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4.0 DESCRIPTION OF THE PRODUCT
4.1 Working principle
The gas sample is taken in through the gas probe, by a diaphragm suction pump inside the instrument.
The measuring probe has a sliding positioning cone that allows the probe to be inserted in holes with a diameter
of 11 mm (0.43") to 16 mm (0.65") and to adjust the immersion depth. It is recommended to have the gas
sampling point roughly in the center of the flue/stack.
The sample gas to be analyzed shall reach the measurement cells after being properly dehumidified and purified
from the residual combustion products. For this purpose, a condensate trap is used, which consists of a
transparent polycarbonate cylinder placed along the rubber hose of the sampling probe. Its purpose is to
decrease the air speed so that the heavier fine dust particles can precipitate and the vapor in the combustion
gases can condensate. The condensate trap must be always kept in the vertical position in order to prevent
condensate from touching the measurement cells. This is also the reason why it is important to periodically drain
the trap at the end of each test. A replaceable low-porosity line filter is placed after the condensate trap aimed at
keeping the solid particles suspended in the gases. It is recommended to replace the filter whenever significantly
dirty (see chapter 10.7 'End of the analysis'). The gas is then analyzed in its components by electrochemical and
infrared sensors. The electrochemical cell guarantees high precision results in a time interval of up to about 60
minutes during which the instrument can be considered very stable. When measurement is going to take a long
time, we suggest auto-zeroing the instrument again and flushing the inside of the pneumatic circuit for three
minutes with clean air. During the zero calibrating phase, the instrument aspirates clean air from the environment
and detects the cells' drifts from zero (20.95% for the O2 cell), then compares them with the programmed values
and compensates them. The pressure sensor autozero must, in all cases, be done manually prior to measuring
pressure. The values measured and calculated by the microprocessor are viewed on the LCD display which is
backlit to ensure easy reading even when lighting is poor.
4.2 Measurement cells
The instrument takes advantage of pre-calibrated FLEX-series gas sensors for the measurement of Oxygen (O
Carbon Monoxide (CO - Hydrogen compensated measurement, Nitrogen Oxide (NO), Nitrogen Dioxide (NO
Sulphur Dioxide (SO
) and Hydrogen sulfide (H
2
have to be replaced periodically when exhausted. Measurement of the oxygen (%O
electrochemical cell that loses sensitivity over time because it is constantly exposed to 20.9% Oxygen in ambient
air. The toxic gases (CO, SO
natural deterioration being intrinsically lacking of oxidation processes. The measurement cells are
electrochemical cells made up of an anode, a cathode, and an electrolytic solution, which depends on the type of
gas to be analyzed. The gas penetrates the cell through a selective diffusion membrane and generates an
electric current proportional to the absorbed gas. Such current is measured, digitalized, temperature-
compensated, processed by the microprocessor, and displayed. The gas shall not be at such a pressure to
damage or destroy the sensors; for this reason the suction pump is continuously adjusted, in order to ensure an
appropriate flow to the sensors. The maximum estimated allowed pressure is ±100hPa gage.
The response times of the measurement cells used in the analyzer are:
O
=
20 sec. at 90% of the measured value
2
CO(H
) =
50 sec. at 90% of the measured value
2
CO
=
50 sec. at 90% of the measured value
CO
=
180 sec. at 90% of the measured value
NO
=
40 sec. at 90% of the measured value
NO
=
50 sec. at 90% of the measured value
2
SO
=
50 sec. at 90% of the measured value
2
H
S
=
50 sec. al 90% of the measured value
2
NH
=
90 sec. al 90% of the measured value
3
H
=
90 sec. al 90% of the measured value
2
H
=
240 sec. at 90% of the measured value
2
CH
=
90 sec. at 90% of the measured value
4
It is therefore suggested to wait 5 minutes (anyway not less than 3 minutes) in order to get reliable analysis data.
If sensors of poison gases are submitted to concentrations higher than 50% of their measurement range for more
than 10 minutes continuously, they can show up to ±2% drift as well as a longer time to return to zero. In this
case, before turning off the analyzer, it is advisable to wait for the measured value be lower than 20ppm by in
taking clean air. If there is an automatic calibration solenoid, the device performs an automatic cleaning cycle and
it turns off when the sensors return to a value close to zero.
The auto-zero solenoid valve allows the operator to turn the instrument on with the probe inserted in the flue. Up to
4 alarm set points are programmable with visual and acoustic signals for the relevant measurement parameters.
The UNI 10389-1 standard provides that the instrument must be calibrated by a certified laboratory that is
authorized to issue annual calibration certificates. Exhausted cells can be easily replaced by the user without
depriving himself of the instrument and without complicated calibration procedures with certified mixtures as they
are pre-calibrated before being supplied.
Seitron certifies the accuracy of the measurements only upon a calibration certificate issued by its laboratory or
other approved laboratory.
S). The sensors do not need particular maintenance yet they
2
, NO, NO
) are measured with electrochemical sensors that are not subject to
2
2
11
),
2
),
2
) is carried out with an
2
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