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Theory of Operation Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 249
11.5.7. 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.
11.5.8. 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 11-13, 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. A 6.75 Amp
circuit breaker is built into the ON/OFF Switch.
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 supplies
+12 VDC, for valves and the IR source, while a second supply provides +5 VDC and ±15 VDC for logic and
analog circuitry. All DC voltages are distributed via the relay board.
CAUTION
GENERAL SAFETY HAZARD
Should the AC power circuit breaker trip, investigate and correct the condition causing
this situation before turning the analyzer back on.