- Model APSA-370 - Ambient Sulfur Dioxide Monitor

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The APSA-370 is a device for the continuous monitoring of atmospheric SO2 using UV fluorescence. The APSA-370 employs an proprietary, internal dry-method sampling device to achieve the highest levels of sensitivity and accuracy. The dry-method, due to its minimal maintenance requirements capability of continuous monitoring and instantaneous analysis of gas in its unaltered state, has been a preferred method for monitoring the atmospheric pollution.

  • 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.

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

  • SO2+hv1→SO2
  • SO2→SO2 + hv2
  • SO2→+SO+(O)
  • SO2+M→ SO2+M

Here, (1) shows the excited state of the SO2 molecules that have absorbed the amount of energy hv1 by ultraviolet radiation. (2) shows the amount of energy, hi/2 emitted by the excited molecules as they return to the ground state. (3) shows the decomposition 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 carefully 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.

  • Principle: UV fluorescence (UVF)
  • Application: SO2 in ambient air
  • Range: Standard ranges: 0-0.05/0.1/0.2/0.5 ppm; auto range ~ manual range selectable; can be operated by remote switching.
    Optional (measurable) ranges: 4 ranges selectable from 0-10 ppm, within 10 times range ratio; auto range ~ manual range selectable; can be operated by remote switching.
  • Repeatability: ±1.0% of F.S.
  • Linearity: ±1.0% of F.S.
  • Sample gas flow rate: Approx. 0.7L/min
  • Indication: Measured value, range, alarm, maintenance screen
  • Alarms: During AIC, zero calibration error, span calibration error, temperature error in catalyzer, etc.
  • On-screen messages are available in four languages: English, German, French, and Japanese.
  • Input/output:
  • 0-1 V/0-10 V/4-20 mA, to be specified (2 systems: either (1) momentary value and integrated or (2) moving average value)
    • Contact input/output
    • RS-232C
  • Power: 100/110/115/120/220/230/240 VAC, 50/60 Hz (to be specified)
  • Dimensions: 430(W) x 550(D) x 221(H) mm
  • Mass: Approx. 19 kg.

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