyright © 2006-2012
Campbell Scientific, Inc.
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PWS100 Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.
1. Introduction...............................................................1-1
2. Cautionary Statements.............................................2-1
2.1 Sensor Unit Safety ................................................................................ 2-1
2.2 Laser Safety .......................................................................................... 2-1
3. Initial Inspection .......................................................3-1
4. Overview....................................................................4-1
5. Specifications ...........................................................5-1
5.1 Mechanical Specifications .................................................................... 5-1
5.2 Electrical Specifications ....................................................................... 5-1
5.3 Optical Specifications........................................................................... 5-2
5.3.1 Laser Head Specifications........................................................... 5-2
5.3.2 Sensor Head Specifications......................................................... 5-2
5.4 Environmental Specifications............................................................... 5-2
5.5 CS215-PWS Specifications .................................................................. 5-2
5.6 Measurement Capabilities and Limitations........................................... 5-2
5.6.1 Visibility Measurements ............................................................. 5-2
5.6.2 Precipitation Measurements........................................................ 5-3
5.6.3 Data Storage and Buffering ........................................................ 5-3
6. Installation.................................................................6-1
6.1 Location and Orientation ...................................................................... 6-1
6.2 Unloading and Unpacking .................................................................... 6-2
6.2.1 Unpacking Procedure.................................................................. 6-2
6.2.2 Storage Information .................................................................... 6-2
6.3 Installation Procedures.......................................................................... 6-3
6.3.1 Assembling the PWS100 ............................................................ 6-3
6.3.2 Mounting the PWS100................................................................ 6-3
6.3.3 Connecting Cables ...................................................................... 6-7
6.3.4 Basic Wiring ............................................................................... 6-7
6.3.5 Desiccant..................................................................................... 6-9
6.3.6 Communication Options ............................................................. 6-9
6.3.6.1 RS-485 Half-duplex mode .............................................. 6-11
6.3.7 Installing Power Supply............................................................ 6-13
6.3.8 Start-Up Testing........................................................................ 6-13
6.3.9 Initial Settings ........................................................................... 6-13
6.3.10 Load Factory Defaults............................................................. 6-13
6.3.11 Lubricating the Enclosure Screws........................................... 6-13
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PWS100 Table of Contents
7. Operation .................................................................. 7-1
6.4 Grounding and Lightning Protection .................................................. 6-14
6.4.1 Equipment Grounding............................................................... 6-14
6.4.2 Internal Grounding .................................................................... 6-14
6.4.3 Lightning Rod ...........................................................................6-14
7.1 Introduction........................................................................................... 7-1
7.2 PWS100 Configuration......................................................................... 7-1
7.2.1 Using the Present Weather Viewer Program............................... 7-1
7.3 Terminal Mode...................................................................................... 7-2
7.3.1 Using the Help Command........................................................... 7-3
7.3.2 Entering / Exiting the Menu System ...........................................7-3
7.3.3 Message Polling ..........................................................................7-4
7.4 PWS100 Menu System ......................................................................... 7-4
7.4.1 Top Menu Options 0, 1 and 2 (Message n) ................................. 7-5
7.4.1.1 Message 0 (the Default Output)......................................... 7-9
7.4.1.2 Message Field 1 and 2 User Defined Message.................. 7-9
7.4.1.3 Message Field 10 To 19 Fixed Messages........................ 7-10
7.4.1.4 Message Field 20 Visibility Range (m) ........................... 7-10
7.4.1.5 Message Field 21 Present Weather Code (WMO) .......... 7-10
7.4.1.6 Message Field 22 Present Weather Code (METAR)....... 7-10
7.4.1.7 Message Field 23 Present Weather Code (NWS)............ 7-10
7.4.1.8 Message Field 24 Alarms ............................................... 7-10
7.4.1.9 Message Field 25 Fault Status of the PWS100................ 7-11
7.4.1.10 Message Field 30 External Sensor Temperature,
RH% and Wetbulb........................................................ 7-11
7.4.1.11 Message Field 31 External Sensor Maximum and
Minimum Temperature................................................. 7-11
7.4.1.12 Message Field 33 External Sensor Wetness .................. 7-11
7.4.1.13 Message Field 34 External Sensor Aux......................... 7-11
7.4.1.14 Message Field 40 Precipitation Intensity....................... 7-11
7.4.1.15 Message Field 41 Precipitation Accumulation .............. 7-12
7.4.1.16 Message Field 42 Drop Size Distribution...................... 7-12
7.4.1.17 Message Field 43 Average Velocity (ms-1) and
Average Size (mm)....................................................... 7-12
7.4.1.18 Message Field 44 Type Distribution.............................. 7-12
7.4.1.19 Message Field 45 Size / Velocity Type Map 1
(20 x 20) .......................................................................7-12
7.4.1.20 Message Field 46 Size / Velocity Type Map 2
(32 x 32) .......................................................................7-13
7.4.1.21 Message Field 47 Campbell Scientific Standard Size /
Velocity Map (34 x 34) ................................................7-15
7.4.1.22 Message Field 48........................................................... 7-17
7.4.1.23 Message Field 49 Visibility (m), 10 minute average..... 7-17
7.4.1.24 Message Field 100 Upper, Lower LED temperature..... 7-18
7.4.1.25 Message Field 101 Upper, Lower Detector
Temperature.................................................................. 7-18
7.4.1.26 Message Field 102 Laser Hood, Laser Temperature
and Laser Drive Current ............................................... 7-18
7.4.1.27 Message Field 103 Laser, Upper, Lower Detector DC
Voltage Offsets............................................................. 7-18
7.4.1.28 Message Field 104 Laser, Upper and Lower Dirty
Window Detector ......................................................... 7-18
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PWS100 Table of Contents
7.4.1.29 Message Field 105 DSP PSU Voltage, Hood and
Dew Heater % Duty ..................................................... 7-18
7.4.1.30 Message Field 106 Upper, Lower Detector Differential
Voltage, Calibrated Visibility mV............................... 7-18
7.4.1.31 Message Field 150 Serial Number, Operating System
and Hardware Version.................................................. 7-18
7.4.1.32 Message Field 151 Day Count, Hours, Minutes,
Seconds ........................................................................ 7-18
7.4.1.33 Message Field 152 Product Name................................. 7-18
7.4.1.34 Message Field 153 Statistics Period.............................. 7-18
7.4.1.35 Message Field 154 Watchdog Count, Maximum Particles
Per Second, Particles Not Processed, Time Lag........... 7-19
7.4.1.36 Message Field 155 Processing Statistics ....................... 7-19
7.4.1.37 Message Field 156 Year, Month, Day........................... 7-19
7.4.1.38 Message Field 157 Hours, Minutes, Seconds................ 7-19
7.4.1.39 Message Field 158 Averaged Corrected Visibility
Voltage and Averaged Upper Head Voltage............... 7-19
7.4.1.40 Message Field 159 Output a CCITT CRC-16
(checksum) of the message .......................................... 7-19
7.4.1.41 Message Field Error ...................................................... 7-19
7.4.2 Top Menu Option 3 (Set Time and Date) ................................. 7-21
7.4.3 Top Menu Option 4 (Configuration)......................................... 7-22
7.4.4 Top Menu Option 5 (Password)................................................ 7-30
7.4.5 Top Menu Option 6 (Weather and Alarm Parameters)............. 7-31
7.4.6 Top Menu Option 7 (Terminal) ................................................ 7-34
7.4.7 Top Menu Option 8 (Info) ........................................................ 7-34
7.4.8 Top Menu Option 9 (Done) ...................................................... 7-35
7.5 Message Related Commands.............................................................. 7-36
7.5.1 Automatic and Polled Message Sending................................... 7-36
7.5.2 Retrieving Historical Data ........................................................ 7-38
7.5.3 Viewing Data Output on the Command Line ........................... 7-40
7.5.4 Collection of Data in Text File Format..................................... 7-40
7.6 Weather Related Commands .............................................................. 7-40
7.6.1 Setting and Viewing Weather Parameters................................. 7-40
7.6.2 Receiving Data from Remote Sensors ...................................... 7-41
7.7 System Configuration Commands...................................................... 7-41
7.7.1 Setting System Parameters........................................................ 7-41
7.8 Maintenance Commands..................................................................... 7-43
7.8.1 Loading a New OS.................................................................... 7-43
7.8.2 Running a Diagnostic Test........................................................ 7-44
7.8.3 Running the Calibration............................................................ 7-45
7.8.4 Rotating the Calibration Disc.................................................... 7-45
7.9 Other Commands................................................................................ 7-45
7.9.1 Setting the Time and Date......................................................... 7-45
7.9.2 Resetting the System................................................................. 7-46
7.10 Connecting the PWS100 to a Datalogger ......................................... 7-46
7.10.1 Connections ............................................................................ 7-46
7.10.2 Example Logger Programs...................................................... 7-46
8. Functional Description.............................................8-1
8.1 General.................................................................................................. 8-1
8.2 Optical Measurement............................................................................ 8-1
8.2.1 Optical Arrangement................................................................... 8-1
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PWS100 Table of Contents
9. Maintenance ............................................................. 9-1
8.3 Additional Sensor Connections............................................................. 8-3
8.3.1 Using a CS215-PWS on the PWS100......................................... 8-4
8.3.2 Using Other Sensors on the PWS100.......................................... 8-4
8.4 PWS100 Control Unit........................................................................... 8-5
8.5 Measurement Signal Processing ...........................................................8-5
8.6 Algorithm Description .......................................................................... 8-6
8.6.1 Detecting and Classifying Precipitation ...................................... 8-6
8.6.2 Precipitation Intensity .................................................................8-8
8.6.3 Precipitation Accumulation....................................................... 8-10
8.6.4 Present Weather ........................................................................ 8-10
8.6.4.1 Precipitation Types .......................................................... 8-10
8.6.4.2 Visibility Types ...............................................................8-11
8.6.4.3 Weather Classes............................................................... 8-11
8.6.4.4 Weather Code Selection ..................................................8-11
8.6.5 Visibility.................................................................................... 8-11
8.7 Applications ........................................................................................ 8-12
8.8 Internal Monitoring............................................................................. 8-13
9.1 General.................................................................................................. 9-1
9.2 Cleaning ................................................................................................ 9-1
9.3 Calibration............................................................................................. 9-2
10. Troubleshooting................................................... 10-1
10.1 Introduction....................................................................................... 10-1
10.2 Possible Problems ............................................................................. 10-1
10.2.1 No response from PWS100..................................................... 10-1
10.2.2 PWS100 responds but no data output given ........................... 10-1
10.2.3 Ice has formed in the end of the hoods.................................... 10-2
10.2.4 The visibility output is clearly in error.................................... 10-2
10.2.5 The sensor does not detect particles during a precipitation
event .................................................................................... 10-2
10.2.6 The sensor detects particles when there are none present ....... 10-2
10.2.7 The OS update did not work ...................................................10-3
Appendices
A. PWS100 Output Codes ........................................... A-1
B. Wiring ....................................................................... B-1
C. Cable Selection........................................................C-1
C.1 Power Cable ........................................................................................ C-1
C.2 Communication Cable......................................................................... C-3
D. Software Flowchart .................................................D-1
E. Menu System Map ................................................... E-1
iv
List of Figures
4-1. PWS100............................................................................................... 4-1
6-1. Effect of structure on air flow ............................................................. 6-1
6-2. Hardware for mounting the top of the DSP plate to a pole ................. 6-4
6-3. Placing the PWS100 onto the bracket ................................................. 6-5
6-4. PWS100 mounted to a mast or pole .................................................... 6-6
6-5. Underside of DSP enclosure ............................................................... 6-8
6-6. Mounting the desiccant pack on the DSP cover.................................. 6-9
6-7. Removal of DSP cover...................................................................... 6-10
6-8. Exposing the DSP board ................................................................... 6-10
6-9. DSP board dip switch location (circled)............................................ 6-12
6-10. Dip switches (defaults set - 00011100) ........................................... 6-12
6-11. Labeled DIN-RAIL contacts ........................................................... 6-13
7-1. PWS100 setup menu ........................................................................... 7-5
7-2. Message menu ..................................................................................... 7-5
7-3. Message parameters and fields menu.................................................. 7-6
7-4. Message interval menu........................................................................ 7-6
7-5. Message mode menu ........................................................................... 7-7
7-6. Message field menu........................................................................... 7-20
7-7. Delete message menu ........................................................................ 7-21
7-8. Time and date menu .......................................................................... 7-21
7-9. Configuration menu........................................................................... 7-22
7-10. PWS100 ID menu............................................................................ 7-23
7-11. TRH probe menu............................................................................. 7-23
7-12. Wetness probe menu ....................................................................... 7-24
7-13. Aux probe menu.............................................................................. 7-24
7-14. Hood heater temperature menu ....................................................... 7-25
7-15. Dew heater mode menu................................................................... 7-25
7-16. Output mode menu .......................................................................... 7-26
7-17. Calibration warning screen.............................................................. 7-27
7-18. Calibration top menu....................................................................... 7-27
7-19. Calibration disc constants menu...................................................... 7-28
7-20. View / adjust calibration menu........................................................ 7-29
7-21. Terminal mode menu....................................................................... 7-29
7-22. PSU shut down voltage menu ......................................................... 7-30
7-23. Password menu............................................................................... 7-30
7-24. Weather parameters menu ............................................................... 7-31
7-25. Visibility range alarm menu ............................................................ 7-31
7-26. Snow water content adjustment....................................................... 7-33
7-27. Mixed precipitation threshold adjustment....................................... 7-34
7-28. Terminal active screen..................................................................... 7-34
7-29. Information menu............................................................................ 7-35
7-30. Done menu ...................................................................................... 7-36
8-1. Laser unit............................................................................................. 8-2
8-2. Laser unit showing light sheet production (not to scale)..................... 8-2
8-3. Sensor unit........................................................................................... 8-3
8-4. Sensor unit showing light path extents (not to scale) .......................... 8-3
8-5. Block diagram of PWS100 control unit .............................................. 8-5
8-6. Signal to pedestal ratio values for different precipitation types .......... 8-7
9-1. Baffle removal and fitting ................................................................... 9-1
B-1. Underside of DSP enclosure...............................................................B-1
B-2. DSP PCB to DSP enclosure connections............................................B-2
C-1. PWS100 power cable..........................................................................C-2
C-2. Enclosure wiring details for power cable ...........................................C-2
PWS100 Table of Contents
v
PWS100 Table of Contents
List of Tables
C-3. PWS100 communication cable .......................................................... C-4
C-4. Enclosure wiring details for communication cable............................ C-4
7-1. Command Set ......................................................................................7-2
7-2. Message Field parameters.................................................................... 7-7
7-3. Assumed bulk density of various particle types. ...............................7-32
7-4. Weather parameters. .......................................................................... 7-41
7-5. Detectable sensors. ............................................................................7-43
8-1. Precipitation intensities........................................................................ 8-9
A-1. PWS100 output codes........................................................................ A-1
A-2. Light, moderate and heavy precipitation defined with respect to
type of precipitation and to intensity, i, with intensity values
based on a three-minute measurement period ................................. A-7
A-3. Intensity bounds for rain and drizzle .................................................A-8
A-4. Intensity bounds for rain and snow.................................................... A-8
A-5. Intensity bounds for drizzle and snow ............................................... A-8
A-6. Intensity bounds for rain, drizzle and snow....................................... A-9
A-7. Intensity bounds for rain, drizzle, ice pellets, hail and snow............. A-9
A-8. Intensity bounds for ice pellets, hail and snow.................................. A-9
B-1. Cable identifier................................................................................... B-1
C-1. Communication cable connections .................................................... C-3
vi
Section 1. Introduction
The PWS100 is a laser-based sensor that measures precipitation and visibility
by accurately determining the size and velocity of water droplets in the air. It
can be used in weather stations in road, airport, and marine applications. The
PWS100 uses advanced measurement techniques and algorithms to calculate
individual precipitation particle type.
1-1
Section 1. Product Overview
1-2
Section 2. Cautionary Statements
2.1 Sensor Unit Safety
The PWS100 sensor has been checked for safety before leaving the factory and
contains no internally replaceable or modifiable parts.
WARNING
WARNING
CAUTION
2.2 Laser Safety
Do not modify the PWS100 unit. Such modifications
will lead to damage of the unit and could expose users
to dangerous laser 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.
The PWS100 sensor incorporates a laser diode which is rated as a class 3B
device. This is an embedded laser where the output from the sensor unit,
through the optics, is minimized to class 1M. This classification indicates that
viewing of the beam with the naked eye is safe but looking directly into the
beam with optical instruments, e.g. binoculars can be dangerous.
From the laser head the output has the following characteristics:
Maximum pulse energy: 73 nJ
Pulse duration: 5.2 μs
Wavelength: 830 nm
EN 60825-1:2001
The sensor is marked with the following warning:
INVISIBLE LASER RADIATION
DO NOT VIEW DIRECTLY WITH OPTICAL INSTRUMENTS
CLASS 1M LASER PRODUCT
Opening the laser head unit with the power applied to the PWS100 may expose
the user to hazardous laser radiation. To open the unit requires the use of tools
and should not be carried out except by authorized personnel using appropriate
safety eyewear.
2-1
Section 2. Cautionary Statements
If the laser is operated outside of the housing then the following warning
applies:
INVISIBLE LASER RADIATION
AVOID EXPOSURE TO BEAM
CLASS 3B LASER PRODUCT
WARNING
Check that the laser warning label on the sensor is still
visible and can be clearly read on an annual basis.
When installing the sensor avoid pointing the laser
housing towards areas where binoculars are in
common use.
2-2
Section 3. Initial Inspection
Upon receipt of the PWS100, inspect the packaging and contents for damage.
File damage claims with the shipping company.
3-1
Section 3. Initial Inspection
3-2
Section 4. Overview
The PWS100 Present Weather Sensor is a laser based sensor capable of
determining precipitation and visibility parameters for automatic weather
stations including road, marine and airport stations. Due to its advanced
measurement technique and fuzzy logic algorithms, the PWS100 can determine
each individual precipitation particle type from accurate size and velocity
measurements and the structure of the received signal.
The system can output visibility and precipitation related weather codes such
as those detailed in the World Meteorological Organisation (WMO) SYNOP
code, those used as part of a METAR weather report and those previously used
by the US National Weather Service (NWS).
Further details of precipitation can be given in terms of drop size distributions
(DSD) and particle size / velocity maps to give better indications of
precipitation intensity. Such distributions can then be used in soil erosion
studies.
The PWS100 comprises a Digital Signal Processor (DSP) housing unit
connected to a sensor arm, comprising one laser head and two sensor heads.
Each of the sensor heads is 20° off axis to the laser unit axis, one in the
horizontal plane, the other in the vertical plane. The DSP housing is fixed via a
mounting bracket to a mast, though a tripod can be used for temporary sites.
Figure 4-1 shows the PWS100 mounted on a pole.
An optional CS215-PWS temperature and humidity sensor is normally
supplied and plugs directly into the PWS100. That sensor is used to improve
the accuracy of weather coding by the PWS, in particular in respect of
discriminating between snow and rain and also fog/mist and dust.
FIGURE 4-1. PWS100
4-1
Section 4. Overview
4-2
Section 5. Specifications
5.1 Mechanical Specifications
Measuring Area: 40 cm2 (6.2 in2)
Housing Materials: Iridite NCP conversion coated aluminium
(RoHS compliant) and hard anodized
aluminium. Outer parts also coated with marine
grade paint.
Weight: 8.2 kg (18 lb) excluding power supply /
communications enclosure
Shipping Weight: 20.4 kg (45 lb)
Dimensions: 115 cm × 70 cm × 40 cm (42.3 in × 27.6 in ×
15.8 in)
Mountings: U-bolt mounting to mast or pole with outer
diameter from 1.25 in to 2.07 in
5.2 Electrical Specifications
NOTE
Power Requirements: DSP power 9 to 24 V, (9 to 16 V limit when
using CS215-PWS or other SDI-12 sensors).
Current consumption 200 mA no dew heater or
SDI-12, 1 A with dew heater and SDI-12. The
currents are lower at high supply voltages as
the sensor uses SMPS technology. Hood
heater 24 Vac or dc, 7 A.
It is the responsibility of the user to ensure that any local
regulations, regarding the use of power supplies, are adhered to.
Communication: RS-232, RS-422, RS-485. Baud rate of 300 bps
to 115.2 kbps supported.
Control Unit: Custom DSP board
EMC Compliance: Tested and conforms to BS EN 61326:1998.
Class A device. May cause interference in a
domestic environment.
5-1
Section 5. Specifications
5.3 Optical Specifications
5.3.1 Laser Head Specifications
Laser Source: Near-infrared (IR) diode, eye safe Class 1M
Peak Wavelength: 830 nm
Modulation Frequency: 96 kHz
Laser Head Lens Diameter: 50 mm (1.97 in)
5.3.2 Sensor Head Specifications
Receivers: Photodiode with band pass filters
Spectral Response: Maximum spectral sensitivity at 850 nm, 0.62
Sensor Head Lens Diameter: 50 mm (1.97 in)
unit output
A/W (0.6 A/W at 830 nm)
Lens Check Light Source: Near-IR LED
5.4 Environmental Specifications
Standard Operating
Temperature Range: -25° to +50°C
Optional Extended Operating
Temperature Range: -40° to +70°C
Relative Humidity Range: 0 to 100%
IP Rating: IP 66 (NEMA 4X)
5.5 CS215-PWS Specifications
Please refer to the CS215 manual or product brochure for the specifications.
5.6 Measurement Capabilities and Limitations
5.6.1 Visibility Measurements
5-2
Visibility Range: 0 to 20,000 m (0 to 65,620 ft)
Visibility Accuracy: ± 10% (0 to 10,000 m)
Measurement Interval: User selectable from 10 seconds to 2 hours
5.6.2 Precipitation Measurements
Particle Size*: 0.1 mm to 30 mm (0.004 in to 1.18 in)
Size Accuracy*: ± 5% (for particles >0.3 mm)
Section 5. Specifications
Particle Velocity: 0.16 ms
-1
to 30 ms-1
Velocity Accuracy*: ± 5% (for particles >0.3 mm)
Types of Precipitation
Detected: Drizzle, rain, snow grains, snow flakes, hail,
ice pellets, graupel (heavily rimed solid
precipitation), freezing rain, freezing drizzle,
mixed (combination of types above)
-1
Rain Rate Intensity Range: 0 to 400 mm h
(M-P Distributed)
Rainfall Resolution: 0.0001 mm
Rain Total Accuracy*: Typically ±10% (accuracy will be degraded for
windy conditions, frozen precipitation, and
very high rainfall rates).
DSD bin sizes: 0.1 mm (diameter) 0.1 ms
-1
(velocity)
Data Output: Raw parameter output (particle size, particle
velocity, signal peak value, signal pedestal
value), WMO SYNOP codes (4680, W
a Wa
precipitation and obscurant type), WMO
METAR codes (4678, W
- precipitation
a Wa
and obscurant type), NWS code, drop size
distribution (DSD) statistics, particle type
distribution, size / velocity intensity maps,
precipitation rate, precipitation accumulation,
visibility range and internal checks
(temperatures, lens contamination, processing
limits).
External Sensors: CS215-PWS supported for temperature / RH
*Accuracy values are for laboratory conditions with reference particles and
visibility standards.
5.6.3 Data Storage and Buffering
The PWS100 has a large internal memory that is split up to store different
types of data. One buffer, the particle buffer, is used to hold raw signal data
captured from the detectors. The size of this buffer and the speed at which it
can be processed is a limit on the maximum rainfall rates the sensor can
measure. For most users, this is not a limitation; if it may be a limitation, please
read the description below.
measurement; SDI-12 compatible sensors
supported.
5-3
Section 5. Specifications
The particle buffer is able to hold raw data for 500 typical particles. The
processor is able to process the particles at a rate of 120 particles per second,
typically. This means if more than 120 particles per second fall through the
sample volume of 40 cm
2
the particle buffer will start to fill up. If the rain rate
exceeds 120 particles per second for a prolonged period, the buffer could run
out of space and particles will be lost.
The fact that the processor is running behind real-time and/or particles are
being missed can be monitored in the alarm message which can be selected for
data output.
The particle processor then places data about each particle in the Large Particle
Array (LPA). The LPA is 100000 records long. It uses 5 records every 10
seconds plus a record for every processed particle that passes through the
volume. For example if 20 particles per second are processed then 20.5 records
are used per second. Since 100000 records can be stored, the system can store
100000 / 20.5 = 4878 seconds worth of data in the LPA. The user needs to be
aware of the size of this buffer as it is used to hold data that is processed when
a message is output. The size of the buffer may become a limiting factor if a
very long message interval is selected and rainfall rates are high.
The PWS100 has the capability to store measured data in a buffer called the
message storage buffer, which is 1 MB (1000000 characters) in size. All ASCII
characters including CrLf must be included in any storage calculations. This
buffer stores the user defined messages (see Section 7.5, Message Related
Commands for the types of messages available to the user). A typical message
containing 120 characters can be stored 1000000 / 120 = 8333 times which at
minute intervals for the data output would be over 138 hours worth of storage.
5-4
Section 6. Installation
6.1 Location and Orientation
The PWS100 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.
NOTE
The descriptions in this section are not exhaustive. Please refer to
meteorological publications for further information on the
locating of weather instruments.
The PWS100 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).
To give non-microclimatic measurements the PWS100 should be sited away
from possible physical obstructions that could affect the fall of precipitation.
The PWS100 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 PWS100 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
PWS100 should be located outside this zone of influence in order to obtain
representative values for the region (see Figure 6-1).
FIGURE 6-1. Effect of structure on air flow
6-1
Section 6. Installation
In order to minimize user interaction with the unit, the PWS100 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 orientation of the unit should be such that the horizontal sensor head points
north in the northern hemisphere and south in the southern hemisphere. The
angle of inclination of the second sensor head is such that the deviation from
north/south orientation causes no increase in system noise.
High frequency light sources can lead to increased system noise and hence
erroneous weather classification and so the PWS100 should be positioned in a
location where such interference is minimized. Ideally this should be a
minimum of 100 m from the nearest high frequency light source, with the
sensor heads pointing away from the light source. In any case the sensor heads
should be positioned to be away from any high frequency light source.
Avoid locations where the transmitter is pointing at a light scattering or
reflective surface.
WARNING
When installing the sensor, avoid pointing the laser
housing toward areas where binoculars are commonly
used.
To be at any risk from the laser light source, the operator must look directly
down the beam of light and must be at the same height and in exact alignment
with the sensor. In addition, the beam diverges slightly so the risk decreases
with distance from the sensor.
6.2 Unloading and Unpacking
6.2.1 Unpacking Procedure
Depending on the power and mounting options selected for the PWS100 there
will be up a number of boxes containing the PWS sensor unit, power supply/
external communications enclosure and grounding equipment.
CAUTION
Handle the boxes carefully, taking care not to drop them as
the sensor can be damaged if dropped.
Unpack the boxes carefully and check the contents, ensuring that the contents
match those listed on the packing slip. Carefully remove the items and replace
all packing materials back into the empty boxes and store in case the unit is
required to be repacked for shipping.
6-2
6.2.2 Storage Information
The PWS100 should be stored between -40° to +70°C in a dry place,
preferably with the enclosures securely fastened with desiccant in place. The
optics should be protected from possible accidental damage.
6.3 Installation Procedures
6.3.1 Assembling the PWS100
The PWS100 comes as a single unit, with the DSP enclosure attached to the
base of the sensor arms. The PWS100 and power/communication enclosure (if
purchased) are typically mounted to a Campbell Scientific tripod. Usersupplied mounting structures should be strong enough to withstand high winds,
without significant movement.
See the manuals supplied with your tripod for details on how to set up ready
for PWS100 mounting. Tripods need to be firmly secured to a base with the
central pole vertical to ensure correct measurements with the PWS100. See the
relevant tripod or tower manual for further details.
6.3.2 Mounting the PWS100
Section 6. Installation
NOTE
A PWS100 purchased from Campbell Scientific Europe will
have a different mounting bracket.
A pole mounting kit is supplied with the PWS100. This kit includes a DSP
plate, a bracket, two u-bolts, four flat washers, four split washers, and four
nuts. The PWS100 usually comes with the DSP plate attached to it. The
PWS100 mounts onto a Campbell Scientfiic tripod, tower, or a user-supplied
pole with a 1.5 inch (3.81 cm) to 2.1 inch (5.25 cm) outer diameter as follows.
1. Fasten the bracket to the pole using one u-bolt, two flat washers, two split
washers, and two nuts (see Figure 6-2).
2. Place the DSP plate on the bracket. The tabs of the bracket fit in the
notches at the top of the DSP plate (see Figure 6-3).
3. Fasten the bottom of the DSP plate using the remaining u-bolt, washers,
and nuts (see Figure 6-4).
4. Mount the power supply enclosure if purchased. This enclosure can be
mounted to the same tripod, tower, or user-supplied pole as the PWS100.
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.
CAUTION
Take care not to overtighten the nuts on the u-bolts, as it
may be possible to distort and/or damage the bracket or
DSP plate by doing so, and/or the nuts may seize up. Only
tighten the nuts to a degree necessary to hold the PWS100
firmly in place.
6-3
Section 6. Installation
Bracket Tab
U-bolt
Bracket
DSP Plate
FIGURE 6-2. Hardware for mounting the top of the DSP plate to a pole
6-4
Section 6. Installation
Notches
Bracket Tab
FIGURE 6-3. Placing the PWS100 onto the bracket
6-5
Section 6. Installation
6-6
CAUTION
FIGURE 6-4. PWS100 mounted to a mast or pole
Ensure that the PWS100 is mounted according to Figures
6-2 through 6-4. Do not reposition, once fixings are
tightened, by forcing the arms of the unit as this can
damage the unit.
6.3.3 Connecting Cables
The sensor unit comes with the DSP control unit fixed to the sensor arm. All
cabling between the sensor heads and the DSP unit is premade. An SDI-12
sensor connection is fixed into the DSP terminal strip. The connection is
terminated with a LEMO socket on the lower face of the DSP housing. This is
primarily wired for the CS215-PWS but is also used with the PWC100
Calibrator. Power, communications and additional sensor connections are to
be routed through the cable glands on the lower face of the DSP housing to the
DSP terminal strip. As a factory default, a power cable and a communications
cable are pre-wired in the unit. The third cable gland will be sealed off by
default but can be used for further external sensor connections or a separate
power cable for the hood heaters (rather than sharing the main power cable).
There should be no need to alter any wiring within the DSP housing and the
housing cover should only be removed periodically to renew desiccant packs or
if any of the hardware switches need to be used. However if cable lengths are
to be changed then these will have to be rewired in the DSP housing. If the unit
remains sealed during operation, the packs should only need replacing once
every 6 months. Replace the desiccant pack in the holder and secure the cover.
6.3.4 Basic Wiring
Section 6. Installation
The PWS100 wiring block is shown on the internal layout diagram in Figure
B-2. Connection points for power and communications are shown in the
diagram. There are two power inputs (one 24V for hood heater and one 12V
for the processor board) one communications connection and two SDI-12 ports
for peripheral connection. For RS-485 communications a 120 Ω termination
resistor may need to be placed across the RTS-B and RX-A connections at
either end of the cable, although this is normally not required for most
installations unless electronic noise interference is prevalent or cable runs are
very long.
A 1K LEMO socket (IP66 rated) is used for connection of a peripheral (often
the CS215-PWS temperature / relative humidity probe). The cable for any
peripheral to be connected to the LEMO socket should be terminated with the
appropriate 4 pin 1K series LEMO plug. Ensure when fitting the peripheral
plug into the socket that the red tabs are aligned.
The power and communications cables are routed through two of the three
cable glands on the base of the PWS100 DSP enclosure. If power and
communications cables are replaced refer to Appendix C.1 and C.2 for further
details.
Figure 6-5 shows the lower face of the DSP enclosure with the cable gland and
LEMO connector positions.
6-7
Section 6. Installation
PG9 CABLE GLAND
EARTH GROUND
LEMO 4-PIN
(CONNECTOR FOR
CS215-PWS)
FIGURE 6-5. Underside of DSP enclosure
PG11 CABLE GLAND
(HOOD HEATER)
6-8
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