Decoding and Understanding IECEX and ATEX Markings

Decoding and Understanding IECEX and ATEX Markings

IECEX and ATEX are important safety certification for process analyzers being installed in hazardous environments. The NIR-O has a maximum protection rating of Zone 1, Group IIB+H2, T4. This protection rating is offered with either ATEX and IECEX certification.

What is the difference between Class 1 Div 1 Zone 1 and Class 1 Div 2 Zone 2 protection?

The major difference between Class 1 Div 1, Zone 1 and Class 1 Div 2, Zone 2 IECEX certification is in the assumption of risk. Div 1 or Zone 1 assumes that hazardous gases are always present in the environment. Div 2 or Zone 2 assumes that hazardous gases may be present in the environment, but are unlikely.

To achieve Div 1 or Zone 1 protection rating, a process analyzer must have a clean air purge system that keeps the enclosure under positive pressure. Additionally, if the pressure drops, an interlock must trigger which shuts off the analyzer and prevents the system from exposing the combustible gases to an electrical ignition source. The electronics cannot result until pressure is restored and for some amount of time. This is often referred to as an X-purge.

To achieve Div 2 Zone 2 protection rating, a process analyzer still requires a clean air purge. However, the airflow only must maintain positive pressure. If the pressure inside of the enclosure is lost the analyzer must alarm, but may remain powered on to collect data. This is often referred to as a Z-purge.

Understanding the ATEX Zone rating – the Petrol Station analogy

Gas pump in gas tank

Class 1 Div 1 or Zone 1 – During refilling of the underground storage tank. When the truck arrives to refill the petrol station’s underground tank, it can be assumed that gas vapors are present.

Gas pump in gas tank

Class 1 Div 2 or Zone 2 – The pump. There may be gasoline or diesel vapor present if an automobile was recently filled.

Gas pump in gas tank

General Purpose – Inside of the petrol station. Considered a safe area where explosive gases are never present.

Explaining ATEX Group Markings

The gas and dust protections are defined by groups. A group III rating means that the enclosure is only rated to protect against dust infiltration. A group II rating means that the enclosure is protected against both dust and gas. The lowest gas protection is IIA the best gas protection rating is group IIC.

Group IIA – protection is adequate to prevent ignition of propane gas in the environment.

Group IIB – protection is adequate to prevent ignition of ethylene gas in the environment.

Group IIB+H2 – protection is adequate to prevent ignition of hydrogen gas in the environment.

Group IIC – protection is adequate to prevent ignition of acetylene gas in the environment.

ATEX and IECEX group markings have equivalent IP or Ingress Protection ratings. Guided Wave process analyzers all have NEMA 4 or IP 66 ratings enclosures as part of the protection design for hazardous and explosive environments.

What does the T marking mean in IECEX?

The T stands for the maximum external surface temperature that the analyzer must not exceed. This portion of the specification is to prevent the surface of the analyzer enclosure from igniting combustible molecules in the environment. For example, Ethyl Nitrate will explode if it comes into contact with a heat source or object above 90 ºC. Any analyzer that is going to be installed in an environment containing Ethyl Nitrate must be rated for T6 and never exceed a surface temperature above 85 ºC. The limit for T4 is that the outside of the analyzer will never be hotter than 135 ºC.  All Guided Wave analyzers have a T4 rating they are suitable for installation in petrochemical and refinery facilities

T Rating Surface Temperature Limit
T1 450 ºC
T2 300 ºC
T3 200 ºC
T4 135 ºC
T5 100 ºC
T6 85 ºC

Here is a brief explanation of each IECEx mark to show what they mean.

X-purge:

“Ex db” means that it is Explosion Proof(flameproof enclosure) rated for Zone 1 and designed for safety.

“Ib [ib]” means it is intrinsically safe internally [ib] and externally ib.

“op pr” means optical energy is prevented from creating an ignition source.

“pxb” means it uses and X-type purge system rated for Zone 1.

“IIB + H2” means it can be used in for all gasses in groups IIA, IIB, and Hydrogen.

“T4” means it will not have an external surface temperature above 135C.

“Gb” means the equipment is intended to protect against gases (G) in a Zone 1 environment (b).

Z-purge:

“Ex ic nA” means that it is Explosion Proof(flameproof enclosure) rated for Zone 2 and is intrinsically safe because it has no sparking surfaces.

“op pr” means optical energy is prevented from creating an ignition source.

“pzc” means it uses and Z-type purge system rated for Zone 2.

“IIB + H2” means it can be used in for all gasses in groups IIA, IIB, and Hydrogen.

“T4” means it will not have an external surface temperature above 135C.

“Gc” means the equipment is intended to protect against gases (G) in a Zone 2 environment (c)

Think Safety, Think Guided Wave Process Analyzers

Need an ATEX or IECEX certified inline process analyzer? have a question about using a spectrometer in a hazardous environment? Contact a Guided Wave Sales Representative to talk about your needs today.

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Custom, Certified, and Compatible – Probes and Flow Cells for EXTREME Environments

Custom, Certified, and Compatible – Probes and Flow Cells for EXTREME Environments

Where can you find spectroscopic probes or flow cells in custom designs, certified for strict engineering compliance, compatible with most analyzer manufacturers, and at a competitive price? With average delivery times of 6 weeks or less, Guided Wave’s rugged sample interfaces meet these challenges. Additionally, these probes and flow cells are designed specifically for operation in extreme environments and utilize carefully designed optics, that are among the highest optically efficient designs on the market. 

Corrosive Material? Doesn’t Matter with this Custom Flow Cell

With a long history of designing custom probes and flow cells to meet specific or unique customer applications and challenges, the toughest (and most expensive) flow cell ever built by Guided Wave was recently released. The reason for the high price is that it is made from B2 Hastelloy®, a rare material used only for the most severe chemical processes. Hastelloy, a nickel alloy, is a more exotic and expensive material than stainless steel typically used for standard flow cell body construction. Hastelloy is usually the best alternative when dealing with an extremely corrosive process stream, and stainless steel is deemed unsuitable for the process.

Pyrophoric Fires a Concern? Extinguish your Worries 

For most customers, our innovative- first in the industry, built-in cleaning port is a welcomed feature of our flow cell. It allows the cell’s sapphire windows to be cleaned by simply removing a clean-out plug. This direct access to the windows without disconnecting process lines or fiber optic cables is convenient and makes maintenance easier and more cost effective. However, a recent customer came to us with a pyrophoric process. Their process cannot tolerate the possibility of the flow cell cleaning port being accidentally opened, exposing the stream to outside air. As a result, Guided Wave designed a new flow cell without the window to relieve safety concerns and to remove the “what ifs?”

Whether standard or custom designs, many Guided Wave probes can be optimized for the UV, Visible or NIR spectral regions or supplied with custom fiber diameters and connectors to match a variety of optical requirements. Guided Wave also supplies probes manufactured in compliance with the American Society of Mechanical Engineers (ASME) or Canadian Registration Number (CRN) pressure vessel standards.

CRN Certified Probes for Process Spectroscopy

As of October 2019, Guided Wave has submitted more than 3,500 different design configurations for our probes and flow cells for Canadian Registration Number (CRN) certification. A CRN is a number issued to the design of a pressure vessel or fitting by each province or territory of Canada. The CRN identifies that the design has been accepted and registered for safe installation and use. CRN certified probes and flow cells are engineered by Guided Wave to meet the strict safety and application requirements for the Canadian petrochemical, refining, and polymer markets. By coupling these probes with certified (CSA, ATEX, IECEX) process analyzers, Guided Wave can offer complete process monitoring solutions to Canadian customers. Guided Wave currently has CRN registered designs for Ontario, Alberta and Quebec. However, complete process monitoring solutions for all provinces can be implemented – contact us for more information. All CRN probe sales include hydrotest and x-ray test results.

I’m not using a Guided Wave analyzer; is the SST probe compatible with my Bruker analyzer?

Not using a Guided Wave analyzer, no problem. Our probe and flow cells are compatible with most analyzers on the market.

Large Variety of Compatible Probes and Flow Cells

Guided Wave offers a variety of probes, flow cells and fiber optic cables that meet the harsh demands of the process environment. Several have auxiliary features and are compatible with all Guided Wave analyzers as well as other fiber optic-based analyzers manufactured by different companies. Examples are; ABB, AIT Schneider Electric, Bruker and Yokogawa. At Guided Wave if we do not have a probe or flow cell that meets your precise needs, we will look at your application, judge its feasibility, and make recommendations on how to proceed. With over 30 years of probe design experience we are ready for the challenge! Please contact us with your sample interface questions or requirements.

Hastelloy B2 Characteristics:

  • Great resistance to stress corrosion cracking and pitting
  • Significant resistance to reducing conditions like hydrogen chloride, sulfuric, acetic and phosphoric acids
  • Resistance to hydrochloric acid at all concentrations and temperatures

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Corporate Fellow Dr. Terry Todd Retires

Corporate Fellow Dr. Terry Todd Retires

Guided Wave recently announced the retirement of Corporate Fellow Dr. Terry Todd. Terry was celebrated with a farewell party at the end of 2019 where the entire staff thanked him for his over 27 years of dedication to the company. Susan Foulk, Guided Wave President, stated: “Terry’s vision, knowledge and leadership have been instrumental in our success and we sincerely thank him for all he has done and taught us throughout the years.”

With more than 40 years’ experience in infrared molecular spectroscopy and radiation physics, Terry specialized in optical and spectroscopic instrument design for industrial applications. At Guided Wave since 1992, he was responsible for developing new NIR and UV-VIS analyzer technology and applications. While at Guided Wave Terry was at the forefront of all new product development and introduction, from the introduction of the Hydrogen Peroxide Monitor in 1997 to the release of the NIR-O spectrometer in 2018.  During this time (1998) Terry also re-engineered the Single-Sided Transmission (SST) process insertion probe to improve the optical efficiency and further enhance its ruggedness and reliability. Elements of these improvements were awarded US Patent #6,043,895 (March 2000). This pursuit of continuous improvement demonstrates a fundamental aspect of Dr. Todd business practices. To this day, the SST remains one of the most copied, reliable, rugged, and efficient process insertion probes available and is still producing robust sales after more than 28 years in the marketplace. Author of several technical publications and conference presentations, Terry also taught NIR spectroscopy to Guided Wave customers and sales representatives.

Terry received a BS in Mathematics from Northern Illinois University in 1969. He followed that with an MS in Physics from Penn State University in 1972 with his thesis on the emission spectrum of CO2. In 1976 he was awarded his Ph.D. in physics also at Penn State. His emphasis was on molecular physics, infrared high-resolution spectroscopy and optics. His thesis was titled, “Spectrometer Design, Emission Spectrum of CO2 and Secondary Wavelength Standards”.

Between finishing his Ph.D. and joining Guided Wave in 1992 Dr. Todd held and completed the following positions and accomplishments:

  • 1976-1978   NBS-NRC Post Doc National Bureau of Standards, Gaithersburg, MD
    • 1st IR Spectrum of CS
    • Constructed Diode Laser Spectrometer
  • 1978-1980   Laser Analytics (Spectra Physics), Lexington, MA
    • Diode Laser Spectroscopy/Instrument Development
  • 1980-1991   Exxon R&E Co., Florham Park, NJ
    • Instrument Development
    • Laser Pyrometer
    • NIR Octane Monitoring
  • 1991-1992  Todd Enterprises, Inc., Budd Lake, NJ

Terry plans to spend his retirement enjoying more time with family and pursuing his many hobbies, one of which will be working on the restoration of his Opel sedans and coupes. He also plans to continue with liquids processing (winemaking, maple syrup, and apple cider). Please join us in congratulating Dr. Terry Todd on his illustrious career and newfound retirement!

Curtis Mau was promoted from Sr. Product Development Engineer to the role of Manager of Engineering / R&D and will fulfill many of Dr. Todd’s previous responsibilities.

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Advantages of Redesigned G-SST Probe for use with Hydrogen Peroxide (HPV) and Water Analyzer or other Low-Pressure Gas Applications

Advantages of Redesigned G-SST Probe for use with Hydrogen Peroxide (HPV) and Water Analyzer or other Low-Pressure Gas Applications

Guided Wave has been measuring H2O2 and H2O concentrations in various vapor mixtures for over 25 years using near-infrared (NIR), fiber optic-coupled analyzers. Guided Wave’s HPV analyzer is a simple turnkey solution for the measurement of hydrogen peroxide and water (H2O2 and H2O) concentrations in vapor phase. These are both measured together because they are codependent. The analyzer operates in real time, which takes the guesswork out of determining the H2O2 and H2O concentrations during cycle development and throughout the actual sterilization cycle. 

The complete system consists of an HPV analyzer, one or two G-SST probes, and a pair of fiber optic cables for each probe.

The first generation probe developed for measuring hydrogen peroxide in sterilizers was a single pass 25 cm probe.  Later this probe was vented for vacuum use yielding a path length of 28..3 cm.  This original design, exposed optics the optics (lenses) to the gases being measured.  Since lenses are sensitive to the index of refraction of the surrounding air which is a function of its constituency, in this case varying water and hydrogen peroxide vapor, this resulted in a small but detectable change in the effective focal lengths of the lenses.  As a result, baseline shifts could occur, which would decrease the accuracy of the absorption measurements and ultimately causes a small bias in the reported concentration of vaporized hydrogen peroxide during sterilization.

In 2003, GWI developed the first G-SST vapor probe, a double pass design with a pathlength of 50 cm.  The longer pathlength increased the accuracy of the measurement.  This probe still exposed the process side of the lenses to the sterilization chamber.  Once again, small changes in baseline could be seen as the air pressure and vapor concentrations changed.  Furthermore, the lenses were glued into place and after a couple of years of heavy service, the glue degraded due to exposure to hydrogen peroxide, necessitating service.  Below is a photograph of the original G-SST probe with its perforated tube design.

G-SST original double pass 50 cm probe with sanitary flange

Figure 1:  Original Double Pass 50 cm G-SST Probe with Sanitary Flange

In 2018, the engineering team at Guided Wave began a redesign project with the intention of reducing cost and improving the performance and service life of the G-SST probe.  GWI retained the 50 cm folded pathlength, the gold-coated second surface mirror and the high optical efficiency.  An o-ring sealed window was added to isolate the optics from the process. 

Primary Advantages New 50 cm Pathlength G-SST Over The Previous 25 cm, 28.3 cm and the Original 50 cm G-SST probe

  1. The double pass beam design (folded path) provides double of the beam interaction with the gases in the sterilizer chamber. This increases the achievable signal-to-noise making for a more accurate and stabile measurement. Since the absorbance of water and Hydrogen Peroxide vapor is very weak, this is a significant improvement in the measurement accuracy.
  2. The optics are sealed behind a window which isolates the lenses from the sterilization chamber; thus the probe is no longer sensitive to index of refraction changes, this makes the measurements are more stable under widely varying conditions of deep vacuum to high concentrations of water and hydrogen peroxide vapor.
  3. To allow the probe to be quickly serviced by a technician, the perforated cage around the beam path was to the open structure shown in Figure 2. With the lenses behind an o-ring sealed window, there is no adhesive degradation increasing the service life of the probe.

In addition to these engineering improvements, the newly designed G-SST probe is a form, fit, and function replacement for the older style G-SST probes. This allows for nearly effortless upgrading for existing customers who purchase the new and improved style of G-SST. The G-SST vapor probe is available with either a tri-clover sanitary flange for mounting on a chamber access port or without a flange for placement within the chamber. By inserting the probe into the sterilizer through a 2” [50 mm] flanged port allows the fiber optic cables remain outside of the chamber and reduces measurement noise. Also, both the flanged and flangeless versions of the G-SST vapor probe can be 100% immersed in the sterilizer chamber with the addition of 2 small o-rings and a dual fiber feedthrough.

Improved Signal to Noise Through Folded Path Optics

The original 25 and 28.3 cm path length probes utilized single pass optics. As part of the redesign, a folded mirror configuration was developed, so that the light passes through the probe twice without significantly increasing the footprint of the probe. This design also keeps the optical fiber connections on one end and, when installed through a flanged port, outside of the process. To intentionally avoid measuring scattered light, the two paths are separated. By increasing the effective path length to 50 cm, the absorbance and therefore the signal-to-noise is doubled.

The Original G-SST Suffered From Variable Index of Refraction

The original G-SST probe and the even older 25 cm gas probe had the lenses exposed to the vapors and air.  The lenses collimate the light in the probe and refocus the light onto the end of the small return fiber.  The focal length of the lens is dependent on the index of refraction of the air surrounding the lens.  For most practical applications, the index of air is taken as unity and not of any concern.  However, in this application, the chamber medium can change from vacuum to pure N2 to very high humidity air with Hydrogen Peroxide vapor. Absolute Vacuum is defined to have an index of refraction of 1.0 exactly.  Air has an Index of Refraction of 1.0003.  Water vapor and Hydrogen Peroxide vapor will change the index of the air depending on their concentrations.  As the index of refraction changes, so does the degree of focus of the probe.  This changes the baseline offset of the absorbance measurement.  The baseline offset is also wavelength dependent. 

In other words, Guided Wave found that the original probes suffered from a baseline sensitivity under different operating conditions.  This was most notable when going from vacuum to high relative humidity conditions, such as during sterilization.  The wavelength sensitivity did cause a slight change in the water and Hydrogen Peroxide Vapor measurements produced by the Hydrogen Peroxide Monitor.

Controlling the Index of Refraction in the Redesigned G-SST Probe

The new G-SST probe has a window which separates the lenses from the vapors.  This window is in a collimated portion of the beam, so the focus is not sensitive to the index of refraction of the sample.  The result is a more stable baseline under varying process conditions, hence the removal of one small source of measurement error.

G-SST vapor probe

Figure 2:  New 50 cm G-SST Probe

Improving the Service Life of the G-SST

In the old G-SST probe design, the lenses were glued in using TorrSeal.  This adhesive, while being low outgassing for vacuum use, was attacked by the vaporized Hydrogen Peroxide. As a result, the service life was reduced and many probes had to be rebuilt or replaced.  The window in the new

G-SST probe is o-ring sealed, hence there is no adhesive exposed around the lenses.  The mirror in the far end of the probe remains the same second surface gold-coated mirror.  Being the second surface, the coating is not directly exposed to the gases.  We use gold rather than aluminum because the aluminum would be attacked chemically by the peroxide.  In addition, we pot the backside of the mirror in with RTV to prevent any vapor for getting to the mirror coating.

Existing Installations Can Be Upgraded to the Redesigned Probe Today!

The new style of G-SST is compatible with all generations of Hydrogen Peroxide Vapor Analyzers. However, older analyzers may require a firmware upgrade before they can accept the new double pass 50 cm probe. This is due to a path length normalization feature which must be set to account for what generation of gas probe is connected to the analyzer.

The HPV analyzer along with the G-SST probe delivers accurate, real-time measurement results. The long term stability and no maintenance requirements of this system make it a cost-effective smart choice to help optimize productions, ensure product quality, and ultimately enhancing profitability.

Customers interested in upgrading to the redesigned G-SST probe should contact Guided Wave for price, lead time, and upgrade procedure specific to the serial number of the HPV analyzer.

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Choosing an Instrument for Water Measurements in Liquid Samples

Choosing an Instrument for Water Measurements in Liquid Samples

Water concentration is perhaps the most common measurement made in the near-infrared (NIR) spectral range. This is due to its strong effect on product properties and chemical reactivity of the starting materials. From an analytical perspective, water is easy to measure due to its relatively strong signal compared to the hydrocarbon background.

Moreover, because water is commonly analyzed with a single wavelength, filter photometers are the instrument of choice. Guided Wave’s application note, “A Word (or Two) About Online NIR Water Measurements in Liquid Samples”, explains how we arrive at recommending a system, that is, a photometer with the proper wavelengths and a fiber optic probe with an appropriate sample path length. The following considerations affect the choice (and price) of the appropriate photometer and probe system:

Factors to Consider
• Background hydrocarbon spectral characteristics
• Concentration range of water and desired analytical precision
• Potential interference from hydroxyl species
• Sample temperature variations and clarity Analytical Goals
• Provide maximum sensitivity
• Select wavelength(s) to stay within linear range
• Minimize interference due to background hydrocarbon variations and sample temperature changes
• Use an optical path of >1 mm in the fiber optic probe for ease of cleaning and minimal entrapment of bubbles and particles

Cost Effective Solution
The application note explains these factors and analytical goals in detail. Thus illustrating a cost-effective solution for obtaining the desired sensitivity for water over the concentration range of interest in most organic liquids.

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What Certification is needed for Process Analyzers in a Hazardous Area or Explosive Atmosphere?

What Certification is needed for Process Analyzers in a Hazardous Area or Explosive Atmosphere?

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Alphabet Soup or Calibration Acronyms

Alphabet Soup or Calibration Acronyms

Alphabet Soup or Calibration Acronyms

As process spectroscopy has grown, so too has the number of different acronyms associated with the measurement methods and associated mathematics, not to mention the acronyms for conferences and scientific organizations. For the newcomer this can be quite daunting to try to digest the alphabet soup from presentations and papers detailing different applications of process spectroscopy. The purpose of this blog is to just give a list of relevant acronyms related to calibration that are commonly encountered and a short definition where relevant. The list below is in alphabetical order. This glossary represents the most popular data analysis terms you may use during your conversations about using process spectroscopy.

In reality, PLS, and MLR are used most of the time in NIR applications. These are the two calibration methods that Guided Wave uses in all of their analyzer applications. But there are other techniques, we hope this brief list will help to make conversations easier to follow.

Calibration and Regression Methods Acronyms

ANN – Artificial Neural Networks An Artificial Neural Network (ANN) is an information processing method that is inspired by the way biological nervous systems process information. An ANN is composed of a large number of highly interconnected processing elements (neurons) working together to solve specific problems. An ANN is configured for a specific application, such as pattern recognition or data classification, through a learning process. Learning involves adjustments to the connections that exist between the neurons. In more practical terms neural networks are non-linear statistical data

CLS – Classical Least Squares CLS (the K Matrix method) is a regression method that assumes Beer’s Law applies – i.e. that absorbance at each wavelength is proportional to component concentration. A model generated using CLS in its simplest form, requires that all interfering chemical components be known and included in the calibration data set.

ILS – Inverse Least Squares ILS (the P Matrix method) is a regression method that applies the inverse of Beer’s Law. It assumes that component concentration is a function of absorbance. An ILS model has a significant advantage over CLS in that it does not need to know and include all components in the calibration set.

kNN – k Nearest Neighbor kNN is a classification scheme where a Euclidian distance metric is used to determine the classification. The distance metric calculated for an unknown sample is an indication of the degree of similarity to other samples.

LWR – Locally Weighted Regression In locally weighted regression, sample points are weighted by their proximity to the current sample point in question. A regression model is then computed using the weighted points. In some cases LWR models can produce better accuracy.

MCR – Multivariate Curve Resolution Multivariate Curve Resolution is a group of techniques that can be used to resolve mixtures by determining the number of constituents present and what their individual response profiles (spectra, pH profiles, time profiles, elution profiles) look like. It also provides an estimate of the concentrations. This can all be done with no prior information about the nature and composition of the mixtures.

MLR – Multiple Linear Regression MLR is a regression method for relating the variations in a response variable (concentrations or properties) to the variations of several predictors (spectral data). The goal is to be able to measure the spectral data on future samples and predict the concentrations or properties. One requirement for MLR is that the predictor variables (spectral data) must be linearly independent.

Instrument and Technology Acronyms

NIR-O – Guided Wave’s next generation spectrometer and an evolutionary step-up from the M412, NIR-O stands for Near InfraRed Online process analyzer. NIR-O is suitable for online analyses of most processes and process streams. Having the built-in capacity to add more sampling points (up to 12 total channels) within the same process or across processes, in any combination, gives users the flexibility to invest in exactly the capacity they require now. It also minimizes investment for any expansion users may want in the future. NIR-O operates in the xNIR range of 1000-2100nm, using
process-proven TE-cooled InGaAs detector technology.

FT-NIR – An alternative to dispersive spectrometers, Fourier transform spectroscopy is an effective tool for lab analysis.

DG-NIR – Disperive grating technology was developed over 100 years ago and is the defacto standard for real time monitoring of in-situ process conditions.

Statistical and Mathematical Acronyms

OSC – Orthogonal Signal Correction Orthogonal signal correction is a technique originally developed and used for spectral data to remove variation that is orthogonal (non-correlated) to a particular parameter of interest. This is one way to remove interferences from spectral data prior to calibration.

PC – Principal Component /
PCA – Principal Component Analysis Principal component analysis (PCA) is a bi-linear modeling method that involves a mathematical procedure that transforms a number of possibly correlated variables into a smaller number of uncorrelated variables called principal components. The first principal component accounts for as much of the variability in the data as possible, and each succeeding component accounts for as much of the remaining variability as possible.

PCR – Principal Component Regression In PCR the PCA is taken one step further and a regression between the principal components and one or more response variables (concentrations or properties) is performed. A PCR model can then be used to predict concentrations or properties for unknown samples.

PLS – Partial Least Squares Partial Least Squares Regression is a bilinear modeling method where information in the original X variables (spectral data) is projected onto a small number of underlying “latent” variables called PLS components. The Y variables (concentrations or properties) are used in estimating the “latent” variables to ensure that the first components are those that are most relevant for predicting the Y-variables. Interpretation of the relationship between the X and Y variables is then simplified as this relationship is concentrated on the smallest possible number of components.

RMSEC – Root Mean Square Error of Calibration
RMSEP – Root Mean Square Error of Prediction
RMSEPcv – Root Mean Square Error of Prediction based on Cross Validation
SEC – Standard Error of Calibration
SEP – Standard Error of Prediction

These are all terms that are used to evaluate the performance of calibrations. The SEP terms are indications of how accurate a calibration model will be in predicting future samples. They are calculated using predicted results from true unknown samples. The RMSEP is an average expected prediction error. This differs slightly from the SEC terms that are providing the prediction error for the calibration samples used in developing the model. The relationship between RMSEP and SEP (RMSEC and SEC) is RMSEP2 = SEP2 + bias2

SVM – Support Vector Machines Support Vector Machines are a set of related supervised learning methods used for classification and regression. They belong to a family of generalized linear classifiers. These methods are finding their way into calibration programs and have shown great promise in their power to minimize prediction error for complex calibrations.

  • ANN – Artificial Neural Networks
  • CLS – Classical Least Squares
  • ILS – Inverse Least Squares
  • kNN – k Nearest Neighbor
  • LR – Linear Regression
  • LS – Least Squares
  • LWR – Locally Weighted Regression
  • MCR – Multivariate Curve Resolution
  • MLR – Multiple Linear Regression
  • OSC – Orthogonal Signal Correction
  • PC – Principal Component
  • PCA – Principal Component Analysis
  • PCR – Principal Component Regression
  • PLS – Partial Least Squares
  • RMSEC – Root Mean Square Error of Calibration
  • RMSEP – Root Mean Square Error of Prediction
  • RMSEPcv – Root Mean Square Error of
  • Prediction based on Cross Validation
  • SEC – Standard Error of Calibration
  • SEP – Standard Error of Prediction (Performance)
  • SVD – Singular Value Decomposition
  • SVM – Support Vector Machines

Continue to Part II

Comparison Guide

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NASA uses HPV Analyzer to Help Keep Planets Protected

NASA uses HPV Analyzer to Help Keep Planets Protected

HPVA Helps Keep Plants Clean

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New Intern Joins from US Department of Defense

New Intern Joins from US Department of Defense

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NIR-O and M508plus Process Analyzer Analog Inputs and Outputs

NIR-O and M508plus Process Analyzer Analog Inputs and Outputs

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