Teledyne GFC-7000E - Trace CO2 Analyzer - Manual (Page 172)

Model GFC7000E Instruction Manual THEORY OF OPERATION
04584 Rev A1 161
Particulate Filter
The Model GFC7000E Analyzer comes equipped with a 47 mm diameter, Teflon, particulate filter
with a 5 micron pore size. The filter is accessible through the front panel, which folds down to
allow access, and should be changed according to the suggested maintenance schedule described
in Table 9-1.
10.2.1.4. Valve Options
A variety of optional valve sets can be purchased for the analyzer which allow the user to more
easily supply and manipulate various calibration gases, such as zero air and span gas during
various calibration procedures. For more information of these options see Section 5.4.
10.2.2. Purge Gas Pressure and Flow Control
In order to ensure that all of the ambient CO
2
is purged from the GFC Wheel housing a adequate
supply of dried air, scrubbed of CO
2
must be supplied to the PURGE AIR inlet at the back of the
instrument. The source of purge air must be capable of maintaining a pressure of 20-25 psig at a
flow rate of at least 0.5 liters/min. Purge source air pressure should not exceed 35 pisg.
In order to maintain the proper pressure differential between the inside of the GFC wheel housing
and ambient air, the M360 design includes a manually settable pressure regulator that maintains
the pressure of the purge air feed at 7.5 psig and a flow control orifice that ensures a 0.5 liter/min
flow though the GFC wheel housing.
10.3. Electronic Operation
10.3.1. Overview
Figure 10-9 shows a block diagram of the major electronic components of the Model GFC7000E.
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: