Liquid Nitrogen Level Control Prolonged use of an apparatus which required frequent and tedious replenishment of s. liquid nitrogen trap led to the development of this simple level control device.
a*..
0.
ZZK
A 22 K a/? w carbon resistor is employed a.the level sensor. Upon warming to a few degrees above liquid nitrogen temperature the resistance of the sensor decreases so that the potenbid applied to the grid of the 21121 thyratron tube increases to a point where the tube fires. A low dissipation 110 v relay connected in series with the thyratron is used as a, switch to apply line voltage to a. 110 v solenoid valve. The opening of the valve admits low pressure compressed air into a nitrogen storage dewas, and forces liquid nitrogen into the trap. Using a 5-1 storage vessel the liquid level in B 0.Frl trap fluctuated less than 2 cm. A 10-fiF electrolytic capacitor connected in parallel with the relay coil effectively eliminated relay "chatter." I t should be noted that the sensor resistor is connected to one side of the line, and should t,herefore be well insolated. The partial support of the U.S. Atomic Energy Commission is acknowledged with gratitude. JOHN T. S. ANDREWS JERRYH.CURRENT
Volume 45, Number
7 2, December 7968
/
803
