The frequency relay operates on the principle of frequency comparison, where the measurement frequency is compared to a frequency generated within the device that can be adjusted via a setting knob. When a jumper is connected between terminals X1 - X2, the output relay drops out if the measurement frequency is greater than the set frequency. The relay re-engages when the measurement frequency is less than the set frequency multiplied by the hysteresis factor. When a jumper is connected between terminals X2 - X3, the relay engages if the measurement frequency is greater than the set frequency. The relay drops out again when the measurement frequency is less than the set frequency multiplied by the hysteresis factor. The application of the measurement voltage is indicated by an LED, with low frequencies identifiable by the blinking rhythm. Another LED indicates the switching state of the output relay.