Shel lab SCO5W, Installation & Operation Manual

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OPERATION
T
HEORY OF
O
PERATION
SCO5W incubators are engineered to provide a constant temperature CO
2
incubation environment
that is passively humidified to prevent the premature drying of sample media. Filling the
humidification pan will result in a relative humidity (RH) of 90 – 95% in the chamber. Each incubator
features a glass viewing door that allows visual inspection of samples without compromising the
chamber CO
2
or humidity environment.
Heating
When powered, the unit heats to and maintains the incubation chamber air temperature at the
currently programmed temperature set point. An internal microprocessor stores the temperature set
point. The microprocessor board is wired to a solid-state temperature probe located on the chamber
interior right wall. When the processor detects that the chamber temperature has dropped below the
temperature set point, it pulses power to heating elements on the surface of the water-jacket
insulation space, and in the outer chamber door. Heat from the elements on the jacket propagates
through water inside the jacket to the chamber wall, and then to the chamber airspace. During
normal operations, with the doors closed, most heating pulses correct for deviations of less than
0.1°C.
The processor employs proportional-integral-derivative analytical feedback-loop functions when
measuring and controlling the chamber air temperature. PID-controlled heating pulse intensities and
lengths are proportional to the difference between the measured chamber temperature and the
current set point. The frequency of pulses is derived from the rate of change in that difference. The
integral function slows the rate of pulses when the temperature nears the set point to avoid
overshooting.
The incubator relies on natural heat radiation for cooling. The incubator can achieve a low-end
temperature of the ambient room temperature plus the incubator waste heat.
The chamber door is self-heating to bolster the thermal uniformity and stability of the chamber and to
minimize condensation on the glass viewing door. The protection provided by the door against
temperature and CO
2
disruptions is of limited duration. Minimize sample viewing times when
possible.
Insulation – Water Jacket
Insulation is provided by the water-filled jacket surrounding the incubation chamber on the top,
bottom, back, and left and right sides. The mass of the water, once heated to the set point, provides
a high degree of temperature uniformity in the chamber, as well as thermal inertia. In other words,
the chamber will retain heat in the event power to the heating elements is interrupted for
significantly longer than an air-jacketed incubator. However, the water jacket does require a longer
time to come up to temperature when placing the unit in operation from a cold state.