FAQ

Laser Based – Open Path Gas Detection Common Queries:

  • Open Path vs. Fixed Point Gas Detection

    Open Path vs. Point Gas Detection

    Comparison between technology types

    There are a number of key differences that we want to make sure that you’re aware of.

    To help illustrate the importance of the statements above, this can be visualized by thinking of Traditional Fixed Point Gas Detection as a singular Fence Post and the Laser Based – Open Path Gas Detectors as the whole Chain Link Fence.

    Area Coverage:

    Fence Analogy: The odds of an object coming into contact with the larger Chain Link Fence is greater than that of the small Fence Post based purely on the available surface area.

    Gas Detection: The same is true that the odds of a plume of gas passing through the Active Measurement Path of the Laser Based – Open Path Gas Detector than it is of the small contact area of the Traditional Fixed Point Gas Detector.

    Laser Based – Open Path Gas Detection should seriously be considered if 3-4 Fixed Point Gas Detectors are required not only for its technical benefits but also its commercial advantages (i.e. Capital and Operational Costs).

    Robustness:

    Fence Analogy: If a large object (i.e. vehicle) were to rapidly come into contact with the fence, the Chain Link portion will be the strongest and most robust part of the fence (i.e. think of the vehicle barriers between highways). Under this same example, a singular Fence Posts will not be anywhere as robust as the Chain Link.

    Gas Detection: Extreme environmental conditions (such as high temperature or humidity) and continuous/high concentrations of gas will not consume, poison, or reduce the life span of Laser Based – Open Path Gas Detection like it would for Traditional Fixed Point Gas Detection.

    It is important to note that all types of Sensing Elements have their own specific strengths and weakness but by using Laser Based – Open Path Gas Detection, you can significantly reduce your maintenance burden. By using various Sensing Element Types, this will create multiple layers of protection can increase the up-time in various conditions.

    Fail Safe:

    Fence Analogy: Visually, it is more obvious to see if the whole Chain Link Fence has fallen vs. losing a single Fence Post.

    Gas Detection: Traditional Fixed Point Gas Detection products are Non-Fail Safe and therefore provide no feedback to the Safety System that their ability to detect has been compromised. Alternatively, Laser Based – Open Path Gas Detection is fully Fail Safe and has sophisticated self-diagnostics that will notify the Safety System in the case of an inhibition or fault.

    For example, Laser Based – Open Path Gas Detection will output a specific inhibition status condition for Beam Block conditions and the end-user has the ability to implement Bead Block Time Delays (i.e. 0-300 Seconds with 30 Seconds being the average) to reduce/eliminate nuisance calls for maintenance.

    Side-by-Side Comparison:

    Below is a comparison table between Laser Based – Open Path Gas Detection and Traditional Fixed Point Gas Detectors:

    Early Warning and Rapid Intervention Saves Lives:

    Due to the Large Area Coverage and Fast Speed of Response of Laser Based – Open Path Gas Detection, when compared with Traditional – Fixed Point Gas Detectors, it should:

    Have a higher likelihood of detecting a loss of containment (even with changing air currents within process buildings and/or wind direction/velocity in outdoor process areas)

    If a loss of containment is detected, Laser Based – Open Path Gas Detection:

    Under similar circumstances to Traditional – Fixed Point Gas Detection, should respond to the presence of gas much faster.

    Should register more representative concentrations and exposure duration compared to the small sampling area and the slow to respond/recover Traditional – Fixed Point Gas Detectors.

  • Detector Selection Decision Guide

    Detector Selection Decision Guide

    Important items to Consider

    When selecting the appropriate Sensing Element for an application, it must reliably detect a hazardous release or accumulation of gas as early as practical AND before it is large enough to cause an escalating situation or health hazard.

    Below is a tool to help select if your detector selection is SAFe (Suitable, Acceptable, and Feasible).

    Suitability: Which Sensing Elements could be used for this application? Below are some questions that will help determine if the Sensing Element meets your needs.

    1. Detected Gas: Does this Sensing Element detect the gas of interest in the desired measurement range?
    2. Area Classification: Does this Sensing Element have the appropriate Hazardous Area Classification?
    3. Environmental Conditions: Do the environmental conditions have a detrimental effect on the performance or lifespan of the detector? (e.g. Temperature, Pressure, Humidity, etc.)
    4. Interferences: Are there any other potential Interferences (e.g. Interfering gases, vibration, sunshine, etc.)?
    5. Adverse Effects: Does the presence of the target gas effect the performance or lifespan of the Sensing Element (e.g. Flooding, Saturation, Over Ranging, Poisoning, or Fouling)?
    6. Contaminants: Are there any other contaminants that may effect performance or longevity (e.g. dust, dirt, debris, misting, aerosols, etc.)?

     

    Acceptability: Which Sensing Element are you willing to stake your professional reputation on to protect personnel in a safety critical application (e.g. Input to a Fire & Gas Safety (FGS) System)?

    1. Fail-Safe Design: Does the Sensing Element provide feedback if it operation has been inhibited (e.g. poisoning, flooded, fouled, fallen asleep, bag placed over a sensor, etc.)?
    2. Measurement Drift: Does the Measurement Drift of the Sensing Element still allow you to confidently use it to confirm a loss of containment and initiate executive action?
    3. Response Time: Are you confident in the placement of the Sensing Element that the plume of gas will be present at the detector long enough that it will illicit a response? Is the Response Time fast enough to detect a loss of containment before it is large enough to cause an escalating situation?
    4. Area Coverage: In congested or enclosed areas, it is assumed that plumes of gas will have a diameter of 5 – 10 m (15 – 30 ft). How many detectors will be required to provide acceptable area coverage for the application?
    5. Sensor Lifespan: How long does the Sensing Element survive in both ideal and expected conditions (e.g. Frequent/continuous gas exposure, high temperatures, high humidity, etc.)?
    6. Maintenance: Consider the maintenance burden required because of the lifespan and fail-safe nature of the Sensing Element.
    7. Consumables: Does the requirement for Consumables (e.g. Replacement Sensors, Calibration Gas) and human intervention make the overall Fire & Gas Safety System stronger or weaker?
    8. Poisoning: Will the Sensing Element survive continuous or large releases of gas sufficiently to provide the protection that is required by the Fire & Gas Safety (FGS) System?

    Feasibility: When do the economics of Laser Based -Open Path Gas Detection over come Traditional-Fixed Point Gas Detection? It is vital to weight the Total Cost of Ownership and the performance of the Sensing Element.

    1. Risk Management: What is the value or importance of initiating recovering actions as soon as possible after a loss of containment as been detected?
    2. Capital Costs for Comparable Area Coverage: Comparing the price of Open Path Gas Detection to Fixed Point Gas Detection can be like comparing apples to oranges. However, Fixed Point Gas Detectors should be placed every 5 – 10 m (15 – 30 ft) to provide similar area coverage.
    3. Engineering & Design: There is a cost associated with generating the Technical Specification, P&IDs, Loop Drawings, and Logic & Control for each individual Sensing Element.
    4. Infrastructure & Procurement: Each Sensing Element will require Brackets, Fittings, Junction Boxes, Cabling, Cable Trays, I/O Cards to be designed, procured, manufactured, and delivered. Each additional Sensing Element can add a significant cost.
    5. Installation & Commissioning: A significant amount of time an money is committed to Installation & Commissioning Acitities (e.g. Purchasing, Shipping, Warehousing, Unboxing, Assembly, Location ID, Construction Supervision/planning, Erecting Scaffolding/Using Manlifts, Mounting, Terminating, Cable/Instrument Tags, Loop Tests, Power-Up, Calibration, Calibration Tags/Reports, DCS Programming, and Completing As-Builts).
    6. Licensing Fee for each I/O Point in a DCS System: Typical cost are between $1,000 to $3,000 per Loop per Year on a DCS System. Every Analog and Relay Output from each Sensing Element can add-up to significant operational costs over time.
    7. Time between Planned Intervention Intervals: This is dictated by a number of factors such as Governmental, Industry, Insurance, Corportate, or Site Specific Requirements.
    8. Cost of each Planned Intervention Interval: The costs for these items are not often tabulated and well understood but it is important to consider the time spent by  Maintenance Planners, Request/Procurement/Receiving/Warehousing of Sensors and Gas, Generating Work Orders, Writing Permits, Ensuring that Safety Systems are By-Passed, Technicians Hours, Calibration Report, Calibration Tags, Etc.).
    9. Cost of Known Failure: Loss of Operator Confidence, Decreased effectiveness of Engineered Safety System, and Special Procedures to run within Critical Safety Systems.
    10. Cost of Unknown Failure: What could the cost of having a Sensing Element not detect a loss of containment or dangerous accumulation of gas because of insufficient area coverage, slow speed of response, or even worse that the Sensing Element had unknowingly become non-functional?
  • How to best use Open Path Gas Detection?

    Deployment Strategies

    Get the most out of your investment

    The versatility of the Open Path (OPX) Head Assembly provides the end-user with a number of different monitoring and detection strategies:

    Equipment Specific Monitoring:

    • Path lengths usually range from 0.5 to 5 m (1.5 to 15 ft) and are still technically be considered a Point Measurement.
    • These shorter path lengths are often placed close to process equipment that may have a higher likelihood of having a loss of containment to provide fast localized detection of the leak.
    • The Remote Point (RPX) Probe may also be used for this strategy.

    Area Monitoring (Most Common):

    • Typical path lengths range from 5 to 50 m (15 to 150 ft) and are often placed in areas where personnel are likely to be present (e.g. walkways, galleys, etc.).
    • For this strategy, the purpose is to quickly detect either of a loss of containment or a dangerous accumulation of gas for personnel protection.
    • Rather than just monitoring for one potential leak source, there may be an area with multiple pieces of process equipment that may have higher probability of experiencing a loss of containment.

    Perimeter Monitoring:

    • Typical path lengths range from 50 – 500 m (150 to 1,500 ft).
    • Monitoring the perimeter of an entire process unit can provide the best area coverage to enable early warning for dangerous concentrations of toxic or combustible gases being released from within the perimeter or migrating from another process units all together.
    • The larger area coverage and fast speed of response helps to increase the odds of the plume coming into contact Active Measurement Path.

    The design goal should be to place an appropriate amount of the right type of sensing element in locations that provide the highest area coverage possible.

    By employing multiple monitoring and detection strategies, it will increase the odds of detection and the likelihood of intervening as soon as possible.

    Simple Path Placements

    Typical Orientations for Basic Uses

    The placement of the Open Path (OPX) Head Assemblies allow easy and straight forward installation for the Equipment Specific, Area, and Perimeter Monitoring Strategies.

    Simple Downwind

    Monitoring on one of boundary limits for a Gas Concentration Excursions can be very useful. Use example for this arrangement couple be monitoring between an Identified Possible Emitter (e.g. Well Head) and an occupied building (e.g. Neighboring Farm).

    Simple Upwind + Downwind

    This orientation is useful for helping to identify if the Gas Concentration Excursions are coming from the Identified Possible Emitter or elsewhere. For example, if the concentration excursions are only being detected on the downwind path, then it can be assumed that it is coming from the Identified Possible Emitter. In outdoor applications, the wind can blow in almost all directions within one day and by using the Simple Upwind + Downwind Orientation, it will help increase your odds of detection as the wind changes direction.

    Simple Triangle Perimeter

    By closing off the perimeter with Laser Based – Open Path Gas Detection, this helps eliminate gaps within the monitoring boundary. This three (3) Path Orientation is as efficient as it is economical. This helps to keep the Active Measurement Path close to the source while having extended “points of the triangle” to add additional area coverage.

    Simple Square Perimeter

    This mounting arrangement is the most common orientation because of its ability to provide exceptional area coverage while remaining out of the way for routine operational and maintenance activities.

    Advanced Path Placements

    Used to meet Sophisticated Monitoring Needs

    The use of these Advanced Path Placement Orientations can be used for any of the following reasons: Increased Area Coverage, Leak Localization and Voting Logic Confirmation (e.g. 2ooN).

    Layered Square Perimeter

    While there will be increased Area Coverage with this orientation, the real benefit is having two (or possibly four) Paths Confirm a Loss of Containment to help initiate Executive Action within your Fire & Gas Safety System.

    Layered Square Perimeter

    In addition to providing Loss of Containment Confirmation, the Layered Square Perimeter Orientation helps to combine the Monitoring Strategies such as Equipment Specific, Area, and Perimeter Monitoring. Following traditional Gas Detection Siting Principles, the Gas Concentration Excursions should be greater within the inter green perimeter than it is at the outer blue perimeter.

    Sectioned Square Perimeter

    The Sectioned Square Perimeter provides Loss of Containment Confirmation with two different Sensing Elements but it has additional benefits as well. This orientation provides the ability for better Leak Localization based off of wind direction and which paths are registering a concentration excursion. If Beam Blockage is a concern (e.g. Steam, Fog, etc.) then these shorter path lengths provide better resistant against the GasFinder entering a Low Light Scenario.

    Grid Localization

    By using Logic based off of Wind Direction or just by which Path is registering a leak, an estimate of a general area of the leak location can be inferred. With extending the path lengths beyond just a simple perimeter, this can create additional Area Coverage while still maintaining close proximity to the potential leak source.

    Grid Localization + Perimeter

    These orientations can be combined to further enhance the Area Coverage, Leak Localization and Voting Logic Confirmation.

  • Laser Based - Open Path Gas Detection Examples

    Application Examples

    Deployment of Open Path Gas Detection

    The examples below will highlight the advantages of using Laser Based – Open Path Gas Detection in the following applications.

    Rail (Un)Loading Terminal

    This Simple Downwind Path Orientation for the Area/Perimeter Monitoring Strategy is ideal for providing early warning of a Loss of Containment during the operational activity to protect personnel. With frequent making and breaking of connections to load or unload the rail cars, the odds of leak or release can be significantly increased. Often, there are high concentrations of toxic or combustible gases that can consume or poison Traditional – Fixed Point Gas Detection and make the use of Laser Based – Open Path Gas Detection ideal.

    Heat Exchanger Monitoring

    If the challenge of physically accessing the top of the exchanger to install, commission, and support Traditional – Fixed Point Gas Detection wasn’t difficult enough, the high temperatures and high wind velocity will reduce the lifespan of those Sensing Elements.  By using Laser Based – Open Path Gas Detection for Equipment Specific Monitoring to detect leaks in the tubing bundles, not only is the Open Path (OPX) Head Assembly easily accessible but because of the non-contact nature of the measurement, only the Laser Beam is exposed to the high temperatures.  By placing two, three, or four paths above the Exchanger Louvers, not only is the Area Coverage increased but in the event of a leak, the Fire & Gas Safety System has multiple independent Sensing Elements satisfying the Voting Logic required to Confirm the Loss of Containment.

    Multi-Storied Open Walled Process Areas

    In applications with multiple potential leak sources, it is best to focus your fixed monitoring on personnel protection with an Area Monitoring Strategy. By using a Simple Square Perimeter Path Orientation on each of the floors, regardless of the location of the leak or the direction of the wind, the odds of detecting the plume are significantly increased because the gas is channeled and forced to pass through one or two sides of the perimeter. Due to the Low Detection Thresholds and the Fast Speed of Response, Laser Based – Open Path Gas Detection can detect the presence of Small Intermittent Leaks. For these reasons, this is why this technology is used as a passive Leak Detection & Repair (LDAR) tool that, for example, can help identify the need for intervention in tightening the packing of a leaking valve.

  • How High do you mount Open Path Gas Detection?

    Mounting Height

    Typical height of the Open Path (OPX) Head

    It is typical for Open Path (OPX) Heads to be mounted 2.2m (7.2 ft) to 4m (13ft) above grade or walkways. This is so the height of a typical person does not cause a beam block scenario. This height arrangement is also close to the breathing height to provide warning for personnel detection.

    Estimated Plume Size

    Industry Based Assumptions

    There is a common assumption within the industry that:

    • Within Enclosed or Congested Areas, it is assumed that the plume could be between 5-10 m (15-30 ft) in diameter by the time it passing through the Active Measurement Path.
    • Within Open Areas, it is assumed that the plume could be between 10-20 m (30-60 ft) in diameter by the time it passing through the Active Measurement Path.

  • Can I use these Products in my Fire & Gas Safety System?

    FIRE & GAS SAFETY SYSTEM

    What does it do? Why it is important?

    For the purpose of Risk Management Mitigation, Fire & Gas Systems (FGS) are utilized to enable the recovery after a Loss of Containment (release and/or accumulation) by performing three basic functions:

    • Detect the Hazard with Sensing Elements (e.g. Toxic Gas, Combustible Gas, & Flame Detectors),
    • Confirm Loss of Containment with Logic Solvers or Safety System Controller (e.g. DCS, PLC, etc.), and
    • Initiate Executive Action with Final Control Elements (e.g. Horns, Strobes, Pumps, Valves, Solenoids, HVAC, etc.).

    It is important to note that Recovery Actions (e.g. Annunciation from Horns/Strobes, Manipulation of the Process, Control of HVAC System, etc.), cannot be taken until a Loss of Containment has been confirmed by the Logic Solver which often requires at least two (2) Sensing Elements to detect a leak.

    Therefore, it is vital that your Fixed Sensing Element can reliably and repeatably Detect a hazardous release or accumulation of gas as early as practical AND before it is large enough to cause an escalating situation or health hazard.

  • Who uses this Technology and what do they use it?

    Purpose of Use

    Uses of this Enhanced Sensing Element

    Often referred to as either Open Path Gas Detection or Line-of-Sight Gas Detection, this is considered an Enhanced Gas Sensing Element as it can be used for the purpose of:

    • Leak Detection/Safety Monitoring: Performance requirements are focused on alarm signaling for such purposes as Safety Warning and Executive Action.
    • Industrial Health & Hygiene Monitoring: Focused on the uncertainty of measurement of gas concentrations in the region of Occupational Exposure Limit Values (OELV).
    • Leak Detection & Repair (LDAR): Passive Monitoring for incipient fugitive emissions provides operations with another Process Variable (PV) that could provide them with early warning of an abnormal process condition that could require intervention.
    • Ambient Monitoring: Quantitative monitoring of specific constituents for compliance purposes.

    It is not uncommon for Laser Based – Open Path Gas Detectors to be used for one or more of the purposes listed above.

    Often there is one dominant driver to champion the project but multiple stakeholders can derive value and use from these measurements. Examples of these drivers are shown below.

    Project Drivers

    What drives the need?

    While these drivers may identify the need for detection, there may be latitude in which sensing elements are selected and how they’re used.

    It is important to understand how to best deploy the sensing elements to not only meet the minimum requirements but exceed them as well.

     

  • How to Align the Open Path (OPX) Head?

    For a Technical Walk-Through on how the Align the Open Path (OPX) Head: Click Here

  • Mounting Structures

    For more information: Click Here

General Technology Questions

Below are typical questions about the technology as a whole regardless of the application.

  • What you need to know about TDL

    Understanding the Fundamentals

    What you need to know about TDL/TDLAS

    At a glance, here is what you need to know about the GasFinder3-MC (Multi-Channel) Analyzer that combined with our series of Remotely Mounted Measurement Heads use a Laser Based Gas Detection principle called Tunable Diode Laser Absorption Spectroscopy (TDLAS) to Analyze, Monitor, Measure, and Detect gaseous molecules of a specific target gas.

    Tunable Diode Laser Absorption Spectroscopy (TLDAS) is quickly summarized below:

    • Laser Light is the Sensing Element: Near Infrared (NIR) Laser Light is generated from our High Quality Telecommunication Grade DFB Lasers. Laser Based Gas Analysis is primarily used for its Quantitative Performance in Difficult Applications, Fail-Safe Design, and Maintenance Friendly Operation.
    • This Counts Target Gas Molecules: As the Target Gas Molecules pass through the Active Measurement Path (i.e. Laser Beam), they’re absorbed and a proportional relationship between the number of “counted” target gas molecules and concentration exists.
    • Quantifiable Volumetric Measurement: The great benefit of this technology is its ability to be tuned to only detect the presence of one target gas. Tunable Diode Laser Absorption Spectroscopy is able to identify which gas that is being detected and give a very accurate and repeatable measurement.
    • No Interference + No False Alarms: Due to the selectivity of this technology, we’re able to select absorption lines that are free from interference from other gases, humidity, rain, snow, sunlight, particulates, etc.
  • Units of Measure for Open-Path Measurements
    Start with the Basics – Molecule Counter:

    The Laser Light emitted from the GasFinder is tuned to a specific wavelength/frequency where the Target Gas is absorbed. As Target Gas molecules enter the Active Measurement Path (i.e. laser beam), they’re absorbed and spectroscopic analysis of the collected laser light can very accurately and reliably detect how much of the Target Gas is present in the form of a Path Integrated Concentration (i.e. ppm-m).

    Basically, Laser Based – Open Path Gas Detection can simply be described as a Target Gas Molecule Counter. The number of Target Gas Molecules present in the Active Measurement Path is directly proportional the concentration (ppm-m) outputted by the GasFinder. Specifically, when the GasFinder is performing an analysis of the “counted target gas molecules”, it produces a sample waveform and its height is also directly proportional to the concentration in the Active Measurement Path.

    Path Integrated Concentration: Parts Per Million – Meter (ppm-m)

    The units of measure for Open Path Gas Detectors is Parts Per Million – Meter (ppm-m), which is a Path Integrated Concentration.

    Think of Path Integrated Concentration as each of the target gas molecules within the Active Measurement Path being counted and added together to provide the total concentration.

    Basically, this measurement methodology can be summed up as this being a molecule counter.

    It is important to note that the Path Integrated Concentration is completely independent from the physical path length (distance between the Open Path (OPX) Head and the Retro-Reflector).

    To help visualize what Path Integrated Concentration is, lets assume a background concentration of 10 ppm. The image below shows how the Path Integrated Concentration increases with path length even though the background concentration remains the same. Atmospheric gases like Methane (CH4) and Carbon Dioxide (CO2) will exhibit a similar result.


    Path Average Concentration – Parts Per Million (ppm)

    The Path Integrated Concentration (ppm-m) can be converted to a Path Average Concentration (ppm) by dividing your ppm-m concentration by the physical path length (m) of the Active Measurement Path. The path length can be programmed into the GasFinder to automatically convert the outputted concentration in a Path Average Concentration (ppm).


    Use Applications for Path Integrated Concentrations and Path Average Concentrations:

    Path Average Concentrations are typically used in short path length applications where the plume is either being fully measured or where the concentration assumed to be more or less homogeneous.

    It is typical for Path Average Concentrations to be used with the following Measurement Heads: Remote Point (RPX) Probe, Stack/Duct (SDX) Probe, In-Line (ILX) Probe, and Extractive Measurement (EMX) Probe.

    Path Average Concentrations can be used in Open Path Gas Detection Applications but the end-user needs to understand that this technology cannot spatially resolve the size or the concentration profile of the plume within the Active Measurement Path. The image below can show how a Path Average Concentration can be misleading depending on the size and density of the plume.

    While a large and dispersed plume may not pose a threat – a small and highly concentrated plume may present a hazardous scenario. For Open Path Applications, we recommend using Path Integrated Concentrations for setting alarm thresholds.

  • Measurement Range Specifications
    Measurement Range Specifications:

    The GasFinder has four key performance specifications centered around it’s ability to detect and monitor a specific target gas: Minimal Detectable Limit (MDL), Sensitivity, Zero Gas Noise, and Actionable Concentrations.

    Determining the Minimal Detectable Limit (MDL):

    We define our Minimal Detectable Limit (MDL) as the smallest concentration value that is reliably and repeatedly detected when exposed to a known gas concentration. In a comparable example, think of our Minimal Detectable Limit (MDL) in similar terms to a Signal-to-Noise Ratio where the MDL is the smallest concentration that can be detected through the noise floor. Any values below our published MDL are to be considered noise and not a reliable reading. To help us determine if the gas concentrations are above the Minimal Detection Limit (MDL), we use a Linear Least Squared Regression to compare the generated Sample Waveform to the permanently stored Calibration Waveform. If there is good fit (R2) between the two waveforms then it can be assumed that there is enough Target Gas within the Active Measurement Path to generate a waveform in the correct location (emitting laser light at the appropriate wavelength) and high enough amplitude (gas concentrations above the MDL). To be confident that the reading are above our Minimal Detectable Limit (MDL), the Linear Least Squared Regression will provide an R2 Confidence Factor for each sample. For non-atmospheric gases, it is typical to implement an R2 Cutoff Limit in the GasFinder to minimize instrument noise.

    Sensitivity:

    We define Sensitivity as the smallest incremental change in concentration that is reliably and repeatably detected when above our Minimal Detectable Limit (MDL). In a comparable example, think of our Sensitivity as Shot-to-Shot Noise. As a general rule-rule-of-thumb for all gases, the Sensitivity (i.e. Shot-to-Shot Noise) is a quarter of the Minimal Detectable Limit (e.g. Sensitivity and/or Shot-to-Shot Noise = 0.25 x MDL). For example, Lo-Range Hydrogen Sulphide (H2SL) has a Minimal Detectable Limit (MDL) of 100 ppm-m and a Sensitivity of 25 ppm-m (0.25 x 100 ppm-m). If a Lo-Range Hydrogen Sulphide (H2SL) GasFinder were to be constantly exposed to a nominal concentration above the Minimal Detectable Limit (MDL), then you’d expect to see the readings to fluctuate +/- 25 ppm-m as this is the Shot-to-Shot Noise (i.e. Sensitivity).

    Zero Gas Noise:

    To help with this section, we’ll want to remember that the GasFinder’s analysis will produce a sample waveform and its height is proportional to the amount of target gas present in the Active Measurement Path. Under a Zero Gas Scenario (i.e. no Target Gas Molecules present), the GasFinder will not produce a sample waveform in the shape of the sinusoidal wave but a flat-ish Sample Line. It is important to note two separate points: 1) a Zero Gas Scenario does not produce a perfectly flat Sample Line. 2) a Zero Gas Scenario will have a “dancing” sample line that does not sit still (i.e. this is Noise). This Noise can come from a number of sources that may be spectroscopic, mechanical, or atmospheric. Typically, the Noise from any of these sources will produce gas concentrations that are below our Minimal Detectable Limit (MDL) and may have either low or high R2 values. However, Zero Gas Noise can produce gas concentrations that exceed our Minimal Detectable Limit (MDL) with “good” R2 values and these concentration excursions can be up to 2x of our published Minimal Detectable Limit (MDL). This is consistent with all of our gases and ranges. It is important to note that through optimization you may be able to either reduce the frequency or scale of Zero Gas Noise but it cannot be completely eliminated and under Zero Gas Applications, concentrations below 2x MDL are indistinguishable between Noise and Gas Readings. This brings us to Actionable Concentrations.

    Actionable Concentrations:

    As a general rule across all of our gases, the lowest concentration where you can confidently set alarm thresholds for leak detection (or set points for process control) that are outside of the Zero Gas Noise range is two (2) times the published Minimal Detectable Limit (MDL). In our Instrument Data Sheets, you’ll see the Actionable Concentrations for all of our gases set at 2x MDL. Once the concentrations exceed the 2x MDL threshold, the sample waveform takes a more obvious and consistent shape that is not as overwhelm by the Zero Gas Noise (e.g. Signal is now greater than the Noise). To continue the example of Lo-Range Hydrogen Sulphide (H2S), it is recommended to have Alarm Thresholds greater than 200 ppm-m.

  • Is the Laser Eye Safe?

    The Boreal Laser GasFinder product line meets or exceeds the requirements to be listed as Class 1 laser products under the IEC 60825-1 standard.

    The IEC 60825-1 standard defines Class 1 as any laser product which during operation does not permit human access to laser radiation (accessible emission) in excess of the AEL of Class 1 for applicable wavelengths and emission durations.

    The Boreal Laser GasFinder product line operates in the NIR (Near-Infrared) wavelength region for purposes of gas detection. The appropriate ranges for wavelength and duration have been considered to ensure that products meet or exceed these requirements.

    Boreal Laser makes use of a NIST (National Institute of Standards and Technology) traceable testing program to ensure the NIR thresholds are not exceeded during setup and production of GasFinder products.

    For export into the United States of America, Boreal Laser products are classified as Class 1 and are compliant with the testing, record keeping and reporting requirements of the CDRH (Center for Devices and Radiological Health) which operates under the FDA (Food and Drug Administration). Boreal Laser complies with performance standards for laser products except for deviations pursuant to Laser Notice No.50, dated 06/24/2007.

  • Light Level: Performance Variable
    For more information: Click Here
    Light Levels:

    The invisible Near Infrared Laser Light leaves the Measurement Head as a collimated beam. The image below shows the Open Path (OPX) Head on the left and the Retro-Reflector on the right.

    The Retro-Reflector then returns the collected Laser Light back to the Measurement Head via a focused beam for analysis. The Measurement Heads used are also called Transceivers as they have both the sending and receiving optics built-in.

    The amount of returned Laser Light can be affected by light scattering mediums such as fog, rain, sleet, snow, dust, etc. The functional test used to validated how much beam block the GasFinder can operate with is done with a Neutral Density Filter. This test verifies that the GasFinder can tolerate up to 97% Trans-Obscuration (or simply put, 97% Beam Block).

    The laser light used is in the Near Infrared which is close to the Visible Spectrum. Light in the Visible Spectrum scatters more so than light within the Near Infrared.

    Our anecdotal example of how to explain how much beam block the GasFinder can handle is simply as follows. If the Retro-Reflector can be seen from the Measurement Head then the Near Infrared Laser Light will be able to pass through as well. The image below is an example of looking through the Alignment Scope on the Open Path (OPX) Head at a Retro-Reflector.

    If the Laser Light Levels were to decrease beyond tolerable levels then the GasFinder will automatically enter a Low Light or Beam Block status condition. This specific status/fault condition will be shown as 2.7 mA on an Analog Loop.

    The status/fault condition for Low Light is non-latching and as soon as the sufficient Laser Light Levels return then the system goes back into normal operation.

    To help avoid nuisance alarms caused by intermittent beam blocks (e.g. steam), the end-user can easily implement a time delay of 0-300 seconds on the HMI Touchscreen.

  • Low Light and Beam Block Time Delay

    Light Level (Rx): This provides indication of how much Laser Light has been received from the Active Measurement Path (e.g. Laser Beam at the Measurement Head).

    Below is an explanation of Laser Light and Low Light (Beam Block) Diagnostic Variables:

    • Laser Light Similar to Line-of-Sight:
      • Light Level Performance:  The functional test with a Neutral Density Filter verifies that the GasFinder can function with only 3% of the emitted Laser Light Returned/Collected. Alternatively, the GasFinder can function with up to 97% Transobscuration (i.e. Beam Block).
      • Antidotal Example:  Since Light Scatters more in the Visible Spectrum then it does in the Near Infrared (which is used by the GasFinder), that if you were standing at the Measurement Head (e.g. Open Path (OPX) Head) and you can still see the Retro-Reflector through the rain, then the Near Infrared Laser Light will be able to as well.
    • Low Light = Channel Specific Status: Each Channel/Path is treated as an independent end-device and has independent outputs. If a Low Light or Beam Block Scenario were to occur, then only the specific paths that this occurred would have the Low Light/Beam Block Status Inhibition.
    • Low Light/Beam Block Status Output: This specific Status Inhibition condition is communicated via the following protocols:
      • HART 7 over Analog:
        • Light Level (Rx): With HART, comes the ability to also transmit additional digitized information over the Analog Loop such as outputting the Laser Light Level over the Secondary Variable (SV).
        • Low Light/Beam Block: If a Low Light/Beam Block condition were to exist, then the Analog Loop (Primary Variable) would enter a channel specific Status Inhibition of 2.7 mA. This is Non-Latching and will clear once enough Laser Light has been collected.
      • Analog Loop:
        • Light Level (Rx): Via the HMI Touchscreen, the End-User can select to enable one of the Analog Loops to output Light Level (Rx).
        • Low Light/Beam Block: If a Low Light/Beam Block condition were to exist, then the Analog Loop (Primary Variable) would enter a channel specific Status Inhibition of 2.7 mA. This is Non-Latching and will clear once enough Laser Light has been collected.
      • Dry-Contact Relays:
        • Low Light/Beam Block: If a Low Light/Beam Block condition were to exist, the Relay Outputs can be configured via the HMI Touchscreen to exercise the relays. This is Non-Latching and will clear once enough Laser Light has been collected.
      • MOBUS (RS-485):
        • There are specific Status Registers that can be used to both monitor the Light Level (Rx) and Low Light/Beam Block Status Inhibition Conditions.
    • Low Light = Channel Specific Status: Via the HMI Touchscreen, End-Users can select to implement a Low Light/Beam Block Time Delay between 0 – 300 Seconds (0-5 Minutes). It is common for Open Path Gas Detectors to have Time Delays between 30-60 Seconds and some End-Users chose to enter Time Delays of the full 5 Minutes to minimize Nuisance Alarms caused by known transient events (e.g. Steam, People Walking Through Path, Etc.).
  • R2 Confidence Factor

    R2 Confidence Factor (R2): This variable provides indication to the End-User if the concentration variables being displayed by the GasFinder are over the Minimium Detectable Limit (MDL).

    The following details are used to help to explain what we call the R2 Confidence Factor:

    • Linear Least Squared Regression: After the Factory Calibration is performed, the Calibration Waveform is permanently stored in the GasFinder so that the Sample Waveform generated from the Measurement Head counting Target Gas Molecules within the Active Measurement Path can be compared against each other. A Linear Least Squared Regression is performed to help provide context to low level concentrations that are either below or near to the published Minimal Detectable Limit (MDL).
    • Minimal Detectable Limit (MDL): What we define the Minimal Detectable Limit (MDL) as is the lowest concentration that provides reliable and repeatable results. In other words, concentrations below the published MDL should be treated as Non-Detectable and/or simply as Noise.
    • R2 Confidence Levels (Noise Floor): Each and every Sample (i.e. Concentration Measurement) will have an R2 Confidence Factor associated with it. To generate Confident Results, the concentration has to be above both the Minimal Detectable Limit (MDL) and the desired R2 Confidence Level.
    • Setting an “R2 Cutoff” Limit via the HMI Touchscreen: For most gases and applications, it is not necessary to set an “R2 Cutoff” as the Actionable Concentrations are well above the Minimal Detectable Limit (MDL). In an application such as H2S Leak Detection where the Actionable Concentrations are relatively close to the Minimal Detectable Limit, it is recommended to use the “R2 Cutoff” feature.
  • Why Doesn't TDL Require Re-Calibration?

    The following details are used to help to explain what we call the TDL does not require re-calibration:

    • Spectroscopic Absorption Lines: For analysis, monitoring, or detection of particular target gases, there are spectroscopic absorption lines within the Near Infrared Spectrum. The wavelengths in which a specific target gas absorbs is both well defined and most importantly, predictable.
    • Laser Light is the “Sensing Element”: Tunable Diode Laser Absorption Spectroscopy (TDLAS) utilizes emitted Laser Light within the Near Infrared Spectrum for gas analysis, monitoring, and detection. To detect specific target gases of interest, the wavelength of the emitted laser light is tuned to match the wavelength of where the target gas absorbs spectroscopically. If the wavelength of the emitted laser light matches that of the target gas molecules that pass through laser beam, then they will be absorbed (or more simply put, counted) and the relationship between the number of target gas molecules present in the laser beam is directly proportional to the outputted concentration. The wavelength of the emitted laser light has to match the wavelength of the spectroscopic absorption line.
    • Role of Internal Reference Cell: The Internal Reference Cell provides the GasFinder with a physical reference of where the absorption line is located and therefore ensures that the laser light emitted from the GasFinder is at appropriate wavelength for analyzing, monitoring, or detecting that particular target gas. It is because of the Internal Reference Cell that there is essentially zero measurement drift because the GasFinder continuously remains “Line-Locked”. Due to the autonomous and automatic adjustments made as a result from the GasFinder interrogating the Internal Reference Cell, there is no field calibration or no field intervention available or required.
    • Calibration Waveform Stored/Saved: At the Factory, the GasFinder goes through a sophisticated calibration procedure that involves inserting an optical cell with a known concentration under carefully constructed and controlled laboratory conditions. After the calibration procedure has been performed, the Calibration Waveform is then permanently stored within the GasFinder. The permanently stored Calibration Waveform is then continuously compared against either the Reference Waveform or Sample Waveforms to generate a measurement R2 Confidence Factor (R2). The R2 Confidence Factor is a Linear Least Squared Regression comparison between the calibration waveform which was formed by exposure to a known gas concentration under controlled environments and waveform generated from either the Internal Reference Cell  or the molecules being absorbed/counted within the Laser Beam of the Measurement Head. It is vital that the emitted Laser Light is at the wavelength of the absorption line for the target gas of interest.
  • Health of Internal Reference Cell

    For all Non-Hydrogen Fluoride (HF) gases, it is not a concern for the Internal Reference Cell’s concentration of target gas to deplete over time. Due to the physical properties of Hydrogen Fluoride (HF) and the material used to contain it within the Internal Reference Cell, the concentration may deplete over time.

    Below is a quick explanation of how the Health of the Internal Reference Cell can be monitored:

    • View, Communicate, or Retrieve: Once a minute when the GasFinder interrogates its Internal Reference Cell, the results are available or logged in the following ways:
      • Real-Time Data String: Via the HMI Touchscreen, the Serial Strings can be viewed in real-time to view the results of the checking the Internal Reference Cell.
      • MODBUS (RS-485): If the End-User would like to have this information communicated to their PLC or DCS, they can monitor the specific Registers for Reference Light, Reference Cell Quality, and Reference Cell R2.
      • Logfile: Every line of data generated by the GasFinder is stored and accessible by the End-User via a USB Stick
    • No Reference Cell = Fault Conditions: The Internal Reference Cell is an important component of the GasFinder and along with the Sophisticated Diagnostics and Fail-Safe Design, it can monitor and alert if any of the components are not functioning properly. If there is an issues with the Internal Reference Cell (e.g. not enough gas detected, no laser light received, etc.), then the GasFinder will output very specific status conditions notifying the End-User.
    • Check Current Reference Cell Status: If the End-User would like to see what the performance variables for the Internal Reference Cell, via the HMI Touchscreen, they can be called up to see the Reference Cell Light, Reference Cell Quality, and Reference Cell R2.
    • Visualize all Three (3) Waveforms: Via the HMI Touchscreen, the End-User can “View Array” to see a digitized version of all three Waveforms.
      • The Calibration Waveform is permanently stored within the GasFinder should always appear,
      • If GasFinder successfully interrogates the Internal Reference Cell then the Reference Waveform will appear,
      • If the Measurement Head is being exposed to the Target Gas then the Sample Waveform will be present as well. During “Line Centering”, the GasFinder will adjust the Sample Waveform (e.g. Frequency/Wavelength of Laser Light) to ensure it matches the Reference Waveform (e.g. Absorption Line)
  • MODBUS (RS-485) Table

    Here is the Register Map for implementing MODBUS (RS-485) outputs for a GasFinder:

    In most cases, the common values to pull are “ppmm high”, “R2”, and “Light”.

Standard Term & Conditions

To view Boreal Laser’s Standard Terms & Conditions: Click Here