XLT XD-9006A (GAS Oven Version – C, AVI Hood Version – B) - Manual (Page 12)

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GAS OVEN THEORY OF OPERATION
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) and to the pri-
mary side of the Transformer (XFMR). When used with the optional AVI Hood System, a remote
switch mounted in the front of the AVI Hood replaces 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 a 24 VAC signal to the Temperature Con-
trol (TC) and the Signal Conditioner (SC). It functions as a safety feature to prevent burner opera-
tion if the M1 fails to rotate.
S3 - High Limit Switch (World & Australia ovens only). This is a bi-metal, NC, SPST switch
physically mounted in the side panel of the Bake Chamber. It’s purpose is to provide fail safe op-
eration. If the temperature of S3 exceeds 600°F, it opens and interrupts line voltage to all compo-
nents except the Main Motor (M1).
S4 - (Australia ovens only) The Centrifugal Switch is SPST switch physically mounted inside the
Burner Blower Motor (M4) to prove rotation.
SC - The Signal Conditioner is powered by 24 VAC from the Transformer (XFMR) via the Main
Motor Centrifugal Switch (S2) and the Temperature Control (TC) on terminals 1 & 2. Incoming
power will be interrupted by the Temperature Control (TC) when the actual temperature rises
above the Maximum Operating Temperature (see Specification Sheet). The function of the SC is
to convert a 4-20 mA signal from the TC (Temperature Control) to a 45-250 mA signal and then
applies that signal to the Moduplus valve. This in turn modulates the valve to allow an appropriate
amount of fuel to control temperature.
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 TC (Temperature Control). The milli-volt signal is used to
display the actual temperature.
TC - The Temperature Control (TC) has line voltage applied to terminal T5, and neutral voltage
applied to terminal T4. There are two displays; one for actual temperature and one for set-point
temperature. Actual temperature is determined by the Thermo-Couple (T/C), connected to termi-
nals 9 & 10, with T9 being the negative terminal and T10 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 4-20 mA (milli-amp) signal to the Signal Conditioner (SC) depending
upon the relationship between actual temperature and set-point temperature. An alarm relay exists
between terminals 1 & 2. Incoming power will be interrupted by the Temperature Control (TC)
when the actual temperature rises above the Maximum Operating Temperature (see Specification
Sheet). The voltage being interrupted is 24 VAC from the Transformer (XFMR) to the Signal
Conditioner (SC) and Burner Control (BC) combined. The Maximum Operating Temperature is
set at the factory and cannot be field adjusted.