B E's Profibus Fiber Optic Converter with dual redundant ring has passed the subways project testing in east Europe. The maximum total length of each ring is 1km and the maximum distance between two OLM(Profibus fiber optic converter) is 200m. The OLMs are connected to the Siemens S700 PLC. There are 10 subway stations in total, in one station there is a Profibus ring network. BE's OLM can help the project save much budget.