Distributed data acquisition unit based on GPS and ZigBee for electromagnetic exploration

The design and implementation of the distributed data acquisition unit (DDAU), which is based on GPS synchronization and ZigBee, are described. The DDAU is used in three-dimensional electromagnetic exploration targeted for oil and gas (hydrocarbon) detection. It is composed of data acquisition and DSP module, embedded control module, GPS sync and timing module, and power supply module. The data acquisition and DSP module, which owns 4 signal channels, amplifies, converts, and processes weak signals from electric field and magnetic field sensors. The embedded control module, which includes ZigBee OEM board, temperature sensor, 10M bps Ethernet, 4 UARTs, 4 SPIs, 2 SSCs, 8 GB NAND flash and 8 MB NOR flash, is based on AT91RM9200 and Linux 2.6. The GPS sync and timing module, which ensures precise synchronized data acquisition in field, generates sync signal and precise clock for A/D convertor and digital signal processing. A large-scale distributed data acquisition system can be built by combining large amount of DDAUs to a wireless sensor network based on ZigBee. The testing result showed that the RMS noise of each analog channel was less than 0.63 uV, and the THD is less than -111 dB.