Yokogawa In-Situ Gas Analyzer TDLS200 - Manual (Page 11)

<2. INTRODUCTION AND GENERAL DESCRIPTION> 2-3 2-1
IM 11Y01B01-01E-A 6th Edition :Feb 13, 2013-00
2 INTRODUCTION AND GENERAL DESCRIPTION
The TDLS200 TDLS analyzer is designed to measure
selected target gases in gas phase samples directly
at the process point (across stack, across pipe,
etc.), close coupled/by-pass leg or in full extractive
systems (flow cell).
The analyzer measures free molecules on a path
averaged basis. Unless there is an extractive
sampling system up-stream that removes water (or
other condensables) then the measurements are
considered to be on a ‘Wet Basis’.
Measurements are possible (with correct analyzer
configuration) at the following conditions:
• Gas temperatures up to 1500˚C (2730˚F)
• Gas pressures up to 10 BarG (145 psig)
• High Particulate loading (as a function of mea
surement path length)
Each application may differ in maximum
limitations depending upon the combination of
gas temperature, gas pressure, optical path length
and concentration of the gas being measured. The
standard analyzer is designed for operation in a Safe
Area (General Purpose). The addition of a Purge
System facilitates operation in Hazardous Areas in
accordance with the relevant UL, CSA and ATEX
standards for gaseous releases.
The basic TDLS200 analyzer comprises two units,
the Launch Control Unit and Detect Unit.
Various Process Interface configurations are
available for connecting the analyzer to the
measurement point. Several options may be added
to the standard analyzer such as:
• Mini Display
• 6.5” screen and keypad
• Display sun shield
• Optional Universal Power Supply (with or
without a Mini Display)
• Remote Interface Unit (not required for normal
operation)
• Hazardous Area purge systems
• Other options may also be added.
2.1 functional Description
Tunable Diode Laser Spectroscopy (or TDLS)
measurements are based on absorption
spectroscopy. The TDLS200 Analyzer is a TDLS
system and operates by measuring the amount of
laser light that is absorbed (lost) as it travels through
the gas being measured. In the simplest form a
TDLS analyzer consists of a laser that produces
infrared light, optical lenses to focus the laser light
through the gas to be measured and then on to a
detector, the detector, and electronics that control
the laser and translate the detector signal into a
signal representing the gas concentration. Gas
molecules absorb light at specific colors, called
absorption lines. This absorption follows Beer’s Law.
Using a Tunable Diode Laser as a light source for
spectroscopy has the following benefits:
• Sensitivity. As low as 10 -6 by volume, lower
with path length enhancement.
• Selectivity. The narrow line width of the laser is
able to resolve single absorption lines. This
provides more choices of a particular peak
to use for measurement, usually allowing one
isolated peak to be used.
• Power. Diode lasers have power ranging from
0.5 mW to 20 mW. Also, being highly coherent
this allows measurement in optically thick
environments (high particulate loading).
• Monochromatic, no dispersive element (filter,
etc.) required. Light source itself is selective.
• Tunable Wavelength can be swept across the
entire absorption feature, this allows resonant
(peak) and non resonant (baseline)
measurement during every scan. By
measuring the baseline and peak power at the
detector, transmission can fluctuate rapidly by
large amounts without affecting the
measurement. This is useful for high particulate
applications.
1-3