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GA-40 T plus CONSTRUCTION

4 CONSTRUCTION

The picture on page 53 shows a block diagram of the GA-40 T plusplus.

Here is a description of the individual components.

4.1 Elements of gas circuit

4.1.1 Gas probe with in-line filter

The flue gas is sampled with the probe pipe (typical lengths: 150 mm, 300 mm, 750 mm and 1500 mm) and

drawn through the heated filter. This filter removes the solid material and dust from the flue gas and, due to

the heating, ensures that the water vapour does not condense on the filter. The flter maintains the flue gas

temperatureabove 95 °C. The clean gases are then passed through the heated hose into the cooler block. The

heated hose is likewise designed to prevent condensation in the flue gases.

The cooler of the dryer condenses the water vapour in the flue gases and it is automatically removed by a

peristaltic pump. The dry flue gases pass through a three way valve and the membrane pump, after whichthe

gas stream is split, with part going to the O

, NO and optional sensors, and the other part going through

a non-return valve to the CO sensor.

The gas chamber has been designed to ensure that an over-range of the CO sensor will not lead to an

interruption of the measurements carried out by the other sensors. The automatic operation of the purging

pump will only flush the CO sensor with fresh air.

4.1.2 Gas pump

The internal gas pump draws the gas into the GA-40 T plusplus and passes it through the gas chambers. The self-

cleaning pump is a high quality item and is known to be extremely reliable.

The gas cells operate best with a flow rate of 90 l/h, which is set at the factory and compensates automatically

for flow restrictions or changes in battery voltage.

4.1.3 Gas chamber

The gas chamber is fitted with between three and six gas sensors. Oxygen, carbon monoxide and nitric oxide

sensors are fitted as standard equipment. The other cells are chosen when the instrument is ordered. The gas

chamber of the GA-40 T plusplus system is characterised by minimal dead capacity, which leads to low inertia of

the analyser indications. In addition to the gas sensors, there is a temperature sensor placed in the chamber for

temperature compensation of the sensors.

4.2 Measurement system

4.2.1 Gas sensors

The oxygen concentration is measured using an electrochemical cell. The sensor signal is directly proportional

to the oxygen volume concentration. The oxygen sensor needs no calibration with standard gases - it is fully

calibrated during the initial calibration when a point corresponding with the contents of oxygen in clean air

(20.95%) is determined.

The toxic gases are also measured using electrochemical cells

Table 1 presents all the gas sensors available. Any of them can be used in GA-40 T plusplus system.

To guarantee long-lasting, trouble-free function of electrochemical sensors the following points are important:

G the stated maximum measuring range of the sensor should not be exceeded.

G all the gas sensors can react unpredictably to certain chemicals which are not typical for

combustion gas composition. For this reason, it is absolutely forbidden

to wash the parts of the gas line with chemical

solvents. The vapours from such solvents can get inside the gas chamber and result in

destabilisation or even permanent damage of the gas sensors.

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