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

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GAS OVEN THEORY OF OPERATION
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. The milli-volt signal is used to display the actual tem-
perature.
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 Thermocouple (T/C), connected to terminals
9 & 10, with T9 being the negative terminal and T10 being the positive terminal. The user deter-
mines 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 Ignition Control (IC) combined. The Maximum Operating Temperature is
set at the factory and cannot be field adjusted.
V1-V2 & V3- The Multi-Valve assembly has three (3) Gas Valves. The Main Valves (V1-V2)
operate in series, and are wired in series via the Rectifier Plug. The Rectifier Plug rectifies 24
VAC from the Ignition Control (IC) to 22 VDC. V1-V2 are solenoid valves and are open continu-
ously during burner operation, regardless of either actual or set-point temperature values. V3 is a
modulating valve, and is controlled by a variable electrical signal from the Signal Conditioner
(SC). There are two (2) fuel pressure testing ports; one for incoming pressure, and one for both
high-bias and low-bias pressure. The upper port is used for incoming pressure, while the lower
port is used for high- and low-bias pressure. There are two (2) hex adjusting nuts; an 8mm nut for
adjusting high-bias pressure, and a 5mm nut for adjusting low-bias pressure.
XFMR- The Transformer steps down line voltage to 24 VAC. It supplies power to the Signal
Conditioner (SC), Ignition Control (IC), and the Centrifugal Switch (S2). One terminal on the sec-
ondary side is connected to chassis ground by a green wire. The XFMR is ON whenever the Main
Switch (S1) is on, and is independent of the Cool Down Timer (R1). Note: The XFMR is
equipped with an integrated circuit breaker for standalone protection.