Gas chromatographs perform critical measurements in a wide range of process and natural gas industries. In many applications like natural gas production and custody transfer, these measurements translate directly into profitability, process efficiency, and regulatory and contract compliance. That’s why optimizing the performance of your GC can have a big impact on your bottom line.
To help users get the most from their GC over the course of its lifecycle, Emerson is offering a free webinar series that brings together our GC experts to offer trusted insights and best practices. The webinars will also provide answers to most frequently asked questions and solutions to challenges operators may be facing in the field. The first webinar in the series is coming right up –
WEBINAR 1: GC’s Response Factors and Why They Are Important
Tuesday, May 1, 2018
10 AM – 11 AM CDT (Houston)
Emerson’s GC expert, Bonnie Crossland, will discuss the importance of GC’s response factor. Understanding how a detector responds to the measured components can provide an effective way to validate the correct operation of your gas chromatograph. Changes in the detector’s response to the measured components can indicate changes in the analysis that might cause inaccurate measurements.
This webinar will review the elements that can cause variations in a response factor, and how those variations can be used to help troubleshoot the gas chromatograph.
Knowledge is key to maximizing the capabilities of your Rosemount™ Gas Chromatographs (GC). Understanding how to properly operate and maintain your GC will help increase uptime, reduce maintenance costs, and extend asset life.
Regardless of your experience level, the Rosemount gas chromatograph online course will provide the knowledge and expertise you need to ensure your operations run as safely and efficiently as possible. This free e-course will provide attendees with a basic understanding of the 370XA gas chromatograph and will cover:
Normally, this e-course is valued at $100, but for a limited time, you can sign up for free.
Plus, if you complete this e-course and take our short survey by June 1, 2018, you’ll be eligible for 15% off your next Rosemount course, including any online courses and hands-on courses at one of our Emerson training centers.
Emerson offers a wide range of both online e-courses and more in-depth, in-person, hands-on training classes on the theory, operations, and maintenance practices for analyzers and instrumentation. For more information on Rosemount’s full range of courses, browse our course catalog, or view a calendar of our instructor-led courses at our training centers in Houston, Minneapolis, and Charlotte.
Register today for the online 370XA gas chromatograph course – a flexible, engaging, convenient way to learn about our GC technologies and solutions and how you can maximize the benefits it offers your plant.
by: Bonnie Crossland, Product Marketing Manager – Gas Chromatographs, Rosemount Analytical
Welcome to Analytic Expert – I’m Bonnie Crossland. As you know, gas chromatography has become the absolute standard of quality and excellence in natural gas measurement. As the leader in this technology, Emerson is constantly working to make the measurement faster, more accurate, and lower cost. Today, I’d like to share one of those unique cost reduction features. The Rosemount Analytical 370XA Gas Chromatograph (GC) is equipped with a Cal-Gas Saver that cuts the amount of expensive calibration gas used by the instrument by MORE than half as compared to other GCs. It turns out that this feature doesn’t only save money in the cost of Cal-Gas, but it can also significantly reduce installation costs and the actual footprint of your installation – a big advantage in space constrained applications. These two benefits in turn reduce the rising cost of natural gas measurement. To understand how this feature works and is able to reduce size as well as cost, check out the below video.
I hope that was useful information. If you have any questions on the use of gas chromatography in C6 measurement, just post a comment below, or contact me at firstname.lastname@example.org.
And to learn about another cost saving feature, you might like to view THIS VIDEO on the Auto-Valve Timing.
By Jill Jermain, Senior Product Manager
Hi. Welcome back to Analytic Expert. As promised, this is the second in a two-part series answering questions about pH analysis in various types of industrial process control applications. I’m Jill Jermain and I’m happy to be your analytic expert on this important topic. If you missed Part 1, please click HERE and read through it, since some of those answers will help you understand these better.
What causes poisoning of the sensor?
The common reference electrode used in pH measurements consists of a silver wire coated with silver chloride in a fill solution of potassium chloride. The purpose of the potassium chloride is to maintain a reproducible concentration of silver ions in the fill solution, which in turn, results in a reproducible potential (voltage) on the silver-silver chloride wire. The mechanism of reference poisoning is a conversion of the reference from a silver-silver chloride based electrode to an electrode based on a different silver compound. The ions (bromide, iodide, sulfide) form less soluble salt with silver than does chloride. When these ions enter the fill solution, they form insoluble precipitates with the silver ions in the fill solution. But there is no initial effect on the potential of the reference, because the silver ions lost to precipitation are replenished by silver ions dissolving off the silver chloride coating of the silver wire. It is not until the silver chloride coating is completely lost that a large change in the potential of the reference occurs. At this point, the reference electrode must be replaced.
How can I keep my sensor from frequent coating?
Coating typically increases the response time of the pH sensor and can cause instability in pH control. A process flow velocity greater than 5ft/sec will help minimize coating. Also, be sure to check on the placement of the sensor in the process as this may contribute to the rate of coating as well. For example, if the sensor is barely peeking out into the process, there isn’t a great deal of flow versus if the sensor sticks out a few inches more into the process. The higher flow rate would help the sensor from not coating as quickly since it would act as an artificial scrubber.
Why should I monitor glass impedance and reference impedance?
Glass impedance refers to the impedance of the pH-sensitive glass membrane. The impedance of the glass membrane is a strong function of temperature. As temperature increases, the impedance decreases. The impedance of a typical glass electrode at 25°C is about 100MΩ. Most Rosemount Analytical pH sensors are 50 to 200MΩ, with exception of the PERpH-X pH sensors, which measure 400 to 1,000MΩ. A sharp decrease in the temperature-corrected impedance implies that the glass is cracked. High glass impedance implies that the sensor is nearing the end of its life and should be replaced as soon as possible.
The major contributor to reference impedance is the resistance across the liquid junction plug. The resistance of the liquid junction should be less than 40kΩ. High impedance readings around 140+kΩ typically indicate that the junction is plugged or the filling solution/gel is depleted.
What is a ground loop?
A ground loop exists when a circuit is connected to earth ground at two or more points. Because the potential of the earth varies from point to point, two or more connections to ground cause currents to flow. If the current flows through a signal carrying wire, the result is a noisy, offset signal. The classic symptom of a ground loop is a sensor that reads correctly in buffers, but gives a reading grossly in error when placed in the process liquid. These ground loop currents find a good conductor in the reference electrode and make this electrode part of the current loop. Because the voltage is in series with other cell voltages, the ground loop current causes the pH reading to be substantially different from the expected value. The source of the ground loop could be any pump, motor, or other electrically powered device. To eliminate a potential ground loop, don’t attach any electrically powered device to the same ground on your meter as the pH electrode.
What is a sodium error?
More correctly called alkali ion error, sodium ion error occurs at high pH, where hydrogen ion concentration is very low in comparison to sodium ion concentration. Sodium errors come about because the potential of the glass membrane depends not only on the concentration of hydrogen ions, but also on the concentration of other metal ions, for example, sodium. The sodium ion concentration can be so high relative to hydrogen ion concentration that the electrode begins to respond to the sodium ion. This results in a reading that is lower than the actual pH. Depending on the glass formulation, this can occur as low as 10 pH.
I hope these answers have been helpful to you in understanding and operating your pH sensors. Do you have more questions? Check out our pH Sensor Selection Tool HERE, and feel free to ask any questions here and I’ll answer as soon as possible. Or you can contact me at email@example.com.
Hi and welcome to Analytic Expert! I’m Jill Jermain, senior product manager at Emerson Process Management. Today’s blog is the first in a two-part series answering essential questions about pH analysis. pH measurement plays an important role in virtually every industrial process and an equally essential part in environmental regulatory compliance. Many of the below questions pop up every day whether in chemical processing plants, power plants, or biopharmaceutical processing. Keep this blog handy to refer to regularly. Here we go:
Why is it important to measure pH?
The major function of pH in industry is process control. Controlling pH ensures product quality, reduces corrosion and scaling in equipment, and protects the environment by monitoring and regulating product waste. It’s important that the person performing pH measurements understands how the measurement is made, how to calibrate the instrument, and how to recognize and avoid common problems.
What is the shelf life of a pH sensor?
pH glass electrodes slowly deteriorate in storage overtime and no specific expiration date is given. The best way to determine if the sensor is functioning accurately is to see if it calibrates properly using the two-point calibration method.
What is the two-point calibration method?
This method uses two buffer solutions, usually at least 3 pH units apart, which allows the pH analyzer to calculate a new slope and zero value to be used for deriving pH from the millivolt and temperature signals. The slope and zero value derived from a buffer calibration provide an indication of the condition of the glass electrode from the magnitude of its slope, while the zero value gives an indication of reference poisoning. Ideally, the pH electrode will have a slope of 59.16 mV/pH, but in practice, a well-functioning electrode has a slope of 54 to 59 mV/pH.
How often do I need to calibrate my pH sensor?
The frequency at which sensors should be calibrated can be determined only by experience. Many factors influence calibration frequency. Sensors installed in a dirty or corrosive process stream usually require more frequent calibrations than sensors used in clean water. Sensors measuring extreme pH values also require more frequent calibrations than sensors measuring mid-range pH.
Why isn´t a pH 10 buffer solution recommended for calibrating?
A pH 10 buffer solution absorbs carbon dioxide (CO2) from the air, which depresses the pH. When CO2 is absorbed in water, it forms carbonic acid, which in turn lowers the pH of the buffer. Thus, the true pH is less than the expected value, and the calibration slope is low. If the pH 10 buffer gives a low slope, repeat the calibration using a lower pH buffer. For example, use pH 4 and 7 buffer instead of pH 7 and 10 buffer.
What is the best way to clean a pH sensor?
Again, the frequency at which a sensor should be inspected and cleaned can be determined only by experience. If the process liquid coats or fouls the sensor, frequent cleaning may be necessary. If the process does not contain a high level of suspended solids, the need for regular cleaning will be less. Sensor diagnostic measurements, if available, can also help indicate when a sensor needs cleaning. Often, an increase in glass or reference impedance indicates the electrode is becoming fouled. To remove oil deposit, clean the electrode with a mild non-abrasive detergent. To remove scale deposits, soak electrodes for 1 to 5 minutes in a 5% hydrochloric acid solution. Remember to always recalibrate the sensor after cleaning. If the sensor was cleaned with detergent or acid, soak the sensor in pH 4 buffer for at least an hour before calibrating.
What is the slope of a sensor?
The slope (sensitivity) indicates how well the sensor responds to changes in pH. A theoretically ideal electrode slope has an mV change of 59.16 mV/pH at 25°C. As the electrode ages, its slope decreases and a sensor should be replaced when the slope reaches 48 to 50 mV/pH.
To determine what kind of pH sensor would work best for your application, check out our pH Sensor Selection Tool HERE.
And here’s Part 2 of this blog series, as we continue to address important pH questions – like what is a ground loop, typical causes of sensor poisoning, and what’s a sodium error.