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TW-357 REV E
30
Control Range
CONTROL RANGE can be accessed through the menu system of the control (MENU, 6, 2, 3, 2, 2). KRYOS
maintains a temperature range around the user-selected temperature. A tighter range maintains a temperature
very close to the selected temperature at the cost of greater LN2 usage. A broad range provides more
temperature variability but the LN2 usage is less. The range can be varied from +1º to +15ºC above and below
the selected temperature. The total range therefore, is between 2ºC (1º below and 1º above the selected
temperature) and 30ºC (15º below and 15º above the selected temperature). When the KRYOS is attempting
to control by temperature, it flashes “T.Recov” (Temperature Recovery) in the center of the bottom line.
Freeze-Guard Options
Ice crystals introduced through the supply line are the primary cause of an overfill. Freeze-Guard is a process
designed to reduce the risk of an overfill. Freeze-Guard consists of two options to reduce the risk of a frozen
valve: 1) The maximum valve open duration can be set by the user. (VALVE OPEN DURATION) 2) The valve
can be rapidly turned on and off trying to free it up (VALVE DE-ICING). Option 2 occurs if either the Freeze-
Guard sensor detects that the valve is not fully closed. The special “Freeze-Guard” sensor assembly includes a
plumbing “T” with an in-line thermistor which is placed in the plumbing directly downstream from the
solenoid valve. KRYOS monitors the “Freeze-Guard”
thermistor and detects if the flow of LN2 is stopped when the valve has been commanded to close.
Valve Monitoring
If KRYOS detects that a flow of LN2 is occurring even when the solenoid valve is supposedly closed, an error
message will appear on the screen indicating “Valve Stuck Open.” To confirm, the control waits for 10
seconds after it determines that the valve should be closed before it will indicate that the valve is stuck open.
Valve Open Duration
Valve Open Duration can be accessed through the menu system (MENU, 6, 2, 4, 1). This allows the user to
set the maximum amount of time, which the valve will stay open at any one time. If a fill operation exceeds
the valve open duration time set by the user, the valve closes for 15 seconds and then opens again for another
cycle. This 15 second rest period allows the solenoid valve to warm. The allowable settings are Disabled and
1-15 minutes.
Valve De-icing
Valve De-Icing can be accessed through the menu system (MENU, 6, 2, 4, 2). This feature can be turned on
or off. If enabled, the control will try to free up the valve by rapidly turning it on and off. This feature is
triggered when the Freeze-Guard sensor detects a stuck valve condition. KRYOS will attempt to free up the
valve by De-icing 5 times with a two-minute delay between tries.
Splash-Guard
Splash Guard is a process to reduce or eliminate false signals detected by the thermistor sensor assembly. In
particular this reduces sporadic valve operation when the sensor assembly is splashed with LN2 . When a fill
operation has completed because the level has reached the STOP FILL sensor, the display will flash “Check”
and the control will check the validity of the signals received from the sensor assembly. The splash-guard
check occurs for 20 seconds and the bottom line of the display indicates this by flashing “Check”.