VÚHŽ Automation division tested the usability of the new L-sensor on a modified billet mold at the customer's site. The L-sensor was set for control measurement in the initial phase and than it was used directly for mold level regulation in the second phase. These hot tests were carried out throughout the lifetime of the mold. The operational tests achieved excellent results and proved the applicability of the L-sensor measuring system in terms of reliability and safety.