Development Of Control Device Of High-Current Transmitter With Output Edge Controllable

This article designed waveform control system and the steady flow control device of the high current transmitter with rising edge controllable, the device is achieved on the purpose of aviation exploration, and on the base of time-domain airborne electromagnetic method.Time-domain airborne electromagnetic methods is to make use of the large inductor coil hanged under the aircraft to send the electromagnetic signals into underground , during the interval of the first field sended , measure induced magnetic field (the second field) caused by the underground media with the time changed in order to detect the location of underground heterogeneous body, estimate the size and conductive properties.Aviation exploration equipment includes transmitter and receiver system, for high-resolution controlled source electromagnetic exploration, the launch is a very key aspect of the technology. Modern digital processing technique has done a lot of research to improve the method of resolution and signal to noise ratio. But all these techniques and methods are in terms of the premise that it includes target signal in the observational data. This requires that the source is able to inspire the enough strong target signal. The rapid development of Modern power devices and power electronic technologies meets the requirements of this great power .With the receiving equipment Digital and intelligent, the transmission power increased, the digital model appropriate in the forward and Reverse calculus, the explain level enhanced, the geological problem that transient electromagnetic method will be able to resolve is growing, geophysical work also includes almost all areas. Mineral exploration, construction surveying, hydrology and engineering geology survey, environmental survey and monitoring, as well as archaeological and other. In recent years, it has achieved good results in the aspects of looking for water, municipal engineering, soil salinization and pollution surveys and mapping of shallow structures such as oil.In the air Electromagnetic exploration, the transmitter output power on the inductor and the quality of the output current waveform are a direct impact on reception, thus affect the goal of physical exploration. So for the emission current waveform, this paper design the control device, its control way can be easy to be changed. The device used Calculation method to carry on the PWM current control , modulate rising edge of output current waveform in order to go man-made control of rise time and increased speed of the output current waveform, so as to achieve the required emission current waveform. Generation of PWM wave by the use of Calculation method has required the original modulation signal, that is, the required current output waveform of the mathematical expression. In theory, the rising edge of current slows down In accordance with the law of an exponential that will be satisfied. Therefore mathematical expression of modulation signal can be applied for an arbitrary exponential function. Algorithm generating exponential PWM control wave need be achieved by the PC machine, and then the process will be cured into the master CPU, through the configuration of the FPGA the host CPU results in the required emission current of the PWM waveform control signal wave. Pulse width of the output current can be changed, so we do some regulation by the method of phase-shifting, by controlling the size of phase shift signal to control the bridge switch turn-on time, and thus the host CPU configures the CPLD to realize the generation of phase shift signal. In order to ensure that in any case, When controlling a pair of positive and negative connection switch tubes two signals for exchange phase don't overlap, that is, when a switch tube doesn't turn off completely, another is not on. Then inserting a death area control signal is necessary, the death area is carried out by the CPLD, through host CPU we can adjust the size of death area time.at the premise of high current output and inductive load, On base that current slowly rises by the way of above control, in order to make the output current rise up to a particular value set by control device, and maintain a constant during the turn-on of the switch, preventing the current to Overshoot to have an effect upon steady flow, Current control measures should be taken, by the way of PWM closed-loop control, we regulate emission current in coil to gain the ends.In order to meet the emission power, the output current waveform and the steady flow, this design uses a single-chip microcomputer 51 for main control CPU, CPLD for phase shift network control, and FPGA for digital multi-mode PWM current waveform modulation, and uses touch-screen to achieve man-machine interface by the way of menu.In addition, in practical work, it is needed to maintain receiver and transmitter synchronized with a High precision in the transient electromagnetic method. conventional synchronization method between the receivers and transmitters or receivers haves wires connection, radio telemetry synchronization and high-precision clock synchronization, wires connection synchronization applies in occasions at close range. between the receivers and transmitters. radio telemetry synchronization applies in occasions at far range between the receivers and transmitters , but because of factors such as the impact of the ionosphere, it is difficult to reach a higher accuracy. High-precision quartz clock synchronization required that surrounding temperature are constant, and the quartz crystal has the problem of an aging. Global Positioning System (GPS) will not only provide space location information, but also provide high-precision timing information, the measurement and control synchronized by GPS can overcome the shortcomings of the above synchronization,it can achieve high-precision synchronization measurement without time and distance constraints.Choose the GSU-25 and Jupiter two GPS OEM boards, both of boards provide a 1PPS and 10KHz signal synchronized with 1PPS, we have Taken advantage of the two clocks signal to achieve high-precision synchronization measurement and control, synchronization accuracy is better than 100ns. After the design and debugging, the control system has achieve the desired target in all aspects , this article give the test results and the corresponding control waveform of the experiments, testing the system with satisfactory results.