Listed below are some of the frequently asked questions:
Basic Explanation of our Technology (OP-TDL)
What it does
Our technology is a piece of analytical instrumentation that detects and/or monitors gas concentrations through an Open-Path or Line-of-Sight measurement in the ambient atmosphere.
The primary uses of our gas analyzers is to:
-Continuously monitor gas concentrations over open area sources.
-Provide immediate and unambiguous detection of gas leaks.
What kind of technology is this?
The most commonly referred to name of our technology is Open Path – Tunable Diode Laser (OP-TDL) or Laser.
Our technology uses the detection principle of Tunable Diode Laser Absorption Spectroscopy (TDLAS) and a modulation technique called Wavelength Modulation Spectroscopy (WMS).
OP-TDL belongs to the ‘Open Path – Optical Remote Sensing’ family:
How it works
Every gas is composed of atoms or molecules. These molecules have various frequencies or wavelengths at which they resonate or vibrate when the laser light comes into contact with them. Our technology uses infrared laser light to essentially count the number of absorbed molecules in its measurement path to accurately and reliably quantify the active trace gas concentration.
Explaining Open-Path Measurements and ppm-m
Benefits of using Lasers to make Open Path Measurements
OP-ORS provides far greater spatial (covers larger area) and temporal (fast response time) resolution than compared to traditional point sensors.
With open path measurements you’re less likely to miss the leak or under/over estimate the size. Most point sensors take between 30-90 seconds to register a reading where OP-TDL has a response time of 1 second.
The majority of the point sensors on the market are poisoned by the gas that they have been designed to detect. The benefit of using laser light to detect or monitor gas concentrations in the active measurement path is that it is difficult, if not impossible, to poison or destroy laser light. OP-TDL gas analyzers are great for quantifying gas concentration with little to no measurement drift and the analyzer cannot be mechanically over ranged due to high or constant gas exposure. These OP-TDL analyzers are used in “it is safe to go back in” scenarios as this will continue to work when all other gas detection technologies have failed.
Parts Per Million – Meter
Open-path measurements are slightly different from the traditional point measurement. A good visualization of the how open-path measurements work is stacking the one square meter that we’re used to. The standard unit of measure for an open-path instrument is Parts Per Million – Meter (ppm-m).
There are two different ways to discuss to open-path measurements: Path Integrated Concentration (PIC) and Path Average Concentration (PAC). Path Integrated Concentration units of measure is ppm-m and a good way of thinking of PIC is simply the OP-TDL counting the number of molecules in the active measurement path. The PAC is the PIC divided by the physical path length (or the length of the active measurement path).
Small Highly Concentrated Plume:
Large Dispersed Plume:
How do the specifications work?
How Boreal Laser and other Open Path – Optical Remote Sensing technologies classify their gas performance specifications is with three key variables:
-Minimum Detectable Limit (MDL): The lowest concentration value that the analyzer can reliably and repeatedly observe/detect.
-Sensitivity: The smallest change in concentration above the MDL that the analyzer can reliably and repeatedly observe/detect.
-Full Scale: The end of the analyzers linear and calibration range.
The performance specifications are all classified with a 1 metre path (ppm-m). The great thing about open-path measurements is that when the path length increases, the active measurement path is made larger. With a larger active measurement path it is possible to measure larger plumes of gas. If you remember, the OP-TDL technology simply counts the number of molecules in the active measurement path. This is important because as the path lengths and plumes sizes increase so does the systems sensitivity!
WHAT IT DOES
- Boreal Laser utilizes a mono-static configuration with the analyzer being a transceiver and having a passive retro-reflector returning the laser light.
- The distance between the transceiver and the retro-reflector forms the physical path length and active measurement path.
- Reflected light returns in the same direction as the incident light and the beam is reflected 180 degrees.
- A retro is like a section through a corner and has three faces that form the inside corner of a cube.
- If the location is outside and in a humid climate, a rain hood and some heating in the enclosure may be necessary to prevent condensation on the window.
- The retros can tolerate small vibrations and movement so the retro mounting does not need to be as robust as the mounting for the analyzer.
PATH LENGTH / RETRO TABLE
FOUR DIFFERENT LIGHT LEVEL SCENARIOS
The OP-TDL analyzer is an optical based instrument and requires the sent laser light to be collected. What is important, is that you have “enough” laser light and the GasFinder will let you know if it has enough laser light to perform it’s analysis. The GasFinder can handle up-to 95% beam block from items like dust, fog, sleet, snow, and steam. As a general rule of thumb, the near infrared laser can see slightly better than the human eye, so if you can see the retro-reflector from the transceiver the GasFinder should be able to as well.
Explanation of R2: The Confidence Factor
When the analyzer receives the returning laser signal after it has passed through the sample gas, the receiver converts it to the shape of a specific waveform or curve. This is the sample waveform. The analyzer also has a similar signal from the stored waveform of the calibration gas. These curves are then digitized and compared as two numeric arrays.
An accepted mathematical procedure to compare curves or numeric arrays is the Linear Least Squares Regression analysis. This analysis results in a measure of the similarity (R2), between the waveform of the sample gas and that of the calibration gas. A perfect similarity would give a value for R2 of 1.0, and a total mismatch would be 0.0.
The blue line represents the Linear Least Squares fit of the data and is the best fit of a straight line between the reference (X) and sample (Y) data points. The slope is a component in the ratio-metric calculation of gas concentration.
A typical plot of concentration versus R2 will give the following graph:
With lower levels of sample gas, the R2s decrease, and equal zero when there is no gas present. As the signal from the gas becomes stronger, the effect of noise, both electronic and optical, is reduced and the R2s will increase (i.e., the signal to noise ratio will increase). The general shape of the plot is the same for all gases; however, the x-axis values will depend on the sensitivity of the instrument to the gas species being observed.
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