Timing synchronization using 1PPS for crosswell electromagnetic logging tools

After analyzing the shortcomings of existing synchronization methods based on GPS and the research status of synchronization for Crosswell Electromagnetic Imaging Logging Tool(CEMIT), a feasible synchronization method combined the actual conditions of CEMIT with the basis of existing research is proposed. First of all, GPS receiver provides a high accurate 1PPS, which received by Surface System, and then it will be broadened and driven to achieve transmission through the 7000m cable. After transmission delay between Surface System and Downhole System has been measured, the synchronization clock in Downhole System will be calibrated according to the delay information. Lastly, the synchronization between receiver and transmitter is achieved. Experiment results show that synchronization clock error is less than 1us between receiver clock and transmitter clock, which corresponds to a phase accuracy of 0.36 degree at 1 KHz. The method can meet the needs of phase difference measurement in CEMIT.