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Model 400E Ozone Analyzer
Instruction Manual
THEORY OF OPERATION
P/N 04316 Rev: B
227
At its heart the analyzer is a microcomputer (CPU) that controls various internal
processes, interprets data, makes calculations, and reports results using specialized
firmware developed by T-API. It communicates with the user as well as receives
data from and issues commands to a variety of peripheral devices via a separate
printed circuit assembly called the Mother Board.
The Mother Board collects data, performs signal conditioning duties and routs
incoming and outgoing signals between the CPU and the analyzers other major
components.
An analog signal is generated by an Optical Bench that includes the Photometer UV
Lamp, the Absorption Tube assembly and the UV Detector and Preamp. This signal
constantly cycles between a voltage level corresponding to concentration of O
3
in
the Measure gas and the one corresponding to the lack of O
3
in the Reference gas.
This signal is transformed converted into digital data by a unipolar, Analog-to-
Digital Converter, located on the Mother Board.
A variety of sensors report other critical operational parameters, again through the
signal processing capabilities of the Mother Board. This data is used to calculate O
3
concentration and as trigger events for certain warning messages and control
commands issued by the CPU. They are stored in memory by the CPU and in most
cases can be viewed but the user via the front panel display.
The CPU communicates with the user and the outside world in a variety of
manners:
Through the analyzer’s keyboard and Vacuum Florescent Display over a
clocked, digital, serial I/O bus (using a protocol called I
2
C);
RS 232 & RS485 Serial I/O channels;
Various DCV and DCA analog outputs and;
Several sets of Digital I/O channels.
Finally,
the CPU issues commands via a series of relays and switches (also over the
I
2
C bus) located on a separate printed circuit assembly. Called the Relay Board, to
control the function of key electromechanical devices such as heaters and valves.