Design of parallel conversion multichannel analog to digital converter for scan time reduction of programmable logic controller using FPGA

Abstract

The execution speed of a programmable logic controller (PLC) depends upon the number of analog and digital input it scans, complication in ladder diagram and the time to store the ladder diagram outputs in memory. Next to the ladder diagram, scanning of analog signals consume enough time as they have to be converted into digital. The two facts that limit the conversion speed is that the processor used for analog signal scanning can process only one channel at a time and the multichannel analog to digital converter (ADC) has digital output for only one channel. The hardware nature of field programmable gate array (FPGA) allows simultaneous conversion of all the analog signals into digital and storage of digital data in block RAM. The proposed design discusses the design of multichannel ADC using FPGA. The simulation result shows that the conversion time of ‘n’ channel ADC is 13.17μs. This increases the PLC execution speed.