T400 Ozone Analyzer Operator’s Manual Theory of Operation
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UV LAMP TEMPERATURE SENSOR: This thermistor, attached to the UV lamp in
the optical bench reports the current temperature of the Lamp to the CPU as part of
the lamp heater control loop.
IZS LAMP TEMPERATURE SENSOR: This thermistor attached to the UV lamp of
the O
3
generator in the IZS option reports the current temperature of that lamp to
the CPU as part of a control loop that keeps the lamp temperature constant.
BOX TEMPERATURE SENSOR: A thermistor is attached to the motherboard. It
measures the analyzer’s inside temperature. This information is stored by the CPU
and can be viewed by the user for troubleshooting purposes via the front panel
display. (See Section 12.1.2).
13.3.3.4. Analog Outputs
The analyzer comes equipped with four Analog Outputs: A1, A2, A4 and a fourth (A3)
that is a spare.
A1 AND A2 OUTPUTS: The first two, A1 and A2 are normally set up to operate in
parallel so that the same data can be sent to two different recording devices. While
the names imply that one should be used for sending data to a chart recorder and
the other for interfacing with a data logger, either can be used for both applications.
Both of these channels output a signal that is proportional to the O3 concentration of the
Sample Gas. The A1 and A2 outputs can be slaved together or set up to operated
independently. A variety of scaling factors are available; see Section 5.4 for information
on setting the range type and scaling factors for these output channels.
TEST OUTPUT: The third analog output, labeled A4 is special. It can be set by the
user (see Section 5.10.1.9) to carry the current signal level of
any one of the
parameters accessible through the TEST menu of the unit’s software.
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.
13.3.3.5. 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
CONTROL INPUTS: By connecting these digital inputs to an external source such
as a PLC or Data logger Zero and Span calibrations can be remotely initiated.
13.3.3.6. I
2
C Data Bus
I
2
C is a two-wire, clocked, bi-directional, 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
relay board, optional analog input board and valve driver board circuitry.
