Thermo Scientific Cryo 740 Series, Operating And Maintenance Manual

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4-2 7000740r7 Cryo Series Thermo Scientific
Section 4
Troubleshooting
Mechanical Block
Diagram
It is a good practice to routinely determine how much liquid nitrogen is in
the tank, and to keep a record of these values. It is possible to estimate the
number of liters remaining in the tank, by taking a depth measurement (in
inches).
The procedure for estimating the amount of liquid in the tank is as
follows:
1. With the tank filled and stable, lower the ruler along the edge of the
tank until it is at the bottom. (Take subsequent measurements
lowering the ruler at this same location.) When the LN
2
stops boiling,
pull out the ruler. The actual liquid level will be approximately one
inch lower than the frost line on the ruler.
Caution Some shrinkage of the ruler may occur depending on the level of
liquid nitrogen in the tank. ▲
Two 63mA Slo-Blow fuses (P/N
230162) are located on the Cryo
control circuit board which protects
power transformer T1. Refer to
Figure 4-2.
Figure 4-1. Cryo System Mechanical Block Diagram
Manual Liquid Level
Check (Dip Stick)
Control Board Fuses
Figure 4-2. Fuse Locations