| Oil drilling technology developed rapidly.Underground drilling equipments collected lots of data while drilling,which need to be transmitted to the ground in real-time.but at present,the main data transmission technology,mud-pulse telemetry,with the rate of only 3~5bps,can not meet the requirements.To this end,the data transmission while drilling based on electromagnetic induction were proposed.It is able to reach very high data transfer rate.In this paper,a single coupler circuit model is established,and the parameters of the model are given.On this basis,the circuit model of the electromagnetic transmission channel is established.Simulation by Pspice software is compared with the actual test to verify the accuracy of the channel model.Various characteristics of the transmission channel of magnetic induction can be obtained by the simulation of the model using the software.This paper gives the frequency characteristics of signal transmission,and the choice of the frequency for the communication signal is also provided.In this paper,Frequency shift keying(FSK)is chosen as the digital modulation method.A modem circuit is designed based on AD9850 and DSP,and the software of the modem is written.The maximum data transfer rate of the modem is 75 kbps.Then another modem circuit is designed based on AD9832 and NE564,the circuit has reached 115.2kbps data transfer rate in the experimental channel and achieved a stable and reliable real-time data transmission.Finally the experimental system of electromagnetic induction transmission is established.The system composed of 10 coupler and four simulated drill pipe.The results of electromagnetic induction data transmission experiment show that the system is of practical value.The maximum data transfer rate is up to 230.4kbps,bit error rate is less than 10-7. |
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