Design Of Narrow-hole Digital X-ray Fluorescence Logging Instrument Circuit

Using drilling method to detect and validate the underground mineral rock is the most direct and effective technology in geological survey for mineral resources exploration.With the exploitation of surface ground mine in our country,the deep mineral has became the important exploration orientation and strategic layout of our country.Therefore,deep drilling will be the significant research direction of mineral resources exploration.Consequently,instruments for the high temperature and high pressure environment are also becoming important subject.For demand of deep mineral exploration,a narrow-hole digital X-ray fluorescence logging instrument under high temperature and high pressure based on the principle of energy dispersive X ray fluorescence analysis technology was designed in this paper.On the circuit design,the X-ray fluorescence logging instrument not only greatly reduces the use of analog circuits affected by environmental factors,but also the volume by introducing digital multi-channel pulse height analyzer.The X-ray fluorescence logging instrument was improved the anti-jamming ability,pulse counting rate and restrained system temperature drift by adopting digital filtering,digital accumulation and digital filtering algorithm.Hence the phenomenon that the instrument was improved the level of digital and device performance.The instrument can work in the high temperature environment temperature(-10? to 109?)and high pressure(50MPa)through the experiment,and can analysis wide element of atomic number 22 to 95(titanium-uranium).The instrument's spectral resolution reaches 3.35%,photoelectric spectrum peak drift is less than 2,the accuracy and precision of measurement is less than 20%,the element detection limits as low as 0.005%(the content of Cu is 1%,the model without well liquid conditions).The X ray fluorescence logging instrument is tested by the model well and the scientific research well in the field,Undeniably,the indexes and the performance stability meet the design requirement.Specific contents are as follows:(1)According to the high temperature and high pressure environment of small-bore and deep well,the overall design of the hardware circuit of X-ray fluorescence logging system was proposed.This scheme adopts digital multi-channel pulse height analyzer to replace traditional multi-channel pulse height analyzer that is susceptible to environmental temperature and other factors in the X-ray fluorescence logging hardware circuit,greatly improve the digital level of X-ray fluorescence logging instrument and enhance the level of resisting to high temperature and high pressure environment.This logging instrument can analyse elements in the high temperature of 109 ? and 50 mpa high-pressure of 50 MPa,its spectral resolution can reach 3.35%,and photoelectric spectrum peak drift is less than 2.(2)According to the analysis of the detector output signal,an analog front end circuit was designed in digital multi-channel pulse height analyzer,included CR differential shaping circuit,signal amplification circuit and anti-aliasing filter circuit.CR differential shaping circuit was designed by adopting low noise,distortion voltage feedback operational amplifiers ADA4841 and CR differential circuit,where the operational amplifier was used to isolate and drive.Besides,the CR differential circuit was used to filter 1.7 Hz low frequency sawtooth reset of the detector output and to shape the signals produced by X-ray.We make time constant ?=8?s and cut-off frequency fc=19.9kHz,which successfully filtered the 1.7Hz reset signal and shaped the signal generated by X-ray to be negative Index pulse signal by setting the value of resistance and capacitance.Signal amplifying circuit was designed to control gain by using two high-speed AD829 operational amplifiers and analog switch.The first amplifier can reach 40 times,coupled with the second amplifier reachs 4 times,resulted the whole realize 160 times.The anti-aliasing filter circuit is composed of two three-level RC filter circuit and the voltage follower of the operation amplifier AD829,which has a cut-off frequency of 10.6 MH.(3)According to the characteristics of the analog front-end circuit output signal,high speed A/D conversion circuit was designed to realize the maximum 200 kps pulse passing rate,abandoned peak retainer and other analog circuits.Back-end logic circuit part adopts FPGA + ARM combination to process digital data of high speed A/D conversion circuit output,specifically,the data will be transfered to the terminal display through CAN bus—transmission distance of CAN bus can reach 10 km.(4)Logging powe system is designed into high voltage power supply system and low voltage power supply system.Aiming at 110V-220 V high voltage DC supply for Si-PIN detector,the design of high voltage DC power supply system with small volume and low ripple is realized by using PWM switch control?Royer resonant circuit and voltage-doubling rectifing circuit.The high voltage DC power supply can be continuously adjusted at 0-200 V,the ripple is as low as 0.01%,and the stability is better than 2%/10 h.The low-voltage power supply system provides + 5VD digital power supply,+ 5VA and-5VA analog power supplies for digital multi-channel pulse height analyzer.+5VD digital power supply was designed with ultra-low quiescent current switching regulator LT8610.The current consumption is only 2.5?A when the output voltage is 5V under no load conditions.Under 1A,the efficiency of +5VD digital power supply can be up to 96% when the input voltage is 12 V and the output voltage is 5V.+5VA power supply was designed by using low ripple regulator LT3970,implemented the output ripple voltage is less than 5mVpp.The-5VA power supply uses ultra-low noise LT1931 chip,which can achieve-5V / 350 mA output at 12 V input voltage,coupled with output ultra-low voltage ripples can be close to 1mVpp by using ceramic capacitors.