Ripple-free liquid-nitrogen level controller for long-term operation

Abstract
This article describes the design features, construction, and operation of a liquid-nitrogen level controller which can be used continuously over a period of several weeks. Liquid level is sensed by pairs of thermistors mounted on a dip stick. Replenishing of liquid nitrogen is achieved as a result of self-pressurization of a tank containing the cryogen. The transfer system ensures a ripple-free liquid surface during the replenishing operation. This level controller has been a part of a cryostat for diffusion measurements in liquefied inert gases.