The instrument is based on the measurement of the absorption of the instrument's laser light emitted by the instrument's diode by the HCl molecules. Concentration is linearly related to laser beam weakening. This particular method guarantees the total absence of any interference from other atmospheric constituent. The sensor has been devised to be placed directly on the exhaust chimney, and is made of three distinct modules each containing:
- The laser source and the beam emission optics.
- Reception optics and revelators
- Analyzer's maintenance electronics.
This division allows the positioning of the first two modules
(emission optics and reception optics) inside the chimney
in such a way that the beams cross the chimney from side to
side. This instrument uses the so called "double tone modulation"
survey technique, in order to obtain the required sensitivity,
and employs a reference cell to "actively" stabilize the laser
emission frequency .
The system is wholly controlled with an internal CPU. The
CPU manages the measurements, and analyzes and transmits data.
Among its many functionalities, the system offers the option
of a periodical recalibration. This operation can be done
at any time, without removing the sensor, and without stopping
or hindering in any way the industrial process. The recalibration
is performed by setting a calibrating optic cell containing
a known mix of HCl and Nitrogen along the laser beam. The
entire recalibration procedure lasts about 2 minutes.
The system has been tested at the CIS (Consorzio Intercomunale
Servizi) incinerating plant of Prato-Montale-Agliana, managed
by Ansaldo in Montale (Pistoia).
For this test, the system was set on the top of the exhaust
chimney, about 30 m above the ground, close to the conventional
sampling point of the instrument actually monitoring the plant.
Technical data
- Sizes:
Emission optic: 26·33·20 cm3
Reception optic: 16·21·20 cm3
Electronics: 11·11·11 cm3 - Survey technique: double tone frequency modulation
- CPU: Pentium2 266 MHz
- Output: 0÷10 V, 4÷20mA, RS-232.
- Data can be recorded both on hard and floppy disk..
