Abstract: Introduced one kind of pulse turbulent flow non-destructive inspection system uses multi-profile special-purpose PWM signal generating device design. This signal generating device take the monolithic integrated circuit as the core control unit, through realizes to the periphery chip’s control to the output wave shape frequency, the voltage peak-to-peak value, the dutyfactor continual adjustment, and can carry on the real time display to the movement signal parameter. After the experimental verification, this signal generating device is advantageous for the observation and the adjustment, satisfies the pulse turbulent flow examination system to completely the drive signal the request.
Key word: Non-destructive inspection; Pulse turbulent flow; PWM; Monolithic integrated circuit
1 introduction
The turbulent flow non-destructive inspection takes the non-destructive inspection to apply one of most widespread methods, has the sensor structure to be simple, the sensitivity is high, measuring range big, not medium influences, antijamming ability and so on greasy dirt strong and so on merits, has been widely applied in the metallurgy, the machinery, the chemical industry, the aviation and so on many Industry sectors. However as a result of the skin effect influence, is often limited to the conductor surface and in the Asian surface layer examination, this caused its examination application scope to receive the very big limit. But, if examination coil under pulse excitation function, because in the signal impulse includes richly, the continual frequency component, therefore in the examination coil obtains the information not only contained was examined the test sample the surface, the Asian surface information, but also contained its depth information, could carries on the quantitative evaluation to the material quality as well as the flaw. But parameter and so on signal impulse’s profile, frequency, peak-to-peak value, dutyfactor changes have the different influence to the test result. Therefore to obtain under the different pulse excitation the test result. Has manufactured this special-purpose high accuracy high efficiency signal impulse generator especially.
2 Hardware design
In order to satisfy the experimental request, this signal generating device’s design goal is can have many profiles, and the frequency, the voltage, the dutyfactor may adjust high accuracy, high efficiency signal impulse. This signal generating device hardware part: Through the monolithic integrated circuit control digital-analog conversion chip output different profile, undergoes two levels of enlargements as well as the high frequency analog switch after again carries on the wave shaping obtains a more perfect profile, then uses a group of Darington tube to carry on the electric current enlargement to obtain compares the high efficiency the signal impulse. System hardware diagram like chart 1 shows.
Figure 1 system hardware diagram
2.1 demonstrations and keyboard and monolithic integrated circuit interface circuit design
The observation and the adjustment are convenient for the experiment process, we established to the output wave shape overvoltage, the dutyfactor, frequency have managed the LED demonstration as well as to the profile, the profile overvoltage, the dutyfactor, the frequency keyboard selection. And, LED demonstrated that the arrangement is as follows: The voltage manages by carries on the demonstration, the dutyfactor manages by two, the frequency has three to manage carries on the demonstration; The keyboard arrangement is as follows: Profile choice key 2, voltage regulation key 2, frequency control key 2, dutyfactor adjustment key 2. Six manage demonstrates and the monolithic integrated circuit interface circuit like chart 2 shows, in the chart uses six 74LS164 is the LED tube string enters combines the shifting accumulation, P3.3 uses in control display’s input, 2×4 the keyboard and monolithic integrated circuit interface circuit like chart 2 shows.
Figure 2 LE D demonstration and monolithic integrated circuit interface circuit
Figure 3 2×4 keyboard and monolithic integrated circuit interface circuit
2.2 monolithic integrated circuits control the D/A chip the interface circuit design
The D/A chip selects DAC0832 which Corporation produces by National Semiconductor, it is 20 pin double row in-line type low power loss CMOS component, its interior has two level of data registers, completes 8 electric current D/A transformation. Must obtain satisfies the profile which the experiment requests, but must realize through the DAC0832 output termination operational amplifier. For matches with the DAC0832 high rate of rotation throw over, here selects National Semiconductor Corporation to produce the LF357 operational amplifier with it coordination use. LF357 not only has the high slewing rate, and has: The low input bias current, inputs the displacement electric current (is only lowly 30pA), the low input noise electric current (is only
), high syntype rejection ratio, wideband gain. The monolithic integrated circuit controls the D/A chip junction circuit like chart 4 to show.
Figure 4 D/A chip interface circuit
2.3 wave shapings and amplifying circuit design
Because outputs after DAC0832 and the external connection operational amplifier the profile was not very still smooth, when has DAC0832 carries on the D/A transformation the rise along, must therefore carry on the reshaping to the output wave shape to satisfy our experiment request. The wave shaping chip selects MAX4624, it is the low opening resistance which MAXIM Corporation produces, after the low voltage gathers first, operates the single tool double throw analog switch. It has had the current protection; Can the fast make and break, closed and the separation greatest time be 50ns; The electric circuit opening resistance is very low, when the electric power supply is 5 volts, when Ron is 1 ohm, the electric power supply is 3 volts, Ron is 2 ohms, i.e., the electric circuit internal switch noise is low. In order to obtain compares the high efficiency the signal impulse, must enlarges after the second level the output signal carry on the electric current to enlarge, here selects two JFET tubes to compose a pair of Darington tube to carry on the electric current enlargement. Meanwhile to satisfy time the experiment to different power signal impulse request, second level of enlargement gain design for adjustable. Its junction circuit like chart 5 shows.
Figure 5 wave shaping and amplifying circuit design
As the special-purpose PWM signal impulse generator, the common great instantaneous change, the entire line often met the power source lead wire to have the electric circuit resonance by now, produces the peak unwanted signal, eliminates plants the disturbance the means to be possible adds on the suitable decoupling electric capacity between the chip and the power line and the place. What here uses is two electric capacity parallel methods.
3 software designs
According to the front hardware description, its software realizes like Figure 6, 7 to show. The master routine completes the procedure the initialization, the circulation waited for that accepts and produces the corresponding signal impulse by the keyboard entry data, first determined that the output signal the profile, the initial frequency and act according to its profile and at the beginning of the frequency carry on the code, saves in monolithic integrated circuit’s ROM, then sends in by certain time-gap these digital quantity the D/A chip to carry on the transformation output, to obtain the different pulse frequency, may input the D/A chip through the change the data gap to change the output frequency.
Figure 6 master routine flow chart
Figure 7 PWM subroutine flow chart
4 concluding remark
This signal generating device compares with other has the following merit:①Compares the discrete component signal generating device saying that has the frequency to be high, the work is stable, easy to debug and so on characteristics;②The special-purpose DDS chip’s signal generating device says, has the structure to be simple, cost low status characteristic.
This signal generating device various parameters regulation band is: The pulse dutyfactor regulation band is 2-100%; The voltage regulation scope is 0-5.0V, step-by-steps 0.02V; The frequency control scope is 1KHz-100KHz. Through indicated to the software hardware’s debugging and the examination that this system’s software and the hardware can the very good work, be able to satisfy the pulse turbulent flow crack detection experiment’s special request. Because and uses the keyboard accommodation mode as well as special-purpose LED demonstrated that causes our experiment to be more convenient. But as a result of DAC0832 chip setup time limit (its setup time for 1μs), even if uses the high frequency analog switch to carry on the wave shaping, its output wave shape was not very still perfect. But if replaces DAC0832 with other setup time short D/A transformation chip, if DAC712, then can obtain the very perfect profile.
Reference:
[1] Zhu Dinghua, wears your equality, the monolithic microcomputer principle with applies the [M]. Beijing Jiaotong University Publishing house, the Tsinghua University publishing house, 2003
[2]International Semiconductor Corporation: DAC0832 technical data
[3] International Semiconductor Corporation: DAC712 technical data
[4] International Semiconductor Corporation: LF357 technical data
[5]MAXIUM Corporation: MAX4624 technical data
