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MITRASTransmissometer

Runway Visual Range

Operator Training Material

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Contents

Mitras Overview

System description

RVR assessmentFunctional Description

Operating principle

Mitras VisibilityCalculation

Hardware

LM11

Installation

Operation

Communication

Commands

Troubleshooting

Maintenance

Periodic Maintenance

Operational Check

Calibration andLinearization Check

Aligning Optics

Replacing a Subassembly

HANDS-ONHANDS-ON exercises

Commands and communication

Maintenance

Troubleshooting and repair

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MITRAS Transmissometer

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MITRAS System

Conforms to all ICAO and WMO requirements for RVRand Meteorological Optical Range (MOR)

Accurate RVR assessment is a result of accurate MORmeasurement => reduces airport down-time

Improved accuracy with fully automatic measurementand unique contamination control with compensation(longer maintenance interval)

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Single Baseline System

Double Baseline System

LIGHT TRANSMITTERLIGHT RECEIVER

LIGHT TRANSMITTER LIGHT RECEIVER

LIGHT RECEIVER

Light transmitter and Light receiver

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Double baseline for CAT IIIB

Double baseline for CAT IIIB is implemented by means oftwo different beams from one transmitter.

The assessment of visibility ranges from 2/3 times theshort baseline up to 50 times long baseline.

With 10m and 200m base lines visibility from 7m upto 10 000m.

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Definition of MOR

MOR can be measured by measuring the attenuation of light

attenuation is mainly caused by scattering, to a smalldegree also by absorption (in smoke, dust, )

100 %intensity 5 %intensity

MOR

MOR is defined as the distance where the intensity of a light

beam has been attenuated to 5% of the original intensity

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What is Runway Visual Range?

Runway Visual Range (RVR) = Range over which the pilot on thecenter line of the runway can see:

- Runway markings, or- Edge lights of the runway, or- Center line lights.

RVR is not an observation nor a measurement.

RVR assessment calculation follows Allards law which takes intoaccount:

- Visibility (m)- Background luminance (cd/m2)- Airfield lighting intensity percentage- Airfield lighting characteristics (cd)

For RVR calculations 5 m is used as the average eye level of a pilot inan aircraft.

Traditionally RVR has been assessed by counting edge light lamps bythe runway. The lamps are at 60 m distance from each other. At CAT Iairport at least 14 lamps should be seen and 7 lamps at CAT II airport.

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RVR Assessment

MOR (Visibility)

MITRAS

Backgroundluminance (LM11)

=> Illuminationtreshold

Runway lightsetting

RVR Calculation

MIDAS IVRVR value

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R U N W A YR U N W A YR U N W A Y

ATC/TOWER

Digital display

M

M

RVR Computer and

accessories

MIDAS IV: Small system

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R U N W A Y

CEILOMETER

CT25K

0...25000 ft

Precipitation

Geonor

R U N W A Y

RWY TEMPRWY TEMPRWY TEMP

RWY TEMP RWY TEMP RWY TEMP

WINDS

PTU

PTU

WINDS

MIDAS IV: Large system

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Measurement principle (1)

Light source

- Xenon flashlamp

- Represents the spectrums of sunlight and runway lights

- Very stable, expected lifetime 55000 h

- Light intensity can be controlled

Benefits of reference measurement (transmitted intensity)- Short-term long-term variations are compensated

very accurately

- Transmissometer stability better than 0.3%

- Unusual situation detected immediately

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Optics of MITRAS Transmissometer

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Measurement principle (2)

Averaging time

- Normal operation 30 s or 60 s

- In alignment mode 15 s

Pulse measurement principle

- Light pulse duration 1.5 s (half-width)

- Continuous light doesnt interfere: A 75000W lamp at 30 m

distance has no influence Representative spectral response

- Green optical filters are used to approximate the specralresponse of the human eye

Economy mode The flashing interval automatically changes according to the

visibility.

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Measurement interval andnormal/economy mode

Transmissometer measures the transmittance between theLight Transmitter LP11 and Light Receiver LR11. It calculatesthe moving average over 60 or 30 samples.

In normal mode it measures transmittance every second. In economy mode it automatically changes the flashing

interval according to the visibility.

Visibility (MOR) Flashing interval

under 2 km 1 s

2 km

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LP11 / LR11 Block Diagram

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MITRAS Visibility Calculations

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Meteorological Optical Range (MOR) has been defined by

the WMO as the basic parameter to express the optical state

of the atmosphere

MOR corresponds closely with human visibility

observations (day observations)

MOR has been defined as a purely physical quantity

objective

it can be measured

Visibility & MOR

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100 %intensity

5 %intensity

MOR

MOR can be measured by measuring the attenuation of light attenuation is caused by scattering and absorption

Definition of MOR

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35 m 50 m 75 m 100 m

Transmittance Visibilities (m) at different baselines

0.995 20.947 29.925 44.887 59.8500.990 10.447 14.925 22.387 29.8500.950 2.047 2.924 4.387 5.8490.930 1.447 2.067 3.100 4.1340.900 997 1.424 2.135 2.8470.800 470 672 1.008 1.3440.600 206 294 440 5870.400 115 164 246 3270.200 65 93 140 1860.100 46 65 98 130

0.015 25 36 54 71

Meteorological Optical Range (MOR)

MOR = - 3 x Baseline

ln (Transmittance)

Baseline

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Visibility Calculation

LPC11 software calculates visibility with Koschmieders law.

ICAO has defined the extinction coefficient to be 0.05 which has beentaken into account in the following Koschmieders visibility (MOR)formula:

Mitras transmissometer system uses LPI11 Light Intensity measurement units in

LP11 and LR11 for measuring light.

When calculating the visibility the software takes into account intensities with andwithout contamination calculation. If Contaminantion Compensation Mode is ON

MITRAS transmits the compensated visibility to RVR Computer.

If the LPI11 boards are unlinear the software takes that into account. (The

linearization correction is made by techicians).

Where Transmittance = K1 Received light intensity = K1 R (I)

Transmitted light intensity TM (I)

and K1 is set by technicians during good visibility

Visibility = - 3 x Baseline ln (Transmittance)

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Visibility Measuring Range

Single Baseline Systems

Baseline MOR range RVR range(at night)

35 m 25....1500 m 100....1500 m

50 m 40....2000 m 150....2000 m

75 m 50....3000 m 200....3000 m

100 m 70....4000 m 300....4000 m

200 m 70..10000 m 300..10000 m

Double Baseline Systems

Baseline MOR range RVR range

10 and 75 m 7....3000 m 40....3000 m

10 and 200 m 7..10000 m 40..10000 m

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RVR Computer Calculations

RVR Computer calculates RVR data every 15 s. It pollsMITRAS transmissometers for visibility, backgroundluminance and status data. It receives runway light

percentage data from the interface unit or uses manuallyinput value. It has the characteristics of airfield lights inits memory.

When calculating the RVR the RVR Computer takes into

account marked discontinuity. It calculates instant RVRand following 10 minute values: average, one-minuteminimum and one-minute maximum.

It compares last 5 minute RVR values to those for 5 to 10minutes earlier and calculates tendency (U=up, D=downand N=neutral).

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RVR Computer Calculations

MIDAS IV RVR compoter transmits RVR values to theDD50 digital displays, printers and operators display.

The transmission to the DD50 includes instant RVR dataand the 1 and 10 minute RVR values with following rules:

- average if the one-minute minimum and maximum doesdiffers from the average RVR less than 20% or is

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Hardware

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LP11 Block Diagram

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LR11 Block Diagram

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LPC11 Transmissometer CPU

LPC11 has

- Intel 8031 CPU chip with 7 MHz clock, 512 kb EPROM, 64 kb RAMmaintenance terminal line.

- DUART for modem line (DMX21), current loop (LPT11), frequencycounting (LMB11), peak reset and power error control.

- Analog multiplexer and 12 A/D converter.

- D/A converter.

LPC11 is used in Light Transmitter LP11 andLight Receiver LR11

- same software

- different jumper setting

Blinking LEDs indicate as follows:- Green LED blinking at 1 s interval (normal).

- Red LED indicates Reset, or an error found by star up self-test, orwatchdog circuit has given a hardware reset.

- Yellow LED blinks when LPC11 triggers the flash lamp to flash.

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LPF11 Flash Control Unit

The inputs are High voltage (750 VAC) and logic signals:

- triggering pulse for Xenon flash lamp

- flash voltage signal for controlling high voltage

Intensity control with Flash Gain, charged energyE = CU where C = capacitance and

U = charging high voltage (300-800 V)

Xenon flash lamp is a stable light source. Light pulse duration

is 1.5 micro sec. The arc is bored between 2 electrodes mounted inside a glass

bulb.

Triggering socket is a potted assembly. It is connected to theFlash Control Unit with 4 leads.

Flashing interval is 1 s normal mode and in economy mode1 s to 10 s.

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LPH11 Heating Control Board

Controls the heating of the internal optics and protectionwindow.

The electronics of optics operates best in stable

temperature. The operating temperature range is definedwith a jumper on the LPH11.

The heating of protection windows prevents surfacesfrom condensating water.

The green led light shows that window heating is on.

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Contamination Detector

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DMX21 FSK Modem

MITRAS communicates to the RVR Computer via 300 bpsleased modem line. Line speed 300 bps, Even parity, 7 data bits and 1 stop bit

The DMX21 operates in ANSWER mode and its switchesshould be Up, Middle and Down.

The LEDs indicate polling (RXD), answering (TXD), and Carrierdetected.

Troubleshooting - Cover theLEDs with hands in order to see how the LEDs are blinking.

- Check that RXD LEDblinks every 15 s when RVRComputer polls

it and the MITRASanswers with longer message (TXD LEDs blink).- Check that the green LED on the LPC11 CPU board blinks every

second. If not reset the MITRAS light transmitter LP11.

- Turn off power. Remowe the DMX21 and check the jumper

setting. Restart the LP11 again.- Check cables and their connections.

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LM11 Background Luminance Meter

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LM11 Background luminance meter

Connected to the MITRAS LP11 transmitter

Measurement range: 4 30.000 cd/m2

Spectral response range: 300700 nm, peak = 550nmInternal heating to avoid condensation

Cable totransmitter

Mechanicalinterface

Tilt adustment

Optics

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Background Luminance Meter LM11

Side view: 1 Housing2 Back plate3 Aluminium body4 Hood5 Power transistor6 Cable with connector

7 Matte glass

8 Green filter9 PIN photodiode10 Lens11 Front plate12 O-ring13 Rubber gasket

14 M4 screws

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Installation

S l ti l ti

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Selecting location

Transmissometers should be located in position whichensure representative measurements for intended purpose(see references from Users Guide).

Locations at airport (according to ICAO Annex 3):

CAT I runways

One transmissometer near the touchdown zone, 50mbaseline recommended

CAT II runways

Less than 2400m long: Two transmissometers

More than 2400m long: Three transmissometers

CAT III runways

Three transmissometers, double baseline systems with 10m

and 75m baselines recommended

S L ti t Ai t

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Sensor Locations at Airport

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Communication

I/O Lines

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I/O Lines

Output interfaces

Both the light transmitter and the light receiver have three separate serial lines which are used as follows:

Light transmitter

(Line 0) Maintenance line (CPU) RS-232C

(Line 1) to RVR computer (DUART B) modem or MITIF(Line 2) to light receiver (DUART A) current loop

Light receiver

(Line 0) Maintenance line (CPU) RS-232C

(Line 1) Auxiliary (DUART B) (RS-232C)

(Line 2) to light transmitter (DUART A) current loop

Maintenance line

The maintenance line is used for monitoring, testing and calibration purposes. Maintenance line commands aredescribed in title "Commands".

Line parameters: 300 baud, 7 data bits, 1 stop bit, even parity

Communication protocol:

- Conversation mode, character by character

- XON/XOFF handshake

- Timeout 60 seconds

Transmissometer Message

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Transmissometer Message

where

P, ID, V, B, S constant characters

X variable value

_ ASCII character 20 hex (Space)

ASCII character 0C hex (Carriage return)

ASCII character 02 hex (Start of text)

ASCII character 03 hex (End of text)

ASCII character 0A hex (Line feed)

Status of receiver 2 is set spaces if a single baseline system is used.

Status of each equipment consists of two HEX-ASCII characters.

ID_X_V_XXXXXX_B_XXXXX_SXXXXXX_

Status of receiver 2 (VI)

Status of receiver 2 (V)

Status of receiver 1 (IV)

Status of receiver 1 (III)

Status of transmitter (II)

Status of transmitter (I)

Background luminance

Visibility

Transmitter ID (0...7)

Status

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Transmitter status:

BIT.0 = 1 Meas mode (0 = OFF) (1 = ON)

BIT.1 = 2 Cont/other (0 = OFF) (1 = ON)

BIT.2 = 4 Optical surface (0 = OK) (1 = DIRTY)

BIT.3 = 8 Power supply (0 = OK) (1 = FAIL)

BIT.4 = 1 Heating (0 = OK) (1 = FAIL)

BIT.5 = 2 Flash lamp (0 = OK) (1 = WEAK)

BIT.6 = 4 BL meter (0 = OFF) (1 = ON) 1)

BIT.7 = 8 Measurement loop (0 = OK) (1 = FAIL)

Receiver status:

BIT.0 = 1 Meas mode (0 = OFF) (1 = ON)

BIT.1 = 2 Cont/other (0 = OFF) (1 = FAIL)

BIT.2 = 4 Optical surface (0 = OK) (1 = DIRTY)

BIT.3 = 8 Power supply (0 = OK) (1 = FAIL)

BIT.4 = 1 Heating (0 = OK) (1 = FAIL)

BIT.5 = 2 Calibration (0 = OK) (1 = FAIL)

BIT.6 = 4 Test (0 = OK) (1 = FAIL)

BIT.7 = 8 Consistency (0 = OK) (1 = FAIL) 2)

1)ON if the background luminance (BL) meter is set on with the command MODE2)

Only in double baseline system

Status

I

II

IV

(VI)

III

(V)

Operation and Maintenance Connection

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Operation and Maintenance Connection

Modem line to data processing unit

Normally, the data processing unit uses this line for message polling from the MITRAS light transmitter(s) but onecan also use it for maintenance purposes similar to the MITRAS maintenance line.

Line parameters:

- 300 baud, 7 data bits, 1 stop bit, even parity

- Optional 1200 baud for RS-232 interface (Not used)Communication protocol:

- Data packet protocol

- Data validity confirmed with character parity check

- Timeout 60 seconds

Commands

The MITRAS Transmissometer software has operator's commands for monitoring, testing and calibrating the unit.Commands can be given via both the maintenance line and the modem line,i.e. computer/auxiliary line.

NOTE: The line is automatically closed after 60 seconds, if no commands are given.

If you want to keep the maintenance line open, give a space as input. After a space mark, you can later give the

command you want.All commands or inputs are entered for processing by pressing ENTER or CARRIAGE RETURN. In some cases thecommand can be followed by a space and the desired parameter value(s).

OPEN Opens the line for operator commands.

OPEN for modem line.

HELP Outputs a list of commands.

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Commands

Operation and Maintenance Commands

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Operation and Maintenance Commands

The transmissometer command set consists of six different types of commands:

1. Transmissometer initializing commands for start-up

- not normally used after start-up period

2. Transmissometer initializing commands for operational use- can be used during operational use

3. Message commands

- can be used for maintenance and test purposes and also for data output

4. Mode selecting commands

- aimed at mode altering during operational use- effects of mode selecting commands must be familiar to the operator

before use

5. Routine maintenance commands

- used to maintain accurate operation of the transmissometer

- some of these commands require that the user is authorized to changeparameters, e.g. to calibrate according to visual observation

6. Special maintenance commands

- needed only when troubleshooting failures or when testing specialfunctions of the transmissometer.

Initializing Commands for Startup

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Initializing Commands for Startup

CONF With this command you may initialize (and set) the system parameters.Usually this command is used during installation only.

The system response to CONF command is presented below:

>CONF

CONFIGURATION STARTED 0000-00-00 00:44:51MITRAS SOFTWARE VERSION V3.25 2000-04-19

TRANSMITTER ID 1

SINGLE BASELINE

MEAS MODE ON

ECOM MODE ONAUTO CALIBRATION ON

JUMPER FIELD 00100000

SELECT OPERATION MODES

MEAS MODE (1=ON, 0=OFF) 1

ECON MODE (1=ON, 0=OFF) 1CONT MODE (1=ON, 0=OFF) 1

AUTO CALIBRATION (1=ON, 0=OFF) 1

BL METER (1=ON, 0=OFF) 1

AVE COUNT (1=60, 0=30) 1

Initializing Commands for Startup cont

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Initializing Commands for Startup cont.

SET THE BASELINE

BASELINE 49.40

INITIALIAZE SCALING FACTORS

K1 0.5807

K2 1.0000

K3 1.0000

K4 1.0000

TRANSMITTER OFFSET (mV) 0.0

RECEIVER OFFSET (mV) 0.0

BACKGROUND LUMINANCE SCALE KBL 10.000

INITIALIZE CALIBRATION POINTS

P 1 0.5000

P 2 0.9900

CURRENT FLASH GAIN 127

AP 24.0000

DIRTY LIMIT 0.920

CONFIGURATION END

Initializing Commands for Startup cont

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Initializing Commands for Startup cont.

PAR With this command all the necessary parameters, such as transmissometer scaling

factors, calibration points, baseline etc. can be reviewed at one glance by the operator.> PAR

SYSTEM PARAMETERS

TRANSMITTANCE SCALING FACTORS

K1 0.5807

K1A 1.0000

K2 1.0000

K3 1.0000

K4 1.0000RECEIVER OFFSET (mV) 0.0

CALIBRATION POINTS P1 0.50 P2 0.99

AVERAGING 60S, CONT ON

TRANSMITTER OFFSET (mV) 0.0

BACKGROUND LUMINANCE SCALE KBL 10.000

BASELINE 49.40FLASH GAIN 127

CONTAMINATION SCALES AP 24.0 DIRTY LIMIT 0.920

WINDOW SIGNAL SCALE 1.092

SETF Sets the flashlamp intensity, may be used for calibration and maintenance purposes.

Initializing Commands for Operational Use

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Initializing Commands for Operational Use

OPEN Reserves the communication line and serves as password to the system.

OPEN

In modem line multiple transmissometers are separately connected to the line, when

the operator is using the OPEN mode. Only the unit with correct identification (ID)

switches the carrier on.

CLOSE Is the counterpart of the OPEN command switching the carrier off and releasing theline. Must be used as the last command when maintenance session is finished.

DATE With this command you can ask for the date or change it. To change the date,input a new date after the command as follows:

>DATE 1988 02 31.

TIME With this command you can ask for the time or change it. To change the time,input a new time after the command:

>TIME 23 45.

NOTE: The time and date are mainly for test purposes and not accurate. There is no battery

back-up either.

Initializing Commands for Operational Use cont.

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Initializing Commands for Operational Use cont.

HELP Displays the transmissometer commands. Some of them are not effective in the receiver.

>HELP

MITRAS TRANSMISSOMETER COMMAND SET

MES DISPLAY MESSAGE NUMBER N

PAR DISPLAY SYSTEM PARAMETERS

STATUS DISPLAY STATUS MESSAGECLEAN INIT CONTAMINATION MEASUREMENT

CONF INIT CONFIGURATION

CAL CALIBRATION ADJUST

FCAL TWO POINT FILTER CALIBRATION

CHECK CALIBRATION CHECK

MODE SET OPERATION MODES

SETF SET FLASH LAMP GAIN

DMES RAW DATA MESSAGE

OPEN RESERVE THE COMMUNICATION LINE

CLOSE RELEASE THE COMMUNICATION LINE

ALIG ALIGNMENT HELPTCON CONTAMINATION TEST

AMES AUTOMATIC MESSAGE

FRE BL FREQUENCY INPUT TEST

AN N ANALOG INPUT TEST, CHANNEL N

RESET RESET COMMAND

TIME

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Message commands

The operator may give message commands in the form MES or in the form MES N C T, where

N is the message number; values for N are 0...5.

C is used when continuous output is desired

T is the nominal time interval between output, when certain output

interval is desired in seconds. T may range from 1 to 59 seconds.

MES 1 C 10 Gives message 1 with a 10 seconds delay between messages.

MES 0 (or MES) Output message consists of date, time, transmissometer ID, visibility,

contamination compensated visibility, background luminance and

transmissometer status:

1988-12-31 23:59:59 ID 1 V2450 CV2870 B1200 S4101

Message Commands cont.

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g

MES 1 Output message consists of date, time,

TM(I) = light transmitter flashlamp intensity

R(I) = light intensity from long baseline receiver

T(RAW) = averaged raw transmittance value

T(NOC) = non-compensated transmittance value

V(NOC) = non-compensated visibility value T(COM) = contamination compensated transmittance value

V(COM) = contamination compensated visibility value

DATE TIME TM(I) R(I) T(RAW) T(NOC) V(NOC) T(COM) V(COM)

1988-12-31 23:59:59 2543 3211 1.0500 0.8500 2450 0.8720 2870

MES 2 Output message consists of date, time,

TM(T) = light transmitter optics temperature

TM(C) = average of scaled transmitter contamination measurements

TM(WT) = light transmitter window transmittance

R(T) = light receiver optics temperature R(C) = long baseline receiver contamination measurement

R(WT) = light receiver window transmittance

DATE TIME TM(T) TM(C) TM(WTP) R(T) R(C) R(WT)

1988-02-04 12:30:59 30.8 0.9500 0.9992 31.2 0.9400 0.9985

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Message Commands cont.

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g

Certain airport systems require an automatic message sending mode. If the automatic messagemode is not used, the RVR system polls a message from Mitras.

AMES N T The AMES command defines the data message, which is sent as the

automatic message or as the default polled message. The output of the

automatic message can be seen only in normal data output (modem/MITIF),

not via a maintenance line connection.

The software versions 3.22 or later include AMES command.

N Message number (0...6). Message -1 disables the automatic message.

T Message time interval (1...255 seconds). If value is not given the previous

interval setting is used.

NOTE: The default automatic message mode setting in MIDAS RVR system is

AMES 6 15

Mode Selecting Commands

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g

MODE With this command the operator can change the functional modes of the transmissometer.

These functions are also included in the CONF command (configuration session).

The mode in question is selected simply by inputting 0 or 1.

The following modes and alternatives are available:

MEAS MODE 1) ON - visibility measurements are made

2) OFF - stand-by, flashlamp is not used

ECON MODE 1) ON - during good visibility flashing rate is reduced, for low visibility

automatically increased

- purpose: to save flashlamp and make continuous measurement possible

2) OFF - economy mode is not applied, flashing rate is fixed to 1 flash/second.

CONT MODE 1) ON - contamination compensation is used

2) OFF - no compensation is made

BL METER 1) ON - background luminance measurement is done

2) OFF - no background luminance measurement

AVE COUNT 1) 60 - 60 values used for transmittance averaging

2) 30 - 30 values used for transmittance averaging

AUTOCALIBRATION 1) ON - switches autocalibration on2) OFF - no autocalibration

Routine Maintenance Commands

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HELP Displays the transmissometer commands. All of them are not effective in the

light receiver unit

STATUS Outputs both light transmitter and light receiver(s) status information. Use

only via data processing unit or at the light transmitter.

DMES DMES displays the raw data message in double baseline format.

DMES C Continues the display until ESC is pressed.

DMES C 30 Continues the display until ESC is pressed keeping a 30 seconds' delay

between messages.

DMES command output

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TM(I) RL(I) RS(I) TL(AVE) TS(AVE) V(L) V(S) BL C(TM) C(L) C(S)

1317 1464 //// 0.9524 ////// 4615 ///// 840 0.9998 0.9983 /////

TM(I) = flash light intensity from the A/D converter

RL(I) = received intensity from the long baseline receiver

RS(I) = received intensity from the short baseline receiver in double baseline systems

TL(AVE) = scaled transmission without contamination compensation

TS(AVE) = as TL(AVE) but from the short baseline data

V(L) = visibility calculated from the upper limit corrected TL(NOC)

V(S) = visibility calculated from the upper limit corrected TS(NOC)

BL = background luminance value

C(TM) = scaled (clean = 1) contamination value of the transmitter window

C(L) = scaled contamination value of the long baseline receiver window

C(S) = scaled contamination value of the short baseline receiver window

Routine Maintenance Commands cont.

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CAL The final calibration and routine corrections can be done using this command. Software readjusts the K1 scale and initiates the autocalibration factor K1A. The new K1, K1A and the corresponding transmittance are displayed. K1 should now be close to value 1.0 (if FCAL is first carried out).

The system response to the CAL command is presented below.

>CAL 10000

K1(L) T(L)

0.756 0.9778

CALIBRATION DONE

CLEAN Give the CLEAN command only when it is necessary. The CLEAN command sets new

reference values for contamination measurement. The system response to the CLEAN

command is presented below.

>CLEAN

CONTAMINATION SIGNAL CALIBRATION IS DONE IN FEW MINUTES

Routine Maintenance Commands cont.

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CHECK

The calibration quality is checked with test filters and the CHECK command. The

software displays the 'target visibility' calculated from the current visibility taking into

account the attenuation caused by the filter in use. The software outputs the reached

visibility (VIS) value of each second. It calculates and displays the difference from the

filter visibility (VER) and the filtered reference transmittance (TER).

The system response to the CHECK command is presented below:

>CHECK 0.6

CALIBRATION CHECK

REF TRANSMITTANCE(S) AND CORRECT FILTER VISIBILITIES

CURRENT T, FILTER VISIBILITY

0.9766 421

VIS VER TER 436 15 0.005

CHECK END

Special Maintenance Commands

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FCAL The FCAL (filter calibration) command is used to determine the scaling factors K2, K3, and K4 used in

the transmittance scaling. These factors are automatically recalculated after each filter calibration

procedure. Visibility must be stable during the sequence, which takes about five minutes. Windows

should be clean. The factors K2, K3, and K4 can be initialized to the default value 1.0 with the CONF

command. The command sequence for a double baseline system is presented below.

>FCALFILTER CALIBRATION

GIVE CORRECT VISIBILITY VALUE

GIVE FILTER P1 (LOW) VALUE

SET FILTER AND TYPE ESC WHEN VALUE IS STABLE

INST(L) AVE(L) INST(S) AVE(S)

0.5510 0.5511 0.5510 0.5511

GIVE FILTER P2 (HIGH) VALUE

SET FILTER AND TYPE ESC WHEN VALUE IS STABLE

INST(L) AVE(L) INST(S) AVE(S)

0.9310 0.9320 0.9110 0.9107

NEW SCALING FACTORS K2 K3 K4

0.9078 1.1070 0.9042

ARE THE SCALES OK ? (Y/N) Y

NEW SCALES ARE UPDATED TO EEPROM

FILTER CALIBRATION DONE

Special Maintenance Commands cont.

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TCON This command is for contamination measurement test purposes. The output includes a

direct contamination signal (stray light included), reference intensity from

contamination detector light source and scaled contamination measurement value.

> TCON

CONTAMINATION MEASUREMENT TEST

SIGNAL : REF =

3908 3908 1.0000

3909 3909 1.0000

ALIG This command helps one in the alignment process during the transmissometer

installation. It displays continuously (until ESC is pressed) the maximum transmissionsince start and the difference of the latest value from the maximum. Bel-character

"beep" is echoed when a new maximum is reached.

Special Maintenance Commands cont.

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The normalizing scale for this result value is calculated by the clean command.

AN N Analog channel input test. Outputs A/D conversion result from selected channel

number N.

AN 1 Outputs continuously A/D conversion results of the light intensity measurement

channel.

AN 2 Outputs continuously A/D conversion results of the temperature measurement channel.

AN 3 Outputs continuously A/D conversion results of the contamination measurement

channel.

AN 4 Outputs continuously A/D conversion results of the contamination

measurement reference channel (contamination lamp intensity).

FRE Frequency input test for background luminance meter interface. Result is output in Hz.

>FREQ FREQUENCY INPUT

INST(1S), AVE(10S)

1020 1020

1019 1020

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Troubleshooting

Status

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MES includes status bits in 4 character hexadecimalnumber for single baseline system and 6 character fordouble baseline.

Status 4101 is OK for transmissometer with Backgroundluminance meter and 0101 for others (double baseline410101 and 010101).

STA command gives status in plain language.

Status Information

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The transmissometer output for STATUS command is:

TRANSMISSOMETER STATUS

TRANSMITTER REC(L) REC(S)

MEAS MODE ON ON ON

CONT/OTHER STATUS OK OK OK

OPTICAL SURFACE OK OK OK

POWER SUPPLY OK OK OK

HEATING OK OK OK

FLASH LAMP OK BL METER ON

MEASUREMENT LOOP OK

CONTAMIN. LAMP OK OK OK

CALIBRATION OK OK

TEMPERATURES 30.3 29.5 31.2 CONTAMINATION 0.0 0.0 0.0

MEASURED DATA

T(LONG) T(SHORT) V(L) V(S) BL C(T) C(L) C(S)

0.9523 0.9840 4608 3769 333.0 0.9998 0.9983 1.0044

Alarms Presented in Central Computer

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Alarms on operator's terminal of data processing unit

BLANK = Transmissometer operation is OK.

Transmissometer status

FAIL = Any of transmissometer status alarm bits may be set on, i.e. maintenance

needed.

OFF = Transmissometer measurement mode is OFF; the measurement mode can be set ON by maintenance commands.

Optical surface

DIRTY = The protective windows of the transmissometer should be cleaned.

Cleaning of the background luminance meter lens should be done at the

same time.

If the status DIRTY remains on after cleaning the windows,

check the operation of contamination compensation.

Status Information

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The first eight status bits of the status message are included in the standard message sent to thedata processing unit. The standard message includes 8 status bits for the light transmitter and 8status bits for the light receiver. The CONT/OTHER FAIL is used as a common failure indicationfor status bits 9, 10, 11 etc. Only bit 9 is operative and informs on contamination lamp brightness.Status bits 10, 11, etc. are not presented, they are reserved for future use.

The status information can be analyzed by means of the following alternatives:

MEAS MODE OFF - Transmissometer is in stand-by mode.

MEAS MODE ON - Normal visibility measurement is performed.

CONT/OTHER STATUS OK - Contamination lamp intensity high enough, no failures detected.

CONT/OTHER STATUS FAIL - Contamination lamp intensity below 1000 (too low) or some other failure detected.

OPTICAL SURFACE OK - No cleaning of protective windows is needed.

OPTICAL SURFACE DIRTY - Protective windows should be cleaned.

- Transmittance is decreased with four percent per window and the visibility output is slashed.

Status Information

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Transmissometer status information in detail

The corresponding status bits in the light receiver(s) operate in the same way.There are some special status bits available only at the light receiver side:

CALIBRATION OK - No calibration error detected.

CALIBRATION FAILURE - The transmittance data is continuously 0.998 which is an

unusual situation.

- The autocalibration constant K1A is less than 0.95.

- The cause can be in the light transmitter or receiver.

- If this status occurs from time to time, the optical alignment

should be checked.

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Maintenance

Periodic Maintenance

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The periodic maintenance of the transmissometers guarantees that the MITRASsystem operates within the range of its characteristics and the ICAOrecommendations.

The following table presents the recommended interval for periodic maintenance.

Maintenance Action Recommended

interval

Maximum

Interval

Operational check of

transmissometers via data

processing unit or PC

1 week 2 weeks

Cleaning of windows 1 month or as

indicated

3 months

Cleaning of windows if no

contamination compensation

1 week or as

indicated

2 weeks

Alignment and calibration check 6 months (or after

wet or frostyseason)

12 months

General checking of cables,

connectors, and parts in

electronics box and optics heads,

and Backround Luminance MeterLM11

6 months 12 months

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Calibration and Linearization check

Calibration CHECK-1

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1) Collect tools, filters, laptop terminal, cable, manual, cleaning liquid, unlintedcloth and ladder.

2) Take a copy of Calibration Sheets, visibility over 10 km and no wind overthe runway to the transmissometers.

3) Connect the Laptop PC to LP11 and start Terminal emulation-program at PC.Check STA for status and DMES C for the outputted visibility.

4) Clean optical windows of LP11, LR11 and LM11.

5) Check the current settings of the jumper (X2) from Heating Control BoardLPH11.

6) Switch the AC and heating power on both the transmitter LP11 and receiverunit(s) LR11. Inside temperature need about 30 to 60 minutes to stabilize.

7) Use STATUS command to check that transmissometer status does notindicate FAIL.

Calibration CHECK-2

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8) Use MODE command to select the correct functional modes.>MODE

SELECT OPERATION MODES

MEAS MODE (1=ON, 0=OFF) 1 1ECON MODE (1=ON, 0=OFF) 1 0

CONT MODE (1=ON, 0=OFF) 1 0

AUTO CALIBRATION (1=ON, 0=OFF) 1 0

BL METER (1=ON, 0=OFF) 1 XAVE COUNT (1=ON, 0=OFF) 1 1

9) Test the contamination measurement of the transmitter and receiver unit(s)with the TCON command. The SIGNAL and REF parameters must be at range1000...3500 when protective windows are clean. TCON command must be

given separately for both transmitter and receiver(s).10) Use DMES command to verify that the scaled contamination values C(TM)

and C(L) (and C(S) for short baseline) are close to 1 (0.96...1.04) when thewindows are clean. If the value is below 0.96, clean the windows againg andrepeat test. If the value is below 0.96 after several cleanings, give CLEAN

command. If the value is above 1.04, give CLEAN command.

Calibration CHECK-3

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11) Use the CONF command to check that the baseline length is correct.

12) In the case the Ligth Intensity Measurement Board LPI11 of the receiver isreplaced, check that the scaling factors K1, K1A, K2, K3 and K4 are initializedcorrectly before the calibration and linearization checks are performed. Use

the CONF command to write down the previous set values.

After this initialize all the scaling factors K1, K1A, K2, K3 and K4 of thecorresponding baseline(s) to 1.

13) Use DMES C command to check current visibility value V(L) (and V(S)) andcompare the value with reference visibility value. If the reference visibilityvalue and V(L) (and V(S)) correspond calibration is not needed.

If the V(L) is not close to reference value, give the correct MOR value with CALcommand

>CAL ie. > CAL 1000014) Use MODE command to retreive earlier functional modes (see step 8).

Linearization CHECK-1

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1) Check the calibration and visibility. If calibration needs adjustemnts do thecalibration procedure.

2) Use MODE command to select the correct functional modes.

>MODE

3) Clean all optical surfaces as described in calibration section.4) Use the Mitras calibrator filter set. Use the test filters 0.90, 0.50 and 0.25 and

the combination of 0.50 and 0.25 as 0.125. Clean the filters with a milddetergent and a soft, lint-free cloth.

5) Give command

> CHECK 6) Insert the test filter into the transmitter hood in such a way the filter value can

be seen from front. Wait until the VER and TER values have settled. VER is thedifference from the filter determined visibility and TER is the difference fromthe filter determined transmittance. Stop the output on the screen by pressing

the ESC key.7) Write the FILTER, CURRENT T, VISIBILITY, VIS, VER, and TER values down to

the Calibration Sheet.

Linearization CHECK-2

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8) Remove the test filter. Give the DMES C command and wait until the V(L) (andV(S)) value stabilizes back to the current visibility value without the filters.Stop the output on the screen by pressing ESC.

9) Repeat the steps from a to e with all the filters and filter combinations.

10) Check from the Calibration Sheet that the TER values are within the tolerance

|TER| < 0.02. If a test filter is out of tolerance, perform the check again. Smallamounts of pollution, dust, sand, or other fluctuations may cause erroneousresults. Also check that the test filters are clean and undamaged. In casefurther problems arise, contact Vaisala.

NOTE:

The FCAL command should not be used without permission from Vaisala.

11) Use MODE command to retreive earlier functional modes (see step 2).

Calibration and linerization check sheet

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Filter Calibration with FCAL Command

DATE INITIALS RVR ID

FILTER CURRENT T VISIBILITY VIS VER TER OK

DATE INITIALS RVR ID

FILTER CURRENT T VISIBILITY VIS VER TER OK

DATE INITIALS RVR ID

FILTER CURRENT T VISIBILITY VIS VER TER OK

DATE INITIALS RVR ID

FILTER CURRENT T VISIBILITY VIS VER TER OK

DATE INITIALS RVR ID

CORRECT VIS.

VALUE INST (L) AVE (L) INST (S) AVE (S)

FILTER P1 (LOW)

FILTER P2 (HIGH)

NEW SCALING FACTORS K2: K3: K4:

Linearization Check with CHECK CommandThe recommended visibility tolerances are

given in the table below

MOR Visibility ( metres ) Tolerance ( metres )

< 150 25

150...500 50

500...10000 100

1000...1200 200

>1200 20 % of the reference visibility

Select filters for FCAL

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Linearize the T(NOC) with parameters K1, K2, K3 and K4.At the end K1=K1A=1 and K2, K3, K4 have new values.

Choose the two (2) filter values where the LPI11 are most unlinear. Draw Tfilter/ Toutput graphics indicating TER values

Select the filters where TER are the biggest or on the different side of linar line. If the TER of very short visibility is over 0.015 consider how many meters the visibility differs from correct- often it could be only couple of

meters.

FCAL command

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FCAL Used to determine the scaling factors K2, K3 and K4 used in the transmittance scaling. These factors are recalculated automatically after FCAL procedure. See chapter 4, "Periodic maintenance", for further information. The command sequence is as follows:

>FCAL

FILTER CALIBRATION

GIVE CORRECT VISIBILITY VALUE GIVE FILTER P1 (LOW) VALUE

SET FILTER AND TYPE ESC WHEN VALUE IS STABLE

INST(L) AVE(L) INST(S) AVE(S)

0.5510 0.5511 0.5510 0.5511

GIVE FILTER P2 (HIGH) VALUE

SET FILTER AND TYPE ESC WHEN VALUE IS STABLE

INST(L) AVE(L) INST(S) AVE(S)

0.9310 0.9320 0.9110 0.9107

NEW SCALING FACTORS K2 K3 K4

0.9078 1.1070 0.9042

ARE THE SCALES OK ? ( Y / N ) Y

NEW SCALES ARE UPDATED TO EEPROM

FILTER CALIBRATION DONE

FCAL Linearization -1

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1) Check that there is no filter in the Transmitter hood.

If there is remove the filter and wait one minute for stabilizing.

Follow the stabilizing with MES 1 C command

2) Give FCAL-command with your maintenance terminal.

3) MITRAS ask for following inputs:

VISIBILITY

LOW FILTER VALUE

4) Insert the low filter into the Transmitter hood. The label showing the transmittance of filter shall be away from coming light direction.

5) Hit key when the difference between INSTANT and AVE values has settled. The difference should be less than 0.01.

If not restart the FCAL-command.

FCAL Linearization -2

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6) MITRAS asks HIGH FILTER VALUE

7) Write down INST and AVE values of low filters.

8) Insert the low filter into the Transmitter hood. The label showing

the transmittance of filter shall look at the receiver LR11.

9) Hit key when the difference between INSTANT and AVE

values has settled. The difference should be less than 0.01. If not restart the FCAL-command.

10) MITRAS shows the new K2, K3, K4 and asks:

DO YOU WANT TO STORE THE NEW VALUES INTO EEPROM? (Y=YES)

11) Write down INST and AVE values of high filter.

12) Write down the new K2, K3, K4 values.

13) Perform CHECK-command and check the results.

14) Update your CALIBRATION SHEET for History File.

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Aligning Optics

Aligning Optics

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The long baseline is always aligned first.

The alignment of the optics starts with aligning the light

transmitter LP11. Next go to the LR11.

The horizontal alignment:

The flashing light should be seen at an equal distance ateither side of the receiver unit.

The vertical alignment

The flashing light should be seen (50m baseline and 2,5m

masts) at the height of 0,5m and at the distance of 2m eachsides of the receiver unit.

Aligning Optics

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Remove the LPI11.Align the receiver unit in such a way that the flashing lightpoints roughly to the center of optics when you look throughthe filters.

Connect the LPI11 back and monitor the R(I) values withterminal.

When the R(I) is within the limits of 1500 to 3500 the

alignment is in order.

Perform a calibration check.

Optics Head Alignment

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1 = Allen screw forvertical adjustment

2 = Allen screws for horizontal adjustment

3 = Set screws for horizontal adjustment

4 = Allen screws for horizontal adjustment

Double baseline optics adjustment

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1 Knob for horizontal adjusting

Direction A

Direction A

1

1

2

2

9606-005

3

3

4

4 4 Knob for vertical locking

3 Knob for vertical adjusting

2 Knob for horizontal locking

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Replacing a Subassembly

Replacement of contamination measurement lamp

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4

5

3

7

C

6

A

9606-006

2

1

B

Replacement of flashlamp

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