Operation, Theory of operation – Shellab SCO6AD User Manual
Page 19
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P a g e
OPERATION
T
HEORY OF
O
PERATION
The SCO6AD is engineered to provide a constant temperature CO
2
incubation environment. The
unit can obtain a stable, uniform (±0.25°C) temperature in its chamber, ranging from the room
temperature +5°C up to 50°C for incubation applications, when properly calibrated. The unit is also
provided with an automated high-heat decontamination cycle that does not require the removal of
the CO
2
sensor or other electronic components.
The incubator operates with a relative humidity (RH) in the chamber of up to 95%. Operating with
RH levels in excess of 95% will result in condensation on the incubation chamber surfaces. Please
see the
entry on page 37 of the Operations section for information
on managing humidity.
The incubator features inner glass viewing door that allows visual inspection of samples without
compromising the chamber CO
2
environment.
Heating
The SCO6AD microprocessor controller employs proportional-integral-derivative analytical
feedback-loop functions when measuring and controlling the incubation chamber air temperature.
The rate of PID-controlled heating is proportional to the difference between the measured chamber
air temperature and the user-programed temperature set point. The rate of heating slows as the air
temperature nears the set point to prevent overshooting. During normal operations heating pulses
take place in small bursts to correct for deviations of 0.1
°C. Heating pulses take place near
continuously when first heating up the unit for use after installation, and frequently when recovering
from door openings.
The microprocessor controller is connected to solid-state internal temperature probes for monitoring
the chamber air temperature. Heating is provided by elements located in an insulating air jacket
space surrounding the chamber on four sides and beneath the chamber floor. A fan circulates air
within the jacket. This indirect heating provides a temperature uniformity superior to direct radiant
heating from having an element inside the incubation chamber, and avoids accelerated drying of
samples nearest to an exposed element.
The exterior chamber door is self-heating to bolster the thermal uniformity and stability of the
chamber, and to minimize condensation on the glass viewing door. Leaving the exterior door open
for long durations may adversely impact the temperature performance of the incubation chamber. It
may also create condensation on the viewing door. Door openings should be restricted to the
minimum necessary to view or access samples in the chamber.
The incubator relies on natural heat radiation for cooling. With the doors closed, the lowest
chamber temperature that can be sustained is the ambient room temperature plus the waste heat
generated by internal electrical and mechanical operations (the room temperature +5
C).
The SCO6AD requires periodic calibrations to verify that it is accurately measuring and displaying
the chamber air temperature. If a measurement error is detected during a temperature calibration
procedure (see page 25), the temperature display can be calibrated to the actual temperature by
placing the display in its calibration mode. Temperature calibrations require a reference
temperature sensor accurate to at least 0.1°C