Vaisala FD12P User Manual

Weather Sensor

FD12P

USER'S GUIDE

M210296en-A

May 2002

PUBLISHED BY
Vaisala Oyj	Phone (int.):	+358	9 8949 1
P.O. Box 26	Fax:	+358	9 8949 2227
FIN-00421 Helsinki
Finland

Visit our Internet pages at http://www.vaisala.com/

© Vaisala 2002

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.

_________________________________________________________________________________

Table of Contents
CHAPTER 1
GENERAL INFORMATION ..........................................................................	11
About This Manual..................................................................	11
Contents of This Manual......................................................	11
Version Information................................................................	12
Related Manuals .....................................................................	12
Safety .......................................................................................	12
General Safety Considerations............................................	12
Product Related Safety Precautions ...................................	13
Safety Summary.............................................................	13
Ground the Equipment ...................................................	13
Radio Frequency Interference Statement (USA) ...........	15
ESD Protection ....................................................................	15
Trademarks .............................................................................	16
Warranty ..................................................................................	16
CHAPTER 2
PRODUCT OVERVIEW ................................................................................	17
Introduction.............................................................................	17
Hardware Structure .............................................................	17
Sensing Elements ..........................................................	19
Electronics Enclosure.....................................................	20
Structural Elements ........................................................	20
Operating Principle ..............................................................	21
Using FD12P .......................................................................	22
Equipment Nomenclature ......................................................	23
Specifications .........................................................................	24
Mechanical Specifications ...................................................	24
Electrical Specifications.......................................................	24
Optical Specifications ..........................................................	25
Capabilities and Limitations..................................................	26
Visibility Measurement Specifications .................................	26
Weather Sensing Specifications..........................................	26
Environmental Specifications ..............................................	27
CHAPTER 3
INSTALLATION............................................................................................	29
Organizing Installation...........................................................	29
Location and Orientation .......................................................	30
Grounding and Lightning Protection....................................	32
Equipment Grounding..........................................................	32
Internal Grounding...............................................................	34

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Grounding for Testing Purposes.........................................	34
Grounding Remote Units and Communication Cable.........	34
Cable Selection ......................................................................	35
Line Power Cabling.............................................................	35
Communication Cable.........................................................	35
Unloading and Unpacking.....................................................	36
Unpacking Procedure .........................................................	36
Storage Information ............................................................	36
Installation Procedures .........................................................	37
Constructing the Foundation...............................................	37
Mounting When Casting the Pad...................................	38
Mounting to an Existing Surface....................................	38
Assembling the FD12P .......................................................	40
Attaching the DTS14B Temperature Sensor to the Mast ...	41
Connecting Cables..............................................................	43
Basic Wiring...................................................................	43
Communication Cable EMC-shielding...........................	46
Connecting a Background Luminance Sensor or a
Day/Night Switch to FD12P ...........................................	48
Communication Options .....................................................	50
Serial Communications Settings....................................	50
Serial Transmission RS-232..........................................	50
Serial Multipoint Transmission RS-485 .........................	51
Modem DMX21..............................................................	52
Indicators and Manual Controls.....................................	54
Indicators ..................................................................	54
Manual Controls .......................................................	54
Analog Transmission .....................................................	55
Connecting the Maintenance Terminal..........................	55
Startup Testing....................................................................	56
Initial Settings......................................................................	56
CHAPTER 4
OPERATION ................................................................................................	59
Introduction ............................................................................	59
User Commands in Normal Operation.................................	59
Markings Used in This Manual .............................................	61
Entering/Exiting the Command Mode..................................	61
OPEN Command ................................................................	61
CLOSE Command ..............................................................	62
Automatic Message Sending................................................	62
Message Types...................................................................	63
Message 0 .....................................................................	64
Message 1 .....................................................................	64
Message 2 .....................................................................	65
Message 3 .....................................................................	65
Message 4 .....................................................................	66
Messages 5 and 6 .........................................................	66
Message 7 .....................................................................	68
Message Polling.....................................................................	69
FD12P Command Set.............................................................	70
HELP Command.................................................................	70

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MES Command ...................................................................	71
AMES Command............................................................	71
Weather Related Commands ..............................................	73
WPAR Command ...........................................................	73
WSET Command ...........................................................	73
Precipitation Limit......................................................	74
Weather Update Delay..............................................	74
Haze Limit .................................................................	74
Rain Intensity Scale...................................................	75
Violent Rain Limit ......................................................	75
Heavy Rain Limit .......................................................	75
Light Rain Limit..........................................................	75
Drizzle Limit...............................................................	75
Heavy Drizzle Limit....................................................	76
Light Drizzle Limit......................................................	76
Snow Limit.................................................................	76
Heavy Snow Limit......................................................	76
Light Snow Limit........................................................	76
Snow Pellets Limit.....................................................	77
Snow Grains Limit .....................................................	77
Ice Crystals Limit.......................................................	77
Hail Limit....................................................................	77
DRD Scale.................................................................	77
Warm Limit ................................................................	77
PRW Command..............................................................	77
CLRS Command ............................................................	78
WHIS Command.............................................................	78
System Configuration Commands.......................................	79
PAR Command...............................................................	79
CONF Command............................................................	80
BAUD Command............................................................	84
BLSC Command.............................................................	84
Maintenance Commands.....................................................	85
STA Command...............................................................	85
CAL Command...............................................................	87
TCAL Command.............................................................	87
CLEAN Command..........................................................	88
CHEC Command............................................................	89
FREQ Command............................................................	89
DRY and WET Commands ............................................	89
AN Command.................................................................	90
Analog Output Commands ..................................................	91
Analog Output Calibration ..............................................	91
Data Scaling ...................................................................	92
Hardware Check.............................................................	92
Other Commands ................................................................	93
TIME Command .............................................................	93
DATE Command ............................................................	93
RESET Command..........................................................	94
CHAPTER 5
FUNCTIONAL DESCRIPTION .....................................................................	95
General.....................................................................................	95
Optical Measurement .............................................................	96

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Optical Arrangement...........................................................	96
FDT12B Transmitter Unit....................................................	96
FDR12 Receiver Unit..........................................................	98
Additional Measurements .....................................................	99
General ...............................................................................	99
DRI21 Interface Board ........................................................	99
DRD12 Rain Detector .......................................................	100
DTS14B Temperature Sensor ..........................................	101
FDP12 Control Unit ..............................................................	101
Measurement Signal Processing........................................	103
Optical Signal Processing.................................................	103
DRD12 Signal Processing ................................................	104
Algorithm Description .........................................................	105
Visibility .............................................................................	105
Detecting Precipitation......................................................	106
Precipitation Intensity........................................................	106
Precipitation Accumulation ...............................................	107
Present Weather ...............................................................	108
Precipitation Types ......................................................	108
Liquid Precipitation .................................................	109
Frozen Precipitation................................................	110
Mixed Precipitation .................................................	111
Unknown Precipitation............................................	111
Visibility Types .............................................................	111
Fog..........................................................................	111
Haze and Mist.........................................................	112
Weather Classes .........................................................	112
Weather Code Selection..............................................	113
Applications..........................................................................	113
Internal Monitoring ..............................................................	114
Built-in Tests .....................................................................	114
Memory Tests ...................................................................	115
Signal Monitoring ..............................................................	115
Hardware Monitoring.........................................................	115
Contamination Monitoring.................................................	116
CHAPTER 6
MAINTENANCE .........................................................................................	117
General..................................................................................	117
Cleaning ................................................................................	118
Cleaning Lenses and Hoods.............................................	118
Cleaning DRD12 Rain Detector........................................	118
Calibration ............................................................................	119
General .............................................................................	119
Visibility Calibration...........................................................	119
Calibration Check Procedure.......................................	120
Calibration Procedure ..................................................	123
Calibrating the DTS14B Temperature Sensor.............	124
Removing and Replacing..................................................	126
Removing and Replacing Optical Units .......................	126
Removing and Replacing the DRD12 Rain Detector ..	129

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Calibrating FD12P Weather Sensor after Unit
Replacement ................................................................	130
CHAPTER 7
TROUBLESHOOTING................................................................................	133
Warnings ...............................................................................	133
Troubleshooting Examples..................................................	133
Message Indicating Warning or Alarm .............................	133
Message Missing...............................................................	134
Visibility Value is Missing...................................................	135
Visibility Value is Continuously Too Good.........................	135
Visibility is Constantly Too Low .........................................	136
FDP12 Reports Precipitation When There Is None...........	136
FD12P Reports Frozen Precipitation during Rain .............	136
Have Jumper Settings Been Changed? ............................	137
Values for Internal Monitoring.............................................	137
Getting Help ..........................................................................	140
Return Instructions...............................................................	140
APPENDIX A
NWS AND WMO CODES USED IN FD12P ...............................................	143
The NWS Codes ....................................................................	143
APPENDIX B
JUMPER SETTINGS AND INTERNAL WIRING........................................	147
CPU Board.............................................................................	149
DC-Regulator.........................................................................	149
DRI21 Interface Board ..........................................................	149
APPENDIX C
TRANSMITTER AND RECEIVER TEST POINTS .....................................	151
INDEX .........................................................................................................	153

List of Figures

Figure 1	FD12P Weather Sensor Site ....................................................	18
Figure 2	DRD12 Rain Detector and DTS14B Temperature Sensor .......	19
Figure 3	FD12P Block Diagram ..............................................................	21
Figure 4	Recommended Location for the FD12P ...................................	31
Figure 5	FD12P Equipment Grounding ..................................................	33
Figure 6	Casting a Concrete Foundation................................................	37
Figure 7	Constructing the FD12P Foundation ........................................	39
Figure 8	Tilting the Pole Mast .................................................................	41
Figure 9	DTS14B and the Sensor Holder Assembly to Mast .................	42
Figure 10	Connecting Internal Grounding.................................................	43
Figure 11	Cabling Principle.......................................................................	44
Figure 12	Line Voltage and ON/OFF Switches.........................................	45
Figure 13	Electronics Enclosure Feedthroughs........................................	46
Figure 14	Cable Grounding Instructions ...................................................	47

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Figure 15 Wiring the Connector for the LM11 Background Luminance
Meter ........................................................................................	49
Figure 16 Wiring the Day/Night Photo Switch..........................................	50
Figure 17 Communication Option ............................................................	51
Figure 18 RS-485 Communication Option ...............................................	52
Figure 19 Wiring the Modem....................................................................	53
Figure 20 Analog Current Loop Option ....................................................	55
Figure 21 FD12P Optical System.............................................................	96
Figure 22 FDT12B Transmitter Block Diagram........................................	97
Figure 23 FDR12 Receiver Block Diagram..............................................	98
Figure 24 DRI21 Block Diagram in the FD12P Application....................	100
Figure 25 DRD12 Block Diagram...........................................................	101
Figure 26 FDP12 Control Unit Block Diagram .......................................	102
Figure 27 Optical Raw Data (in Rain) ....................................................	103
Figure 28 Optical Signal Amplitude Distribution (in Rain) ......................	104
Figure 29 DRD12 Surface Signal (Heavy Rain Beginning)....................	104
Figure 30 Precipitation Type Determination Principle............................	109
Figure 31 Assembling the FDA13 Calibrator..........................................	122
Figure 32 DTS14 Sensor Holder Assembly to Mast ..............................	125
Figure 33 Removing the Optical Units ...................................................	127
Figure 34 Replacing the Optical Units....................................................	128
Figure 35 Removing the DRD12 Rain Detector.....................................	129
Figure 36 Basic Electronics Enclosure Wiring .......................................	148
Figure 37 Test Points, Transmitter.........................................................	151
Figure 38 Test Points, Receiver.............................................................	152

List of Tables
Table 1	Manual Revisions.....................................................................	12
Table 2	Related Manuals ......................................................................	12
Table 3	Basic Set ..................................................................................	23
Table 4	Options.....................................................................................	23
Table 5	Mains Cable Selection .............................................................	35
Table 6	Communication Cable Lengths................................................	35
Table 7	Transmit Frequencies of the DMX21 Modem Board ...............	53
Table 8	LED Indicators of the DMX21 Modem .....................................	54
Table 9	Manual Controls of the DMX21 Modem...................................	54
Table 10	Default Communication Settings..............................................	57
Table 11	Commands for Changing the Default Settings ........................	57
Table 12	Commands for Displaying and Changing the Parameters ......	57
Table 13	Settings and Corresponding Commands.................................	60
Table 14	Routine Command for Maintenance ........................................	60
Table 15	Status Report Command .........................................................	60
Table 16	Transmitter Status Correspondence between MITRAS and
	FD12P ......................................................................................	67
Table 17	Receiver Status Correspondence between MITRAS and FD12P67
Table 18	HELP Command Sets..............................................................	70
Table 19	Commands for Displaying or Setting Weather Analysis
	Parameters...............................................................................	73

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Table 20	Commands for Displaying System Parameters and Editing the
	Current System Configuration ..................................................	79
Table 21	Maintenance Commands..........................................................	85
Table 22	Hardware Error Texts ...............................................................	86
Table 23	Hardware Warning Texts..........................................................	86
Table 24	Parameters for Optical Measurement.....................................	131
Table 25	Parameters for DRD12 Precipitation Detector .......................	131
Table 26	Parameters for DTS14 Temperature Sensor..........................	131
Table 27	Updating Parameters..............................................................	131
Table 28	Parameters and Commands...................................................	132
Table 29	Values for Internal Monitoring.................................................	138
Table 30	Internal Weather Types, NWS Code .....................................	143
Table 31	WMO SYNOP Codes (4680, WaWa) ......................................	143
Table 32	WMO SYNOP Codes (4680, WaWa) ......................................	144
Table 33	WMO SYNOP Codes (4680, WaWa) ......................................	144
Table 34	WMO Code Table 4678. Codes Used by FD12P...................	145
Table 35	CPU Board Jumpers...............................................................	149
Table 36	CPU Board Connectors ..........................................................	149
Table 37	DC-regulator Connectors........................................................	149
Table 38	DRI21 Interface Board Jumpers .............................................	149
Table 39	DRI21 Interface Board Connectors ........................................	150
Table 40	Electronics Enclosure/Transducer Cable Signals ..................	150
Table 41	Transmitter Test Points...........................................................	151
Table 42	Receiver Test Points...............................................................	152

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Chapter 1 _________________________________________________________ General Information

CHAPTER 1

GENERAL INFORMATION

About This Manual

This manual is a general information source as well as a detailed operational guide to the FD12P Weather Sensor.

Contents of This Manual

This manual consists of the following chapters:

-Chapter 1, General Information, provides important safety, revision history, contact, and warranty information for the product.

-Chapter 2, Product Overview, introduces the FD12P Weather Sensor features, advantages, and the product nomenclature.

-Chapter 3, Installation, provides you with information to help you install this product.

-Chapter 4, Operation, contains information needed to operate this product.

-Chapter 5, Functional Description, gives a functional description on the product.

-Chapter 6, Maintenance, describes the overall maintenance of the product.

-Chapter 7, Troubleshooting, deals with troubleshooting information.

-Appendix A, NWS and WMO Codes Used in FD12P

-Appendix B, Jumper Settings and Internal Wiring

-Appendix C, Transmitter and Receiver Test Points

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Version Information

Table 1	Manual Revisions
Manual Code		Description
FD12P-U106en-1.2		Weather Sensor, User's Guide
M210296en-A		This manual.

Related Manuals

Table 2	Related Manuals
Manual Code		Manual Name
DMX21T0496-1.1		DMX21 CCITT Modem
LM11T0545-1.2		LM11 Background Luminance Meter

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.

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Chapter 1 _________________________________________________________ General Information

			Product Related Safety Precautions
			The FD12P Weather Sensor delivered to you has been tested for
			safety and approved as shipped from the factory. Note the following
			precautions:
		WARNING	Ground the product, and verify outdoor installation grounding
			periodically to minimize shock hazard.
		CAUTION	Do not modify the unit. Improper modification can damage the
			product or lead to malfunction.
			Safety Summary
			The following are general safety precautions must be observed during
			all phases of installation, operation and maintenance.
		WARNING	Neglecting to follow these precautions or specific warnings and
			cautions elsewhere in this manual violates safety standards of design,
			manufacture and intended use of the instrument. Vaisala Oyj. and its
			Subsidiaries do not answer for the consequences if the customer
			neglects to follow these requirements.
			Ground the Equipment
			To minimize the hazard of electrical shock, follow accurately the
			installation procedure in Chapter 3, Installation, on page 29.
		NOTE	Note that the chassis of the FD12P Weather Sensor must be
			connected to a good electrical earth. The instrument is equipped with
			a three-conductor AC power cable. Be sure that the earth wire of the
			cable is connected to an electrical ground.
			There is also a grounding clamp at the bottom of the electronics
			enclosure of Weather Sensor FD12P. Good grounding with a 16-mm2

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cable must be provided. Besides increasing safety, this also protects the Weather Sensor against lightning induced voltages.

To prevent operator injury or damage to the Weather Sensor, check that the LINE VOLTAGE SETTING is correct before connecting the line power (See Figure 12 on page 45.) Also ensure that the line power outlet is provided with a protective ground contact.

WARNING Do not operate in an explosive atmosphere.

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.

WARNING Do not service or adjust alone.

Do not attempt internal service or adjustment unless another person, capable of rendering first aid and resuscitation, is present.

WARNING Keep away from live circuits.

Component replacement or internal adjustments must be made by qualified maintenance personnel. Operating personnel must not remove instrument covers. Do not remove or replace any components with the power cable connected. Under certain conditions, dangerous voltages may exist even with the power cable disconnected. To avoid injuries disconnect power, and discharge all circuits before touching them.

WARNING Do not substitute parts or modify the instrument.

Because of the danger of introducing additional hazards, do not modify or substitute parts in the instrument. Contact Vaisala or its authorized representative for repairs to ensure that safety features are maintained.

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Chapter 1 _________________________________________________________ General Information

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 Weather Sensor 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.

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.

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To make sure you are not delivering high static voltages yourself, take the following precautions:

-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

Intel® is a registered trademark of the Intel Corporation in the U.S. and other countries.

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

CHAPTER 2

PRODUCT OVERVIEW

This chapter introduces the FD12P Weather Sensor features, advantages, and the product nomenclature.

Introduction

The FD12P Weather Sensor is an intelligent, multi-variable sensor for automatic weather stations and airport weather observing systems. The sensor combines the functions of a forward scatter visibility meter and a present weather sensor. In addition, the sensor can measure the intensity and amount of both liquid and solid precipitation.

The FD12P can be used to automatically determine the visibility and precipitation related weather codes in the World Meteorological Organization (WMO) standard SYNOP and METAR messages. The sensor can also be employed as an observer's aid in a semi-automatic weather observing system. The sensor is also suitable for other weather observing systems providing valuable information, for example, to road and harbor authorities.

The versatility of the FD12P is achieved with a unique operating principle. The FD12P measures precipitation water content with a capacitive device and combines this information with optical scatter and temperature measurements. These three independent measurements together provide data sufficient for an accurate evaluation of current visibility and weather type.

Hardware Structure

The structural basis of the FD12P is the pole mast that supports the transducer crossarm (FDC115). The crossarm contains the optical

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units, FDT12B Transmitter and FDR12 Receiver. The DRD12 Rain Detector is fastened to the crossarm. The electronics enclosure with the main data processing and interface units is mounted to the pole mast as seen in Figure 1 below.

0201-085

Figure 1 FD12P Weather Sensor Site

The following numbers are related to Figure 1 above:

1 = Transducer crossarm

2= DRD12 Rain Detector

3 = DTS14 Temperature Sensor

4= Pole mast

5= Electronics enclosure

The FD12P Weather Sensor consists of three parts: sensing elements, electronics enclosure, and structural elements. They are described in detail on the next page.

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Sensing Elements

The FDT12B Transmitter emits pulses of near infrared light. It is permanently tilted 16.5º downwards. The optical power is stabilized by a closed hardware loop. The unit also includes a receiver circuit for monitoring lens contamination.

The FDR12 Receiver measures the scattered part of the FDT12B light beam. The FDR12 contains also an additional light transmitter for monitoring lens contamination. Like the transmitter, the receiver is also tilted 16.5º downwards. Therefore, the receiver unit measures light scattered at an angle of 33°.

The DRD12 Rain Detector outputs a signal proportional to the amount of water on two RainCap™ sensing elements. These elements consist of thin wires protected by an insulating glass coating. The presence of water changes the capacitance of the elements. The combined capacitance of the plates is measured by the DRD12 electronics. Integrated heating resistors keep the elements dry when, for example, fog and melt snow fall on them. The Rain Detector is protected by a windshield to decrease the effect of wind on the measurement results. The DRD12 is illustrated in Figure 2 below.

The DTS14B Temperature Sensor is a Pt100 thermistor that is used to measure the crossarm temperature. See Figure 2 below.

0201-086

Figure 2 DRD12 Rain Detector and DTS14B Temperature

Sensor

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The following numbers refer to Figure 2 on page 19:

1 = Two RainCapTM elements

2 = DRD12 Rain Detector

3= Wind shield

4= Assembly clamp

5= DTS14 Temperature sensor

Electronics Enclosure

The FDP12 Control Unit is the main data processor and communication unit of the FD12P.

The DRI21 Interface Board is a Vaisala, general-purpose sensor interface, with several analog and digital input channels. In the FD12P, one of the DRI21 Interface Board channels is used for measuring the crossarm temperature and the DRD12 analog signal. In addition, the DRI21 controls the DRD12 heating and reads the precipitation ON/OFF status.

The FDW13 Mains Power Supply converts the mains voltage to

24 VAC power for the FDS12 regulator and the heater elements. The FDW13 includes also the mains voltage selector and the mains ON/OFF switch, which also functions as an automatic fuse.

The FDS12 DC Voltage Regulatorconverts the AC or DC input voltage (min. 18 V) to 12 VDC power used by FD12P electronics. The FDS12 also includes one relay used to control heater power.

The DMX21 Modem (optional) is a standard, 300-baud modem used only in the leased line mode with the FD12P.

The FDE12 Backup Temperature Sensor is included.

Structural Elements

The structural elements include the pole mast with a standard height of 2 meters and the FDC115 Transducer Crossarm with a length of 1.5 meters, which is also the total width of the FD12P.

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Chapter 2 ___________________________________________________________Product Overview

Operating Principle

The FD12P Weather Sensor is a microprocessor controlled, intelligent sensor combining optical forward scatter measurement, capacitive precipitation sensing, and temperature measurement. The main units of the FD12P are shown in Figure 3 below.

9502-091

Figure 3 FD12P Block Diagram

The FD12P evaluates Meteorological Optical Range (MOR) by measuring the intensity of infrared light scattered at an angle of 33°. The scatter measurement is converted to the visibility value (MOR) after a careful analysis of the signal properties. Special processing is used in case of precipitation.

The FD12P software detects precipitation droplets from rapid changes in the scatter signal. The droplet data is used to estimate optical precipitation intensity and amount. In addition to the optical signal, the analog output of the DRD12 Rain Detector is used to estimate the precipitation intensity and type.

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The output of the DRD12 is proportional to the water amount on the capacitive sensing surfaces while the optical intensity is proportional to the total 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 with the DTS14B Temperature Sensor connected to the DRI21 interface card. The temperature data together with the optical signal profile and the DRD12 surface sensor data are used to determine the actual weather code.

The software performs all signal analyses in the FD12P except the DRD12 Rain ON/OFF status, which is hardware-based and is used as an auxiliary parameter. The FD12P has a fixed program that is divided into tasks executed under control of a real-time operating system kernel. Each task is like an endless loop with a limited function. The operating system kernel controls the timing of the tasks and the interactions between the tasks.

Using FD12P

The FD12P is typically used as a component of a weather observing system. The final weather message (SYNOP, METAR) is then coded in the central unit of a weather observation system (for example, Vaisala MILOS 500) or by a human observer using the FD12P as an observation aid.

The FD12P output is a digital serial interface, which can be configured into two different operating modes: the sensor can be set to send a data message automatically at selected intervals, or the FD12P can be polled by the host computer. The same serial line is also used as an operator interface.

The operator controls and checks the operation of the FD12P by using a maintenance terminal. A set of built-in commands and test routines is provided for configuring and monitoring the multiple functions of the FD12P.

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 view a special status message. It contains detailed results of the diagnostics and a written description of the fault. Using this information, the operator can take corrective action or provide the maintenance personnel with valuable advice.

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Chapter 2 ___________________________________________________________Product Overview

Equipment Nomenclature

The standard equipment nomenclature and common names are listed in Table 3 and Table 4 below.

Table 3	Basic Set
Type	Name	Description
FDC115	Transducer Crossarm	Optics, analog, monitoring
		assembly
FDT12B	Transmitter
FDR12	Receiver
16614ZZ	Crossarm Cable
FDB12	Electronics Enclosure	Power, conversions, interfacing
		assembly
FDP12	Processor Board
FDS12	DC Voltage Regulator
FDW13	Mains Power Supply
DRI21	Interface Board
16615ZZ	Transducer Cable
16737ZZ	I/O Bus Cable
DRD12	Rain Detector
FD30513	Pole Mast	Standard 2-m mast
13145	Base Plate and
	Installation Set

Table 4	Options
Type	Name	Description
FDA13	Visibility Calibration Set
FD45094	Maintenance cable	RS232 cable with 9-pin D-
		connector.
Termbox-48	Mains and Signal	Adapting/extending the local
	Junction Box	cable. Contains heavy-duty
		transient protection circuitry.
FD12MODEM	Modem Option	For remote communication.
FD12PLM11	LM11 Option	For ambient light
		measurement.
16616ZZ	Extended Transducer	For optional high-mast
	Cable	mounting.

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User's Guide _______________________________________________________________________

Specifications

Mechanical Specifications

-Dimensions: 2.3 m × 1.6 m × 0.6 m (H × W × D)

-Weight: 35 kg, excluding the installation plate for the pole mast

-Mounting: on a concrete foundation with three 16-mm bolts

-Material: anodized aluminum, natural gray

Electrical Specifications

-Mains supply: 115/230 VAC ± 20 %, 45 ... 65 Hz

-Maximum power consumption: 35 W + 100 W defrosting heaters (in cold weather)

The sensor electronics:

-Lock-in amplifier

-LED power stabilizer

-Contamination monitor

-Lens heater

The control unit:

-Intel 8031 microprocessor

-Program memory, 64 Kbytes

-Read/write memory, 32 Kbytes

Outputs:

-Serial data line may be used either as RS-232 level signals or interfaced via an optional data modem

-RS-485 (2-wire)

-4 - 20 mA analog current (sink) output

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Chapter 2 ___________________________________________________________Product Overview

The output data:

-Automatic or polled data message

-Visibility, present weather, precipitation and status data

-Automatic message type and interval is selectable at 15 seconds to n × 15 seconds (n < 18) intervals

The analog visibility output:

-Selectable range and mode (linear or logarithmic)

-Status control bit for remote alarm relay, etc.

-Alarms and warnings (hardware failures, visibility limits)

Optical Specifications

Operating principle:

-Forward scatter at an angle of 33o and capacitive rain sensor. The light transmitter:

-Light source: near-infrared LED

-Peak wavelength: 875 nm

-Modulation frequency: 2.3 kHz

-Transmitter lens diameter: 71 mm

-Reference photodiode: for light source control

-Backscatter photodiode: for contamination and blockage measurement

The light receiver:

-Photodiode: PIN 6 DI

-Spectral response: max. responsivity at 850 nm, 0.55 A/W

(in range 550 ... 1050 nm over 0.3 A/W)

-Reception lens diameter: 71 mm

-Backscatter light source: near-infrared LED for contamination and blockage measurement

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User's Guide _______________________________________________________________________

Capabilities and Limitations

Visibility Measurement

Specifications

Measurement range of Meteorological Optical Range (MOR):

-10 ... 50 000 m according to a 5 % Contrast Threshold Definition

Accuracy:

-± 10 %, range 10 ... 10 000 m

-± 20 %, range 10 000 ... 50 000 m Instrument consistency:

-+ 4 %

Update interval:

- 15 seconds

Weather Sensing Specifications

Precipitation detection sensitivity:

-0.05 mm/h or less, within 10 minutes Weather type identification:

-11 different types of precipitation

-Fog (mist) and haze (smoke, sand) Weather type reporting:

-WMO code table 4680 (with some additions from code table 4677)

-Code letters for precipitation, NWS

-WMO code table 4678 (supported codes are shown in Table 34 on page 145).

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Chapter 2 ___________________________________________________________Product Overview

Precipitation intensity measurement:

-Range 0.00 ... 999 mm/h

-Accuracy ± 30 % (range 0.5 ... 20 mm/h, liquid precipitation)

Environmental Specifications

Operating temperature range:

-− 40 ... +55 oC Operating humidity range:

-Up to 100 % RH Wind speed:

-Up to 60 m/s (standard mast) Sun orientation:

-Direct and reflected sunlight into the light receiver must be avoided.

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Chapter 3 ________________________________________________________________ Installation

CHAPTER 3

INSTALLATION

	This chapter provides you with information to help you install this
	product.
NOTE	Before installation, read section Product Related Safety Precautions
	on page 13.

Organizing Installation

Before you begin to install the FD12P Weather Sensor, make a plan of the installation steps. The following is an example of how to organize the installation process.

1.Surveying the site:

-Find the most representative measurement site.

-Determine orientation of the Weather Sensor.

2.Cabling plan is required for the following:

-Grounding cabling layout and cable type.

-Power supply cabling layout and cable type.

-Modem/signal cabling layout and cable type.

3.Ordering the construction materials and cables.

4.Digging for cables and foundation.

5.Casting the concrete:

-Prepare concrete blocks by using a casting mold.

-Cast the fixing bolts in their places at the same time.

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User's Guide _______________________________________________________________________

6.Installing the base plate and the pole mast:

-Install the base plate with the bolts on the concrete block.

-Level the plate.

-Mount the pole mast on the base plate.

-Mount the junction box to the pole mast (optional). Junction boxes are available from Vaisala.

7.Connecting cables:

-Connect the mains and signal cables of the site to the junction box or have them ready for direct connection to the sensor.

8.Final installation:

-Install the electronics enclosure and the crossarm of the FD12P to the pole mast.

-Connect the power and signal cables of the FD12P.

-Connect the modem/signal line to the host computer, display, etc.

9.Start-up tests for the system.

Location and Orientation

The main requirements for the location of the FD12P are as follows:

1.Place the FD12P at a site where the measurements will be representative of the surrounding weather conditions.

The ideal site has a minimum clearance of 100 meters from all large buildings and other constructions that generate heat and/or obstruct precipitation droplets. Also avoid shading of trees as this may cause changes in the microclimate.

2.Make sure the site is free of obstacles and reflective surfaces, which disturb the optical measurements and act as obvious sources of contamination.

There must not be any obstacles in the line-of-sight of the transmitter and receiver units (see Figure 4 on page 31). If the transmitter beam is reflected from obstacles back to the receiver unit, the sensor will indicate too low MOR values as the reflected signal cannot be distinguished from the real scatter signal. Reflections are detected by rotating the sensor crossarm. They will change depending on the crossarm orientation. Also the visibility reading will change accordingly.

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