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Theory of Operation T400 Ozone Analyzer Operator’s Manual
288
13.3.3.7. Power Up Circuit
This circuit monitors the +5V power supply during start-up and sets the Analog outputs,
External Digital I/O ports, and I
2
C circuitry to specific values until the CPU boots and
the instrument software can establish control.
13.3.4. RELAY PCA
The CPU issues commands via a series of relays and switches located on a separate
printed circuit assembly, called the relay PCA, to control the function of key
electromechanical devices such as heaters and valves. The relay PCA receives
instructions in the form of digital signals over the I
2
C bus, interprets these digital
instructions and activates its various switches and relays appropriately.
The relay PCA is located in the right-rear quadrant of the analyzer and is mounted
vertically on the backside of the same bracket as the instrument’s DC power supplies.
Power
Connection
for DC
Heaters
Status LED’s
(D2 through D16)
DC Power Supply
Test Points
Watchdog
Status LED (D1)
(JP5)
Thermocouple
Configuration
Jumpers
Thermocouple
Signal Output
I
2
C Connector
V
alve Control
Drivers
Pump Power
Output
(JP7)
Pump AC
Configuration
Jumper
AC Power
IN
DC Power
Distribution
Connectors
V
alve Control
Connector
(J15)
TC1 Input
(J16)
TC2 Input
AC Relay
(
Only present if optional.
Metal Wool Scrubber
installed)
Figure 13-7: Relay PCA Layout (P/N 04523-0100)
06870C DCN6332