XLT XD-9007A (ELEC Oven Version – B1, AVI Hood Version – B) - Manual (Page 14)

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HOOD THEORY OF OPERATION
S2, 3, & 4 - These DPST (NO) switches are located on the front of the hood and control the ov-
ens, as well as initiating and sequencing the operation of the VFD and damper circuits.
Line voltage is continuously applied to pin 1 of REC 4, 5, & 6, which is connected by a wire to a
contact in S2, 3, & 4. This is shown on the schematic as the lower RH connection point of S2, 3,
& 4. When the switch contacts are closed, shown on the lower LH connection point on the sche-
matic, power is applied to pin 2 of the receptacles, as well as terminal B of R1, 2, & 3. Wires also
connect terminal B and pin 4 of the receptacles. In essence, S2, 3, & 4 replace the switches on the
ovens, and also energize the coils of R1, 2, & 3, which closes the relay contacts and send a signal
to dampers in RTU’s.
The other set of contacts, shown as the upper set on the schematic, connect terminal 24 of the VFD
and terminals 3, 2, & 1 respectively. The VFD generates it’s own 24 VDC signal voltage, and the
switches serve as inputs to the VFD. The VFD outputs user-selected frequencies depending upon
the combination of switches that are closed.
S5 & S6 - These are keyed SPST switches that are used for manual mode operation in case of
VFD failure. S5 is NO (OFF) and S6 is NO (OFF). When S5 is OFF, the key cannot be removed.
It can only be removed when the switch is turned ON. The same key is used to operate S6, and
can only be inserted or removed when S6 is OFF.
Incoming line voltage is applied to terminals 7, 8, & 9 on R7. In normal mode, the voltage is con-
nected to terminals 1, 2, & 3, which feed the VFD. When the contacts of S5 are closed, in manual
mode, the incoming line voltage is connected to terminals 4, 5, & 6, causing the voltage to be di-
verted away from the VFD and sent to terminals 7, 8, & 9 of R5. S5 is also connected to R6, and
when the contacts of S5 are closed, the switch contacts of R6 change state, resulting in the com-
plete isolation of the VFD on both the input and output sides.
At this point in time, there should be no voltage supplied to either the VFD or M1.
The key is then removed from S5 and inserted into S6. When the contacts of S6 are closed, the
contacts of R5 change state and incoming power and frequency is applied to M1 via the TS.
TS - this is a terminal strip, which serves as a connection point for wires.
VFD - The Variable Frequency Drive (VFD) converts the AC supply voltage to DC and then con-
verts the DC to s suitable three-phase frequency source for M1. Incoming power connects to ter-
minals L1, L2, & L3. M1 connects to terminals U, V, & W through R6 & TS1. The VFD gener-
ates it’s own 24 VDC control voltage on terminal P24. S2, S3, & S4 serve as user-controlled in-
puts and connect terminals 1, 2, & 3 to terminal P24. User inputs include a <RUN> and <STOP/
RESET> button switch, as well as <UP> and <DOWN> arrow button switches. A complete man-
ual can be found at www.xltovens.com.