Blodgett MT2136 Series, Service And Repair Manual

Page: 48 / 94

OPERATION
3-24
6. On a call for heat from the cooking computer
(1), as sensed by an RTD probe (18), the heat
relay (4) closes sending 24 VAC to the main
burner valve (17). This valve opens sending
gas to the flame blower (13) for ignition.
NOTE: The RTD probe is located in front of the
combustion motor. It should be checked
with an ohm meter.
7. The conveyor belt is driven by a closed loop
D.C. drive system consisting of a 130 VDC moĆ
tor (10), a #2 Hall effect pickup (20), a DC
speed control board (8) and the DAC located
in the cooking computer. The motor speed varĆ
ies based on the time programmed into the
cooking computer. If time is programmed, a
voltage from .3 to 3.8 is applied to the DC
speed control board. The output voltage meaĆ
sured at terminals A1 and A2 varies from 20 to
130 VDC based on the DAC voltage applied to
the board or the time programmed into the
computer.
NOTE: The DAC receives 20 VDC from the
speed control board. The DAC returns
a portion of the voltage (between .3
and 3.8 VDC). The amount of voltage is
dependent on the time programmed
into the computer.
NOTE: This type of system does sense the
weight of the product and will not slow
down if the belt is fully loaded.
8. There are two cooling fans (21) located in the
rear convection fan compartment and one loĆ
cated in the computer control compartment.
These fans are activated when the belt stop
relay (3) is energized. The fans are also actiĆ
vated when a single pole double throw thermal
switch (22) toggles from common/NC to comĆ
mon NO. The switch toggles due to high ambiĆ
ent heat. It will toggle if the temperature passĆ
ing its face exceeds the rating on the back of
the switch.
NOTE: The switch is located between the two
blowers in the rear convection fan
compartment. It protects the convecĆ
tion fans from high ambient heat.