Design And Research Of A New Constant Current Transmitter For The Advanced Forecast System Of Water Bearing Structure In Tunnel Construction

Nowadays,as the construction of large-scale infrastructure projects carrying out,the number and the scale of tunnel construction in China has become the largest in the world,and the construction difficulty has become the highest.In order to avoid the water inrush and chung mud geology disaster in tunnel construction,many domestic and foreign research workers has done a lot of research work on advance geological forecast of tunnel.The accuracy of the advance geological prediction has been greatly improved with the advanced forecast technology of water bearing structure in tunnel construction.Meanwhile,it also puts forward new requirements on the induced polarization instrument,especially on the current source.The traditional design of voltage source and single channel single point output current source has been unable to meet the new demand.In order to put forward a stable and reliable energy source for electrical exploration system,this thesis presents a new design of constant current transmitter with multiple outputs,high precision and strong adaptability.This paper uses the modular design methods,that the transmitter system is divided into three function parts,the inverter module,the constant current module,and a main control board.Every module was designed independently to minimize the interference,and to improve the reliability and accuracy of the transmitter system.DC/DC-DC/AC multilevel scheme was adopted in the inverter module design to realize the voltage transformation from 48VDC to 220VAC.The constant current module uses the technology of PWM pulse width modulation based on switching,to realize the 0?500mA constant current out.The maximum output of voltage is 600VDC.The mainboard mainly designed on MSP430F149.Multi-channels and high precision AD,DA chips were adopted to realize the output control and signal acquisition.In this design the transmitter receives the control signal from the receiver or a PC and gives a state feedback through the serial communication.The main control board was electrically isolated to improve the reliability;the inverter module and the six constant current modules were controlled by the main board with efficient driver.Each constant current output can be controlled separately and the constant current output channel is optional.The output mode includes constant current output and the pulse output.The transmitter system sets up a number of protective measures to give a well protection for the operating person,such as the protection circuit for the reverse connection of DC input,the indicator led,and the protection drivers.The test results show that the design of the transmitter system well meets the need of advanced forecast system on tunnel water bearing structure.The transmitter system has been applied in engineering practice.