AUTOMATIC DEVICE FOR MAINTAINING A CONSTANT LIQUID-NITROGEN LEVEL.

A description is given of an automatic electronic device for maintaining a constant level of liquid nitrogen, in which a plane air capacitor immersed in liquid nitrogen is used as the liquid-level sensor (the permittivity of the liquid and of the gaseous nitrogen differ by a factor of 1. 4). For a change in the level of liquid nitrogen the sensor capacitance changes, and there is a corresponding change in oscillator frequency. As a result, cutoff of the oscillations of the Q-multiplier occurs. The voltage which blocks the dc amplifier vanishes, and it unblocks and turns on the relay. The control voltage is applied to the thyristor through the relay contacts, and the thyristor turns on the electromagnetic valve that controls the feed of liquid nitrogen As soon as the liquid nitrogen reaches the stipulated level, the circuit returns to its original state. The accuracy with which the level of the liquid nitrogen is maintained constant equals 1. 5 to 2 mm. A schematic diagram is given.