Vaisala PWD22 User manual

Present Weather Detector
PWD22
USER'SGUIDE
M210543EN-B
January 2004

PUBLISHED BY
Vaisala Oyj Phone (int.): [phone]
P.O. Box 26 Fax: [phone]
FIN-00421 Helsinki
Finland
Visit our Internet pages at http://www.vaisala.com/
© Vaisala 2004
No part of this manual may be reproduced in any form or by any means,
electronic or mechanical (including photocopying), nor may its contents be
communicated to a third party without prior written permission of the copyright
holder.
The contents are subject to change without prior notice.
Please observe that this manual does not create any legally binding obligations for
Vaisala towards the customer or end user. All legally binding commitments and
agreements are included exclusively in the applicable supply contract or
Conditions of Sale.

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VAISALA _________________________________________________________________________1
Table of Contents
CHAPTER 1
GENERAL INFORMATION............................................................................ 7
About This Manual................................................................... 7
Contents of This Manual....................................................... 7
Version Information............................................................... 8
Related Manuals................................................................... 8
Feedback .............................................................................. 8
Safety ........................................................................................ 9
General Safety Considerations............................................. 9
Product Related Safety Precautions..................................... 9
ESD Protection ................................................................... 11
Trademarks............................................................................. 11
License Agreement................................................................ 11
Warranty.................................................................................. 11
CHAPTER 2
PRODUCT OVERVIEW ............................................................................... 13
Introduction to Vaisala Present Weather Detector PWD22 13
Hardware Structure................................................................ 14
Sensing Element in PWD22 ............................................... 14
PWT11 Transmitter........................................................ 14
PWC22 Controller/Receiver........................................... 15
Vaisala RAINCAP®Rain Sensor ................................... 15
Temperature Sensor (TS).............................................. 15
Power Supply................................................................. 15
Operating Principle ............................................................. 15
Using PWD22 ..................................................................... 17
Product Nomenclature .......................................................... 18
CHAPTER 3
FUNCTIONAL DESCRIPTION..................................................................... 19
Optical Measurements........................................................... 20
Optical Arrangement........................................................... 20
Transmitter Unit PWT11 ..................................................... 20
Light Receiver..................................................................... 21
Additional Measurements ..................................................... 21
Vaisala RAINCAP®Rain Sensor......................................... 21
Background Luminance Sensor PWL111 (optional)........... 22
BLSC Command............................................................ 23
Continuous Mode...................................................... 23
Day/night switch Mode ............................................. 23
Disabling PWL111.................................................... 23
BLCAL Command.......................................................... 23

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Temperature Sensor ...........................................................24
RAINCAP®Signal Processing.............................................24
Algorithm Description............................................................25
Visibility ...............................................................................25
Detecting Precipitation ........................................................25
Precipitation Intensity..........................................................26
Precipitation Accumulation..................................................27
Present Weather .................................................................27
Precipitation Types.........................................................27
Liquid Precipitation....................................................28
Frozen Precipitation..................................................29
Mixed Precipitation....................................................29
Precipitation Type Unknown.....................................29
Visibility Types ...............................................................30
Fog Codes ................................................................30
Weather Classes............................................................31
Weather Code Selection................................................31
Applications............................................................................32
Internal Monitoring.................................................................32
Built-in Tests........................................................................32
Memory Tests......................................................................33
Signal Monitoring.................................................................34
Hardware Monitoring...........................................................34
Monitoring Contamination...................................................34
CHAPTER 4
INSTALLATION............................................................................................37
Selecting Location .................................................................37
Grounding and Lightning Protection ...................................39
Equipment Grounding.........................................................39
Internal Grounding of PWD22.............................................39
Grounding the Remote Units and the Communication Cable39
Installation Procedure............................................................40
Unpacking Instructions........................................................40
Unpacking Procedure.....................................................40
Storage...........................................................................40
Initial Settings......................................................................41
Weather Parameters......................................................42
Mounting..............................................................................43
Verification...........................................................................45
Connections............................................................................45
Connecting Cables..............................................................45
Basic Wiring...................................................................46
Supplying Power to PWD22................................................48
Internal Heaters without PWL111 (default)....................48
Internal Heaters with PWL111 (optional).......................48
Hood Heaters PWH111 .................................................49
Communication Options......................................................49
Serial Communication Settings......................................49
Serial Transmission RS-232 ..........................................49
Serial Multipoint Transmission RS-485..........................50
Connection of the Maintenance Terminal......................50
Relay Controls.....................................................................50

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RELAY Command ......................................................... 53
CHAPTER 5
OPERATION ................................................................................................ 55
Getting Started....................................................................... 55
Operating Instructions .......................................................... 55
Entering and Exiting the Command Mode.......................... 56
OPEN............................................................................. 56
CLOSE........................................................................... 57
Message Types................................................................... 57
Message 0 ..................................................................... 58
Message 1 ..................................................................... 59
Message 2 ..................................................................... 60
Message 3 ..................................................................... 60
Message 4 ..................................................................... 60
Messages 5 and 6 ......................................................... 60
Message 7 ..................................................................... 61
Automatic Message Sending.............................................. 62
Message Polling............................................................. 62
Precipitation Sums................................................................. 64
List of Commands.................................................................. 65
PWD22 Command Set........................................................ 65
HELP.............................................................................. 65
MES............................................................................... 66
AMES............................................................................. 66
Weather Related Commands ............................................. 67
WPAR............................................................................ 68
WSET............................................................................. 68
CLRS ............................................................................. 70
System Configuration Commands...................................... 70
PAR................................................................................ 71
CONF............................................................................. 71
Hood Heaters................................................................. 76
BAUD............................................................................. 76
Analog Output..................................................................... 76
Analog Output Modes.................................................... 78
Mode 0...................................................................... 78
Mode 1...................................................................... 79
Mode 2...................................................................... 79
Mode 3...................................................................... 80
Mode 4...................................................................... 80
Analog Output Calibration.............................................. 80
Maintenance Commands.................................................... 82
STA................................................................................ 82
CAL................................................................................ 84
CLEAN........................................................................... 84
ZERO............................................................................. 85
CHEC............................................................................. 85
DRY ON and WET......................................................... 86
DRY ON.................................................................... 86
WET.......................................................................... 86
HEAT ............................................................................. 87
Other Commands................................................................ 87
TIME .............................................................................. 87

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DATE..............................................................................88
RESET ...........................................................................88
VER................................................................................88
CHAPTER 6
MAINTENANCE ...........................................................................................89
Periodic Maintenance ............................................................89
Cleaning..............................................................................90
Cleaning Lenses and Hoods..........................................90
Cleaning RAINCAP®......................................................91
Calibration...............................................................................91
Visibility Calibration.............................................................92
Calibration Check Procedure.........................................92
Calibration Procedure ....................................................93
Removing and Replacing ......................................................94
Removing and Replacing the Optical Units ........................94
Removing PWT11..........................................................95
Removing PWC22..........................................................96
Replacing RAINCAP®....................................................97
CHAPTER 7
TROUBLESHOOTING .................................................................................99
Common Problems ................................................................99
Message Indicating Warning or Alarm................................99
Message Missing...............................................................100
Message Exists but Visibility Value Does Not...................101
Visibility Value is Continuously Too Good ........................101
Visibility Constantly Too Low ............................................102
PWD22 Reports Precipitation When There Is None.........102
PWD22 Reports Frozen Precipitation during Rain............103
PWD22 Electrical Troubleshooting ...................................103
Technical Support................................................................104
Return Instructions..............................................................105
CHAPTER 8
TECHNICAL DATA....................................................................................107
Specifications.......................................................................107
Mechanical Specifications.................................................107
Electrical Specifications ....................................................108
Optical Specifications........................................................108
Visibility Measurement Specifications...............................109
Weather Sensing Specifications .......................................109
Environmental Specifications............................................110
APPENDIX A
VALUES FOR INTERNAL MONITORING.................................................111
APPENDIX B
PWC22 CONNECTORS AND JUMPER SETTINGS.................................115

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APPENDIX C
NWS AND WMO CODE TABLES ............................................................. 117
INDEX......................................................................................................... 121
List of Figures
Figure 1 PWD22 Present Weather Detector.......................................... 14
Figure 2 PWD22 Block Diagram ............................................................ 16
Figure 3 PWD22 Optical System ........................................................... 20
Figure 4 RAINCAP®Block Diagram....................................................... 22
Figure 5 PWL111 Block Diagram........................................................... 24
Figure 6 RAINCAP®Surface Signal (Heavy Rain Beginning)................ 25
Figure 7 Principle for Determining Precipitation Type............................ 28
Figure 8 LED Indicators on the PWC22 Board ...................................... 33
Figure 9 Recommended Location of PWD22. Alternative Ways to Mount
the Sensor (A or B). ................................................................. 38
Figure 10 Location of Jumpers and Connectors on the PWC22
Processor/Receiver Board....................................................... 43
Figure 11 Installing PWD22 to the Support Arm...................................... 43
Figure 12 Installing the Subassembly to the Mast with the Vaisala Clamp
Assembly.................................................................................. 44
Figure 13 Testing the Connector.............................................................. 44
Figure 14 Cabling Principle...................................................................... 47
Figure 15 Maintenance Cable.................................................................. 48
Figure 16 Relay Connection: PWD22 Supplies ....................................... 52
Figure 17 Relay Connection: External Relay Supply............................... 53
Figure 18 Illustration of Contents of Messages 0, 1, and 2...................... 58
Figure 19 Analog Current Output Connection.......................................... 77
Figure 20 Analog Current Output Connection (External Current Source) 78
Figure 21 Assembling the Opaque Glass Plates ..................................... 93
Figure 22 Removing PWT11.................................................................... 95
Figure 23 Opening Box Screws (1).......................................................... 96
Figure 24 Removing the PWC22 Board................................................... 97
Figure 25 Removing the Rain Sensor...................................................... 98
List of Tables
Table 1 Manual Revisions....................................................................... 8
Table 2 Related Manuals........................................................................ 8
Table 3 Model and Performance Table................................................. 13
Table 4 Vaisala Present Weather Detector PWD22 Nomenclature...... 18
Table 5 Nomenclature for Options of the Vaisala Present Weather
Detector PWD Family............................................................... 18
Table 6 WMO SYNOP Code Limits...................................................... 30
Table 7 WMO METAR Code Limits...................................................... 31
Table 8 Default Communication Settings.............................................. 41
Table 9 Commands for Changing Default Settings .............................. 41
Table 10 Commands for Displaying and Changing Parameters............. 42
Table 11 Receptable Connector Default Wiring ..................................... 46
Table 12 PT-100 Sensor Cable Wiring................................................... 47
Table 13 Control Logic of Relay Controls 1 and 2.................................. 51
Table 14 Control Logic of Relay Control 1, 2, and 3............................... 51
Table 15 Initial Settings and Corresponding Commands ....................... 56

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Table 16 Commands for Routine Maintenance Operations....................56
Table 17 Command Set ..........................................................................65
Table 18 Hardware Error Texts...............................................................83
Table 19 Warnings ..................................................................................83
Table 20 PWD22 Specifications............................................................107
Table 21 PWD22 Electrical Specifications............................................108
Table 22 Optical Specifications of the Light Transmitter.......................108
Table 23 Optical Specifications of the Light Receiver...........................109
Table 24 Visibility Measurement Specifications....................................109
Table 25 Weather Sensing Specifications ............................................109
Table 26 Environmental Specifications.................................................110
Table 27 Values from STA message for Internal Monitoring ................111
Table 28 Internal Weather Types and Supported NWS Codes ............117
Table 29 WMO SYNOP Codes (Table 4680, WaWa) Used by PWD22 118
Table 30 WMO METAR Codes (Table 4678) Used by PWD22............119

Chapter 1__________________________________________________________General Information
VAISALA _________________________________________________________________________7
CHAPTER 1
GENERAL INFORMATION
This chapter provides general notes for the product.
About This Manual
This manual provides information for installing, operating, and
maintaining Vaisala Present Weather Detector PWD22.
Contents of This Manual
This manual consists of the following chapters:
- Chapter 1, General Information, provides general notes for the
product.
- Chapter 2, Product Overview, introduces Vaisala Present Weather
Detector PWD22 features, advantages, and the product
nomenclature.
- Chapter 3, Functional Description, describes the functionality of
the product.
- Chapter 4, Installation, provides you with information that is
intended to help you install this product.
- Chapter 5, Operation, contains information that is needed to
operate this product.
- Chapter 6, Maintenance, provides information that is needed in
basic maintenance of the product.
- Chapter 7, Troubleshooting, describes common problems, their
probable causes and remedies, and contact information.

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- Chapter 8, Technical Data, provides the technical data of the
Product.
- Appendix A includesValues for Internal Monitoring.
- Appendix B includes Jumper Settings.
- Appendix C includes NWS and WMO Code Tables.
- INDEX is located at the end of the manual.
Version Information
Table 1 Manual Revisions
Manual Code Description
M210543EN-A This manual.
Related Manuals
Table 2 Related Manuals
Manual Code Manual Name
M210542EN-A Vaisala Present Weather Detector PWD12,
User's Guide
M210541EN-A Vaisala Visibility Sensor PWD10/20, User's Guide
Feedback
Vaisala Customer Documentation Team welcomes your comments
and suggestions on the quality and usefulness of this publication. If
you find errors or have other suggestions for improvement, please
indicate the chapter, section, and page number. You can send
comments to us by e-mail: [email protected]

Chapter 1__________________________________________________________General Information
VAISALA _________________________________________________________________________9
Safety
General Safety Considerations
Throughout the manual, important safety considerations are
highlighted as follows:
WARNING Warning alerts you to a serious hazard. If you do not read and follow
instructions very carefully at this point, there is a risk of injury or
even death.
CAUTION Caution warns you of a potential hazard. If you do not read and
follow instructions carefully at this point, the product could be
damaged or important data could be lost.
NOTE Note highlights important information on using the product.
Product Related Safety Precautions
Vaisala Present Weather Detector PWD22 delivered to you has been
tested for safety and approved as shipped from the factory. Note the
following precautions:
WARNING The chassis of the PWD22 must be connected to a good electrical
earth.
WARNING Do not touch the surface of the RAINCAP®Rain sensor plate. When
you need to touch the sensors plate, for example during cleaning,
touch first metallic part of PWD22 to discharge possible electrostatic
load of your body. The measuring principle does not allow for proper
ESD protection.

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WARNING Do not operate the equipment in the presence of flammable gases or
fumes. Operation of any electrical instrument in such an environment
constitutes a definite safety hazard.
CAUTION Do not modify or substitute parts in the instrument. Contact Vaisala
or its authorized representative for repairs.
CAUTION The component boards including CMOS microchips should be
transported and stored in conductive packages. Although new CMOS
devices are protected against overvoltage damages caused by static
electric discharge of the operator, careful handling is recommended:
the operator should be properly grounded. Unnecessary handling of
component boards should be avoided.
RADIO FREQUENCY INTERFERENCE STATEMENT (USA)
The United States Federal Communications Commission (in 47 CFR
15.838) has specified that the following notice must be brought to the
attention of users of this kind of a product in the USA:
Federal communications commission radio frequency interference
statement
This equipment generates and uses radio frequency energy and if not
installed and used properly, that is in strict accordance with the
manufacturer's instructions, may cause interference to radio and
television reception. The Present Weather Detector is designed to
provide reasonable protection against such interference in an airport
installation. However, there is no guarantee that interference will not
occur in a particular installation. If this equipment causes
interference to radio or television reception, which can be determined
by turning the equipment off and on, the user is encouraged to try to
correct the interference by one or more of the following measures:
- Reorient the receiving antenna
- Relocate this device with respect to the receiver
- Move this device away from the receiver
If necessary, the user should consult the dealer or an experienced
radio/television technician for additional suggestions.

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VAISALA ________________________________________________________________________11
ESD Protection
Electrostatic Discharge (ESD) can cause immediate or latent damage
to electronic circuits. Vaisala products are adequately protected
against ESD for their intended use. However, it is possible to damage
the product by delivering electrostatic discharges when touching,
removing, or inserting any objects inside the equipment housing.
To make sure you are not delivering high static voltages yourself:
- Handle ESD sensitive components on a properly grounded and
protected ESD workbench. When this is not possible, ground
yourself to the equipment chassis before touching the boards.
Ground yourself with a wrist strap and a resistive connection cord.
When neither of the above is possible, touch a conductive part of
the equipment chassis with your other hand before touching the
boards.
- Always hold the boards by the edges and avoid touching the
component contacts.
Trademarks
RAINCAPis a registered trademark of Vaisala. Microsoft,
Windows, and Windows NTare registered trademarks of
Microsoft Corporation in the United States and/or other countries.
License Agreement
All rights to any software are held by Vaisala or third parties. The
customer is allowed to use the software only to the extent that is
provided by the applicable supply contract or Software License
Agreement.
Warranty
For certain products Vaisala normally gives a limited one-year
warranty. Please observe that any such warranty may not be valid in
case of damage due to normal wear and tear, exceptional operating
conditions, negligent handling or installation, or unauthorized
modifications. Please see the applicable supply contract or Conditions
of Sale for details of the warranty for each product.

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Chapter 2___________________________________________________________ Product Overview
VAISALA ________________________________________________________________________13
CHAPTER 2
PRODUCT OVERVIEW
This chapter introduces Vaisala Present Weather Detector PWD22
features, advantages, and the product nomenclature.
Introduction to Vaisala Present Weather
Detector PWD22
PWD22 is an intelligent, multi-variable sensor for automatic weather
observing systems. The sensor combines the functions of a forward
scatter visibility meter and a present weather sensor. PWD22 can
measure the intensity and amount of both liquid and solid
precipitation. As the detector is equipped with a background
luminance sensor, it can also measure ambient light.
PWD22 suitable for automatic weather station applications especially
for low-power requirement installations.
Table 3 Model and Performance Table
Model Performance
Visibility Sensor PWD10 Visibility range 10 m ... 2000 m
Present Weather Detector PWD12 Visibility range 10 m ... 2000 m
4 different precipitation types
Visibility Sensor PWD20 Visibility range 10 m ... 20000 m
Present Weather Detector PWD22 Visibility range 10 m ... 20000 m
7 different precipitation types
Present Weather Detector PWD22M For Vaisala TACMET stations
The versatility of PWD22 is achieved with a unique operating
principle. PWD22 measures an estimate of the precipitation water
content with a capacitive device Vaisala RAINCAP®Rain Sensor and
combines this information with optical scatter and temperature

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measurements. These three independent measurements together
provide sufficiently data for an accurate evaluation of prevailing
visibility and weather type.
Hardware Structure
PWD22 is a self-contained instrument that can be fastened to the side
of the mast and into a crossarm using the mounting clamps.
0308-002
Figure 1 PWD22 Present Weather Detector
The following numbers refer to Figure 1 above.
1 = Transmitter
2 = Controller/Receiver
3 = PWR211 Vaisala RAINCAP®Rain Sensor
(PWR111 in PWD22M)
4 = Pt100 temperature sensor in the tube
5 = Mounting clamp
6 = Hood heaters (optional)
7 = Place for Vaisala Luminance Sensor PWL111 (optional)
Sensing Element in PWD22
PWT11 Transmitter
PWT11 Transmitter emits pulses of near infrared light. It is
permanently tilted 20°downwards. The optical power is stabilized by
a closed hardware loop. The unit also includes a receiver circuit for
lens contamination monitoring.

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VAISALA ________________________________________________________________________15
PWC22 Controller/Receiver
PWC22 Controller/Receiver measures the scattered part of the PWT11
light beam as the data signal. PWC22 contains an extra light
transmitter for monitoring lens contamination. The receiver is tilted
20° downwards. Therefore, in addition to a small side angle, the
receiver unit measures light scattered at an angle of 45°. PWD22
contains enhanced signal processing functions, which allows for a
wider measurement range.
Vaisala RAINCAP®Rain Sensor
The Vaisala RAINCAP®Rain Sensor Assembly produces a signal
proportional to the amount of water on the RAINCAP®sensing
element, which is the sensing part of RAINCAP®. This element
consists of thin wires protected by an insulating glass coating. The
presence of water changes the capacitance of the plate. The
capacitance is measured by the integrated electronics. The integrated
heating resistors keep the elements dry from condensation.
RAINCAP®has an integrated temperature sensor for heating control.
Vaisala Present Weather Detector PWD22 is equipped with a double-
plate Vaisala RAINCAP®Rain Sensor Assembly, which has two tilted
RAINCAP®elements. The tilted two-plate construction give better
sensitivity for detecting light drizzle.
Temperature Sensor (TS)
Temperature Sensor (TS) is a Pt100 thermistor that is used to measure
the crossarm temperature. See Figure 1 on page 14.
Power Supply
The power supply can be connected separately for the measurement
electronics and heating. Thus, the battery backup can be limited to the
measurement power supply.
Operating Principle
Vaisala Present Weather Detector PWD22 is a microprocessor
controlled sensor that combines optical forward scatter measurement
capacitive precipitation sensing, and temperature measurement. All

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data processing is done by the embedded software. The main units are
shown in Figure 2 below.

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VAISALA ________________________________________________________________________17
The output of RAINCAP®is proportional to the water amount on the
capacitive sensing surfaces while the optical intensity is proportional
to the volume of the reflecting particles. The ratio of optical and
capacitive intensities is used to determine the basic precipitation type.
The crossarm temperature (TS) is measured using the Pt100
temperature sensor. The temperature data together with the optical
signal profile and the RAINCAP®surface sensor data are used to
determine the actual weather code.
Several parameters are available for the operator for configuring and
adjusting the PWD22 operation.
Using PWD22
PWD22 is typically used as a component of a weather observing
system.
The PWD22 output is either a digital serial interface or an analog
current signal. The digital serial interface can be configured into two
different operating modes: the sensor can be set to send a data
message automatically at selected intervals, or PWD22 can be polled
by the host computer. The same serial line is also used as an operator
interface. The analog current signal can be used to report the
prevailing visibility. Three relay controls can be used, driven by
visibility limits.
The operator controls and checks the operation of PWD22 using a
maintenance terminal. A set of built-in commands and test routines
are provided for configuring and monitoring the multiple functions of
PWD22.
The standard data messages contain a status character for indicating
faults detected by the internal diagnostics. If the error status is set, the
operator can display a special status message, which contains the
detailed results of the diagnostics and a written description of the
fault. With this information the operator can take corrective action or
give the maintenance personnel advice.

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Product Nomenclature
Table 4 Vaisala Present Weather Detector PWD22
Nomenclature
Code Common Name Description
PWT11 Transmitter LED Transmitter circuit board.
PWC22 Controller/Receiver Controller and photo diode circuit
board for PWD22.
PWR211 RAINCAP®Double-Plate
Rain Sensor A capacitive detector to sense water droplets and/or moisture. Two plate
in a 90-degree angle towards each
other.
Table 5 Nomenclature for Options of the Vaisala Present
Weather Detector PWD Family
Code Common Name Description
PWL111 Background Luminance
Sensor
PWH111 Hood Heater Foils
PWA11 Calibration Set Includes a pair of precalibrated
scatterers, a piece of cloth for
cleaning the lenses and tools.
16385ZZ RS-232 (9-pin)
maintenance cable Connects to standard PC communication port.