Teledyne instruction manual M100AH SO2 Analyzer, Principle of Operation

Teledyne API Model 100AH SO2 Analyzer Instruction Manual, 02417, Rev. D

4 THE M100AH SO2 ANALYZER

4.1 Principle of Operation

The operation of Teledyne API Model 100AH Analyzer is based upon the well proven technology from the measurement of fluorescence of SO2 due to absorption of UV energy. Sulfur Dioxide absorbs in the 190 nm - 230 nm region free of quenching by air and relatively free of other interference.

The UV lamp emits ultraviolet radiation which passes through a 214 nm filter (allowing 214 nm light through), exciting the SO2 molecules and producing fluorescence which is measured by a PMT with a secondary UV filter. The equations describing the above reactions are as follows:

SO2 + hv1 →Ia SO2* (1)

The ultraviolet light at any point in the system is given by:

Ia = I0 [1 − exp(− ax(SO2 ))] (2)

Where I0 is the UV light intensity, a is the absorption coefficient of SO2, x the path length, and (SO2) the concentration of SO2. The excited SO2 decays back to the ground state emitting a characteristic fluorescence:

SO2 * →KF SO2 + hv2 (3)

The block diagram in Figure 4-1illustrates the general operation principle of the Model 100AH. Ultraviolet light is focused through a narrow 214 nm bandpass filter into the reaction chamber. Here it excites the SO2 molecules, which give off their characteristic decay radiation. The sample is under vacuum to minimize quenching effect from CO2 and O2. A second filter allows only the decay radiation to fall on the PMT. The PMT transfers the light energy into the electrical signal in the sample stream being analyzed. The preamp board converts this signal into a voltage which is further conditioned by the signal processing electronics.

The UV light source is measured by a UV detector. Software calculates the ratio of the PMT output and the UV detector in order to compensate for variations in the UV light energy. Stray light is the background light produced with zero PPM SO2. Once this background light is subtracted, the CPU will convert this electrical signal into the SO2 concentration.

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