Small nitrogen fertilizer plants mainly produce urea, ammonium bicarbonate and other common agricultural fertilizers, involving gasification, carbonization, ammonia recovery, wastewater treatment and other complex production processes. The production environment features corrosive ammonia liquid, circulating desulfurization solution, high humidity, flammable and explosive ammonia gas, as well as medium adhesion and foam interference. Traditional level measuring instruments such as float level gauges and ultrasonic level gauges are prone to failure, stuck movement and inaccurate readings under such harsh working conditions