CS PWS100 User manual

PWS100
Present Weather
Sensor
Issued: 17.11.15
Copyright © 2006-2015 Campbell Scientific Ltd.
CSL 658
USER GUIDE

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
We will repair or replace products which prove to be defective during the
guarantee period as detailed on your invoice, provided they are returned to us
prepaid. The guarantee will not apply to:

Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific

Batteries

Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
in removing and/or reinstalling equipment. This guarantee and the Company’s
obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
Scientific is not liable for consequential damage.
Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
request. It is the policy of Campbell Scientific to protect the health of its
employees and provide a safe working environment, in support of this policy a
“Declaration of Hazardous Material and Decontamination” form will be
issued for completion.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package. Complete the “Declaration of
Hazardous Material and Decontamination” form and ensure a completed copy
is returned with your goods. Please note your Repair may not be processed if
you do not include a copy of this form and Campbell Scientific Ltd reserves
the right to return goods at the customers’ expense.
Note that goods sent air freight are subject to Customs clearance fees which
Campbell Scientific will charge to customers. In many cases, these charges are
greater than the cost of the repair.
Campbell Scientific Ltd,
80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

PLEASE READ FIRST
About this manual
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
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: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

Precautions
DANGER —MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON
OR AROUND TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS,
CROSSARMS, ENCLOSURES, ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE,
INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS, TOWERS, AND ATTACHMENTS, AND FAILURE TO HEED
WARNINGS, INCREASES THE RISK OF DEATH, ACCIDENT, SERIOUS INJURY, PROPERTY DAMAGE, AND
PRODUCT FAILURE. TAKE ALL REASONABLE PRECAUTIONS TO AVOID THESE HAZARDS. CHECK WITH YOUR
ORGANIZATION'S SAFETY COORDINATOR (OR POLICY) FOR PROCEDURES AND REQUIRED PROTECTIVE
EQUIPMENT PRIOR TO PERFORMING ANY WORK.
Use tripods, towers, and attachments to tripods and towers only for purposes for which they are designed. Do not
exceed design limits. Be familiar and comply with all instructions provided in product manuals. Manuals are
available at www.campbellsci.eu or by telephoning [phone] (UK). You are responsible for conformance
with governing codes and regulations, including safety regulations, and the integrity and location of structures or land
to which towers, tripods, and any attachments are attached. Installation sites should be evaluated and approved by a
qualified engineer. If questions or concerns arise regarding installation, use, or maintenance of tripods, towers,
attachments, or electrical connections, consult with a licensed and qualified engineer or electrician.
General
•Prior to performing site or installation work, obtain required approvals and permits. Comply with all
governing structure-height regulations, such as those of the FAA in the USA.
•Use only qualified personnel for installation, use, and maintenance of tripods and towers, and any
attachments to tripods and towers. The use of licensed and qualified contractors is highly recommended.
•Read all applicable instructions carefully and understand procedures thoroughly before beginning work.
•Wear a hardhat and eye protection, and take other appropriate safety precautions while working on or
around tripods and towers.
•Do not climb tripods or towers at any time, and prohibit climbing by other persons. Take reasonable
precautions to secure tripod and tower sites from trespassers.
•Use only manufacturer recommended parts, materials, and tools.
Utility and Electrical
•You can be killed or sustain serious bodily injury if the tripod, tower, or attachments you are installing,
constructing, using, or maintaining, or a tool, stake, or anchor, come in contact with overhead or
underground utility lines.
•Maintain a distance of at least one-and-one-half times structure height, or 20 feet, or the distance
required by applicable law, whichever is greater, between overhead utility lines and the structure (tripod,
tower, attachments, or tools).
•Prior to performing site or installation work, inform all utility companies and have all underground utilities
marked.
•Comply with all electrical codes. Electrical equipment and related grounding devices should be installed
by a licensed and qualified electrician.
Elevated Work and Weather
•Exercise extreme caution when performing elevated work.
•Use appropriate equipment and safety practices.
•During installation and maintenance, keep tower and tripod sites clear of un-trained or non-essential
personnel. Take precautions to prevent elevated tools and objects from dropping.
•Do not perform any work in inclement weather, including wind, rain, snow, lightning, etc.
Maintenance
•Periodically (at least yearly) check for wear and damage, including corrosion, stress cracks, frayed cables,
loose cable clamps, cable tightness, etc. and take necessary corrective actions.
•Periodically (at least yearly) check electrical ground connections.
WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL
SCIENTIFIC PRODUCTS, THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER
INSTALLATION, USE, OR MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS
SUCH AS SENSORS, CROSSARMS, ENCLOSURES, ANTENNAS, ETC.

i
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.
Section 1. General Information......................................1
1.1 About this Manual......................................................................................1
1.2General Safety............................................................................................2
1.3 Sensor Unit Safety......................................................................................2
1.4 Laser Safety................................................................................................2
Section 2. Product Overview .........................................5
2.1 Introduction...............................................................................................5
2.2 Specifications............................................................................................6
2.2.1 Mechanical Specifications .............................................................6
2.2.2 Electrical Specifications.................................................................6
2.2.3 Optical Specifications....................................................................6
2.2.4 Environmental Specifications ........................................................7
2.2.5 CS215 Sensor Specifications .........................................................7
2.3 Measurement Capabilities and Limitations...............................................7
2.3.1 Visibility Measurements ................................................................7
2.3.2 Precipitation Measurements...........................................................7
2.3.3 Data Storage and Buffering............................................................8
Section 3. Installation.....................................................9
3.1 Location and Orientation ..........................................................................9
3.2 Grounding and Lightning Protection.......................................................10
3.2.1 Equipment Grounding..................................................................10
3.2.2 Internal Grounding.......................................................................11
3.2.3 Lightning Rod (optional) .............................................................11
3.2.4 Grounding Spike Kit (optional) ...................................................11
3.3 Cable Selection .......................................................................................12
3.3.1 Heater Cable ................................................................................12
3.3.2 Power and Communication Cable................................................14
3.3.3 Full duplex RS485 operation .......................................................15
3.4 Unloading and Unpacking ......................................................................16
3.4.1 Unpacking Procedure...................................................................16
3.4.2 Storage Information .....................................................................16
3.5 Installation Procedures............................................................................16
3.5.1 Mounting the PWS100..................................................................16
3.5.2 Optional Campbell Scientific Mount ............................................19
3.5.3 Connecting Cables ........................................................................20
3.5.4 Desiccant.......................................................................................20
3.5.5 Basic Wiring.................................................................................22
3.5.6 Communication Options ...............................................................23
3.5.7 PWS Power Supply.......................................................................27
3.5.8 Start-Up Testing............................................................................27
3.5.9 Initial Settings...............................................................................27
3.5.10 Load Factory Defaults ................................................................27
3.5.11 Lubricating the enclosure screws................................................28

ii
Section 4. Operation......................................................29
4.1 Introduction ............................................................................................29
4.2 Using the Present Weather Viewer program...........................................29
4.3 Terminal Mode .......................................................................................30
4.3.1 Using the Help Command.............................................................31
4.3.2 Entering / Exiting the Interactive Menu System ...........................31
4.3.3 Message Polling............................................................................32
4.4 The PWS100 Menu System....................................................................32
4.4.1 Top Menu Options 0, 1 and 2 (Message n)...................................33
4.4.2 Top Menu Option 3 (Set Time and Date).....................................48
4.4.3 Top Menu Option 4 (Configuration).............................................49
4.4.4 Top Menu Option 5 (Password)....................................................54
4.4.5 Top Menu Option 6 (Weather and Alarm Parameters).................55
4.4.6 Top Menu Option 7 (Terminal) ....................................................59
4.4.7 Top Menu Option 8 (Info)............................................................59
4.4.8 Top Menu Option 9 (Done)..........................................................60
4.5Message Related Commands ..................................................................60
4.5.1 Automatic and Polled Message Sending.......................................61
4.5.2 Retrieving Historical Data ............................................................62
4.5.3 Viewing Data Output on the Command Line................................64
4.5.4 Collection of Data in Text File Format.........................................64
4.6Weather Related Commands...................................................................64
4.6.1 Setting and Viewing Weather Parameters.....................................64
4.6.2 Receiving data from remote sensors .............................................65
4.7System Configuration Commands...........................................................65
4.7.1 Setting System Parameters............................................................65
4.8Maintenance Commands.........................................................................67
4.8.1 Loading a New OS........................................................................67
4.8.2 Running a Diagnostic Test............................................................67
4.8.3 Running the Calibration................................................................68
4.8.4 Rotating the Calibration Disc........................................................68
4.9Other Commands....................................................................................68
4.9.1 Setting the Time and Date..............................................................68
4.9.2 Resetting the System......................................................................69
4.9.3 Status .............................................................................................69
4.10 Connecting the PWS100 to a Datalogger .............................................70
4.10.1 Connections ................................................................................70
4.10.2 Example Logger Programs..........................................................70
Section 5. Functional Description...............................75
5.1 General....................................................................................................75
5.2 Optical Measurement..............................................................................75
5.2.1 Optical Arrangement....................................................................75
5.3 Additional Sensor Connections...............................................................77
5.3.1 Using a CS215 on the PWS100 ...................................................77
5.3.2 Using Other Sensors on the PWS100 ..........................................78
5.4 PWS100 Control Unit.............................................................................78
5.5 Measurement Signal Processing .............................................................78
5.6 Algorithm Description ............................................................................79
5.6.1 Detecting and Classifying Precipitation.......................................79
5.6.2 Precipitation Intensity..................................................................81
5.6.3 Precipitation Accumulation..........................................................82
5.6.4 Present Weather...........................................................................83
5.6.5 Visibility......................................................................................84
5.7 Applications............................................................................................85
5.8 Internal Monitoring.................................................................................85

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Section 6. Maintenance................................................87
6.1 General....................................................................................................87
6.2 Cleaning..................................................................................................87
6.3 Calibration ..............................................................................................88
Section 7. Troubleshooting .........................................89
7.1 Introduction.............................................................................................89
7.2 Possible Problems...................................................................................89
7.2.1 No response from PWS100..........................................................89
7.2.2 PWS100 responds but no data output given ................................89
7.2.3 Ice has formed in the end of the hoods.........................................89
7.2.4 The visibility output is clearly in error.........................................90
7.2.5 The sensor does not detect particles during a precipitation
event............................................................................................90
7.2.6 The sensor detects particles when there are none present............90
7.2.7 The OS update did not work........................................................91
7.3 Contact Details for Help .........................................................................91
Appendix A. PWS Output Codes ............................... A-1
Appendix B. Software Flowchart............................... B-1
Appendix C. Menu System Map................................. C-1
Figures
2-1. PWS100...................................................................................................5
3-1. Effect of structure on air flow..................................................................9
3-2. Attaching a lightning rod.......................................................................11
3-3. Enclosure wiring details.........................................................................13
3-4. PWS100 Comms and Power Cable Connector......................................15
3-5. Hardware for mounting the top of the DSP plate to a pole....................17
3-6. Placing the PWS100 onto the bracket ...................................................18
3-7. PWS100 mounted to a mast or pole ......................................................19
3-8. Mounting the desiccant pack on the DSP cover ....................................21
3-9. Underside of DSP enclosure..................................................................23
3-10. Removal of DSP cover ........................................................................23
3-11. Exposing the DSP board......................................................................24
3-12. DSP board dip switch location ...........................................................26
3-13. Dip switches (defaults set –00111100)...............................................26
4-1. PWS100 setup menu..............................................................................33
4-2. Message menu .......................................................................................33
4-3. Message parameters and fields menu.....................................................34
4-4. Message interval menu ..........................................................................34
4-5. Message mode menu..............................................................................35
4-6. Message field menu...............................................................................47
4-7. Delete message menu.............................................................................48
4-8. Time and date menu...............................................................................48
4-9. Configuration menu...............................................................................49
4-10. PWS100 ID menu................................................................................49
4-11. TRH probe menu.................................................................................49
4-12. Hood heater temperature menu............................................................50

iv
4-13. Dew heater mode menu .......................................................................50
4-14. Output mode menu ..............................................................................50
4-15. Calibration warning screen..................................................................51
4-16. Calibration top menu...........................................................................51
4-17. Visibility only calibration process.......................................................52
4-18. Mounting visibility calibrator..............................................................52
4-19. View/adjust calibration menu..............................................................53
4-20. Terminal mode menu...........................................................................53
4-21. PSU shut down voltage menu..............................................................54
4-22. Password menu....................................................................................54
4-23.Weather parameters menu ...................................................................55
4-24. Visibility range alarm menu.................................................................56
4-25. Snow water content adjustment ...........................................................57
4-26. Mixed precipitation threshold adjustment ...........................................58
4-27. Terminal active screen.........................................................................59
4-28. Information menu ................................................................................60
4-29. Done menu...........................................................................................60
4-30. System status information....................................................................69
5-1. Laser unit ..............................................................................................76
5-2. Laser unit showing light sheet production (not to scale) .......................76
5-3. Sensor unit.............................................................................................76
5-4. Sensor unit showing light path extents (not to scale).............................77
5-5. Block diagram of PWS100 Control Unit...............................................78
5-6. Signal to pedestal ratio values for different precipitation types.............80
6-1. Baffle removal and fitting......................................................................87
Tables
3-1. Power and Communication cable connections ......................................14
4-1. Command set.........................................................................................30
4-2. Message field parameters ......................................................................35
4-3. Configuration defaults...........................................................................54
4-4. Assumed bulk density of various particle types.....................................56
4-5. TRH sensor types ..................................................................................66
5-1. Precipitation intensities..........................................................................82
A-1. PWS100 SYNOP 4680 output codes..................................................A-2
A-2. PWS100 NWS output codes...............................................................A-4
A-3. PWS100 METAR codes.....................................................................A-4
A-4. 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-5
A-5. Intensity bounds for rain and drizzle...................................................A-6
A-6. Intensity bounds for rain and snow.....................................................A-6
A-7. Intensity bounds for drizzle and snow ................................................A-6
A-8. Intensity bounds for rain, drizzle and snow ........................................A-6
A-9. Intensity bounds for rain, drizzle, ice pellets, hail and snow ..............A-7
A-10. Intensity bounds for ice pellets, hail and snow .................................A-7
A-11. PWS100 precipitation size criteria ...................................................A-7

1
Section 1. General Information
Important Safety Instructions –please request a translation or further advice if you cannot
understand this document.
Wichtige Sicherheitshinweise - bitte kontaktieren Sie uns bzgl. einer Übersetzung falls Sie
Schwierigkeiten haben Inhalte dieses Dokumentes zu verstehen.
Consignes de sécurité importantes - N'hésitez pas à demander un avis ou une traduction, si vous
ne pouvez pas comprendre ce document
Instrucciones de Seguridad Importantes –solicite por favor traducción o asesoramiento
adicional si no entiende este documento.
Istruzioni di sicurezza importanti - chieda prego una traduzione o avanti il consiglio se non
potete capire questo documento.
Instruções de segurança importantes - por favor, solicitar uma tradução ou conselho mais se
você não consegue entender este documento.
1.1 About This Manual
This manual is the operational guide and reference for the Campbell Scientific
Present Weather Sensor unit (PWS100). This manual consists of the following
sections:
Section 1 –Consists of general information on manual revisions and
safety considerations.
Section 2 –Provides a product overview with specifications of the
optical, electronic and physical aspects of the system. Advantages and
features of the system are described in detail.
Section 3 –Is a guide for installation of the PWS100 including choosing
cables, locating the sensor and assembly of the unit.
Section 4 –Describes the operation of the sensor including the sensor
command set and an introduction to the Present Weather Sensor Viewer
program.
Section 5 –Is a functional description of the PWS100, including a
description of algorithms used for particle classification.
Section 6 –Provides information on maintenance routines and cycles for
the PWS100.
Section 7 –Is a troubleshooting guide for the PWS100.
Appendix A –A list of output codes used for particle classification under
a number of different common code structures.
Appendix B –Gives software flowcharts for the PWS100 system.
Appendix C –Gives a menu system map for the PWS100.

PWS100 Present Weather Sensor
2
1.2General Safety
This manual provides important safety considerations for the installation,
operation and maintenance of the PWS100. 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.
1.3Sensor Unit Safety
The PWS100 sensor has been checked for safety before leaving the factory and
contains no internally replaceable or modifiable parts.
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.
1.4Laser Safety
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 minimised 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
WARNING
CAUTION
NOTE
WARNING
WARNING
CAUTION

Section 1. General Information
3
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 class 3B laser
radiation. To open the unit requires the use of tools and
should not be carried out except by trained personnel.
The laser should not be operated outside of the housing.
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.
WARNING
WARNING

PWS100 Present Weather Sensor
4

5
Section 2. Product Overview
2.1 Introduction
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
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 2-1 shows the
PWS100 mounted on a pole.
An optional CS215 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 PWS100, in particular in respect of discriminating between
snow and rain and also fog/mist and dust.
Figure 2-1. PWS100

PWS100 Present Weather Sensor
6
2.2 Specifications
2.2.1 Mechanical Specifications
Measuring Area: nominally 40 cm2
Housing Materials: Iridite NCP conversion coated aluminium (RoHS compliant)
and hard anodised aluminium. Outer parts also coated with marine grade paint.
Weight: 8 kg Excluding mounting pole and power supply / communications
enclosure.
Dimensions: 1150 mm × 700 mm × 400 mm
Mountings: PWS mounting bracket to pole (diameter 32 mm to 52.5 mm).
2.2.2 Electrical Specifications
Power Requirements: DSP power 9 - 28 V. Current requirement (maximum at 9V
supply) 200mA with the dew heater off. 1 A with dew heaters and SDI-12 sensors.
These currents are lower at higher supply voltages as the sensor uses SMPS
technology. Optional hood heater 24 V AC or DC, 7 A.
If used with older CS215 sensors, before S/N E13405, the
maximum voltage is 16V.
It is the responsibility of the user to ensure that any local safety
regulations, regarding the use of power supplies, are adhered to.
Communication: RS-232, RS-422, RS-485. Baud rate 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.
This may cause interference in a domestic environment.
2.2.3 Optical Specifications
2.2.3.1 Laser Head Specifications
Laser Source: Near-IR diode, eye safe Class 1M unit output.
Peak wavelength: 830 nm.
Modulation Frequency: 96 kHz.
Laser Head Lens Diameter: 50 mm
CAUTION
NOTE

Section 2. Product Overview
7
2.2.3.2 Sensor Head Specifications
Receivers: Photodiode with band pass filters.
Spectral Response: Maximum spectral sensitivity at 850 nm, 0.62 A/W (0.6 A/W
at 830 nm)
Sensor Head Lens Diameter: 50 mm
Lens Check Light Source: Near-IR LED.
2.2.4 Environmental Specifications
Standard Operating Temperature Range: -25C to +50C
Optional Extended Operating Temperature Range: -40C to +70C
Relative Humidity Range: 0 to 100%
Maximum Wind speed: 60 ms-1
IP Rating: IP 66
2.2.5 CS215 Sensor Specifications
Please refer to the CS215 sensor manual for detailed of the accuracy and
specifications of this optional probe.
2.3 Measurement Capabilities and Limitations
2.3.1 Visibility Measurements
Visibility Range: 0 to 20000 m.
Visibility Accuracy: ± 10% (0 to 10000 m)*
Measurement interval: User selectable from 10 seconds to 2 hours.
2.3.2 Precipitation Measurements
Particle Size: 0.1 mm to 30 mm*
Size Accuracy: ± 5% (for liquid particles >0.3 mm)*
Particle Velocity: 0.16 ms-1 to 30 ms-1
Velocity Accuracy: ± 5% (for particles >0.3 mm)*
Basic 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).
Rain Rate Intensity Range: 0 to 999 mmh-1 (M-P Distributed)
Rainfall Total Resolution: 0.0001 mm
Rain Total Accuracy: ± typically 10%* (accuracy will be degraded in windy
conditions, for frozen precipitation and very high rainfall rates)
DSD bin sizes: 0.1 mm (diameter) 0.1 ms-1 (velocity)

PWS100 Present Weather Sensor
8
Data Output: Raw parameter output (particle size, particle velocity, signal peak
value, signal pedestal value), WMO SYNOP codes (4680, WaWa- precipitation
and obscurant type), WMO METAR codes (4678, WaWa- precipitation 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 supported for temperature / RH measurement OR this
data can be sent to it from the controlling system from a remote sensor.
*The accuracy figures quoted are for laboratory conditions with reference particles
and visibility standards. In practice, the proportion of particles detected will fall
off significantly below about 0.5 mm diameter.
2.3.3 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 please read the description below.
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 area of 40 cm2the 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 MByte (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 ‘4.5 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.