Model 360E Instruction Manual THEORY OF OPERATION
10.3. Electronic Operation
10.3.1. Overview
Figure 10-9 shows a block diagram of the major electronic components of the Model 360E.
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 Teledyne Instruments. 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 analyzer’s other major components.
Data is generated by a gas-filter-correlation optical bench which outputs an analog signal corresponding to the
concentration of CO
2
in the sample gas. This analog signal is transformed into two, pre-amplified, DC voltages
(CO2 MEAS and CO2 REF) by a synchronous demodulator printed circuit assembly. CO2 MEAS and CO2 REF
are converted into digital data by a unipolar, analog-to-digital converter, located on the mother board.
A variety of sensors report the physical and operational status of the analyzer’s major components, again
through the signal processing capabilities of the mother board. These status reports are used as data for the
CO
2
concentration calculation and as trigger events for certain 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 I2C);
RS 232 & RS485 Serial I/O channels;
Via an optional Ethernet communications card:
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 to control the function of key electromechanical devices such as heaters,
motors and valves.
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