The relative motion sensor is intended to monitor the relative motion of launch vehicle separable parts. It may be used to monitor the motion of the elements of different devices in an area difficult to access or hazardous for people (radio active, gas-polluted, high temperature et al.).
A circular potentiometer is used as a sensitive element. A contact arm of the potentiometer rotates when a rope reeled on a drum reels out. A spiral spring of the sensor ensures tension of the rope when it reels out of the drum and ensures its reeling on the drum. After the rope reels out of the drum, the end of the rope is automatically separated from the sensor.

The sensor is reliable and does not require regular maintenance in the process of storage and operation; it withstands increased dynamic loads.

It may be equipped with an individual indicator (pointer-type indicator, character display et al.).