Features
 
The APSA-370 uses an innovative detector and a new optical system for low background, high sensitivity (0.05 ppm F.S.), and greatly improved stability.

The fluorescent chamber design gives measurements with minimum influence from moisture.

The unit has built-in aromatic hydrocarbon cutter with a selective transmission membrane. This reduces the influence of interference components. Coupled with Horiba's unique flow-path, it also makes it possible to extend the working life of the cutter and to take measurements effects of sample flow variations.

In comparison with the FPD method, the APSA-370 design is (1) highly selective for SO2, (2) requires no supplemental gas, and (3) gives linear output.

Compensation for the lamp's luminous energy decline guarantees prolonged calibration stability.

The sample inlet has a built-in Teflon filter.

Principles

UV fluorescence
The UV fluorescence method operates on the principle that when the SO2 molecules contained in the sample gas are excited by ultraviolet radiation they emit a characteristic fluorescence in the range of 220-420 nm. This fluorescence is measured and the SO2 concentration is obtained from changes in the intensity of the fluorescence.
The reactive mechanism is
(1) SO2+h ν1 → SO2*
(2) SO2* → SO2+h ν2
(3) SO2* → SO+(O)
(4) SO2*+M → SO2+M
Here, (1) shows the excited state of the SO2 mole-cules that have absorbed the amount of energy h ν1 by ultraviolet radiation. (2) shows the amount of energy, h ν2 emitted by the excited molecules as they return to the ground state. (3) shows the decomposi-tion by the light emitted from the excited molecules. (4) shows the quenching, i.e., the energy lost by the excited molecules colliding with other molecules. The APSA-370 uses an Xe lamp as the light source, and the fluorescent chamber design minimizes scattered light. The optical system has been care-fully designed with low background light, making it possible to take measurements with a highly stable zero point. In addition, a reference detector monitors any fluctuation in the intensity of the light source. This allows the unit to calibrate itself automatically for sensitivity, resulting in greater span stability.


Specifications