data acquisition

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Data logging devices (Fig. 1) interrogate a series of environmental sensors. Signals are tension, resistance, counter, and digital (SDI-12), and are registered in 1s to 15 min intervals. The dataloggers are connected to a ethernet LAN which is linked to the intranet of the observatory via an optical fibre. They have an internal memory for continuous data logging, and an external USB memory where, in our case, daily copies of the data are stored and made available via ftp.  The loggers are monitored and configured using a webinterface. They are powered by an external 24V DC power supply, and an internal battery allows autonomy in case of mains failure. Four multiplexers (Fig. 2) are placed at the outer end of each arm of the cross allowing to reduce cable lengths of the sensors.

 

Fig 1.: DATATAKER datalogger DT-80 (Thermofinigan, AU)   Fig. 2: Multiplexer CEM20

Using Modbus communication via the ethernet, data is exchanged between the logging devices and the automate (Fig. 3) driving the rain exclusion covers

 
Fig. 3: Automate SAIA PCD3