Characterizing the Tolerance Performance of PLCs to Voltage Sag Based on Experimental Research

The sensitivity of PLC to voltage sags have been present in many papers in recent years because of the increasing concern to voltage sags, but the claims in most of the papers have been either from earlier standards or earlier references such as the corresponding books published in 2000. Because of the renewal rate of PLC technique, the validity of conclusions drew more than a decade ago may be reconsidered. At the same time, it's necessary to determine the difference between the tolerance performance of present PLCs and previous PLCs to voltage sags. In the paper, three PLCs, which are used widely at present, namely, FX3U of Mitsubishi, S7-200 CPU224 CN of Siemens and domestic XD3 of XinJE of Wuxi in China are selected. The experimental platform is built using Chroma 61860 (i. e., Regenerative Grid Simulator Model 61860) as the voltage sag generator. By programming code for PLCs to control a lamp, 0 or 1 state response of discrete 110 is detected with various voltage sags including different sag magnitudes, sag durations and points-on-wave of sag initiation. Tolerance curves are plotted with numerous experimental datas in the paper and the difference of the tolerance performance for ' a new generation' of PLCs is showed by comparing with previous given sensitivity curves. Besides, boundary condition between output error instructions and outage when PLCs suffer voltage sags is discussed on the basis of a special experimental waveform.