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

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

FAQtwoHi. 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


faq1Hi 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.

15 Jan, 2015  |  Written by  |  under Education

By Patrick Naillon, Global Blended Learning Developer

Many of today’s plants are facing a labor shortage issue as experienced technicians and operators are retiring and new employees require additional training to ensure consistent productivity. One way many plants are dealing with this issue is by re-evaluating their training programs to ensure they are meeting their current needs.

Computer-based learning, or eLearning, is dramatically improving employee training and productivity. It is estimated that more than 40% of Fortune 500 companies use some form of eLearning technology, while companies that use eLearning tools have a potential to boost productivity by 50%. Companies that offer best practice eLearning generate around 26% more revenue per employee.

Clearly, eLearning is the way to go. But how does that impact the world of O2 sensors, pH calibration, and electronic analyzers in your plant?

Emerson offers Rosemont Analytical online, self-paced training courses, featuring animated lessons, professional narration, 3D modeling, knowledge checks, and a final assessment to test your staff. These courses can be taken any time, from any internet-connected pc, laptop, or tablet. Even a smart phone can manage many eLearning courses. Courses can also be ‘paused’ allowing your users to return to the instruction without needing to start over again – a valuable tool if time is limited to view instructional materials.

Self-scoring courses allow a company to assign a number of I&E techs, sales reps, plant managers, and others, to take a required training course, and have the final scores for each person routed to your HR department for confirmation of course completion and score. A series of courses may be created for a particular job classification in your company – for example: pH Theory, Electronic Analyzers, pH Sensors, Conductivity Theory – allowing companies to create an ‘online university’ of course material and track each employee and their career goals.

RAI.pullquoteAnd this increase in training actually comes at a lower cost – no more scheduling employees for training that eats into working hours or brings your company to a halt; no more hiring expensive trainers, or flying trainers (or employees) long distances; no more hotel and meal bills. Plus, you realize cost savings from elimination of prep time for training (booking meeting rooms, printing handout materials, providing meals and coffee service).

Best of all – eLearning has the best record of retention of all training types. By allowing your employees to work at their own pace, and allowing lessons to be revisited prior to the final assessment, eLearning provides a better environment for any student. Many types of eLearning are meant to be accessed at any time – for example, tutorials showing how to use a 1056 Analyzer could include lessons showing how to run a sensor calibration. Your employees could at any time access this tutorial, for a refresher or to learn a new skill for their job. The tutorial functions like a hardware guru available 24/7 to everyone in your organization.

Online learning can help your plant improve employee productivity at all levels to ensure operational efficiency; address the looming labor shortage issue and increase production quality.