MEASURING INSTRUMENTS AND METHODS for AWOS

Generally, when basic meteorological sensors are sampled, several samples are taken into a count so 1 minute average value can contain 4 to 20 samples. In case all samples are not available, certain percentage (40%) of samples is allowed to be missing, and the computation is still performed and respective calculated value is reported.

Atmospheric Pressure Sensor PTB 330 

Digital Barometer PTB330 measures atmospheric pressure. It contains 3 independent transducers. The barometer is located in the Automatic Weather Station (AWS) enclosure. 

 

Air Temperature and Humidity Sensor HMP155 

 

Air  temperature  is  measured  by  a  platinum  type  (PT100)  sensor  and  relative  humidity  is  measured  by  a  thin  film  type  sensor  Vaisala  Humicap  180.  The  changes  of  humidity  are  detected  by  change  of  capacitance  in  polymer  layer  of  the  sensor.  Both the sensors are installed inside of naturally ventilated solar radiation shield, protecting measurement result from effect of direct solar radiation. 

WMT700 Ultrasonic Wind Sensor 

The WMT700 Wind Sensors uses ultrasound to determine horizontal wind speed and direction. The WMT700 is installed on the instrument mast parallel to the runway at the touchdown zone of the runway. The measurement  principle  is  based  on  transit  time,  the time  it  takes  for ultrasound to travel from one transducer to another, depending on the wind  speed  along  the  ultrasonic  path.  The  method  for  one  path  is repeated  to  determine  the  wind  speed  along  each  of  the  three  paths which are offset by 120º with respect to each other. The microcontroller computes  the  wind  speed  and  direction,  as  well  as  the  rectangular components and reports them to the data logging system. The WMT700 series  is  available  in  two  models:  Standard  WMT702 with  heating  in transducers  and  WMT  703  with  heating  in  transducers and measurement arms.

Present Weather Sensor FS11P

Installed Runway Visible Range ( FS11 P )

Visibility and Present Weather Sensor FS11P the FS11P Sensor provides measurements related to meteorological visibility.  It is specially designed for Runway Visual Range (RVR) applications.  The sensor can be used for visibility measurements on airfields and remote automatic weather stations. The FS11P Sensor is a microprocessor controlled forward scatter measuring instrument.  It  will  transmit  pulses  of  infrared  light  and detect  the  light  scattered  by  airborne  particles.  The  intensity  of  the received  pulses  are  measured  and  converted  to  Meteorological  Optical Range (MOR) by proprietary algorithms, based on extensive calibration against the Transmissometer. Visibility Meter automatically compensates for visibility measurement errors caused by window contamination.

The  FS11P  sensor  uses  a  115/230  VAC  power  supply  and  a  single  pair modem  line  for communication.  The instrument sends visibility and status messages to a data processing system. A set of built-in commands and test routines are provided for the configuration and monitoring of the multiple visibility meter functions.

Ceilometer CL31

Ceilometer CL31 measures cloud heights and vertical visibilities.  The CL31 employs pulsed diode laser LIDAR technology, where short and powerful laser pulses are sent out in a vertical ornear-vertical direction. The  reflection  of  light  -  backscatter  -  caused  by  haze,  fog,  mist,  virga, precipitation and clouds is measured as the laser pulses traverse the sky. The resulting backscatter profile, i.e. signal versus height, is stored and processed and the cloud bases are detected. The CL31 is able to detect three cloud layers simultaneously.  Besides cloud  layers  it  detects  whether  there  is  precipitation  or  other obstructions  to  vision.  It  detects  the  cloud  base  reliably  in  fog,  rain, snow  and  haze.  If the cloud base is obscured, the CL31 measures and reports the vertical visibility. Nocalibration on the field is needed. The cloud height and vertical visibility data are sent to the central computer every 15 seconds via modem communication. The ceilometer CL31 is typically located close to touchdown point or at the  final  200  -  1000  m  from  the  threshold  or  at  the middle  marker station.  Where  the  ceilometer is  located  at  the  middle  marker,  avoid installation  close  to  the  middle  marker  antenna.  Keep a distance of a minimum of 5 meters from the antenna and antenna support devices. It is  recommended  to  operate  the  unit  in  a  slightly  tilted  angle  (10...20°from  vertical)  wherever  possible.  Unless  a  tropics  window  is  used,  the ceilometer  must  never  be  directed  so  that  the  sun  shines  directly  into the optics of the unit. 

Automatic Weather Station (MAWS301) 

Installed MAWS in Masts

An Automatic Weather Station (AWS) is located at RWY ends. It collects data from wind, rain, pressure, temperature and humidity sensors and forwards it to CDU via F/O.  The  unit  includes  a  data  logger  QML201 which  is  based  on  32-bit  microprocessor  architecture  and programmable  to  give  optimum  measurement  response.  Several optional input ports are available for future expansions. AWS is located in a stainless steel enclosure with radiation shield. The QML201 is a complete data logger with a highly specialized single board computer (CPU) which makes the measurements and controls all system functions.  The  simplicity  of  the  single  board  approach  reduces the  need  for  excess  interconnecting  wires  and  cables.  It  also  greatly enhances  reliability  and  reduces  the  cost  of  maintaining  a  spare  part stock. This board contains the 32-bit Motorola CPU for data processing and 10 differential (20 single ended) analog sensor inputs.  There  are also  three  (3)  frequency  sensor  interfaces,  the  16  bit  A/D  converter RS232  and  RS-485  serial  ports,  a  real-time-clock  and a  power  supply also  providing  sensor  excitations.  The  QML201  has  an  internal  Real Time-Clock  with  a  resolution  of  1  second (internally  in  milliseconds) and stability better than 20 seconds/month. The RTC is backed up with

a lithium battery. There is also the possibility of synchronizing the RTC from the central data collection software. Optional modules include, for example, a Compact Flash (CF) memory card, various communication modules and a built-in pressure transducer. The  printed  board  uses  the  latest  SMT  and  CPLD  (Complex Programmable  Logic  Device)  technologies  and  is  uniformly  coated  for better protection  and  reliability  in  high  humidity  environments.  Each the maintenance terminal connection (RS-232, COM0) also has transzorb diodes in its inputs. When long signal cables are needed, these will be equipped with optional devices for surge voltage protection. These  surge  arrestors  consist  of  a  combination  of  VDR,  gas-filled discharge  tube,  transzorb  diodes  and  coils,  thus  providing  excellent protection.  These DIN-rail mountable devices are easy to change without any special tools.

 

Met Farm at RWY 02 side

Installed sensors on Mast