g. Prog. Adv.
The up and down arrow keys allow the user to
scroll through the programs.
CONTROL NAME FUNCTION
UP ARROW
Increments through the program to
the next section; repeats approxi-
mately three times per second if held
depressed.
DOWN ARROW
Decrements through the program to
the previous section; repeats approxi-
mately three times per second if held
depressed.
Note:
In full access mode, these arrow keys raise or lower
the setpoint.
h. Numerical and Special Functions
This keypad is used to select
and enter numerical values and
functions when programming the
controller.
CONTROL NAME FUNCTION
NUMERIC KEYS
Represent numerical values, zero
through nine.
HOLD TIME
Used when programming to enter a
specific amount of time (in minutes)
that the temperature, within a cycle,
is to be held.
COOL +
Used when programming to select a
COOL+ function, for rapid cooling.
Important:
Should be used on all low temperature pro-
grams.
SAMP
Used when programming to enter a
setpoint value, corresponding to the
SAMPLE temperature. When used
with “HOLD”, permits seconds to be
programmed.
ENT
Used to enter and store values and
parameters, previously keyed into
the computer memory (active only
when in Program mode).
END
Used to program a “label” the end or
last section of a program (active only
when in the PROG position).
CLR -/.
Used when programming to remove
and entry (active only when in the
PROG position).
Used when programming a negative
number.
Used to enter a decimal point when
entering a program number in the
user-definable half of memory.
4.3 System Operation
The Model 8018 Programmable Controller regulates the
flow of liquid nitrogen to the freezing chamber. Additionally, it
supplies temperature information to the strip chart recorder.
The freezing cycle consists of the following steps and oper-
ations:
Note:
Typically the biological sample is mixed with a solution
of cryoprotective agent and placed in a plastic cryoampule.
1. STARTING TEMPERATURE. Sample temperature
prior to being loaded into the freezing chamber. The
sample is usually at room temperature (+22C) or ice
bath temperature (+4C).
2. LIQUID PHASE COOLING. The rate at which the liq-
uid sample is cooled. A typical rate of cooling is
1°C/min.
Note:
A regulated flow of LN2 into the freezing chamber is cir-
culated by an internal electric fan. This assures even sample
cooling.
3. SUPER COOLING. The temperature drop achieved just
prior to liquid-to-solid phase change. It is generally three
to four degrees centigrade below the freezing point.
4. PHASE CHANGE. The beginning of the liquid-to-solid
phase change process, characterized by a rapid increase
in temperature, from super cooled temperature to freez-
ing temperature. To minimize temperature rise during
phase change, chamber temperature is rapidly dropped.
This rapid cooling absorbs latent heat of fusion, mini-
mizing any temperature rise above the freezing point.
Note
: Refer to the chart (Figure 4-1) at the end of this section
for the freezing point temperature of the biological sample cor-
responding to the percentage of cryoprotective agent added to
the sample.
5. SOLID PHASE I FREEZING. The freezing rate
selected for solid phase cooling is independent of liquid
phase cooling rate. This rate is determined by the opera-
tor, as required, and is typically the same as liquid phase
cooling rate of 1°C/min.
Models 1010 and 1011__________________________________________________________________________Operation
4 - 3
Figure 4-7
Figure 4-8