XLT XD-9007A (ELEC Oven Version – B1, AVI Hood Version – B) - Manual (Page 11)

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ELECTRIC OVEN THEORY OF OPERATION
relay is a safety feature to allow the oven to cool down to room temperature, and to eliminate heat
stress on the components of the oven.
S1 - The Main Switch is a SPST normally open switch, mounted on the front of the Control Box.
Activating this switch applies voltage to Terminal T6 of the Cool-Down Timer (R1). When used
with the optional AVI Hood System, a remote switch mounted in the front of the AVI Hood re-
places it.
S2 - This Switch is a SPDT centrifugal switch physically mounted inside the Main Motor (M1).
When M1 comes up to full speed, S2 closes and sends voltage to the Temperature Control (TC)
and the Contactors (C1 & C2). It functions as a safety feature to prevent burner operation if the
M1 fails to rotate.
S3 - This Switch is a SPDT thermal switch, located in the side panel of the oven, and it monitors
the internal temperature of the bake chamber. It is normally closed, and will open when the tem-
perature reaches and exceeds 600° F. If it opens, it will interrupt power to all of the single phase
components. This event will initiate the 30 minute off-delay timer, which will result in the main
fan operating for 30 minutes, then turning off.
SSR 1-4 - A Solid State Relay is an electronic switching device in which a small control signal
from the Temperature Control (TC) controls a larger load current and voltage. It comprises a volt-
age sensor which responds to the TC, a solid state switching device which switches power to the
Heating Elements (H1-6) either on or off, and does this without mechanical parts.
T/C - The thermocouple is a type K. It consists of two different conductors that produce a voltage
proportional to a temperature difference between either end of the pair of conductors. The T/C is
connected to terminals 9 & 10 of the Temperature Control (TC). The milli-volt signal is used to
display the actual temperature.
TC - The Temperature Control (TC) has line voltage applied to terminal 10, and “neutral” voltage
applied to terminal 9. There are two displays; one for actual temperature and one for set-point
temperature. Actual temperature is determined by the Thermocouple (T/C), connected to terminals
2 & 3, with terminal 2 being the negative terminal and terminal 3 being the positive terminal. The
user determines the set-point temperature by pressing and holding the up or down arrow button
switches. The TC sends a 14-24 VDC signal to the Solid State Relay (SSR) depending upon the
relationship between actual temperature and set-point temperature. If the actual temperature rises
above maximum temperature, an internal switch contact opens thereby interrupting power.