<2 INTRODUCTION AND GENERAL DESCRIPTION> 2-1
IM 11Y01B02-01E-A 3rd Edition June 19, 2012-00
2 Introduction and General Description
The TDLS220 TDL analyzer is designed to measure concentrations of selected target chemical species
(most often Oxygen or Moisture) in gas phase samples that have been extracted from the process.
Typically, there is a continuous flow of analyzed gas through the TDLS220 optical gas cell. The gas
should be pre-conditioned to meet the sample inlet requirements including (but not limited to) particulate
removal, dew point control (heated), flow and pressure control, etc. Chemical composition of the sampled
gas mixture is determined by the end user. It is the end user responsibility to ensure safe delivery of the
sampled gas to the analyzer and the subsequent return of the gas to the process or its utilization after
analysis.
The analyzer measures chemical concentrations on a path averaged basis. Unless the extractive sampling
system up-stream 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 120˚C (248˚F)
• Gas pressures up to 4 BarG ( 75psig)
Each application may differ in maximum limitations depending upon the combination of gas temperature,
gas pressure, 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.
The basic TDLS220 analyzer comprises a mounting panel with three units attached, the Controller housing,
the Power Supply/Heating enclosure and Flow Cell (or optional heated flow cell).
Several options may be added to the standard analyzer such as:
• Mini Display (4 line, 20 character) or 6.5” screen and keypad
• Remote Interface Unit (not required for normal operation)
• Insulated and Heated flow cell
• Hazardous Area purge systems
• Other options may also be added
2.1 Functional Description
Tunable Diode Laser (or TDL) measurements are based on absorption spectroscopy. The TDLS220
Analyzer is a TDL 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 TDL analyzer consists of a laser that
produces infrared light, optical lenses to focus the laser light through the gas to be measured onto a mirror
and back through the gas 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 pathlength 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 0.5mW to 20mW.
•
Monochromatic, no dispersive element (filter, etc.) required. Light source itself is selective.
• Tunable. Wavelength can be swept across the entire absorption feature, which allows
resonant (peak) and non resonant (baseline) measurement during every scan.
