A low cost auto-filling and refrigeration rate regulated liquid nitrogen controller for near infrared instruments

Liquid Nitrogen is one of the key refrigerating element in cooling near infrared science instruments, to reduce the dark, readout noises and thermal emissions in the near infrared originated from the instrument structure.  Usually, a small liquid nitrogen tank connected to the instrument is auto filled from a large reserved Dewar in order to maintain required low temperatures during the experiment, for several hours. The detectors used in these instruments are quite expensive and they need to be cooled down steadily, to avoid mechanical damage. In this paper, presented a refrigeration rate regulated algorithm implemented controller which auto-fills and controls the refrigeration rate. This low cost controller can be used for any student laboratory and research. This controller is used very successfully for the GRAVITY acquisition camera instrument of an ESO project.