Chamber Temperature Control - HP Designjet 3D Service Manual

AC line voltage comes into the PDB
the solid state relay to an auto switching circuit. The circuit is used to supply
the chamber heater voltage: 240 VAC in series, or 120 VAC in parallel. The
solid state relay is controlled by the controller board, and turns the heater
on/off to regulate the chamber temperature. A second solid state relay
provides AC line voltage to the system. It is controlled by the controller board
and safely shuts down the system when the power down switch is turned off.
• The 5 VDC and 12 VDC are used by the controller board, single
board computer, and hard drive. The 12 VDC also powers the fila-
ment motors.
• The 24 VDC powers the stepper motors, solenoids, fans, and cham-
ber lights.
• The 120 VDC circuit powers the model heater and a separate 120
VDC supply powers the support heater.
There are two fuses on the power distribution board.
• Fuse F1 fuses the AC input to the +120 VDC supply.
• Fuse F2 fuses the +120 VDC output.

Chamber Temperature Control

The chamber thermocouple (T/C) connects via the I/O board to the PDB
and is sent to the controller board. The T/C generates a variable low level
voltage that depends on the temperature of the chamber. This analog signal
from the chamber thermocouple is amplified on the I/O board and sent to
the PDB. From the amplifier, the signal goes to an A to D converter in the
ColdFire. The controller reads the chamber temperature and turns the heaters
on and off to maintain 77° C. The chamber fans run continuously when the
system is on. Temperatures can be read on the PDB using a volt meter at test
points TP22 for model, TP20 for support, and TP28 for the chamber NOTE:
10 mV = 1 degree C.
(Figure 5). The voltage is routed through
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