Thermo Fisher Scientific CryoExtra CE8100 Series
Operation | 23
Hot Gas Bypass
The Hot Gas Bypass is a feature on all CryoExtra freezer
series equipped with a Controller. The Hot Gas Bypass is able
to vent the warm nitrogen gas from the supply line before
initiating a fill cycle. This prevents warm gas from entering the
freezer space. The bypass system helps to maintain a stable
temperature gradient inside the freezer and increases the
efficiency by preventing excess LN
2
evaporation while filling.
This feature is advantageous for any freezer setup and is
especially ideal for sites where longer transfer hoses cannot
be avoided.
The Hot Gas Bypass system consists of these components:
•
Solenoid Valve (24 VDC)
•
Temperature sensor (Pt- 1000 RTD)
•
Muffler
•
Plumbing and electrical connections
Freezers will complete a bypass cycle prior to filling. When a
fill is initiated, the bypass solenoid valve will open first and
begin venting nitrogen gas from the supply line through the
muffler and into the atmosphere. The Controller monitors and
displays the temperature in the plumbing system throughout
the bypass cycle. As LN
2
begins flowing, the temperature in
the plumbing system will decrease.
Once the bypass temperature sensor readings reach the
user-defined Bypass Temperature Setpoint, the bypass
solenoid valve will close terminating the bypass cycle. The fill
solenoid valves will then open and the freezer will begin filling.
The default Bypass Temperature Setpoint is -70°C and can
be adjusted based on the freezer setup.
The Bypass Alarm Time Delay is the maximum allowable
bypass time. If the temperature in the plumbing system does
not reach the Bypass Temperature Setpoint within the
Bypass Alarm Time Delay setting, the Controller will terminate
the bypass cycle, initiate the fill cycle and trigger a Hot Gas
Bypass Time Alarm. Once the immediate fill cycle is complete,
auto fill will be disabled until the Hot Gas Bypass Time Alarm
is acknowledged. This feature prevents a freezer from
continuing to attempt to fill from an empty supply. A Hot Gas
Bypass Time Alarm could be a sign of an empty supply, a
supply with too low of pressure or it could mean that the
Bypass Alarm Time Delay needs to be increased in order to
effectively purge the supply line of nitrogen gas. The default
Bypass Alarm Time Delay is 5 minutes, but should be
adjusted based on the freezer setup. It should be arranged so
that the Bypass Temperature Setpoint is easily reached within
the Bypass Alarm Time Delay setting.
Note:
If a Hot Gas Bypass Time Alarm is triggered, once the
immediate fill cycle is complete, auto fill will be disabled until
the alarm is acknowledged.
Battery Backup (Optional)
The Battery Backup comes standard on all MDD freezers.
The Controller is able to run seamlessly on power from this
external battery system when the primary power source is
interrupted. The Controller is able to run fully functional on the
Battery Backup for approximately 72 hours in the event of a
power failure. While the Controller is running on its primary
power source, it continuously provides a 27 volt trickle charge
to keep the Battery Backup fully charged. A Low Battery
Alarm will trigger if the Controller is running on Battery Backup
and the voltage falls below 21 volts. The Controller will begin
losing select functionality when its power source falls below
18 volts. Non-essential circuits are disabled first to conserve
power.
The battery status can be viewed in the Add-on Menus. With
a Battery Backup connected while the Controller is running on
main power, the battery status screen will read On AC Power.
While running on Battery Backup, the battery status screen
will display on battery backup 26 VDC 80%-100%. With no
Battery Backup connected, the battery status screen will
display On AC Power. This feature is available with Firmware
Version 2.02 or higher.
The Battery Backup system consists of these components:
•
Two, 12 VDC lead acid batteries wired in series
•
Inline fuse (4A 250 V F)
•
Battery housing
•
Electrical connections
Note:
The amount of time that a freezer will operate on power
from the Battery Backup will vary depending on the fill status,
the fill intervals and the size of the freezer.
Adjusting Settings and
Options
Password Entry
This section describes how to access the Controller menus
and adjust the various settings and options. With password
entry enabled, the Controller will prompt for a password
anytime a user attempts to access the setup menus. A
flashing cursor on the password entry screen will make it clear
which digit is being changed. Feature is available with
Firmware Version 2.02.
These instructions will start from the main monitoring display
screen, assume password entry mode is enabled and the
user has Security Level 4 clearance. Once in the setup
menus, the user can press the “ESC” key to exit that menu
level or press the “ESC” key repeatedly until the display
returns to the main monitoring screen. After 30 seconds of
