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T
HEORY
HSM-24/3S-CT (120V)
26
Electrical power is supplied into the unit and connected at the main terminal
block. When the ON/OFF switch is selected to the ON position, line voltage is
supplied to the L1 terminal block, the fans, and the 12 VDC power supply. The
L2/N terminal block acts as neutral.
12 VDC is supplied to fuses FB1 and FB2 from the power supply. The DC+ and
DC- terminal blocks are the connection points for the lights.
Line voltage (L1) is supplied to the L1 and COM terminal of the temperature
controller from the L1 terminal block. The RTD temperature sensor provides a
resistance signal to the temperature controller corresponding to surface
temperature of the shelf it is mounted to.
The temperature controller monitors the requested temperature from the
temperature control knob setting and the shelf temperature from the RTD
temperature sensor. When a call for heat is made, the temperature controller
closes the NO contacts of the relay. L1 voltage is supplied to the terminal block
and then to the two coils within the heating pad. The white wire from the heating
pad is connected to the L2/N terminal block. The two coils in the heating pad are
connected in parallel. The indicator light illuminates signaling the call for heat
from the temperature controller.
When the shelf has reached the requested temperature, the temperature
controller opens the NO contacts of the relay. L1 voltage is no longer supplied to
the heating pad. The indicator light goes out.
Heated S h el f M erch an di s er
S e r v ice Man u a l
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