A TEM Transmitting System Based On Flat Section Chopping And Constant Voltage Clamp Control

The transient electromagnetic method is used as an effective detection method.And this method uses the long wire(electrical source)or the coil(magnetic source)as the load.Because the load is inductive,and the transmitting current falls freely,when the circuit is turning off.The turn-off time is too long.For this reason the method is mainly used for the detection of depth and the ability of the shallow detection is limited.The international and domestic experts carried out many extensive researches on how to shorten the current turn-off time.Among them the constant voltage clamp method has a high energy utilization rate,whose circuit is simple and the components is less,that can strengthen the received signal of the secondary field,improve the signal-to-noise ratio of the received signals.In view of the above advantages,this method is widely used.This paper analyzes the current constant voltage clamp circuit,control method and the disadvantages.After that the improved mothed is put forward.By anslyzing the transient electromagnetic transmitter's energy release loop of the load with the small resistance,combined with previous research results,this paper designs the improved constant voltage clamp circuit,and uses a new clamp capacitor discharge method.The method saves the number of required components and power supply system,reduces the complexity of the whole system,and also can reduce the electromagnetic interference during the feeding process.The improved waveform is more close to ideal trapezoidal wave and the frequency component is more abundant,the received signal amplitude is larger,has a higher signal-to-noise ratio,increases the amount of available data,at the same time the detection range is broadened,reduce the shallow area.First of all,this paper designs the parameters of the circuit,and then simulates the circuit topology according to the design parameters with the Simulink environment and verifies the rationality of the scheme.At the same time in order to improve the reliability of transmitting system in the field,according to the system working state the heat generated by different devices is analyzed,and uses the Icepak simulation environment combining with the finite element method(fem).By Altium Designer and Catia hybrid mixed modeling,using fluid solver,the thermal analysis is used to the whole system.By comparing the device temperature of natural convection and forced-air cooling.At the same time verified under the environment of high temperature,the heat dissipation of the whole system are still able to meet the requirements,so as to enhance the reliability of the whole system and speed up the design speed.In order to verify the actual effect of the whole system,the transmission circuit designed was tested and ran a indoor simulation experiment with the receiving system.The test results of the current waveform,the clamping voltage,the device temperature and the turn-off time are given.The theoretical calculation,computer simulation and measured results conform well.And compares the traditional transmitting system turn-off time with the improved transmitting system and compares the quality of the received signal using the two methods,and analyzes the measured results.Finally,all the paper is summarized and in view of the disadvantages and the next step work suggestions are put forward.