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THEORY OF OPERATION
Model 300E Carbon Monoxide Analyzer
Instruction Manual
178
P/N 04288 Rev: A
I
2
C Data Bus
An I
2
C data bus is used to communicate data and commands between the CPU and
the Keyboard/Display Interface and the Relay Board. I
2
C is a two-wire, clocked,
digital serial I/O bus that is used widely in commercial and consumer electronic
systems. A transceiver on the Motherboard converts data and control signals from
the PC-104 bus to I
2
C. The data is then fed to the Keyboard/Display Interface and
finally onto the Relay Board.
Interface circuits on the Keyboard/Display interface and Relay boards convert the
I
2
C data to parallel inputs and outputs. An additional, interrupt line from the
Keyboard to the Motherboard allows the CPU to recognize and service key presses
on the keyboard.
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.
10.3.7.
Power Supply/ Circuit Breaker
The analyzer operates on 100 VAC, 115 VAC or 230 VAC power at either 50Hz or
60Hz. Individual units are set up at the factory to accept any combination of these
five attributes. As illustrated in Figure 10-14, power enters the analyzer through a
standard IEC 320 power receptacle located on the rear panel of the instrument.
From there it is routed through the ON/OFF Switch located in the lower right corner
of the Front Panel.
AC Power is distributed directly to the Sample Gas Pump. The Bench and GFC
Wheel Heaters as well as the GFC Wheel receive AC power via the Relay Board.
AC Line power is converted stepped down and converted to DC power by two DC
Power Supplies. One su12 VDC, for valves and the IR source, while a
second supply pr5 VDC and ±15 VDC for logic and analog circuitry. All DC
Voltages are distributed via the Relay Board.
Power Switch / Circuit Breaker
A 6.75 Amp circuit breaker is built into the ON/OFF Switch.
CAUTION
Should the AC power circuit breaker trip, investigate and correct the
condition causing this situation before turning the analyzer back on.