
11 K600000000EJ 032438 220519
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 gas sample is cleaned of humidity and impurities by a condensate trap and filter positioned along the rubber
hose that connects the probe to the analyzer.
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 (O2),
Carbon Monoxide (CO - Hydrogen compensated measurement, Nitrogen Oxide (NO), Nitrogen Dioxide (NO2),
Sulphur Dioxide (SO2) and hydrogen sulphide (H2S).
The sensors do not need particular maintenance yet they have to be replaced periodically when exhausted.
Measurement of the oxygen (%O2) is carried out with an electrochemical cell that loses sensitivity over time
because it is constantly exposed to 20.9% Oxygen in ambient air.
The toxic gases (CO, SO2, NO, NO2) are measured with electrochemical sensors that are not subject to 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 ±40 WC gauge (±100hPa).
The response times of the measurement cells used in the analyzer are:
O2 =20 sec. at 90% of the measured value
CO(H2)=50 sec. at 90% of the measured value
CO =50 sec. at 90% of the measured value
NO = 40 sec. at 90% of the measured value
NO2=50 sec. at 90% of the measured value
SO2=50 sec. at 90% of the measured value
H2S=50 sec. at 90% of the measured value
H2=90 sec. al 90% of the measured value
It is therefore suggested to wait 5 minutes (anyway not less than 3 minutes) in order to get reliable
analysis data.
If sensors of toxic 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.
E Instruments certifies the accuracy of the measurements only upon a calibration certificate issued by its
laboratory or other approved laboratory.
4.3 CO dilution
One of the characteristics of the electrochemical sensor for the measurement of CO is the need to require very
long self-calibration time in case it has been in contact with high gas concentration (greater than the full scale) for
a long time. The CO sensor is therefore protected in this instrument by an automatic dilution system that allows to
extend the measuring range of the sensor without overloading the sensor itself.
The dilution system allows to have the CO sensor efficient any time and ready to perform properly even in case
4.0 DESCRIPTION OF THE PRODUCT