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Model 9110T NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 339
The core of the analyzer is a microcomputer/central processing unit (CPU) that controls various internal
processes, interprets data, makes calculations, and reports results using specialized firmware developed
by Teledyne. 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 onto which the CPU is mounted: the
motherboard.
The motherboard is directly mounted to the inside rear panel and collects data, performs signal
conditioning duties and routes incoming and outgoing signals between the CPU and the analyzer’s other
major components.
Data are generated by the sensor module which outputs an analog signal corresponding to the amount of
chemiluminescence present in the reaction cell. This signal is converted into digital data by a unipolar,
analog-to-digital converter, located on the motherboard.
A variety of sensors report the physical and operational status of the analyzer’s major components, again
through the signal processing capabilities of the motherboard. These status reports are used as data for
the various concentration calculations and as trigger events for certain warning messages and control
commands issued by the CPU. This information is stored in memory by the CPU and in most cases can
be viewed by the user via the front panel display.
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 PCA, to control the function of key electromechanical
devices such as heaters and valves. It also issues some commands directly to the Sensor module (e.g.
initiate Electric Test or Optical Test).
By controlling the state of various valves the CPU directs the flow of sample gas through the various gas
paths of the analyzer (NO measurement path; NO
x
measurement path; Auto Zero Path). Based on which
path is active, the CPU interprets the sensor output to derive raw data representing concentrations for
NO
x
, NO and zero (dark condition), accesses the operational data stored in memory then calculates final
concentrations for NO
x
, NO and NO
2
.
The CPU communicates with the user and the outside world in several ways:
Through the analyzer’s front panel LCD touch-screen interface
Through the serial I/O channels
Various analog voltage and current outputs
Several sets of Digital I/O channels
Ethernet
13.3.2. CPU
The unit’s CPU card, installed on the motherboard located inside the rear panel, is a low power (5 VDC,
720mA max), high performance, Vortex86SX-based microcomputer running Windows CE. Its operation
and assembly conform to the PC 104 specification.