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.
DMX21T0496-1.1DMX21 CCITT Modem
LM11T0545-1.2LM11 Background Luminance Meter
Safety
WARNING
CAUTION
General Safety Considerations
Throughout the manual, important safety considerations are
highlighted as follows:
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 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 highlights important information on using the product.
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
CAUTION
WARNING
Ground the product, and verify outdoor installation grounding
periodically to minimize shock hazard.
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.
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 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-mm
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
WARNING
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.
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.
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.
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.
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.
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.
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
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 1FD12P 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.
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 2DRD12 Rain Detector and DTS14B Temperature
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.
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 3FD12P 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.
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.
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.
-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.
The receiver and transmitter optics should not point towards
powerful light sources or, in bright daylight, reflective surfaces
such as snow or sand. The receiver should point north in the
Northern Hemisphere and south in the Southern Hemisphere.
The receiver circuit may become saturated in bright light, and
the built-in diagnostics will indicate a warning. Intense light can
generate false contamination alarms from the transmitter unit.
Bright daylight will also increase the noise level in the receiver.
The transmitter and receiver should face away from any obvious
source of contamination such as spray from passing vehicles.
Dirty lenses will cause the sensor to report too high visibility
values. Excessive contamination is automatically detected by the
sensor.
Harmful reflections are typically avoided if the transmitter beam
is directed towards a surface, which will reflect most of the light
away from the sensor. The distance of 6 meters shown in Figure
4 below is only for guidance; it is not an absolute requirement.
There should be no flashing lights near the sensor. A flashing
light can cause errors in detecting precipitation towards
3.Power supply and communication lines must be available.
When the site for the FD12P is selected, take into consideration
the available power supply and communication lines. This
influences the amount of work and accessories needed and thus,
the actual installation costs.
Grounding and Lightning Protection
Equipment Grounding
Equipment grounding protects the electrical modules of the FD12P,
for example, against lightning and prevents radio frequency
interference. The FD12P equipment is grounded using a jacketed
grounding cable and conductive grounding rod(s).
The FD12P must be grounded by means of the grounding clamp,
which is located under the cable flange (See Figure 5 on page 33). A
16-mm² jacketed grounding cable is connected to the clamp.
Depending on the need, one to four copper-sheathed steel rods are
driven into the ground. If several rods are needed, the alignment from
the foot of the base plate must be radial.
The grounding principles are the following:
-The grounding rod must be isntalled as close to the pole mast
as possible to minimize the length of the grounding cable.
The grounding cable can be also cast inside the concrete base.
-The length of the grounding rod depends on the local
groundwater level. The lower end of the grounding rod must
continuously touch moist soil.
The grounding quality can be checked with a georesistance meter. The
resistance must be less than 10 ohms. This way the lowest possible
resistance is achieved.
The junction box must be also grounded via the grounding cables in
the same way as the electronics enclosure (Figure 5 on page 33). The
junction box is optional.
The electronics enclosure and the bottom plate of the FD12P are
secured by a 1.5-mm², yellow-green ground cable and the crossarm is
grounded through the transducer cable shield. The other parts of the
crossarm are in galvanic contact with each other.
CAUTION
When installing the FD12P, the grounding flat connector must be
plugged to the ground terminal socket, which is located beside the
MIL-connector in the crossarm. See instructions in section
Assembling the FD12P on page 40 and Figure 10 on page 43.
Grounding for Testing Purposes
The FD12P is provided with a two-meter mains cable. The cable has a
grounded plug. The plug must be connected only to an outlet that has
a ground terminal. This grounding is sufficient when the instrument is
used indoors, for example, for testing purposes.
Grounding Remote Units and
Communication Cable
Remote units, such as, the PC data logger, must be grounded and
protected against lightning.
A lightning strike through a communication wire can cause a voltage
surge dangerous to life at remote sites if the remote units are not
properly grounded.
The FD12P is supplied with a two-meter power cable. If a local
terminal for 115/230 VAC power supply is not available, use an
extended mains cable from the FD12P to the nearest power source.
This cable should be armored and of underground type. The armored
reinforcing acts as a mechanical shield and also provides protection
against lightning. Ground the cable screen at both ends.
The recommended mains wire cross sections are shown in Table 5
below for mains voltage 230 VAC. For 115 VAC, divide the
maximum distances by four.
Table 5Mains Cable Selection
Maximum
Distance from
Voltage Source
2 km1.5 mm
4 km2.5 mm
8 km4.0 mm
One-wire
Cross-section
Area
2
2
2
Nearest
AWG-gauge
No 15 AWG10 mm
No 13 AWG14 mm
No 11 AWG18 mm
Typical Nonarmored Cable
Diameter
NOTE
Cables with diameters more than 12 mm require a separate junction
box which is also available from Vaisala.
Communication Cable
The FD12P provides the RS-232C, RS-485, CCITT V.21 modem, and
analog transmission interfaces. Consider your needs for
communication before the installation. The communication method
depends on the distance between the computer or display and the
FD12P and the number of the FD12P sensors. Table 6 below describes
the possibilities.
For a modem and RS signal cable, use a screened, 2 × 0.22-mm²
twisted pair cable with a minimum diameter of 5 mm. For details, see
section Communication Options on page 50.
Unloading and Unpacking
The contents of the delivery in question are specified in the packing
list included with the delivery documents. The FD12P equipment is
normally delivered in three cases containing the following parts:
-Crossarm FDC115 containing the optics.
-Electronics enclosure FDB12 with radiation shield.
-Pole mast.
Two persons can easily move the cases from a truck to the installation
site.
NOTE
Handle gently the case containing the optical parts. Do not drop either
end of the case.
Unpacking Procedure
1.Read the packing list supplied within the delivery documents.
Compare the packing list against the purchase order to make
sure that the shipment is complete.
2.Open the covers.
3.In case of any discrepancies or damage, contact the supplier.
4.Place the packing materials and covers back in the cases and
store them for possible reshipment.
Storage Information
Store the FD12P in its packages in dry conditions, not in the open air.
The storage conditions are as follows:
Cast a concrete foundation or use an existing construction that is level
and rigid. The recommended minimum dimensions for the foundation
are illustrated in Figure 6 below. It is easiest to mount the foundation
screws while casting the pad. If the pad was casted earlier, drill three
holes into the concrete for the wedge bolts.
The Installation Set included in the FD12P delivery contains the
required equipment both for mounting when casting the pad and
mounting to an existing surface. Use the triangle shaped template as
an auxiliary device and remove it before mounting the base plate.
Reinforcing steel or use steel mesh 150 × 150 mm
Mounting When Casting the Pad
1.Fasten the three reinforcing plates to the lower end of the
foundation screws with six M16 nuts. See Figure 7 (C, top view)
on page 39.
2.Fix the template to the upper ends of the foundation screws with
six nuts.
3.Embed the assembly in the concrete foundation as shown in
Figure 7 on page 39.
4.After the concrete has set, remove the template.
Mounting to an Existing Surface
1.Drill three, ∅20-mm holes using the template, minimum depth
65 mm. Refer to Figure 7 on page 39.
2.Remove the template.
3.Clean the holes.
4.Fasten the foundation screws to the wedge bolts by hand.
5.Protect the tops of the screws with two nuts tightened together.
6.Then place the wedge bolt and foundation screw combinations
in the holes, wedge bolts down, and hammer the combinations
down.
7.Tighten the foundation screws as tight as possible.
If you use another, longer cable, make sure to connect the wires
in a correct way, especially the protective ground wire (usually
yellow-green). Refer to Figure 11 below.
2.Connect the power cord to the screw terminals in a junction box
or bring the power line directly to the electronics enclosure. The
selected method depends on the thickness of the power cable,
which should be checked before the installation. The electronics
enclosure has a cable outlet with a diameter of 10 - 12 mm.
3.Feed Neutral N (normally blue) and protective earth PE
(normally yellow-green) via separate conductors.
4.Feed the communication cable through one of the two cable
feedthroughs. For cable shield connections, see instructions in
section Communication Cable EMC-shielding on page 46.
5.Wire the communication cable according to instructions in
section Communication Options on page 50.
If the line voltage used differs from 230 V (the initial setting at the
factory), check the voltage setting of the FDW13 Mains Power
Supply (alternatives 115 VAC and 230 VAC). You can find the line
voltage setting switch on the left side of the FDW13 unit (see Figure
12 below).
0110-183
Figure 12Line Voltage and ON/OFF Switches
The following numbers are related to Figure 12 above:
1=Electronics enclosure
2=Pole mast
3=DMX21 modem
4=DC regulator FDW13
5=ON/OFF switch
6=Line voltage setting
7=FD12P control unit
1=Grounding
2=DTS14 cable feedthrough
3=Temperature sensor (TE)
4=Cap (Pg 13.5) of optional opening for the LM11
background luminance meter
5=Main power cable
6=FDC115 transducer cable feedthrough
7=Standard communication cable feedthrough
Communication Cable EMC-shielding
The electronics enclosure has one cable outlet for a cable diameter
from Ø7 to Ø10 mm, which is reserved for a signal or modem cable.
Although the shielding of the cable may be just grounded after cable
inlet, an efficient procedure against RF-interference requires special
care. Ground the cable gland to keep EMI levels within specifications.
For a proper RF-grounding of any jacketed cable, the instructions are
the following:
1.Lead the signal cable through the cable inlet. If the field cable is
thicker than 10 mm, use a separate signal junction box. See
Figure 14 on page 47.
2.Strip 80 mm of the cable sheath leaving approximately 40 mm
of the shield.
Connecting a Background Luminance Sensor or a
Day/Night Switch to FD12P
The FD12P Weather Sensor supports two different methods for
ambient light sensing. The Background Luminance Meter LM11 can
be connected to the FD12P for accurate ambient light measurement.
The LM11 sensor and necessary wiring are included in option
FD12PLM11 (see Figure 15 on page 49 for the wiring details). The
background luminance measurement is typically used in the RVR
systems.
The LM11 output frequency is measured with the DRI21 interface
board and then converted into background luminance by the FD12P
software. The conversion uses a scaling factor, which needs to be
configured by the user. For details, see section BLSC Command on
page 84.
In certain applications it is necessary to calculate night visibility
separately using a formula that differs from MOR. In these cases a
simple day/night photo switch is sufficient for discerning between day
and night ambient light conditions. The switch can be connected to the
serial line control input on the FDP12 processor board. For wiring
details, see Figure 16 on page 50.
Positive voltage is interpreted as a night condition and the background
luminance value in the FD12P output message is set to 0. Negative
voltage or an open circuit is interpreted as a day condition and the
luminance value is set to 1. For details, see section BLSC Command
on page 84.
The Vaisala recommendation for the maximum length of the RS-232
cable is 150 m (500 ft).
Serial Multipoint Transmission RS-485
The RS-485 transmission standard allows several FD12Ps to
communicate (half duplex) with the host computer using a single
twisted pair. For the RS-485 communication, connect the signal wires
to 4-pin screw connector X21 at the CPU board. See Figure 18 on
page 52.
In the multidrop configuration, where several FD12P Weather Sensors
are on the same communication line, units are differentiated by an ID.
Set a different unit ID to each FD12P with the CONF command. Set
FD12 P to the polling mode with the AMES 0 2 command. The host
system must ask data messages by polling each FD12P.
The Modem DMX21 is a CCITT V.21 modem, operating at 300 bps.
Connect the signal wires to MODEM LINE 1 and 2, and screw
terminals 7 and 9 on Interface board 16127FD. See the wiring diagram
in Figure 19 on page 53.
In the multidrop configuration, where several FD12P Weather Sensors
are on the same modem line, the units are differentiated by an ID. Set
a different unit ID to each FD12P with the CONF command. In the
multidrop configuration, only one FD12P modem carrier can be active
at the time. To set the modem carrier under the FD12P software
control, set jumper X2 to position 1-3 in the modem interface board as
shown in Figure 19 on page 53. If the X2 jumper is in position 3-4 and
if the unit ID is not set, FD12P keeps the modem carrier signal on all
the time. Set the FD12P to the polling mode with the AMES 0 2
command. The host system must ask data messages by polling each
FD12P.
Usually, the modem of the FD12P operates in the answer mode, and
the modem of the host computer in the originate mode. In the standard
FD12P system, the S3 switch on the DMX21 board is in the DOWN
position and the answer mode is selected. When the switch is in the
UP position, the originate mode is selected. The transit frequencies of
the DMX21 modem are presented in Table 7 below.
Table 7Transmit Frequencies of the DMX21 Modem Board
This section describes the alternatives of the indicators and manual
controls available in the FD12P DMX21 modem.
Indicators
The LED indicators of the DMX21 modem are listed and described in
Table 8 below.
Table 8LED Indicators of the DMX21 Modem
LED IndicatorDescription
LED V16 RRing indicator, normally off.
LED V17 ON LINENormally lit when the S2 switch is in the UP position.
The line, however, is permanently connected by
jumper connections. The V17 LED may also be off
although the modem is online. The S2 switch in the
DOWN position switches the V17 LED off.
LeV18 CDIndicates when a carrier frequency is detected. To
make date interchange possible, the modems must
first detect the carrier frequency.
LED V19 TxDTransmitted data stream when the data is 1, the LED
is lit.
LED V20 RxDReceived data stream. When the received data is 1,
the LED is lit.
Manual Controls
The manual controls and their positions are listed and described in
Table 9 below.
Table 9Manual Controls of the DMX21 Modem
ControlPositionDescription
S2
S1
S3
¹
The ORIG mode may also be used depending on the host computer modem. When they
operate in the ORIGINATE mode, the modem of FD12 P should be set in the ANSWER
mode and vice versa.
UPLine relay permanently on (recommended
position).
MIDDLELine relay controlled by software (switched lines).
DOWNLine relay permanently off.
UP
MIDDLESoftware-readable switch (recommended
position).
DOWN
UPORIG mode permanently on.
MIDDLEORIG/ANSWER modes under software control.
DOWNANSWER mode permanently on (normally
For 4-20 mA analog visibility measurement only two wires are
needed. Do the following:
1.Connect the voltage supply either from remote or internal supply
(from +Vb = 12 V or +V
100 ohm).
2.Connect the signal wire to screw connector X20 pin 3 "sink" at
the CPU board. In the drawing, a remote voltage supply is used
and the return signal is wired from pin 4 "gnd". See Figure 20
below.
For more information of the analog output port functioning and
configuring, see section Analog Output Commands on page 91.
= 23 V) to resistor R (for example,
bb
9607-007
Figure 20Analog Current Loop Option
Connecting the Maintenance Terminal
Any computer equipped with a terminal emulation software or a
VT100 compatible terminal with the RS-232 serial interface can be
used as a maintenance terminal for the FD12P. The optional
maintenance cable provides a 9-pin D-connector for the computer and
a 3-pin connector for the FD12P.
To connect the maintenance terminal, do the following:
1.Disconnect the serial line screw connector or modem interfacing
cable (or the RS-485) from X18.
2.Plug the maintenance cable into X18.
3.Refer to Figure 17 on page 51 (RS-232).
Startup Testing
Before closing the cover of the electronics enclosure, a short startup
must be done as follows:
1.Connect a terminal via serial line to the sensor (See sections
Serial Transmission RS-232 on page 50 or Connecting the
Maintenance Terminal on page 55). Set the terminal baud rate to
300 and set the data frame to contain 7 data bits and 1 stop bit,
even parity.
2.Turn on the main switch at the power supply FDW13.
3.Check that the red LED on the CPU board is lit for a few
seconds, after which the green LED should start blinking. If not,
continue with troubleshooting.
4.After startup, the FD12P outputs:
VAISALA FD 12P V1.XX 19YY-MM-DD SN
(ID is also included, if configured.)
5.Wait for one minute and enter the command mode with the
OPEN command. Check with the STA command that no
hardware errors or warnings are detected.
6.Enter the automatic message mode by typing CLOSE and check
that a message appears every 15 seconds in the display.
Initial Settings
The FD12P Weather Sensor is typically interfaced to a host computer
or a data logger in an automatic weather observing system. After the
physical connection has been made, the communication details can be
configured in the FD12P software. Suitable communication settings
depend on the implementation of the whole system.
By default the sensor transmits a new ASCII data message through the
serial line every 15 seconds. The user can change the interval and
message type. The sensor can also be used in a polled mode, that is, a
data message is only sent when the host computer requests one with a
special command. In addition, the baud rate of the serial line can be
changed to a higher value. The default communications settings are
listed in Table 10 below.
Table 10Default Communication Settings
SettingDefault
Baud rate300 baud (7E1)
Polled or automatic mode,
message type
Sensor IDNo ID set
Automatic mode, message 2
interval 15
In multipoint communication where several sensors share the same
communication line, the FD12P should be used in the polled mode
and individual sensors must have distinct identifiers (ID).
The baud rate should not be changed if the optional 300-baud modem
is used.
The commands for changing the default settings are listed in Table 11
below. Detailed descriptions of the commands can be found in
Chapter 4 on page 59.
Table 11Commands for Changing the Default Settings
OperationCommand
Baud rate selectionBAUD
Polled or automatic mode, message type setting AMES
Sensor ID configurationCONF
The FD12P has also several changeable parameters, which control the
operation of the present weather algorithm and precipitation
measurement. The factory set parameter values have been found
appropriate in tests and usually do not need to be changed. However,
there may be conditions where other parameter values give better
results.
The commands for displaying and changing the parameters are listed
in Table 12 below.
Local practice may require changes, especially in the precipitation
intensity limits and the haze threshold value. For details, see the
description of the WSET command in section WSET Command on
page 73.
When the precipitation intensity and amount measurement is not
factory calibrated, higher accuracy can be achieved by adjusting a
scaling factor with the WSET command. The new scaling factor can
be calculated by comparing the FD12P against a reference rain gauge.
For details, see the description of the WSET command in section
WSET Command on page 73.
This chapter contains information needed to operate this product.
Introduction
The FD12P Weather Sensor is a fully automatic instrument for
continuous weather measurement. Normally, the FD12P Weather
Sensor is either set to send a data message automatically or it is polled
by a host computer. In addition, a set of user commands is provided
for configuring and monitoring the system performance. These
commands can be given in the command mode. See section
Entering/Exiting the Command Mode on page 61.
The FD12P Weather Sensor has seven different standard message
formats for data message output. The FD12P presents the weather
type using the World Meteorological Organization (WMO) code table
4680 (WaWa Present Weather reported from an automatic weather
station). Code numbers 77 (snow grains), 78 (ice crystals), and 89
(hail) are from the code table 4677 because the types are not included
in the code table 4680. In addition, the United States National
Weather Service (NWS) abbreviations are available. The list of NWS
and WMO codes is presented in Appendix A on page 143.
User Commands in Normal Operation
User intervention is not required in the normal operation of the FD12P
Weather Sensor. Operator commands are used only in the initial setup and during routine maintenance. Several commands are also
available for troubleshooting.
When the sensor has been installed, the user may need to change some
of the default settings. For details, see section Initial Settings on page
56.
Table 13 below lists the settings and the corresponding commands.
Table 13Settings and Corresponding Commands
OperationCommand
Baud rateBAUD
Polled or automatic mode, message type
setting
Sensor IDCONF
Weather algorithm parametersWSET
AMES
Table 14 below lists the routine maintenance commands.
Table 14Routine Command for Maintenance
OperationCommand
Sensor cleaningCLEAN
(optional)
Visibility calibrationCHEC, CAL
Temperature calibrationFREQ, TCAL
Weather algorithm parametersWSET
The standard output messages contain a status character, which
presents the results of the internal diagnostics to the host computer or
the user. If the sensor indicates a warning or an alarm in a standard
output message, the host computer or the user can obtain a detailed
status report by using a special command (STA). The status report can
also be polled (message 3) in place of the standard data message.
Usually, the detailed status information is sufficient for locating the
fault.
The general format of the command is the following:
COMMANDparl...parn ↵
where
Command= An FD12P command given by the user
parl...parn= Possible parameters of the command
↵↵↵↵
= Symbolizes pressing the ENTER key
NOTE
All the command parameters are separated from each other by a
space character. Every user command must be ended with ENTER,
illustrated in this manual by ↵↵↵↵.
The system output is illustrated as Courier type font, for example,
BACKSCATTER INCREASED
Entering/Exiting the Command Mode
Before any commands can be given to the FD12P, the communication
line in the FD12P has to be assigned to the operator. Otherwise, it is
assigned to automatic messages or polled communication. The user
assigns the command mode with the OPEN command.
-Given in multiples of 15 seconds (= measuring interval).
Therefore, intervals 15, 30, 45 ... are valid. Other intervals
are converted to multiples of 15 seconds. The maximum
sending interval is 255 seconds (4 minutes 15 seconds).
For example, typing
AMES 1 60 ↵
selects message number 1 to be sent once in a minute.
Messages can also be displayed in the command mode with the MES
command, described in section MES Command on page 71.
Message Types
All the data messages are of fixed length and the data is in fixed
fields. Message 2 is intended to be used as the standard present
weather message. The length of the status message depends on the
possible alarm and warning states.
The FD12P adds frame strings to the polled and automatic messages.
The content of the frame strings is presented in the following:
!FD id"message body#-*
where
!
FD=FD12P sensor identifier
id=Unit identifier 2 characters, if ID is not defined
"
#
-*
=Start of heading (ASCII 1, non-printable character, in
terminal screen typically seen as the □ mark)
=Space character
characters space and 1 are shown
=Start of text (ASCII 2, non-printable character)
=End of text (ASCII 3, non-printable character)
=CR + LF (ASCII 13 + ASCII 10)
Message 7 consists of four lines. METAR present weather codes are
output on the second and third lines. These lines are not of fixed
length because METAR codes can be combined in many ways. The
METAR codes may also be left out but the lines of the message are
always terminated by a carriage return and line feed characters.
The background luminance value displays the measured luminance in
cd/m², if the Vaisala LM11 Background Luminance Meter is attached
to the FD12P (option FD12PLM11). If a day/night switch is
connected to the processor board, the background luminance value
displays the switch state (1 = day, 0 = night).
In the polled (CLOSEd) mode, the FD12P sends a data message when
the host computer transmits a polling command. The message polling
mode is selected by the following command:
AMESMessage_number Message_interval↵↵↵↵
where
Message_number
-The valid range is 0 ... 7, refer to section Message Types on
page 63.
-Selects the corresponding message as the default polled
message. Any negative message number is converted to 0.
Message_interval
-Negative or zero interval is used to disable the automatic
sending. This is used when messages are polled.
For example, AMES 0 0 ↵ selects message 0, and cancels the
automatic sending.
The polling command format is the following:
<ENQ> FD <SP> id <SP> message_number <CR>
where
<ENQ>=ASCII character 05 hex
<SP>=ASCII character 20 hex (space)
id=Selected in the configuration
message_
=Optional
number
If only one FD12P unit in on the line and no id is set, the command
format is the following:
<ENQ> FD <CR>
When the FD12P unit number two (id = 2) is polled for message
number 3, the command format is the following:
This format is also used when several devices are on the same line.
Use character 1 as the id if the id has not been set but a specific
message type is polled.
The FD12P does not echo the polling character string.
The answer message format is the following:
<SOH> FD <SP> id <STX> text <ETX><CR><LF>
The id field always contains two characters. If only one character has
been set as the id, the sensor will output an <SP> as the first character
in the field.
When there are several devices on the same line, the polled unit turns
the modem (DMX21) carrier on after it has acknowledged the request.
When the carrier is switched on, additional characters will appear
before the <SOH> (01 hex) character. The FD12P waits about 100 ms
after turning the carrier on before it starts to send the message. When
the FD12P has sent the message, it turns the carrier off. This will also
generate additional characters, which have to be ignored by the host.
FD12P Command Set
HELP Command
The operator receives information about available commands by
typing
HELP ↵
The HELP command sets are listed in Table 18 below.
Table 18HELP Command Sets
CommandDescription
OPENAssigns the line for operator commands
CLOSEReleases the line for automatic messages
MESDisplays data message
AMES Number Interval
CHECDisplays average signal
CAL Calibrator_frequency
CLRSClears precipitation sums
ACALAnalog output calibration
TIME hh mm ss
DATE yyyy mm dd
BAUD ratepar
AN channel
DAC data
RESETHardware reset by watchdog
WHISPresent weather history
WSETPRW reference values
DRY ONSets DRD dry offset
WET ONSets DRD wet scale
BLSCSets/Displays background luminance scale
Calibration
Sets/displays system time
Sets/displays system date
Baud rate setting
(Rate 300, 1200, 4800, 9600)
(Par E(7E1) or N(8N1)
Analog channel
(0,1,3,8 ... 15 or ANALOG ID)
(Without DATA = SWEEP)
MES Command
After opening the line for operator commands (see section
Entering/Exiting the Command Mode on page 61), a data message can
be displayed using the MES command. There are eight messages
available for different uses and they numbered from 0 to 7. Refer to
section Message Types on page 63 for message type descriptions.
The command format is the following:
MESMessage_number↵↵↵↵
with a valid range from 0 to 7. For example, when choosing the data
message number 2, type
MES 2 ↵
AMES Command
The AMES command defines the message, which the FD12P
transmits as the automatic message or as the default polled message.
Messages can also be displayed by the MES command, described in
MES Command on page 71.
-Selects the corresponding message. Any negative message
number is converted to 0.
-The message number is also the default number for the MES
command and polling.
-If only the message number is given, the previous interval
setting is used.
Message_interval
-Given in multiples of 15 seconds (= the measuring interval).
Therefore intervals 15, 30, 45 ... are valid. Other intervals are
converted to integer multiples of 15 seconds. The maximum
sending interval is 255 seconds (4 minutes 15 seconds).
-Negative or zero interval ignores the automatic sending. This
is used when messages are polled. Refer to section Message
Polling on page 69 for details.
For example, typing
AMES 1 60 ↵
selects message number 1 to be sent once in a minute.
Typing
AMES 0 0 ↵
selects message 0, and cancels the automatic sending.
The AMES command without parameters displays the current
selection and it is the following:
The WSET command is used to modify the present weather analysis
parameters.
The command asks for one parameter at a time, showing the
parameter name and the current setting. Accept the current value by
pressing ENTER. You can give a new value by typing the value
before pressing ENTER.
The Precipitation limit parameter is the threshold of accumulated
particle magnitudes (in FD12P internal units) that reports the
precipitation on state. The typical parameter value is 40. The smaller
value represents a more sensitive operation and faster response at the
beginning of an event.
Weather Update Delay
The Weather update delay parameter is a time as multiple of 15
seconds, during which the instant precipitation type is not changed.
The intensity may change faster.
Haze Limit
The Haze limit parameter specifies the visibility threshold for
reporting haze or mist. When the visibility is between 1000 m and the
Haze limit, the FD12P will report either haze or mist depending on the
air humidity.
The Rain intensity scale parameter is multiplied by the measured raw
intensity, which gives the reported precipitation intensity (optical).
The rain amount is scaled with the same coefficient because the
amount is a direct integral of 15-second intensities.
The typical value for the Rain intensity scale is 0.8. as the optimal
value is complex to determine; it depends on the optical, optoelectronic, and electronic parameters. No applicable factory
calibration method has been developed yet.
The precipitation measurement can be calibrated by comparing the
FD12P rain amount to measurements made with a suitable reference
rain gauge. Make the comparison after a few rainfalls with 5 mm or
more of total accumulated rain. A new scaling factor can be calculated
using the following formula:
Newscale = Oldscale × (Ref_Amount/FD12P_Amount)
where
Oldscale=Old value of Rain Intensity Scale
Ref_Amount=Amount measured with the reference rain gauge
FD12P_Amount =Corresponding amount measured by the FD12P
Violent Rain Limit
The Violent rain limit parameter defines the minimum rain intensity
(mm/h), when the intensity is violent.
Heavy Rain Limit
The Heavy rain limit parameter defines the minimum rain intensity
(mm/h), when the intensity is heavy.
Light Rain Limit
The Light rain limit parameter specifies the maximum rain intensity
(mm/h), when the intensity is light. If the rain intensity is between the
above heavy and light limits, it is moderate.
Drizzle Limit
The Drizzle limit parameter refers to the maximum drop size (in
FD12P internal units), which can be detected as drizzle. The typical
value is 15, which has been found to be the optical signal from a 0.5
mm diameter droplet measured by typical FD12P hardware. The
parameter value relates to the square of droplet radius. The
relationship is the following:
X = 240× R
2
where
X=Parameter value
R=Droplet radius
Parameter value 30 would correspond to about a 0.7-mm droplet
diameter.
Heavy Drizzle Limit
The Heavy drizzle limit parameter refers to the minimum number of
drizzle droplets detected in 15 seconds. They must be detected before
drizzle becomes heavy (dense).
Light Drizzle Limit
The Light drizzle limit parameter defines the maximum number of
droplets detected in 15 seconds, when drizzle is light.
Snow Limit
The Snow limit parameter specifies the minimum ratio of optical
precipitation intensity to surface sensor (DRD12) precipitation
intensity, when the precipitation is snow. A half of this value is used
for separating sleet and ice pellets.
The typical value for Snow limit is 5. A smaller value directs the
FD12P to report more wet precipitation as snow.
Heavy Snow Limit
The Heavy snow limit parameter defines the minimum visibility (m)
on a two-minute average in heavy snow.
Light Snow Limit
The Light snow limit parameter defines the maximum visibility (m) on
a two-minute average in light snow. If snow is detected and the twominute visibility average is between the above heavy and light snow
limits, snow intensity is moderate.
The Snow pellets limit parameter specifies the minimum particle size
(in FD12P internal units), which is detected as snow pellets.
(Additional internal criteria are used before the precipitation type is
determined to be snow pellets.)
Snow Grains Limit
The Snow grains limit parameters refers to the maximum particle size
(in FD12P internal units), which is detected as snow grains.
Ice Crystals Limit
The Ice crystals limit parameters defines the maximum particle size
(in FD12P internal units), which is detected as ice crystals.
(Additional internal criteria are used before the precipitation type is
determined to be ice crystals.)
Hail Limit
The Hail limit parameters refers to the minimum particle size (in
FD12P internal units), which is detected as hail. (Additional internal
criteria are used before the precipitation type is determined to be hail.)
DRD Scale
The DRD scale parameter is the scaling factor for the calculated
intensity of the DRD12 surface sensor. The typical value for this
parameter is 1.5. The value is also good for a very clean DRD12.
When the DRD12 becomes dirty after some precipitation events, it
becomes more sensitive, especially for light rain. Thus, a smaller
value of the scale could be used.
Warm Limit
The Warm limit parameter defines a more flexible, maximum snow
reporting temperature limit, which is required in some areas. The
nominal value is +8 °C.
PRW Command
The Present Weather command (PRW) command, displays a verbal
format message.
VISIBILITY7161 mAVE 10 MIN7533
RAIN INTENSITY0.16 mm/h CUMULATIVE SUM 12.16
SNOW INTENSITY0.0 mm/hCUMULATIVE SUM 0
TEMPERATURE2.7
TS1.8
DRD SUM22.04
CLRS Command
The CLRS command resets (to 0.00) the cumulative sums of
precipitation. This resetting can also be done in the protocol mode by
the host computer, using the following command format:
<ESC> FD id C <CR>
Then the FD12P responds to the accepted command with the
following ASCII character:
<ACK>(06 hex)
WHIS Command
The WHIS command displays the instant precipitation type codes
(NWS) for one hour.
The configuration command, CONF, is used to set or update system
parameters and to adjust certain calibrations, reference values, and
limits. You can limit the use of this command by protecting it with a
password. New parameter values are saved in the non-volatile
memory (EEPROM).
The CONF command displays the parameters one by one and asks for
a new value. In most cases, the current value is shown as the default
value. The parameter is not updated if the user only presses the ↵↵↵↵ key.
You can modify the following system parameters using the CONF
command:
-Vis Alarm Limits
-Offset Freq Reference
-Temperature TE Scale
-Password Characters
-Unit Id Characters (2)
-References And Limits for Contamination Monitoring
-Analog Output Minimum Visibility
-Analog Output Maximum Visibility
-Analog Output Lin/Log
To prevent unauthorized change of the system parameters, a four-
character password can be set at the beginning of the CONF setting.
You can also modify the password then. When you do not want to set
or modify the password, press ↵↵↵↵ .
When a password has been set in the previous session, the command
format is the following:
When no password has been set, the command format is the
following:
CONF ↵
The system response to the CONF command is presented below (The
bold text refers to user actions.)
CONF. PASSWORD (4 CHARS MAX)
UPDATE CONFIGURATION PARAMETERS
UNIT ID (2 CHAR)( 1)
SET REFERENCE PARAMETERS(25.9)
TE
OFFSET
OFFSET REFERENCE UPDATED
ALARM LIMIT 1(1000)
ALARM LIMIT 2
ALARM LIMIT 2UPDATED
TRANSMITTER CONTAMINATION
LIMITS
WARNING LIMIT
WARNING LIMIT UPDATED
ALARM LIMIT(5.0)
RECEIVER CONTAMINATION LIMITS
WARNING LIMIT(100)
ALARM LIMIT
ALARM LIMIT UPDATED
ANALOG OUTPUT MODE
0 = LINEAR1=LN(0)
ANALOG OUTPUT RANGE
MAX VISIBILITY(10000)
MIN VISIBILITY(50)
END OF CONFIGURATION
(127.48) Y
(200) 300
(1.0) 1.5
(500) 600
The questions asked by the system are described below.
First the system asks for a new password:
CONF. PASSWORD (4 CHARACTERSMAX)
This question is asked when there is no valid password or the existing
password is updated. If updating is requested by the N parameter and
an empty line is given for an answer, the password is removed.
Otherwise, the user gives a new password to the system.
The system asks the following:
UPDATE CONFIGURATION PARAMETERS
UNIT ID (2 CHAR)( 1)
If the FD12P unit is named by one- or two-character ID codes, the
OPEN and POLLING commands use it as a parameter. The ID code is
also included in the data message heading. ID 1 is used as a default in
the message heading if no other ID is given. The current ID can be
removed by pressing " - " as an answer to the question.
In the multidrop configuration, where several FD12 Weather Sensors
are on the same communication line, the units are differentiated by the
ID.
The next CONF parameters are hardware- or system-dependent. They
can be changed from the factory set values for better performance or
maintenance purposes. The example configuration session is
explained in the following.
The single point calibration of the TE backup temperature
measurement can be done by giving the temperature.
SET REFERENCE PARAMETERS
TE (25.9)
The default value is the current temperature. If it is not correct, a new
value must be typed as the answer. The new value is used to correct
the internal TE scaling factor. The TE temperature is used as a backup
in FD12P. The temperature is used in the visibility measurement to
control the precipitation effect correction algorithm. Snow and rain
have a different kind of effect on the scattering signal when it is used
for the visibility calculation.
The currently measured offset value (not a parameter) is shown in the
brackets (see next page).
OFFSET (127.48) Y
OFFSET REFERENCE UPDATED
After receiving Y as an answer, the system accepts the offset
frequency to be the reference parameter for hardware monitoring. The
parameter value is further compared with the current value to detect
drift or other failure in the optical signal measurement electronics.
The visibility alarm limits are checked. Limit 1 is expected to be
higher than Limit 2. The limit values are expressed in meters.
In the above example, alarm Limit 2 receives a new value, 300 m.
When the visibility now weakens below Limit 2, then the data
message (0 to 2) data status is set to 2. The visibility alarm is not
shown in the status message.
The backscatter/contamination control is done by comparing the
current values of backscatter signal with the reference values given
with the CLEAN command. The limits given here are limits for the
change in backscatter signals.
The transmitter values are expressed in volt (V). The measurement
range is 0 to 13 V, where 0 V is a blocked lens. The limit value is
given as a positive value although the signal becomes smaller when
contamination increases.
A contamination change of 5 V represents about a 10 % decrease in
the transmitter's lens transmittance (as also does the same increase in
the visibility indication).
The receiver values are expressed in hertz (Hz). The measurement
range is from 0 to 10000 Hz, where 10000 Hz is a blocked lens.
A contamination change of 500 Hz represents about a 10 % decrease
in the receiver's lens transmittance.
The analog output mode and visibility range are set last. In the
logarithmic mode, the minimum visibility must be different from 0 as
LN(0) is not defined.
ANALOG OUTPUT MODE
0 = LINEAR1=LN(0)
ANALOG OUTPUT RANGE
MAX VISIBILITY(10000)
MIN VISIBILITY(50)
END OF CONFIGURATION
The baud rate and communication type can be changed by typing
following the operator command:
BAUD value communication_ type
The baud rates are 300, 1200, 2400, 4800, and 9600. The
communication types are E (7E1) and N (8N1).
The new value is saved in EEPROM and it is used also after reset or
power up. The default baud rate set at the factory is 300 baud (7E1).
Defining the communication type is optional. It does not change if the
baud rate is changed. Other baud rates than 300 baud are not allowed
with the DMX21 modem.
The BAUD command displays the current baud rate and
communication type. For an example, see the following:
BAUD RATE: 300E71
BLSC Command
The Vaisala LM11 Background Luminance sensor can be connected
to the FD12P for ambient light measurement. Each LM11 sensor has
an individual scaling coefficient, which is defined at the factory. The
scaling coefficient is written on a label in the LM11 sensor. This
coefficient should be configured to the FD12P for correct scaling of
the measured background luminance values.
The BLSC command is used to set or display the background
luminance scale.
When you type
BLSC↵
↵
↵↵
it displays the current background luminance scale.
If the LM11 is not connected, the scaling factor should be negative.
Value -1.0 has been set at the factory as the default value. If a positive
value is used, the sensor expects a signal from the LM11.
For an example, see the following:
>blsc
BL SCALE-1.000
>blsc 10.4
BL SCALE10.400
If a day/night switch is connected to the serial line control input on the
FDP12 processor board, the FD12P can read the switch state and
report it as a background luminance value of 1 (day) or 0 (night). The
FD12P firmware will read the switch if the background luminance
scaling factor is set to 0.
Maintenance Commands
The maintenance commands are listed in Table 21 below.
Table 21Maintenance Commands
CommandDescription
STA
CAL Calibrator_frequency
TCAL
CLEAN
CHEC
FREQ
DRY ON
WET ON
ANCHANNEL
STA Command
The STA command displays the results from the built-in test system
as a status message. Message 3 gives the same status message as the
STA command.
Displays status.
Calibration.
Temperature measurement calibration.
Sets clean references.
Displays average signal.
Displays internal signals.
Sets DRD12 dry offset.
Sets DRD wet scale.
Analog channel (0,1,3,8 ... 15 or ANALOG ID).
An asterisk (*) before a value indicates an exceeded limit.
In the end, there are verbal comments on the combined errors
detected. These comments can be one or many of the following listed
in Table 22 below.
Table 22Hardware Error Texts
Error textDescription
BACKSCATTER HIGH
TRANSMITTER ERROR
+15 V POWER ERROR
OFFSET ERROR
SIGNAL ERROR
RECEIVER ERROR
DATA RAM ERROR
EEPROM ERROR
The receiver or transmitter contamination signal
has increased more than the ALARM limit given
in the configuration.
The LEDI signal is more than 7 V or less than
-8 V.
The receiver/transmitter power is less than 14 V
or more than 16 V.
The offset frequency is zero (cable is
disconnected).
The signal frequency is less than 50 % of the
offset frequency.
Too low signal detected in the receiver
backscatter measurement.
The error is in RAM read/write check.
This is an EEPROM checksum error.
The hardware warning texts are listed in Table 23 below.
The receiver or transmitter contamination signal
has increased more than the WARNING limit
selected in the configuration.
The LEDI signal is less than -3 V.
The AMBL signal is less than -9 V.
The offset has drifted more than ±5 Hz from the
reference value.
No current flowing to lens heaters.
The DRI21 board cannot be detected.
The DTS14B measurement is off limits.
The DRD12 analog signal is close to zero.
The LM11 signal is zero (not checked if the BLSC
is negative).
Box temperature sensor TE measurement is off
limits.
The visibility calibration coefficient has not been
changed from the default value.
CAL Command
The CAL command is used to calibrate the visibility measurement.
The calibration is done by using opaque glass plates with known
scatter properties.
The command type is the following:
CAL Calibrator_signal_value↵↵↵↵
Type, for example, the following:
CAL 985 ↵
↵
↵↵
The calibrator signal value is printed on the labels of the glass plates.
Typically, the signal is close to 1000 Hz. The FD12P calculates a new
scaling factor and stores it in the non-volatile memory (EEPROM).
Refer to section Calibration on page 119 for instructions.
TCAL Command
The TCAL command is used to calibrate the sensor crossarm
temperature (TS) measurement. Only 0 °C temperature is important in
its accuracy because it is used in the identification of freezing rain.
When you type
TCAL ↵
↵
↵↵
the command displays the current scaling factors.
Without a parameter, the command displays the current scaling factors
and current TS.
the command initializes the two-point calibration sequence, where two
temperatures must be simulated.
When you type
TCAL TS DTS14B_temperature ↵
↵
↵↵
a single-point calibration to the TS is made. That is, the scaling factor
TS 0 is adjusted by the command routine.
The following command
TCAL TS 0.0 ↵
↵
↵↵
makes a zero calibration, if the temperature sensor DTS14B is in an
ice bath or otherwise at a temperature of 0 °C .
The following command
TCAL TS 0.0581 -59.0 ↵
↵
↵↵
sets both scaling factors.
The system output is as follows:
DRI TEMPERATURE SCALES
TS 1 0.0581 TS 0 -59.0000 TS2.8
CLEAN Command
The CLEAN command has no parameters and it is used to set the
clean references for contamination control. This command is given
during maintenance procedures after cleaning the lenses or after
replacing the transmitter or receiver board.
The CHEC command is used in the visibility calibration procedure to
display the two-minute average signal frequency in hertz. The
command has no parameters.
The display is terminated by pressing ESC. Pressing any other key
will pause the display. In the beginning, the eight-location buffer is
filled with the first value. The buffer is used to calculate the average
When the FDA13 calibrator is installed, the value displayed in the
message should be the same as printed on the calibrator glass plate. In
clear air the value should be near zero.
When you type
CHEC ↵
↵
↵↵
the output is the following:
SCALED FREQUENCY AVE (2 MIN)
999.9938
999.9880
>
FREQ Command
The FREQ command is for hardware monitoring. Message 4 gives the
same data line as the FREQ command.
An example of the output is the following:
>freq
SIGNAL+ OFFSET DIST SWID MAXI OWID TE LEDI BACKSVBBTS DRD
0.03 129.79 1.0042424.45.3 1303 19.5 23.1 900
0.03 129.79 1.0042424.45.3 1303 19.5 23.1 900
A new line is printed every 15 seconds. The command output is
terminated by pressing the ESC key. The first line is a title line with
the signal names.
DRY and WET Commands
The DRY and WET commands are used to check and adjust the
operation of the Rain Detector DRD12 analog signal measurement.
The DRY command is used to set the dry signal end of the DRD12
signal normalization calculation.
When you type
DRY ↵
↵
↵↵
the output is, for example, the following:
DRD DRY OFFSET915.6
The DRY OFFSET value must be between 850 and 980 when the
DRD12 hardware operates normally. The DRY command shows this
parameter. The parameter is set by the DRY ON command.
When you type
DRY ON ↵
↵
↵↵
the WET command without a parameter shows the scaling factor that
normalizes the DRD12 signal change from the dry state to the wet
state to 1.00. A typical value is 0.0015. An example is shown in the
following:
WET ↵
DRD WET SCALE0.00169
The WET ON command is used to set the parameter. The DRD12
measuring surfaces must be coated with a wet cloth or immersed in
water, when the WET ON command is given. An example of the
command is given below:
WET ON ↵
AN Command
The AN command can be used continuously to display the selected
analog monitor channel. The channel ID can be used as a parameter,
instead of the channel number. Thus, the AN AMBL command is the
same as AN 12.
The message consists of the raw binary number from the A/D
converter and the corresponding scaled and filtered value.
The DAC output voltage is converted to current, 0 to 22 mA unscaled.
This current is then software-calibrated to give 4 mA at the minimum
visibility and 20 mA at the maximum visibility. The minimum and
maximum visibility values are set in the configuration session. A
hardware error is indicated by 0 mA.
The ACAL command sets two-bit values, 4000 and 800, to the
digital-to-analog converter. The corresponding currents measured by a
multimeter must be given as answers to the questions asked in the
commands. The analog output scaling factors, which define the
bits/mA relation, are then calculated by the software. The scaling
factors are Scale 0 and Scale 1. The FD12 calculates them as follows:
Scale 0 = 4×((4000-800)/(high current - low current))
The bit value that gives 4 mA. Scale 1 depends on the mode.
the command gives, for example, the following output:
MEASURED CURRENT (mA)22.16
MEASURED CURRENT (mA)4.52
Data Scaling
The FD12 scales the visibility value to a binary number for the DAC
( = DACBITS) so that the minimum visibility corresponds to the
4 mA-calibrated value and maximum visibility to the 20 mAcalibrated value.
If visibility is less than minimum visibility then
DACBITS = bits4mA = scale 0
If visibility is more than maximum visibility then
DACBITS = bits 20mA
Hardware Check
The DAC bit value from 0 to 4095 can be given as a parameter. The
value does not change until you press ESC. When the DAC command
has been given without a parameter, the analog output sweeps slowly
from 0 to maximum and from 0 until you press the ESC key.
This chapter gives a functional description on the product.
General
The FD12P Weather Sensor is an optical sensor that measures
visibility (meteorological optical range, MOR, and precipitation
intensity and type. The FD12P measures visibility using the forward
scatter measurement principle. Light scatters from particles whose
diameter is in the order of magnitude of the light wavelength. The
amount of scatter is proportional to the attenuation of the light beam.
Larger particles behave as reflectors and refractors and their effect on
the MOR must be handled separately. Usually, these particles are
precipitation droplets. The FD12P optical arrangement allows for
individual droplets to be detected from rapid signal changes. The
FD12P software calculates the precipitation intensity by analyzing the
amplitudes of these changes. This intensity estimate is proportional to
the volume of the precipitation droplets.
The optical signal also contains some information about the
precipitation type but not enough for reliable identification. Additional
information is needed, especially in conditions where the precipitation
is very light or the weather is windy. As the extra parameter, the
FD12P measures an estimate of the water content of precipitation with
the DRD12 rain detector. In rain, the water equivalent and the volume
are equal. However, in snow the optical volume estimate is about ten
times larger. This difference of approximately one decade is used to
discern between rain and snow.
The FD12P measures light scattered at an angle of 33°. This angle
produces stable response in various types of natural fog. Precipitation
droplets scatter light in a different manner than fog. Thus, their
contribution to visibility must be analyzed separately. The FD12P can
detect and measure precipitation droplets from the optical signal and
use this information in processing the scatter measurement results.
The FD12P has a small sample volume of about 0.1 liters (see Figure
21 above). This enables independent particles to be measured even at
quite heavy precipitation intensities. The signal levels from even the
smallest droplets can also be detected.
FDT12B Transmitter Unit
The transmitter unit consists of an infrared LED, control and
triggering circuits, LED intensity monitor, backscatter receiver, and
analog multiplexer.
The transmitter unit electronics pulses the IR-LED at a frequency of
2.3 kHz. One PIN-photodiode monitors the transmitted light intensity.
The transmit level measurement is used to automatically keep the
LED's intensity at a preset value. The "LEDI" feedback voltage is
channeled through the analog multiplexer to the CPU for monitoring.
The feedback loop compensates for temperature and aging effects of
the light-emitting diode. On the other hand, the active compensation
slightly accelerates the LED aging. For this reason, the initial LED
current is set to a value, which guarantees several years of
maintenance-free operation.
A reset pulse (RES) from the FDR12 Receiver synchronizes the IRLED timing with the receiver's lock-in amplifier. The CPU can also
delay the transmitter firing for a special out-of-phase measurement.
This feature is used in measuring the internal noise level (offset) of the
circuitry.
An extra photodiode measures the light scattered backwards from the
lens, other objects, or contaminants. This signal as well as several
internal signals are monitored via MUX-line.
The CPU board supplies only one voltage Vb = 10 - 13 V for both the
transmitter and receiver. This is used for heating the lenses, for the
transmitter LED heating and for producing both +5 V digital and
+15 V analog supplies. The +15 V supply is located on the FDT12B
board.
FDR12 Receiver Unit
The Receiver Unit consists of a light receiver, preamplifier, voltage to
frequency converter, backscatter measurement light source LED, and
some control and timing electronics.
9611-003
Figure 23FDR12 Receiver Block Diagram
The receiving PIN photodiode senses the transmitted light pulses
scattered from the aerosol particles. The signal voltage is filtered and
detected by a phase-sensitive, lock-in amplifier synchronized with the
transmitter.
The lock-in circuits take two samples of the background level and one
sample of the active signal level while the transmitter LED is lit. The
difference between the sampled voltages is amplified and then
converted into frequency.
The frequency signal is buffered by a differential line driver and sent
to the CPU board for accurate counting.
An ambient light level as high as 30 kcd/m2 does not influence the
detection of the photo diode, neither does it saturate the A4 preamplifier. The Ali signal (proportional to the ambient light) is led to
the CPU for monitoring.
An extra IR-LED is needed for backscatter or contaminant
measurement. The light level is sampled and converted into frequency
using the same method of detection described with the scattering
signal measurement.
Additional Measurements
General
The FD12P includes the DRD12 Rain Detector for estimating the
water content of precipitation and the DTS14B Temperature Sensor
for measuring the sensor crossarm temperature (TS). Both additional
sensors are measured using the DRI21 Interface Board, which is
coupled on the FD12P PICOBUS.
DRI21 Interface Board
The DRI21 is a Vaisala general-purpose sensor interface with several
analog and digital input channels. One of the DRI21 temperature input
channels (Pt100) is used to measure the crossarm temperature
(DTS14B). One 10-bit analog input channel is used to measure the
DRD12 analog signal. In addition, the DRI21 controls the DRD12
heating and reads the rain ON/OFF status.
Figure 24DRI21 Block Diagram in the FD12P Application
DRD12 Rain Detector
The DRD12 analog signal is proportional to the water amount on the
sensing surfaces. Water on the DRD12 changes the capacitance of the
sensor elements. The capacitance of the elements controls the output
frequency of an oscillator. This frequency is amplified and also
converted into a voltage signal for direct analog measurement. With
dry surfaces, the DRD12 outputs about 3 V and with totally wet
surfaces 1 V. Refer to Figure 29 on page 104, section DRD12 Signal
Processing on page 104.
A droplet detector monitors the voltage signal. When a new droplet
hits the DRD12 sensing surface, the voltage changes rapidly and the
detector circuit reacts. The detector triggers a delay circuit, which
controls the precipitation ON/OFF output. When new droplets are
detected often enough, the delay circuit output will stay constantly on.
The voltage signal is measured once a second by an analog channel of
the DRI21 interface board. In addition, the precipitation (ONN/OFF
signal) is read with a digital input.