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4 DESCRIPTION OF THE CONTROL SYSTEM.
4.1 System Summary
The hardware portion of the control system consists of a keyboard and
3 additional electronic boards designed specifically to match the
requirements of the EHS autoclave. The main board is the digital
board, DIG-T2, which contains the microprocessor and is responsible
for controlling the system. The analog board, ANL-T2, interfaces with
the DIG-T2 board and the various system components processing
signals traveling to and from these areas. The AC-T1 board consists of
AC power filters and drivers for the AC components in the system. DC
power (12V and 5V) for all the DC components is supplied by a
switching type power supply. In addition the system is capable of
direct communication with a printer over a parallel interface and/or a
PC via an RS 232 port (for more detail see individual descriptions
below).
CONTROL SYSTEM BLOCK – DIAGRAM
The following paragraph applies only to the 3870EHS
From S/N 2307040, a Varistor is connected, in parallel, to each of the
SSR’s contacts, in order to decrease the voltage spikes, caused by the
operation of the power devices (pumps and heating elements).
In the 3 phase system (in our case, the 3870EHS) the current, to the
heating elements, is supplied via a contactor. A “CUT OFF” thermostat
is connected to the contactor's coil. If the temperature of the heating
elements exceeds the alarm value, the “CUT OFF” thermostat
disconnects the contactor coil, the contactor's contacts open ("off"
position) and the heating elements are disconnected from the electrical
power.
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