Everyone should know that the method of storing samples in liquid nitrogen tanks is that when the samples are frozen below the liquid nitrogen level, they will be completely “submerged” by liquid nitrogen, which requires that the liquid level should not be lower than the top surface of the frozen object. However, the liquid level cannot be observed with the naked eye, and the neck plug cannot be seen when the neck plug is closed. When the neck plug is opened, there will be fog, and it is not accurate to barely see it. The correct inspection method should be the “wood stick method”!
Do this as follows:
1.Wooden stick method:
Find a wooden ruler or a solid wooden stick about 80cm, insert it into the center of the bottom of the container, wait for 10 to 15 seconds, and then take it out. The length of the frosting is the height of the liquid level.
Remember: Do not use a hollow tube for inspection, because the hollow tube is prone to “events” that hurt people by spraying liquid nitrogen.
2.Liquid level alarm
A liquid level alarm can be added.
The liquid level alarm is placed at the tank mouth every other week, the equipment starts automatically, the ultrasonic transmitter emits ultrasonic waves to the surface of the liquid nitrogen, the sound waves are reflected by the liquid nitrogen surface, and part of the reflected echoes are received by the ultrasonic receiver. The propagation speed and time in the air can be calculated to measure the liquid level, which can be displayed in real time through the liquid crystal display.