Multi-channel Data Acquisition System Development And Debugging

According to the deficiency existing in domestic laser granularity instrument in terms ofperformance, in this paper, multi-channel data acquisition system of laser particle sizer hascarried on the design and research. At the same time, in order to design the data acquisitionsystems that can perform the correct reasonable evaluation, and the corresponding test systemdesign, the acquisition performance of the system of evaluation.Multi-channel data acquisition system adopts the direct current switch, and then carrieson the I/V conversion, so only need the same I/V transform circuit can achieve the purpose ofthe signal conversion, simplifies the circuit design, eliminate the differences due to multipleI/V transform circuit performance parameters and dispersion error. System design of thechannel number is36, so consider to choose single throw switch for channel selection,however, found in the test, cannot adopt single throw switch, because the switch of thechannel will be in a high impedance state, leakage current, the actual output of the current isclosed channel electric current and disconnection of the sum of the leakage current. Toeliminate this effect, the system adopts the single pole double throw switch, testing found thatpeak pulse switch when the switch occurs, this phenomenon will continue for some time todisappear, this phenomenon is caused by the parasitic capacitance between each channelanalog switch, to reduce this effect, we design a circuit that is every channel using two controlswitch, switch the channel before a switch and the grounding resistance in series, in the closedstate, the other a level switch with the I/V conversion circuit is connected, is open, so can passto programming control switch, ensure when making channel switching, capacitance on thedischarge current and eliminate the phenomenon of spike pulse. Automatic comparisoncoding circuit system design to realize automatic switch range, from the perspective ofhardware acquisition rate.USES the C8051F020as MCU, the data processing speed, pin resources is rich, can meetthe needs of36road passage, and internal ADC and PGA, can simplify the circuit design. Theresolution of the ADC itself by single chip microcomputer12, the conversion rate of100KSPS ADC0, can meet the accuracy requirement of the base, because of the traditionalRS232serial port data transmission speed is slow and inconvenient, so consider a new way of communication instead of RS232, final choose USB communication mode, the USBcommunication transmission rate is high, stable and convenient, is the inevitable trend in thefuture communication interface. Finally, the test system using Labview to design anddevelopment, complete right to judge the performance of the acquisition system.