Vulcan-Hart 3-130, Service Manual

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4 – 1
SECTION 4 - CIRCUIT DESCRIPTION - 3-STAGE
4.1 INTRODUCTION
The purpose of this section is to familiarize the user or
service personnel with the circuit level operation of the
VULCAN. This knowledge is necessary to aid in trou-
bleshooting of a unit's failure and may also allow the
user to gain greater insight into the VULCAN’s versatility
for particular applications. A detailed description is
given for the following circuit functions:
* Display Readout
* Front Panel Control
* Muffle Control
* Power Supply
* Motor Drive Control (option for 3-Stage)
*Temperature Measurement
The muffle temperature is derived from a Thermocouple
(type "K") which generates an output voltage of up to
50mV. This feedback signal is then manipulated by the
electronics to control the muffle temperature.
4.2 CIRCUIT DESCRIPTION 3-STAGE
4.2.1 LCD DISPLAY READOUT
The display board converts serial data from the
microprocessor to 8-bit parallel data. Each byte
transferred is either a command or a data byte
depending on the state of the two control bits RS and E
(DIS ENA). The 16 character LCD module is controlled by
the microprocessor via its Serial Peripheral Interface
(SPI) port. The display is updated every 0.5 sec or when
a corresponding front panel key has been activated.
4.2.2 FRONT PANEL CONTROL
The power on/off switch switches the AC line voltage.
The membrane switches are arranged in a 8x4 matrix.
The microprocessor scans the entire matrix every 50
msec by setting one column at a time to a logic 0 and
then reading the rows. Once a contact closure has been
detected this value is stored.
4.2.3 MUFFLE CONTROL
The microprocessor (U9) sends a serial digital signal to an
octal peripheral driver (U6) which in turn converts and
latches it to parallel data. This data is then used to drive
several peripheral devices. U9 is connected to an opto
isolator (U7). The isolator's output is connected to the
gate of the muffle triac. The muffle triac may be activated
anytime during an AC cycle, but once activated it can only
be opened when the AC sine wave passes through 0
volts. U9 accesses U7 0.5 msec before zero crossing to
turn the triac off. At this time a value calculated by the
control routine determines how much time should elapse
before the triac is turned on again.
4.2.4 POWER SUPPLY
One DC power supply voltage is generated on the
control circuit board +5V.
4.2.4.1 +12V SUPPLY
The +12 VDC is generated from 15 watt switching power
supply mounted onto the main control PC board.
4.2.4.2 +5V SUPPLY
Refer to schematic, page 5-9. DC voltage from the output
of the switching power supply is used by the +5V linear
regulator U3 to generate the +5V. The capacitor C21
provides additional filtering. The 1.23V reference diode
D1 generate their outputs from this supply.
4.2.5 MOTOR DRIVE CONTROL (3-550 PD)
The +12VDC motor which moves the door vertically is
controlled by a 16 pin motor controller/driver I.C. This
I.C. provides all necessary functions for a complete
closed loop system. A two wire cable connects the
motor to the 1 Amp H-bridge switch on the I.C. The
microprocessor (U9) activates the H-switch through two
input pins. If both are low the motor will turn in one
direction, if both are high the motor turns in the
opposite direction. A third pin sends a signal from the
motor controller/driver I.C. to the microprocessor when
the motor has stalled (up or down position).
4.2.6 FAN DRIVE CONTROL 3-550A/1750A
The air exchange fan is controlled by means of the front
panel membrane switch. Speed selections are from
0 - 9 (0 is off and 9 is highest speed). Speed 1 selection
changes the air in the muffle twice a minute.
NOTES:
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