1. CTIO Weather Station renewal
E. Bustos
La Serena, Aug. 28th 2009

2. Summary
Current system on Tololo is a temporary solution build after lightning strike on Sept. 2008
The Weather Tower (24m) needs a replacement urgently
More reliable measurements are required
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3. Background
Wind speed is one the most important weather measurements for telescope operations. The reliable measurement under bad weather conditions is a must. According with our experience on Site Testing, mechanical wind sensors are not reliable under snow and rain conditions on astronomical sites and on observatories. They have to be check once per month and usually they have to be replaced almost every winter because are destroyed or damaged by dust or rusted.
The ultrasonic wind sensor technology has demonstrated to be very reliable and usually these sensors don’t need service in years.
The state-of-the-art of weather sensors is the smart sensors technology. These are sensors with embedded communication protocols and they can be connected directly to the computer without a logger. This is an advantage when a calibration or a quick check is required and when software interface is developed.

4. Background
Nowadays weather multi-sensors are been developed. These units can measure virtually all weather variables in one unit. A single operator can install a new unit in minutes by connecting just one cable.
CTIO requires a new weather station tower soon, because the tower used as a temporary location has to be removed in 2 months because a new telescope will be installed in the Columbia Dome. By other hand, the current CTIO weather tower reached the end of its life and it can’t be used anymore.
The current tower altitude is 24 meters, but only the last 12 meters are actually above the Tololo summit.
In order to research Blanco Dome condition, the weather sensors have to be at least at the altitude of the Blanco Primary Mirror. So the new tower must be more than 12m above the summit.

5. Sensors proposed System with no moving parts
Redundancy for wind measurements
Smart sensors: embedded serial protocol without dataloggers & accessories.
Low power consumption (suitable for solar power)
Easy installation and maintenance: one bolt clamp, installation without extra cables.
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6. WXT520: multiparameter transmiter
Temperature
Pressure
R. Humidity
Wind speed and direction
Rain
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Vaisala WXT520

7. WS425: Ultrasonic Wind Sensor
Very reliable and free of maintenance for years.
With heater option for better behavior under snow conditions
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Vaisala WS425

8. New Tower A new 40 meters tower is needed:
Sensors will be at the same height of Blanco Primary mirror (~24 meters)
CTIO Telescopes visibility is not blocked:
1m Tel. minimum observation angle will be ~27o
28 meters effective height (not 12m)
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9. 40m Tower

10. 40m Tower

11. Power and Communications
Wireless communications
Reduce installation and maintenance costs
Reduce effects of lightning strikes
Solar Power System
Low installation costs
Reduce effects of lightning and surge events
Solar panels and cabinet available

12. Cost WXT520: multiparameter sensor(*) 2500
WS425: ultrasonic wind sensor (**)
2800
Surge protectors for sensors
650
Wireless communication equipment
1000
Grounding system + sensor/communications housing
1500
Acquisition Computer (rack-mounted)
Solar power system (***)
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(*) including accessories
(**) including accessories and a wind field verifier
(***) includes AGM batteries, load regulator (PV panels and battery housing are already available)

13. Work time estimation 1 man/week for specification and purchasing
4 man/week for tower installation by contractors
1 man/week for cabling and sensor installation
1 man/week for interface development and web integration
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14. Comparative chart
Monitor Sensors Pty. Is the Australian brand of equipment used on site testing by CTIO and TMT, they are in use in LSST site and SOAR. Both the wind speed and the wind direction sensors are mechanicals There are 2 types of anemometers: AN2 and AN3. They are smart sensors and the communications is based on a custom serial protocol Monibus. To transform in a RS232 protocol an interface is required. The rainfall sensor has moving parts.
RM Young is the brand used by the CTIO Weather Station. Those sensors listed were selected because they have similar specs with the used and proposed sensors. Not all the sensors are 都mart� so in case of the Temperature/Humidity sensors and the precipitation gauge they require a logger. Both the B. Pressure sensor and the Ultrasonic Wind sensor have serial communication.
Monitor Sensors Pty. has been used by CTIO & TMT Site Testing
RM Young is the brand used by CTIO in the old weather station.