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Model 400E Ozone Analyzer
Instruction Manual
In its standard configuration, the Analyzer comes with all four of these channels set
up to output a DC voltage. However, 4-20mA current loop drivers can be purchased
for the first two of these outputs, A1 and A2.
Output Loop-back: All three of the functioning analog outputs are connected back
to the A/D converter through a Loop-back circuit. This permits the voltage outputs
to be calibrated by the CPU without need for any additional tools or fixtures (see
Section 0).
External Digital I/O
This External Digital I/O performs two functions.
STATUS OUTPUTS: Logic-Level voltages are output through an optically isolated
8-pin connector located on the rear panel of the analyzer. These outputs convey
good/bad and on/off information about certain analyzer conditions. They can be
used to interface with certain types of programmable devices (see Section 6.8.1).
CONTROL INPUTS: By connecting these digital inputs to an external source such as
a PLC or Datalogger (see Section 6.8.2), Zero and Span calibrations can be
remotely initiated.
2
I
C Data Bus
2
I
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
Keyboard/Display Interface and finally onto the Relay Board.
2
An I
C data bus is used to communicate data and commands between the CPU and
the Keyboard/Display Interface, the Relay Board and the power supply for the
Photometer UV Lamp. On instruments with IZS Options, the power supply for the
O
Generator UV Lamp is also controlled by via the I
3
Interface circuits on the Keyboard/Display interface and Relay boards convert the
2
I
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
boots and the instrument software can establish control.
P/N 04316 Rev: B
2
C. The data is then fed to the
2
C bus.
2
C circuitry to specific values until the CPU
THEORY OF OPERATION
235
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