CFHT Logo   Weather Tower Documentation


  • OVERVIEW:
The CFHT-Gemini Weather Tower Control System (Weather Tower System) is a joint venture between the Canada-France-Hawaii Telescope Corporation and the Gemini 8-Meter Telescope Project.  The system is designed to collect the weather data from the CFHT tower mounted sensors, transmit data to the CFHT dome and provide weather data for the Gemini Telescope.

This portion of the manual  id dedicated to information associated with the collection of data from the tower sensors, transmission to the CFHT dome as well as providing the weather data to the CFHT Data Logger.  The tower sensors include measurements of wind speed,  wind direction, ground level  relative humidity and air temperature.  This data is read by an Allen Bradley modular unit and transmitted via fiber optic to the CFHT dome.  A second Allen Bradley unit receives the transmitted data nd manipulates it for displays and the CFHT Data Logger (data-logger). 


Simple block diagram of system.  Drawing is not to scale.



  • INTRODUCTION:
The Weather Tower Control Junction Box is mounted at the tower approximately 6 feet off the ground.

    Weather Tower Control Junction Box

The junction box contains the necessary electronics to collect and transmit the data from the sensors at the tower to the CFHT observatory building. 

The inside of the junction box can be seen below.
Inside the Weather Tower Control Junction Box
Top:            Anemometer/Vane Heater Control
Btm-Lft:      Terminal Board Electronics
Btm-Rht:      Allen Bradley Modular Unit

Between AB Unit and terminal board (Silver Object) RS232 to Fiber Converter.


  • Allen Bradley Unit:
    • The Allen Bradley unit collects, manipulate and drive the data collected from the tower sensors.  The unit consists of several modules mounted in their proprietary rack.
    • One rack is mounted at the base of the tower in the tower junction box and the other is mounted in CFHT's control room. 





Allen Bradley unit mounted in Tower Junction Box.
L-R:  Power Supply, SLC5/03 processor, 1746-NI4 Analog Input Module

Key Switch normally switched to the left "Run" position.  Switched to "REM" for remote programming. 

Telebyte Tech  RS232 to fiber converter mounted to left of Allen Bradley unit.

  • The terminal board contains electronics used to interface the wind speed and direction signals to the Allen Bradley Analog Input Module.  Also,  24 volt reference sent to RH/Temp sensor passes through this board on the very right side. RH/Temp signals coming back from their sensors pass through this board on their way to the Allen Bradley Analog Input Module.  Finally, not pictured but mounted at this location is the power switch used to turn power on and off to the Allen Bradley unit.
L-R Components on board.
5K potentiometer and 10K 1% resistor used for wind speed calibration.

Regulator takes 24Vdc and creates +5Vdc reference for wind direction (wind direction is a 0-5K potentiometer).

Terminal connections at top go out to sensors.  Terminal connections at bottom are wire to Allen Bradley unit. 

  • Hydro-Tech Wind Speed (WS-3) and Direction Sensor (WD-3):

    The Hydro-Tech wind speed (anemometer) and direction (vane) sensors are rugged, electrically heated units designed for use atop our mountainous environment.  These units are mounted atop the CFHT tower.  The unit consists of two pieces and its own heater control unit to prevent icing,  The anemometer is a DC tach model which puts out a proportional voltage per RPM of rotation.  The vane uses a  5K ohm potentiometer to indicate wind direction.
Anemometer:
Heater cable seen coming down the right side.

Vane:
Heater cable coming down left side of post.
Signal cable coming out from bottom.

Weather Head:
Four cables entering weather head from Anemometer and Vane.
Two cables are signal cables and two are heater cables.

  • The electronic controls for the heaters used to prevent the anemometer and vane from icing in severe freezing storms is mounted inside top of the junction box.  This panel is divided into two parts.  The two parts are  identical controls for both the anemometer and vane.   There is a breaker to turn power on and off.  The knob is used to set the controlled percent of maximum heat.  70% is normal.  The toggle switch works in conjunction with the red indicator light.  When switched to the “input” position, the light indicates the presence of input AC power.  When switched up to the “output” position, the light is indicating relative power to the heaters themselves.
Anemometer/Vane Heater Controls:
Dials set to 70% sets heat.  Toggle switch
monitoring (Red Indicator) to input
AC power or power to heaters.  Grn/Whit wires
are heat sense lines coming back from
heater.  AC In and AC Out to heaters are
connected in back of panel for safety.

  • Vaisala HMP45A Humidity/Temperature Sensor:

    The Vaisala humidity/temperature sensor (probe) is housed in an aspirated radiation shield approximately 10 feet up from the base of the tower.  The sensor uses a 7-35 volt input and provides two output voltages (0-1 volt).  -40 to +60 degrees C  and  0-100 percent RH represented by this voltage. 





Vaisala HMP45A Relative Humidity/Temperature sensor:

Top photo is of sensor prior to installation into radiation shield

Bottom photo is of sensor removed from head.  This allows easy
replacement of the sensor. 



Aspirated radiation shield.  Uses Comair AC fan to circulate
ambient air through tube and across sensor.

Radiation shield junction box:
MS Connectors:
Top:  AC Fan Power
Middle:  RH/Temp signal wires from sensor to PLC
Bottom:  Sensor Power from PLC

Close up of radiation shield RH and Temperature wiring:
Wires from bottom of terminal block go out to sensor.
Wires from top of terminal block go back to PLC controller.



  • Telebyte Technology, Inc Fiber Optic Converter:

    • The RS-232 data is transmitted from one Allen Bradley unit at the tower to the CFHT dome via fiber optic link. <><>This conversion is done via Telebyte Technology’s 271F/ST converter.
Telebyte Tech Inc. RS232 to fiber converter.
Notice DB25 connector entering converter from top.
Three wire hook up from DB9 of AB unit. Fiber
exits control junction box and enters AC junction box below
and goes through conduit to CFHT building.
    
AC Junction box pictured far left.

Inside AC junction box:
Notice fiber optic cable entering the junction box
from the left side.  The cable exits through the bottom and enters the building
via a junction box mounted on the wall inside the main stairwell.


  • The data enters the CFHT Observatory via pair of fiber optic which is laid in conduit underground.  The conduit is connected to a junction box (JBW2) located on the wall in the main stair well of the building.   In this junction box, the data is converted from fiber to RS232 and goes up to the fourth floor control room into another junction box (JBW3) mounted on the wall in back of the control console.   From there, the data leaves the junction box and goes to the second Allen Bradley unit mounted close by.
Telebyte Tech Inc. RS232 to fiber converter (Obs Bldg).
Mounted in junction box at base of  main stair well to left
of door.  Notice fiber entering unit from right side with data from tower.
DB25 connector takes serial data (2, 3, 7) and puts on
terminal block in junction box.

Close up of serial communications wire hook up in ground floor junction box.
Yellow, green, brown are pins 2, 3, 7 respectively of DB25 connector.
.These wires correspond to wires 38, 39, 40 in the junction box.

  • The data is taken from the junction box mounted in the back of the control room and wired directly to the RS232 port of the Allen Bradley unit.   The software in the control room Allen Bradley unit receives the data and separately scales analog outputs to drive the appropriate gauges or data logger lines.
Serial hook up in junction box in back of telescope control room.
Red, Green, Black correspond to 2, 3, 7 respectively.

Control Room Allen Bradley Unit:
L-R Power supply, SLC-5/03 Processor,
two 1746-NO4V 4 channel analog output modules,
1746-NIO4V Analog 2 input, 2 output module.

First 1746-NO4V module used to drive data logger.
Second 1746-NO4V module used to drive control room gauges.
Last analog module in far right slot is used for CFHT dome RH/Temp
measurement (not yet used).