A measurement system used in conjunction with a conveyor includes a first sensor with a first transceiver and a second sensor with a second transceiver. The transceivers transmit a first light beam and a second light beam towards a movable portion of the conveyor. A control unit communicably coupled to the first sensor and the second sensor, wherein the control unit calculates a first distance between the first sensor and the movable portion based on the first sensor and a second distance between the second sensor and the movable portion based on the second sensor. The control unit determines a difference value between the first distance and the second distance; and stops the unloader in response to the difference value being above a predefined threshold value.