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OPERATION
THEORY OF OPERATIONS
Heating
When powered, the TFO oven heats the oven chamber atmosphere to the current constant temperature
set point. The oven can also be programmed with multi-step automated heating recipe profiles. When
launched, a profile overrides the constant temperature set point. In its default setting, the oven resumes
heating to the constant temperature set point after a profile completes or is aborted.
Along with storing set points and profile steps, the temperature controller monitors the oven chamber air
temperature using a solid-state probe located in the airstream on the right wall of the chamber. When the
processor detects that the chamber temperature has dropped below the currently active temperature set
point, it pulses power to a heating element in a recirculation air duct space located below the oven
chamber.
The controller uses 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 the difference. The integral function slows the
rate of pulses when the temperature nears the set point to avoid overshooting.
TFO ovens rely on natural heat radiation for cooling.
When the oven is powered, the chamber air temperature cannot operate below the ambient room
temperature plus the internal waste heat of the oven. Waste heat is generated primarily by the operation of
the blower fan motor and the resulting air compression in the duct spaces.
The heating rates given in the Unit Specification chapter of this manual are for a 25°C environment. The
ambient temperature of the workspace around the oven affects its heating and cooling performance.
Heating Profiles
The oven temperature controller stores the constant temperature set point and 40 programmable heating
recipe steps. The steps come allocated to 4 ten-step profiles, but successive profiles may be combined to
run sequentially as one profile. Step types include timed-interval ramping (heating or cooling), soaking
(constant temperature), and ending states. Please see the EZ-Zone Profile Programming Guide included
with this oven for more details.
Air Circulation
The oven continually circulates air internally while powered in order to maintain temperature uniformity and
stability in the oven chamber and to speed drying rates. Air is forced through vent holes on the right side of
the chamber, blows across the shelf space, and is then pulled into a duct that makes up the left chamber
wall. From there, the air is drawn downward into a heating duct by the action of the blower fan. The oven is
intended to be run as a closed air-cycle system.
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