Research And Implementation Of Data Acquisition System For Laser Particle Size Analyzer

This paper studies the multi-channel data acquisition method of weak signal, the parameter mismatch between I/V conversion resistor and the error multi-channel amplifier circuit is now a major obstacle for multi-channel weak signal acquisition circuit. we first directly made a program on switching current and then I/V converter. This requires only one I/V converter circuit can achieve the purpose of signal acquisition, simplifies circuit, greatly reduce circuit area, and the dispersion error between the channels will also be eliminated. Which, however, reduces rate of data acquisition, experimental results show that there is distribution capacitance between the current source inputs. The presence capacitance distributed at the switching moment of analog switches have a long spikes, and to disappear after a period of time. based on this phenomenon, this paper also proposed a new program of the current switching, each channel is controlled by two switches, in the channel before switching the switch connect the resistor and ground in series is in the closed state. Another one connected I/V conversion is opened. When switching channel, the switch connected with the resistance is opened. And the switch connected to lower I/V conversion circuit is closed. This can eliminate the generation of peak pulse, in order to reduce the number of switches, and further optimize the circuit, multi-channel analog switches is used to achieve the program. Each CD4053 contains three separate single-pole double-throw switch. After switching a channel is connected I/V converter to convert the current signal into voltage signal, then get through the coding circuit generated by the voltage comparator and PGA module built in lower computer to achieve the purpose of automatically compares the range conversion. The design expands the dynamic range of the circuit, greatly improve acquisition speed.In this paper 8051F020 is used as the main controller of lower machine, which is a high-performance microcontroller, the interior of which includes an analog-digital conversion module, the digital-analog conversion module, voltage comparator, PGA, and low power consumption by use of CMOS technology, supports serial communication and USB communication the moment the lower machine receive sampled data, the first process the sampled data, the processed good data is through the serial or USB communication sent to the host computer and to display or powerfully analysis through the PC. The lower machine is to use the 3.3V power supply, while the analog switch is powered by +5V. therefore, when designing the circuit, CMOS level will be converted to levels TTL. The dedicated level conversion chip SNLVC164245 can achieve this condition. In addition, the notice during the PCB design is also briefly introduced.