The HRN-31 is a multifunction voltage monitoring relay designed to detect voltage exceeding upper level (Umax) and falling below lower level (Umin) according to selected monitoring function. It features smooth adjustment of both voltage levels with the lower level Umin set as a percentage of the upper level Umax, and an adjustable time delay to eliminate short-term voltage drops and spikes. The relay measures true root mean square (TRUE RMS) voltage value and offers multiple function options including OVER, UNDER, and WINDOW modes with optional fault state memory (Latch) that can be reset via control input. With a 1-pole changeover contact rated at 16 A/AC1 and breaking capacity of 4000 VA/AC1, the HRN-31 is ideal for industrial control systems, power distribution monitoring, and equipment protection applications requiring reliable voltage supervision.