By Amanda Gogates, Cascade Global Product Manager, Emerson Automation Solutions

Precise and cost-effective measurement of gas purity significantly impacts the bottom line in a number of industrial applications. I’d like to share a new technology with you that will overcome many of the most common problems manufacturers face in this area, including poor sensitivity, costly consumables, and outmoded equipment requiring high levels of technician resourcing to operate and maintain. You may be aware of the Emerson line of Quantum Cascade Laser (QCL) technology for measurement applications such as Continuous Emission Monitoring or CEMS. Now, this remarkable technology has been extended to some of the most demanding markets in the world and is a quantum leap over previous generation solutions.

First, a little background on the technology. Emerson’s QCL technology offers fast, high-resolution spectroscopic detection to identify a range of compounds. QCLs operate in the mid-infrared spectral region, where molecules typically exhibit strong absorption bands that can be exploited to improve measurement sensitivity. Coupled with Tunable Diode Laser (TDL) spectroscopy, a single instrument is now able to broaden measurement capability and exploit both the near- and mid-infrared regions.  The result is that a single analyzer is able to monitor an increased number of compounds compared to preceding technologies. The system uses what is called a laser chirp technique. In this technique, a QCL is pulsed with electrical energy and heats up and as the temperature increases, the wavelength of the emitted light also increases. A laser chirp lasts about one microsecond, and in this time a spectrum of between one and three wavenumbers is scanned, sufficient to detect unique absorption features from one or multiple gases. This data can then be interpreted in terms of absolute concentration, minimizing the need for complex and frequent instrument calibration. QCLs can be chirped at a frequency of up to 100 KHz, enabling many thousands of spectra to be gathered in a few seconds, resulting in a high signal-to-noise ratio, while maintaining a rapid response time.

As a result of this unique design, the new CT5800 enables highly accurate measurement of concentrations of impurities down to sub-ppm levels in a variety of gas streams. This makes it ideal for hydrogen purity, nitrogen purity, and ethylene purity applications. With up to six laser modules housed inside the same enclosure, the CT5800 analyzer can measure up to twelve components simultaneously, greatly reducing the need for multiple analyzers while still meeting the real-world analysis needs of these markets.

The key outcome of this new technology is that the combination of this measurement performance and analyzer capabilities has not been possible before – not with existing lasers or other measurement technologies. Of course, not every application needs this level of performance, but when taking the example of ethylene product quality, time and product contamination is money in this volatile industry. When multiple, highly sensitive measurements can be made in seconds by a QCL, excursions in the product quality can be rapidly detected, facilitating decisions to suitably manage plant operation, and minimize losses. QCL technology provides a speed and quality level never before possible. Likewise, the low levels of detection not only improve product quality for the user, but they also open up wider market options and help meet guidelines.

Over the next months, I’ll be sharing about ways to optimize gas analysis in different critical markets. For now, if you have questions about how QCL technology might work for you, please contact me at

How do you currently measure gas purity?


Hi. I’m Ruth Lindley and I’m happy to get the chance to tell you how to solve a significant problem in refining in a relatively simple and straightforward manner. The problem is ammonia slip.

TypicalNOxNitrogen oxides result from the combustion process in turbines, crackers, combustion engines, boilers, and other locations within a plant. NOX is a powerful pollutant, so it is important to control and contain NOX emissions. Both selective catalytic and selective non-catalytic reduction (SCR and SNCR) are techniques used worldwide to remove NOX. However, this process can result in a byproduct of unreacted ammonia, or ammonia slip. Continuous measurement and monitoring of ammonia slip can be a challenge to ensure sample integrity is maintained, especially in high-dust, high-temperature applications. But regardless of the complexity, to adhere to environmental guidelines, operators must balance using the precise amount of ammonia – not enough ammonia results in waste, too much can lead to emissions.

So how to solve the ammonia slip problem? The answer is QCL/TDL laser technology. (You may not have been expecting that!) In fact, capable, fast Rosemount QCL/TDL technology delivers the needed measurement precision (0–100 ppm) to ensure production is at its optimum and avoid overdosing issues that result in both economic and environmental problems and cost.

Quantum Cascade Lasers monitor ammonia slip to avoid the formation of damaging ammonia salts downstream or emission of 5100captionammonium chloride or gaseous ammonia, and the regulator fines and penalties that result. Here are some of the benefits of Quantum Cascade Lasers in this challenging application –

  • Interference-free monitoring of the presence of ammonia slip in the toughest environments
  • Thousands of measurements per second are recorded using patented laser chirp techniques to ensure identification of even trace levels of ammonia
  • Ammonia slip detection and insight into the efficiency of the plant’s NOX reduction system resulting from real-time measurement and analysis
  • Rugged, modular design delivers outstanding reliability and measurement stability in extreme operations
  • Monitoring of up to twelve critical component gases for all industrial applications, toxic gas detection, and plant-wide emissions monitoring
  • No consumables, no calibration, and no in-field enclosure or shelters reduce cost and simplify maintenance and upgrades

For additional information on the specific QCL/TDL laser products that might work for you, click HERE.

The QCL/TDL laser solution to ammonia slip may seem almost too good to be true – but it’s real and operating in plants worldwide. It’s time for all of us to adjust our thinking on the ammonia slip issue, accepting that there is a better way to overcome it efficiently, reliably, and cost-effectively.

Have thoughts or questions about QCL/TDL laser technology? Post them HERE!

By Amanda Gogates, Product Manager for Quantum Cascade Laser Analyzers, Emerson Process Management

You may have seen a few stories already on the innovative QCL laser technology. That technology has now been successfully implemented in Emerson’s Rosemount™ CT5100 continuous gas analyzer. It is the world’s only hybrid analyzer to combine Tunable Diode Laser (TDL) and Quantum Cascade Laser (QCL) measurement technologies for process gas analysis and emissions monitoring. The CT5100 provides the most comprehensive analysis available (down to sub ppm) for detecting a range of components, while simplifying operation and significantly reducing costs. The CT5100 can measure up to 12 critical component gases and potential pollutants in a single system – meeting local, state, national, and international regulatory requirements.

But if you’re thinking that the CT5100 is remarkable but “bleeding edge” technology that your application can’t afford – think again. The Rosemount CT5100 operates reliably with no consumables, no in-field enclosure, and a simplified sampling system that does not require any gas conditioning to remove moisture – truly “next generation” technology which chartsaves you money at every turn. The CT5100 is a unique combination of advanced technology and rugged design, and is highly reliable. Its patented laser chirp technique expands gas analysis in both the near- and mid-infrared range, enhancing process insight, improving overall gas analysis sensitivity and selectivity, removing cross interference, and reducing response time. This laser chirp technique produces sharp, well-defined peaks from high resolution spectroscopy that enables specificity of identified components with minimum interference and without filtration, reference cells, or chemometric manipulations.

The rugged Rosemount CT5100 analyzer features –


  • Multi-laser, hybrid QCL/TDL configuration for up to 12 measurements simultaneously per analyzer
  • Accurate and sensitive gas measurement
  • Excellent linearity of response and repeatability
  • Fast and continuous gas measurements using the patented chirp technique
  • Low maintenance and low lifetime costs
  • No long-term drift due to inherent stability of spectroscopic measurement technique
  • Continuous health diagnostic reporting
  • Embedded ARM processor for fully autonomous operation
  • Modular architecture is easily serviceable and upgradeable in the field
  • Superior spectral analysis to eliminate cross-interference and improve measurement accuracy
  • Intuitive, simple front-panel user interface allows access to all instrument functions

Give your Emerson representative a call and discuss the potential of the CT5100 in your process gas analysis, continuous emissions monitoring, and ammonia slip applications. This could be a whole new solution to some costly problems. Click HERE for more information on the CT5100.

By Jeff Gunnell

How would you like an online analyzer that, after commissioning, starts up already in perfect calibration? That during its life, checks that it is in calibration without needing test samples? That works for very long periods without maintenance, but when eventually intervention is required, the analyzer raises a flag, gives a description of why maintenance is needed, and explains exactly what to do? Would this be desirable? Of course! But is it feasible?

Cascade Technologies analyzers from Emerson open up a powerful new approach to real-time validation. They are based on Quantum Cascade Lasers (QCLs): semiconductor devices which produce radiation in the mid infrared range. For spectroscopy, this is the fingerprint region where most molecules exhibit strong, sharp absorptions.


An Information Rich Spectral Region Showing the Absorptions of Many Components


It might seem that congested spectra would make reliable measurements difficult to achieve, but in fact the opposite is the case. Using the complete set of information in a spectrum can reveal sources of error and hence remove the need for validation tests.

In order to develop a measurement application, first the absorption spectra of all components that are active in the measurement region must be obtained. This is done in the development lab and the information created is called a spectral database: it includes wavelengths, absorptions, and peak shapes as well as the effects that temperature and pressure have on spectra.

To make a measurement on a process stream, a spectrum is obtained. A mathematical process is then used to work out the concentrations of the components in the stream. An initial estimate of the stream composition is combined with the spectral databases to calculate a spectrum. This is compared to the measured spectrum and the result is used to generate a better estimate. As this process is repeated, a path is followed which eventually leads to the calculated spectrum almost exactly equalling the measured spectrum, and at that point, the estimated concentrations of the components almost exactly equal the real concentrations.


The Measured and Calculated Spectra of CO Plus Ethylene with the Residuals


This iterative methodology gives a novel way of validating measurement integrity. The process automatically takes into account all of the factors which could affect a spectrum. It starts with fundamental, unchangeable properties of the components in a sample, such as the absorptivity at each wavelength across a spectrum and the effects of temperature and pressure on peak shapes. It combines these properties in a way which matches the measured spectrum and looks at how close the calculated spectrum is to the measured one. A poor match is evidence of a failure somewhere in the system. For example, if an unexpected new component is present, that will be detected by failure to model peak shapes correctly and the details of why the match failed will indicate that it was due to something new in the stream. Similarly, such effects as laser drift can also be readily identified.

In addition to raising alarms when a failure is present, there is another powerful advantage of this approach. If the quality of fit is high, that is strong, positive evidence that the analyzer is operating perfectly; a good fit could never be obtained unless every part of the system, including its calibration, was working correctly.

It is the case, backed by field experience that the iterative approach is extremely robust and leads to very high reliability. The capability to have very long periods between maintenance visits, positive evidence of good operation, and smart identification of problems – together with a highly stable calibration – makes this technology especially valuable when analyzers are installed remotely from skilled maintenance resources, such as on natural gas pipelines. These are also important characteristics for legislative reporting, such as CEMS measurements. In a production environment robust, reliable measurements minimize losses so QCL technology is advantageous for online monitoring in manufacturing industries as diverse as petrochemicals and pharmaceuticals.

Emerson’s Cascade Technologies QCLs are innovative spectroscopic analyzers which provide multicomponent measurements at high sensitivity and with extremely high reliability. You can find out more about the technology in this blog: Cascade Technologies QCL Analyzers. And if you have a potential application that might be solved by this approach, please contact the Emerson team to discuss your needs.


By Ruth Lindley and Jeff Gunnell

With a range of technologies on the market for gas analysis, it can be a challenge to know which is best suited to your particular measurement requirement. This blog gives you a guide to choosing between two popular measurement techniques: gas chromatographs (GCs) and quantum cascade laser (QCL) analyzers, as with the recent acquisition of Cascade Technologies, Emerson can now offer QCL technology alongside its existing range of GCs. Both techniques offer excellent sensitivity and accuracy, but depending on application and measurement needs, one or the other will be preferred.


The 700XA Process Gas Chromatograph

The purchase price of QCL and GC analyzers are similar and both offer multicomponent capability. The main way to choose between the two techniques is by the analysis required for the particular application. GCs are an excellent general purpose analyzer. They can measure liquid samples as well as gases and a wide range of molecules – both large and small. They can separate out complex mixtures and often measure the concentrations of isomers. In principle, dozens of components can be measured. QCL can typically measure up to 12 components per analyzer, but they all must be small gaseous molecules such as CO, ammonia, or hydrocarbons up to C4s. As such, for liquids and larger gaseous molecules, or for very large numbers of components in a stream, a GC is the correct choice.

Sometimes the speed of analysis is important in an application, and in that case, QCL has a clear advantage. In a QCL, the sample flows through a measurement cell where laser beams continuously analyze the the gas. The response time depends on how long it takes to flush the cell, typically <10 seconds to get to 90% of a step change, so the output is effectively continuous and real time. GCs on the other hand work on the principle of injection followed by analysis. Cycle times for a GC vary

from 1 minute to over 15 minutes, depending on the application, and thus the concentration data is periodic rather than continuous. For applications where fast, continuous measurements are required, QCL is therefore the preferred technique.In terms of sensitivity and dynamic range, QCL can offer better performance than GC. QCLs can measure down to low ppb concentrations for some compounds and offer a dynamic range from ppb through to percent concentrations in one analyzer by using multiple pathlengths or spectral lines of varying strengths. GCs are often used for measuring the entire composition of a sample and can measure down to ppm concentrations while also measuring the majority component up to 100%. However, to reach ppb measurements along with high percent level measurements in a GC usually requires separate injection and column trains, making for a more complex and expensive analyzer. So if high sensitivity is needed or there’s a wide dynamic range (for example for online purity measurement with the ability to follow process upsets), then QCL is the better option. If every component in the sample (including the background) needs to be measured, a GC may be more suited.

The CT5200 Industrial Gas Analyzer

The CT5200 Industrial Gas Analyzer

On cost of ownership, QCL is usually better than GC. GCs require a carrier gas, typically hydrogen, helium, or nitrogen. These are not needed by QCL analyzers, meaning that the cost of ownership, due to the use and management of consumables, is higher for GCs. QCLs inherently have a very stable calibration and they can often carry out validation and calibration checks in real time, using the process gases which are being measured. This is due to the way that spectra are obtained and analyzed, and consequently, checks using injected test gases may only be required every 12 months for QCLs. For GCs, it is more usual to carry out validation checks every few weeks. So if low cost of ownership is essential, then QCL is favorable. If the required measurements can be made by QCL this is likely to be the preferred choice due to lower cost of ownership and reduced maintenance requirements.

The table below gives a summary of the types of applications and measurements commonly encountered for gas analysis and the suitability of the GC and QCL technologies to each.


QCL and GC analyzers are both excellent options for industrial gas analysis and can be utilised across a range of applications and measurement points. The differences in the detection methods can make one or the other better suited to a particular application, and the table above is a guide to selecting the best fit to your application.

The Emerson sales team will be able to further assist in determining the best analytical method for your needs. Please click HERE for find out more information on QCL analyzers, and HERE for more information on gas chromatographs.