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Depending on application, this basic
concept is applied in three different ways:
SBSW (Single
beam single wave)
Used where a miniature transducer
is required. The light source is electronically modulated,
removing the need for a motor and rotating filters.
Benefits:
- Fast response - used where real-time
measurements are required, faster compared to commonly
used alternative solutions, such as electrochemical
techniques.
- High stability and accuracy - a specially
designed source and temperature control sensor.
- Low maintenance requirements - quality
manufacture and design.
SBDW (Single
beam double wave)
A pair of optical filters are mounted on a rotating disc.
They pass through the beam of light alternately. One filter
(the measure filter) is chosen to pass light only at a
wavelength that the gas to be measured absorbs. The other
filter (the reference filter) has a light passed through
it at a wavelength unaffected by the gas to be measured.
The difference in absorbance is measured by the detector
and provides a direct output of the gas concentration.
Benefits:
- Fast response - used where real-time
measurements are required, faster compared to commonly
used alternative solutions, such as electrochemical
techniques.
- High stability and accuracy - the
single-beam, dual wavelength technique and gas filter
correlation (Gfc) are virtually immune to obscuration
of the optics. This prevents drift hence reducing calibration
frequency.
- Unaffected by background gases -
a result of Servomex application expertise enhanced
by the inherent selectivity of gas filter correlation.
- Low maintenance requirements - quality
manufacture and design.
(Gfc) Gas filter correlation
Used where extremely accurate low level measurements are
required or where background gases have the potential to
interfere with the measurement.
The measure and reference filters are replaced with gas
filled cuvettes. The reference cuvette is filled with a
sample of the gas to be measured, the measure cuvette with
(typically) nitrogen. This technique is known as 'Gas Filter
Correlation'.
Benefits:
- Fast response - used where real-time
measurements are required, faster compared to commonly
used alternative solutions, such as electrochemical
techniques.
- High stability and accuracy - the
single-beam, dual wavelength technique and gas filter
correlation (Gfc) are virtually immune to obscuration
of the optics. This prevents drift hence reducing calibration
frequency.
- Unaffected by background gases -
a result of Servomex application expertise enhanced
by the inherent selectivity of gas filter correlation.
- Low maintenance requirements - quality
manufacture and design.
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