Research On Key Technology Of Trapezoidal Wave Transmitter Based On Constant Voltage Clamping Technology

Along with the economic take-off of China, the status of mineral resources which isclosely related to the economic development is becoming more and more prominent.Transient electromagnetic method has advantages such as its good earth penetrating power,high probe density, a large number of reaction geological information and it has become themost widely used geophysical method. It’s application areas include energy exploration, urbanconstruction, and disaster prevention.Since the1950s, the transient electromagneticinstrument has began to appear. So far, it has developed a variety of systems, multi-instrument. The waveform quality, the strength of the electromagnetic interference, stable performance ofthe transmitter output are the important factors that determine the overall performance of thesystem. At present, the common excitation waveforms are square wave, trapezoidal wave,triangle wave and the sine wave. Square wave excited best results from the waveform of thestimulus-response. However, in most cases, the load transmitter is an inductive load. Whenthe transmitted waveform is a square wave, it is easy to generate a distortion waveform, so weuse the trapezoidal wave instead of square wave. In this article，we discuss trapezoidal wavetransmitter.Trapezoidal wave transmitter has been made certain research at home and abroad.Although the instrument has been used，in the aspect of the use of rising edge，thestabilization of the flattened segment of the trapezoidal wave，the controlled falling edge timeneed to be improved. This paper designs a trapezoidal wave transmitter based on the constantvoltage clamp technology to solve the above problems. And improves the quality of thewaveform, reduces the waveform distortion.Introduces the factors of affecting the quality of waveform，and they are verified bytheoretical calculations. By comparing the advantages and disadvantages of the variousoptions, an idea of current segmentation control has been proposed. This paper use thesimulink software to select the best option of the trapezoidal wave control. Transmitterconsists of the clamping unit, charging unit, energy transfer unit, voltage monitoring unit,main control unit, and drive protection unit.Msp430microcontroller is the core of the main control unit. Through the keyboard inputthe operating frequency of the system and in1602LCD display. Logic control circuit is usedfor the logic and gate and logic or gate operation of output signals to prevent the short-circleof the bridge road, which is caused by programming errors. By designing signal isolationcircuit between the driving signal and transmitting bridge road to improve the security of thesystem.A charging unit of the transmitter using the RC charging circuit to maintain the voltageof the flatten capacitor and the clamp capacitor. Voltage monitoring unit use VSM025A Hallvoltage sensor to get capacitor voltage. By constantly monitoring the capacitor voltage andcontrol IGBT switch off, to maintain the voltage on the capacitor stable. In order to increasethe anti-interference of the system，this paper designed a Schmitt trigger circuit, by setting a reasonable threshold width, in order to make the power switch does not frequent switching.When the emission current value drops to zero, the energy transfer unit use the boost choppercircuit to transfer the excess energy in the clamp capacitor to the power supply ends. In thisway the utilization of system power can be improved. In order to ensure the system isnormally worked, this paper reasonably choose the booster chopper circuit inductanceparameter and make the circuit work in discontinuous current working status. Driverprotection unit is the gate voltage controlled protection circuit，by controlling the gate voltagedecreasing rate, make the gate voltage drop slowly and softly to avoid the device currentovershoot. At the same time, set a certain block time, to prevent the protection circuit workfrequently when the failure occurs in the system.According to the design option，this paper design the current circle. The experimentalresults verify the correctness of theoretical analysis by using constant voltage clampingmethod to achieve controlled falling edge trapezoid current pulse. Control the rising edge ofwaveform and the falling edge of the waveform symmetry, effectively use the power of thesystem, and maintain the flat section of the waveform stable. Its falling edge has high linearity,high reliability, the output characteristics have a good anti-interference ability. This optioneffectively improves the quality of the transmitted waveform. At the same time, somesuggestions have been made for the transmitter improvement.