TELEMETRY DEVELOPMENTS

S. Vidal and R. Ordiales

Networking is a central part of the Observatory technology. It includes a telemetry development for data acquisition from each field site terminal, as well as data storage and transmission through the Observatory Network, in such a way that the whole system can be operated remotely through Internet. This telemetry system will be built in two steps: first, by developing and testing of a prototype at the Estacion Experimental de Zonas Aridas (CSIC), in Almería, and second, linking the other field site terminals become linked to the prototype.

To-date only the first step has been completed. A telemetry system has been developed to link the field sites of Rambla Honda and El Cautivo, located in the Tabernas Depression, with the EEZA-CSIC headquarters in Almeria. The system specifications include the following functions:

· Implementation of geographically dispersed telemetry and monitoring based at field site terminals.

· Surveillance and control of the devices built withinin the system.

·   Data acquisition, calibration and networking.

·   Local data mass storage.

·   Data concentration, edition, purging and publishing.

·   Real time accessibility to monitoring, through Internet.

·   Public access to the final data bases through Internet.

The hardware is organised hierarchically and includes, in ascending order:

1. Specific sensors, some of which,  have been developed within the project. This is the case of the SBIB (Self Balanced Impedance Bridge) for continuous recording of volumetric soil moisture, temperature and electrical conductivity (Vidal 1996).

2.    Telemetry Stations (TSs) are front-ends or universal interfaces that link different neighbouring sensors and electrically interconnected actuators. Each TS includes a range of analogue and digital signal processors, and uses a common access protocol. A microprocessor system in each TS allows the control and surveillance of its linked devices, and provides some buffer capacity for local storage.

3.    Telemetry Areas (TAs) are clusters of neighbouring TSs linked to a Telemetry Area Controller (TAC). Each TAC is based on an industrial PC, that performs autonomous temporal local data acquisition and control functions, using radio networks. TACs are powered by 12V 600 Ah accumulators, which are charged by 90W solar panels and 140W wind generators.

4. The Main Telemetry Controler (MTC) that automatically downloads data from different TACs and builds a raw data base with original data.

5. The communication system using high and low speed data networks, wireless Internet coverage in field site terminals, and communication routing devices.

This hardware structure is better perceived through a diagram .

The software is designed to perform the following tasks:

a) Data acquisition: The Telemetry application that controls each Telemetry Area (TA) through its Telemetry Area Controller (TAC).

b) Data logging: Data are locally stored in each TAC, so a link loss does not means data loss. Later, the Telemaster application automatically downloads the data into a central computer in a single centralised raw data base called Datamaster, which is kept as a backup, where data are stored as they were recorded.

c)  Data publishing: The Teleserver application builds up a new data base from the Datamaster by controlling the automatic data supervision and calculates simple statistics by grouping the data in fixed and selected time intervals, from a few minutes to one year.

d) A non automatic data supervision is included in the Teleserver protocol. This task is performed by authorised specialists of each kind of information. They are helped by the Telescan application, and may include the occasional removal of questionable data and interpolation of missing data using a menu of available procedures . As a security measure for users, supervised data include a stamp with the supervisor’s identification.

e) Data accessibility.: A video image of the field sites, which is rp-dated every few minutes, and the raw data from the last 24h, are freely accessible in graphic format through Internet (cautivo.eeza.csic.es and rhonda.eeza.csic.es). This facility allows the real time perception of the system performance. Consolidated data are managed by  Teleweb, which is an end user client downloadable software. It allows authorised persons to download data, in selected formats, from the server to their own data bases. A guided tour through both kinds of access to data procedures provides an idea of how they work.

A diagram showing the space and time structure of the telemetry software may help in understanding its functioning.