7.1.3.
Liquid Nitrogen Usage
The TEC 3000 controller is able to calculate and display an estimated rate of LN2 evaporation
inside a freezer. This liquid usage is displayed in inches or millimeters per day. It takes time for
the real-time data to accumulate in order for the liquid usage rate to be calculated.
The liquid usage is calculated by measuring the time it takes the LN2 level in a freezer to
decrease 0.5 inches (12.7 mm) and then extrapolating that value out to a 24 hour period in
order to obtain a per day liquid usage.
= (
𝐿
1
− 𝐿
2
𝑎
𝑖
(
ℎ
)
)
×
24
ℎ
For example:
If the LN2 level to decrease from 6.0 to 5.5 inches in 12 hours, then the displayed liquid usage
will be 1.0 inch/day. See below.
6.0" − 5.5"
= (
12
ℎ
)
×
24
ℎ
=
1.0"
⁄
𝑎
𝑦
This calculation is suspended during fills and will resume 15 minutes after a fill to allow the LN2
level in the freezer to stabilize. The liquid usage calculation can be reset by restarting the
controller or cycling the power. For liquid usage display options, refer to the Liquid Nitrogen
Level Options section.
NOTE: Several scenarios can lead to a temporarily exaggerated liquid usage. If the
level abruptly decreases 0.5 inches, then there will be a spike in the liquid usage.
Having the freezer lid off for an extended period of time, adding or removing samples
and racks, attempting to fill from an empty LN2 supply, or moving the freezer all can
lead to an accelerated evaporation rate. Although the liquid usage is an accurate
estimate of the daily evaporation rate, it can be temporarily skewed by certain events;
however, because of method used to calculate the usage, it will recover as more data
is acquired.
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