Missed Data Rates of Data Transfer Methods from Programmable Automation Controller to SQL Database

Abstract

Data transfer methods between data acquisition equipment and a SQL database were tested for missed data rates. Tests included different data loads, server loads, test durations, and data update intervals. The missed data rate was measured by the percentage of data changes missed by the transfer method. HTTP, FTP, and web services data transfer methods were subjected to an initial evaluation with preliminary results but were not subjected to complete tests due to hardware limitations. OPC and SQL proxy methods were subjected to a broader range of tests using data loads of 20, 40, and 60 variables; server loads of one and three UIOs; test durations of one and eight hours; and update intervals of 150 ms to 2500 ms. The OPC method resulted in better performance compared to the SQL proxy method with no missed data at update intervals as low as 250 ms compared to 500 ms at the lightest loads or 400 ms compared to 2500+ ms at the highest loads. The results of this study provide initial data for selecting a data transfer method.