Emerson Exchange 365

The following insights are part of an occasional series authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. This article was originally published at the ISA Interchange blog site. Ultimately what we want to know and control is the concentration of key components. Relatively inexpensive inline measurements can be used under the right conditions to provide concentration measurements. Understanding the limitations as well as the capabilities is essential to success. Here we look at how we can elevate the use of capacitance, conductivity, density, pH and turbidity to provide process knowledge to control biological and chemical reactor concentration. The inferential measurement of the concentration of a component (e.g. reactant or reagent) in a feed, exit, or recycle stream or vessel is possible if the component of interest has a large definitive effect on capacitance, conductivity, density, pH, and turbidity. To infer composition in vessels, sensors are installed in nozzles on the vessel, in recirculation lines, or sample lines in close proximity to vessel. If the component of interest has a higher conductivity than other components or solvent, conductivity can be used if the conductivity is restricted to be always on one side of the peak in the conductivity curve. The process gain changes sign as an operating point crosses the peak, which is disastrous to a control loop because the PID control action sign must be the opposite of the process action sign (assuming valve action is correctly configured). The measurement and control of biological and chemical reactors is the key to product quality and the yield and production rate of most processes in the process industry. See Greg McMillan’s new ISA book Advances in Reactor Measurement and Control for an extensive view of practical opportunities for building and effectively using online estimators to improve process knowledge and control. If the PID has the wrong sign, the PID output will ramp to its output limit. Plots of conductivity versus concentration have a peak if the entire concentration range is covered. A few ionic species such as sulfuric have two peaks. The second peak for sulfuric acid occurs at 93 percent concentration. For product conductivity that traverses across the peak, concentration control cannot start until the conductivity is well to the right of the peak. For a very low concentration of a single acid and base (e.g. < 0.01 percent) pH provides a more sensitive inferential measurement of concentration. Insight : One or more signal characterizer blocks are used to give a piecewise linear fit that enables the online computation of the X axis ( percent concentration) from the Y axis of a conductivity plot or pH titration curve generated from samples at various operating conditions. For conductivity and pH, a signal characterizer is commonly used to compute the X axis (e.g. salt, acid, or base ion concentration) from the Y axis (conductivity or pH). The 20 or more data points of signal characterizer is usually enough to provide a piecewise linear fit. The points are more closely packed in the operating regions of greatest interest or nonlinearity. A cascade of characterizers can be used to provide greater resolution where a secondary signal characterizer is added to the output of the primary characterizer. A simple temperature correction should be generated based on the results of samples that cover the entire possible range of temperatures including abnormal operation. Insight : The effect of process temperature on the actual conductivity and pH of the sample must be measured and used in customized solution pH or conductivity temperature compensation. For a two component liquid mixture where the density the components differ by more than 1 percent an extremely accurate concentration measurement is attainable by the use of a Coriolis meter. The accuracy of the density measurement in Coriolis meter is 0.0002 gm/cm3. There is no drift and installation effects are essentially negligible. The meter never needs recalibration. There are no upstream and downstream straight run or field calibration requirements. High performance meter designs are now able to measure the concentration of bubbles and solids as well. The use of Coriolis meters on raw material feeds provides not only an incredibly accurate true mass flow measurement independent of composition but also an inferential concentration measurement from density. Insight : An extremely accurate and drift free measurement of liquid density by Coriolis meter can be used as an inferential measurement of concentration in a two component mixture. Turbidity offers an inferential measurement of biomass concentration for bioreactors. The turbidity measurement does not distinguish the number of cells or how many are alive (viable) or dead (lysed). The addition of a capacitance probe to provide a dielectric spectroscopy can provide inferential measurements of cell size, homogeneity, and membrane integrity. Viable cells have membranes intact whereas lysed cells have holes or fractures in their membranes. Insight : Dielectric spectroscopy in combination with an inferred measurement of biomass from turbidity can provide inferential measurements of cell size, and the relative concentration of viable (live) versus lysed (dead) cells. The inferential measurement of concentration must be periodically corrected by taken a fraction of the error between a synchronized computed concentration and an at-line or off-line analysis result. The synchronization is achieved by passing the change in concentration through dead time and integrator blocks with the proper sign of process feedback to match process dynamics and then adding the change to an original corrected value and passing the result through a final dead time block representing the analysis delay. To get the most out of inline meters and probes, fundamental relationships should be used to compute concentration measurements. The computed concentration measurements must be gradually corrected by comparing the computed concentration synchronized with an analysis result somewhere and sometime whether in the field, plant lab, or offsite lab.

A time constant can be beneficial or detrimental. A single large time constant in the process can reduce the variability of process inputs to the point of being negligible in the process output. This effect is rarely included in the analysis of potential... Read the full text.

The following insights are part of an occasional series authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. Simple online inferential measurements of cell growth rate, crystal growth rate, and chemical reaction rate are possible using conventional online measurements of flow and temperature. These inferential measurements enable the monitoring and control of process efficiency and capacity. For continuous operations, the indication of product formation rate can be used for maximizing yield at an operating point and making smooth, fast, and efficient transitions to new operating points. For batch operations, the indication of product formation rate can be used to achieve more repeatable batches and make intelligent decisions on batch end points. A computation of heat removal rate in a cooling system with a sensible heat correction can provide an inferential measurement of conversion rate for exothermic reactors. If there are no significant side reactions, the conversion rate can be taken as being specific to production rate. If the jacket circulation rate is constant and well known, a flow measurement is not necessary. The heat removal rate (cooling rate) uses temperature sensors on the inlet and outlet of the jacket. The inlet temperature measurement is sent through a dead time block with a dead time setting equal to the transportation delay so the inlet temperature can be synchronized with the outlet temperature. Resistance temperature detectors (RTDs) provide a more accurate inferential measurement. The heat removal rate is the outlet temperature minus the synchronized inlet temperature multiplied by the jacket flow and the heat capacity of water at the operating temperature. If the jacket circulation flow is not constant, the heat removal computation and the transportation delay must be updated based on a jacket flow measurement. For a constant coil or jacket flow and cooling or chilled water temperature, the difference between the reactor and coil or jacket outlet temperature (approach temperature), can be used as a simpler computation. The integration of the heat removal rate over the batch or for the residence time of a continuous reactor can provide an inferential measurement of total conversion. The measurement and control of biological and chemical reactors and crystallizers is the key to product quality and the yield and production rate of most processes in the process industry. See Greg’s new ISA book Advances in Reactor Measurement and Control for an extensive view of practical opportunities for building and effectively using online estimators to improve process knowledge and control. Wireless temperature transmitters and temperature and pressure compensated annubar mass flow meters can be used to establish the variability in coil and jacket flow and utility temperature besides inexpensively prototyping inferential measurements. The portability of wireless measurements enables one to demonstrate and quantify the benefits of online metrics and diagnostics in less than the time spent in meetings guessing the value and feasibility. The sensible heat correction can be readily computed. The net sensible heat is computed for each feed stream as the reactor temperature minus the stream temperature multiplied by the stream flow rate and specific heat. The feed sensible heat correction is summation of the net sensible heat for all feed streams. Typically the feed streams are cooler than an exothermic reactor temperature. Part of the heat of reaction goes into bringing the feed added up to the operating temperature. The cooling effect of these streams is added to the heat removal rate to get at a better estimate of the exothermic. If the feed streams are hotter than the reactor, the sign of the correction is negative. A similar methodology can give an inferential measurement of crystal growth rate. For startup and batch operations, there is an optimum cooling profile. At the beginning of the operation, the cooling rate is kept low to reduce the amount of small crystals (fines) being formed that would end up coating heat transfer surfaces and reducing final crystal size. Toward the end of the batch when crystals are growing rather than forming, the cooling rate is increased to maximize crystal size and minimize batch cycle time. The computation of an oxygen uptake rate (OUR) can provide an inferential measurement of cell growth rate. Because the Dissolved Oxygen (DO) PID output is continuously adjusted to match the amount of oxygen taken up by cells, the OUR can be roughly estimated from the air or oxygen flow demand when a DO controller is in automatic. A more sophisticated OUR calculation uses a mass spectrometer to measure the amount of oxygen in the off-gas. The oxygen flow rate departing the bioreactor is the off-gas oxygen concentration multiplied by the vent gas flow. The oxygen flow rate entering is the sparge gas oxygen concentration multiplied by the sparge flow. Note that some bioreactors use oxygen besides air in the sparge to meet peak oxygen demand; others use inert gas in the sparge to sweep dissolved carbon dioxide out of the bioreactor. Repeatable, sensitive and low noise flow meters are essential. For continuous operations, growth and reaction rates are indicative of feed stoichiometry and can be consequently used for improving the ratio control of feeds (e.g. substrates and amino acids for biological reactors, slurries and solvents for crystallizers, and reactants for chemical reactors). For fed-batch operations, a similar opportunity exists. For all batch operations there is an additional opportunity of monitoring and controlling the profile of cell and crystal growth and product formation. See the Control Talk blog Batch Optimization Recommendation Tips for more details. A decision can be made near the end of the batch as to whether to extend the batch for additional yield or end the batch for additional capacity. The next post will discuss how inferential measurements of composition can be built and future values predicted. For chemical reactors and crystallizers make the most of conventional RTD measurements of coolant in and out temperatures and knowledge of coolant flow to provide a simple online measurement of cooling rate. The resulting reaction rate and crystal growth rate can to be used to increase production efficiency and capacity. For biological reactors (e.g. fermenters), use precise flow meters and if available, an at-line mass spectrometer to provide an oxygen uptake rate that is indicative of cell growth rate.

What comes at you too fast? How do people know you are a process control engineer? What is more disturbing than talk shows? Is a flea market indicative of a project behind schedule? These and other questions you have not asked will be answered. Read the full text.

The following insights are part of an occasional series authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. Project meetings and startups can be stressful times to say the least. Here we gain insights by looking at the more laughable things we hear and see as automation engineers. The more ridiculous the statements and actions, the funnier they are. Humor makes the experience more memorable and can enable one to deal with the situation rather than just get frustrated. We start out with humor in project definition meetings and move on to batch songs and startups culminating in a performance review. Top 10 Things You Don’t Want to Hear in a Project Definition Meeting (10) I don’t want any smart instrumentation talking back to me. (9) Let’s study each loop to see if the valve really needs a positioner. (8) Lets slap actuators on piping valves & use them for control valves. (7) We just need to make sure the control valve spec requires the tightest shutoff. (6) What is the big deal about process control, we just have to set the flow per the PFD. (5) Just make sure all the flows and the process variables are constant. (4) The operators can tune the loops. (3) Let’s do the project for half the money in half the time. (2) Let’s go with packaged equipment and let the package supplier select and design a low cost automation system (e.g. cheap cheap). (1) Let’s go out for bids and have purchasing pick the best deal. Top 10 Songs for a Batch Project (10) Does Anybody Really Know What Batch This Is? (9) Another Batch Bites the Dust. (8) We Gotta Get Data Out of this Process [If It’s the Last Thing we Ever Do]. (7) Good Batches, Bad Batches [You Know I’ve Had My Share]. (6) Correlation Dreaming. (5) Changes in Variables, Changes in Attitudes. (4) [There Must Be] 50 Ways to Model Your Process. (3) This Project ‘s So Bright, I Gotta Wear Shades. (2) Gimme All Your Data [All Your QA Too]. (1) In-A-Planta-Da-Vida. For a more comprehensive taste of Greg McMillan’s humor, check out his ISA books:  How to Become an Instrument Engineer, Part 1.523 , Dispersing Heat Through Conviction , Logical Thoughts at 4:00 AM , The Life and Times of an Automation Professional – An Illustrated Guide , and The Funnier Side of Retirement for Engineers and People of the Technical Persuasion . Also at the end of each of Greg’s Control Talk Column is a Top 10 List Top 10 Things You Don’t Want to Hear on Startup (10) We never really could figure out what the old system was doing. (9) Do I have a system backup?!? I thought you were making backups! (8) They want to make our start-up into a reality show. (7) The displays are fine and dandy, but where are the panel boards? (6) We have changed our mind. We want the old system back. (5) Can you reprogram it so the wrong valve still works? (4) Didn’t you get the revised batch sheets? (3) Is a blue screen bad? (2) What is that burning smell? (1) We are out of coffee! Top 10 Signs you need to Tune the Loops (10) Lots of trials and errors. (9) When asked what the gain setting is, the answer is given in percent. (8) When asked what the reset time setting is, the answer is given in repeats/min. (7) The data historian compression setting is 25 percent. (6) There is more recycle than product. (5) Valves are wearing out. (4) Tempers are wearing thin. (3) Operators are placing bets on what loop will cause the next shutdown. (2) The output limits are set to keep the valve from moving. (1) Preferred mode is manual. Top 10 Things You Don’t Want to Hear in Your Performance Review (10) I see you refused to be a sumo wrestler in our team building exercise. (9) What have you done lately to get me promoted? (8) Do you have an evil twin? (7) Can you be replaced by something in the “cloud?” (6) You are at the top; the only way is down. (5) Have you thought about another career? (4) Pick a number from one to 10. (3) Boy, you are ancient. (2) What is all this jibber jabber about tuning and loop performance? (1) Who are you? These Top 10 lists work best in a presentation to a group of ten or more experienced automation professionals, people who have been in these situations and can appreciate the humor. A large group is good because humor is contagious and there are people with a great sense of humor and no sense of humor. If possible, invite prospective customers, or at least show them the presentation with the ability to hear the audience laughter. I start with a Top 10 list and scatter a few lists throughout my presentation to open minds and provide some comic relief in what is normally a very serious subject. Feel free to use my lists, just give me credit. Of course you can use these lists simply among friends to relax, smile, and enjoy.

Before the 1990s relatively few choices in PID structure were offered. There were also various supplier specific rules as to how to set the proportional mode and integral mode tuning settings to get proportional-only and integral-only control. A different model controller may have been needed for a different structure. The modern DCS offers the flexibility to readily choose 8 structures to take advantage of what each has to offer. Here we take a look at the type of applications where each structure offers an advantage.

The following technical insight is part of an occasional series authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. Humor can provide insights by opening the mind to the strange but true aspects of ourselves and our profession. Successful humor can cause a smile before the participant realizes the full nature of the situation. The humor in my books tends not to be slapstick in your face humor but more cerebral in nature. Hopefully the ideas bounce around in our brains finding many avenues to make us smile and relax. I express my humor most concisely in Top Ten Lists over the last 30 years. Here are some of my favorites in terms of gifts with the extended view that a distributed control system (DCS) can be a gift. Top Ten Reasons Why an Automation Engineer Makes a Great Spouse or at Least a Wedding Gift (10) Reliable from day one (9) Always on the job (8) Low maintenance (minimal grooming, clothing, & entertainment costs) (7) Many programmable features (6) Stable (5) Short settling time (4) No frills or extraneous features (3) Relies on feedback (2) Good response to commands and amenable to real time optimization (1) Readily tuned Top Ten Reasons I Use a Virtual Plant to Optimize a DCS (10) You can’t freeze, restore, and replay an actual plant (9) Imagination rather than culture is limitation (8) No waiting on lab analysis (7) No raw materials (6) No waste (5) Virtual instead of actual problems (4) Bioreactor batches done in 14 min instead of 14 days (3) Plant can be operated on a tropical beach (2) I don’t have $100,000K for an actual plant (1) Actual plant doesn’t fit in my briefcase Top 10 Reasons for a BBQ DCS (10) Automated recipes (9) Predicted BBQ times (8) Five-course meal no problem (7) Don’t have to watch cooking shows (6) So much feedforward control you eat before you are hungry (5) Process control comes home (4) Children want to become automation engineers (3) Spouse finally appreciates your expertise (2) Griller not grilled (1) More time to drink beer For a more comprehensive taste of Greg McMillan’s humor, check out his ISA books: How to Become an Instrument Engineer, Part 1.523 , Dispersing Heat Through Conviction , Logical Thoughts at 4:00 AM , The Life and Times of an Automation Professional – An Illustrated Guide , and The Funnier Side of Retirement for Engineers and People of the Technical Persuasion . Also at the end of each of Greg’s “ Control Talk Column ” is a Top Ten List. Top 10 Things A DCS Consultant Shouldn’t Say When Entering a Control Room (10) Does this hard hat protect me against the school of hard knocks? (9) At the last plant I was in we always did it this way. (8) I added alarms to each loop. (7) Does that flare out there always shoot up that high? (6) Ooooh! Did you mean to do that? (5) Can’t somebody do something about all those alarms? (4) We just downloaded the version released yesterday. (3) Here, I will show you how to operate this plant. (2) Are you ready to put all your loops in Remote Cascade? (1) We want a “lights out” plant! Top 10 Apps as Gifts from Spouse to Automation Engineer (10) Translate common speech to engineer talk (9) Translate engineer talk to common speech (8) Explain automation without causing glazed eyes (7) Guide for grooming (6) Guide for clothing (5) Learn to be as funny as “Big Bang” characters (4) Chill out (3) Enjoy mindless fun (2) Forget about logic for a moment (1) Anticipate and understand needs of spouse In my next blog post, I plan to continue with humor on what not to do in the control room and on projects. Even funnier than these lists are the actual quotes of control room operators captured in my ISA books. Relax, smile, and enjoy.

Not knowing the implications of the PID Form in an existing control system being migrated or the PID Form learned in a University course can cause gross errors in the tuning parameters and potential instability. The PID Form predominantly used today is not the Form in most of the controllers installed before the 1990s and is not the Form seen in most control theory textbooks. Here we alert you to the differences and consequences. An Appendix provides simple equations to convert between the different PID Forms and block diagrams in the time frame that are not available in the literature.

The question for the day is where to locate measurements. My first choice would be a Caribbean island but if the plant is not there, the sensing or sample lines and the associated transportation delays would be quite long. The additional loop dead time would cause all sorts of performance problems that might take years to troubleshoot. I might even have to move to the island. Hmm, sounds good for my golden years. Read the full text.

The following technical insight is part of an occasional series authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. This insight was adapted from Greg’s book, Advanced Temperature Measurement and Control . In industrial environments, high process temperatures, pressures, and vibration make it necessary to have a robust temperature sensor. Fast response time, accuracy, and stability are also needed. While several types of temperature sensors are available, such as thermistors, infrared pyrometers, fiber optic, and others, the two most commonly used in the process measurement industry are resistance temperature detectors (RTD) and thermocouples (TC). The RTD provides sensitivity (minimum detectable change in temperature), repeatability, and drift that are an order of magnitude better than the thermocouple, as shown in Table 1-1. Threshold sensitivity and repeatability are two of the three most important components of accuracy. The other most important component, resolution, is set by the transmitter. Drift is important for extending the time between calibrations and the temperature loop running at the right setpoint. The data in this table dates back to the 1970s and consequently doesn’t include the improvements made in thermocouple sensing element technology and premium versus standard grades. However, the differences are so dramatic that the message is still the same. The temperature range shown for the RTD in the table is optimistic. At temperatures above 500°C, changes in sensor sheath insulation resistance have caused errors of 10°C or more. There are many stated advantages for thermocouples, but if you examine them more closely you realize they are not as important as perceived for industrial processes. Thermocouples are more rugged than RTDs. However, the use of good thermowell designs and good installation practices makes an RTD sturdy enough even for high-velocity streams and nuclear applications. Thermocouples appear to be less expensive until you start to include the cost of extension lead wire and the cost of additional process variability from less sensor sensitivity and repeatability. The case of using TC or RTD input cards in a distributed control system (DCS) is not considered because of the error introduced by these input cards as a percent of span is large and individual sensor offset and drift errors cannot be individual corrected as they are with a dedicated temperature transmitter. Table 1-1 Accuracy, range, and size of temperature sensing elements The IEC 751 standard describes an ideal relationship between the resistance of a platinum RTD and the temperature to which the RTD is subjected. The difference between the actual RTD curve and the ideal RTD curve results in a measurement error, which is referred to as a sensor interchangeability error . The Callendar-Van Dusen equation offers an alternative to the IEC 751 standard. This equation... Read the full text.

Batch processes pose particular challenges for closed loop control and optimization due to inherent process nonlinearity and non-self-regulation. At the same time there are is a greater potential for increasing capacity in batch than in continuous processes. Solutions need to address the interrelationship between yield, capacity, quality, and repeatability. Here are opportunities and techniques for getting the most out of your batch. Read the full text.

The following technical insight is authored by Greg McMillan , industry consultant, author of numerous process control books and a retired Senior Fellow from Monsanto. This insight was adapted from Greg’s book Advanced pH Measurement and Control . Since we learn by example, here is a neutralizer tank that has the major mistakes I have seen in waste treatment system pH design and installation. Each mistake is the result of a fundamental lack of understanding of the heightened sensitivity of pH control systems to dead time, process and measurement noise, insufficient process attenuation (filtering) and valve backlash and stiction . 1. Insufficient number of stages of neutralization (inadequate rangeability and sensitivity) 2. Improper vessel geometry and agitation patterns (excessive equipment dead time) 3. Backfilled reagent dip tube (excessive reagent delivery delay) 4. Incorrect location of reagent injection point (excessive reagent delivery delay) 5. Gravity flow reagent (excessive reagent delivery delay) 6. Incorrect location of reagent control valve (excessive reagent delivery delay) 7. Control valve with excessive stick-slip (poor sensitivity and excessive variability) Advanced pH Measurement and Control by Greg McMillan and Robert Cameron provides a clear, concise, and comprehensive view of how to select, install, and maintain electrodes, control valves, and control strategies for pH applications critical for product and water quality in the process industry. The book covers every aspect of system design including the mixing and reagent piping requirements that are important for a successful application. 8. Electrodes submersed in vessel (coating and maintainability problems) 9. Electrodes located in pump suction (bubbles, clumps, and wrenches) 10. Electrodes located downstream in recirculation line (excessive measurement delay) The example serves to illustrate many underlying principles and resulting guidance required to meet the extreme challenges and achieve the extraordinary opportunities for concentration control. In pH control systems reagent piping and injection must minimize transportation delays, volumes must have proper geometry and agitation to maximize the process time constant that filters pH oscillations, several volumes may be needed to provide multiple process filters in series, valves must be able to precisely make extremely small changes in reagent flow, and electrodes must be installed to minimize noise and response time and maximize reliability. Read the full text.

The highest value added products use batch operations. Batches can take days to complete and be worth millions of dollars. In many cases bad batches cannot be fixed downstream. Bad batches must be avoided. There are many techniques for making batches more repeatable and faster by better monitoring and control. Essential are an appreciation of automation and an understanding of the non-self-regulation inherent in a batch process and the implications in terms of control strategy and controller tuning. Read the full text.

Software for auto tuning and adaptive control provide the opportunity to identify key loop dynamics besides providing a sound fundamental and automated basis for getting the best PID settings. Presented are uses of the knowledge gained and the setup of the automation system and testing/monitoring of PID performance to get the best results. Read the full text.

Automating any process can yield big improvements by eliminating human error and adding repeatability and predictability. The benefits are greatest when the best technology and practices are automated, the novice is protected against mistakes, and the specialist is enabled to capitalize on creativity and expertise. The same is true for PID tuning. Read the full text.

Here we look at how to make sure the measurement system is able to provide the analysis, metrics, and control needed for process control improvement. Also outlined is the opportunity sizing and assessment process, the use of statistical tools, the tracking down of the source of variability, and the finding of more optimum setpoints. Read the full text.

And so we have finally reached our last tip. Trust me when I say that this has NOT been an easy task. Distilling a career of engineering experience into one- or two-page tips is tough! For the last tip, we chose this subject because we believe an individual should never stop learning and improving … [...] Read the full text.

The pressure to reduce inventories, coupled with changing market demands and fluctuations in raw material and energy prices, requires a process plant to be able to respond quickly to maintain optimum operation. To most efficiently support changes in production rate or product grade, flows must change in unison throughout the plant. Feedback loops cannot do [...] Read the full text.

The benefits from process control improvement originate from increases in process efficiency, flexibility, and capacity. Often, there is a tradeoff where an increase in flexibility or capacity is accompanied by a decrease in efficiency. Better measurements, process knowledge, online metrics, and an enhanced PID can provide a more intelligent and effective optimization that minimizes the tradeoff between benefits. Read the full text.

Of all of the engineering fields, I have to think that our field of automation has one of the fastest rates of change. Every day new processes, new technologies, new instruments, and new control techniques invade the market, and an automation engineer must constantly strive to stay abreast of the latest offerings or face becoming [...] Read the full text.

In Tip #70, we learned that deadtime was the key to loop performance. The Control Talk blog The ABCs of Controller Tuning describes how tuning settings can be reduced to a simple function of deadtime. The InTech article PID Tuning Rules and the article’s online appendices describe the fundamental relationships between deadtime, performance, and tuning. [...] Read the full text.

This tip is really an extension of Tip #47 and 48, and it discusses what can happen when those two tips are not followed. I have had a number of bosses during my career. Most were superb, providing professional and technical guidance and support when I needed it and giving me the reins and responsibility [...] Read the full text.

A compressor going into stall is like jumping off a cliff with a bungee cord. If the bungee cord has no losses to dampen the oscillation, we have something akin to surge. A 0.5% drop in efficiency can occur for each surge cycle. Several surge cycles can occur due to delays and lags in high temperature, thrust, and vibration shutdown systems. In some compressors the damage is so severe after multiple surge cycles that rotors and seals need to be replaced. The cost of process downtime can be significant particularly when a compressor feeds parallel trains of equipment. The restart of exothermic fluidized bed reactors in the petrochemical industry may be the most hazardous mode of operation. Read the full text.

Processes often include a mixture of batch and continuous operations. For liquid products made in a batch operation, most of the time the batch flow is off because the drain valve is closed during the batch. When done, the batch is drained quickly. This discontinuous batch flow cannot directly feed continuous operations downstream. For traditional [...] Read the full text.

Over the course of my career, I have never been given a reference that provided anything but glowing reports and testimonials. Perhaps your experience will be different than mine, but the odds are slim. In every case each reference I contacted gushed ad infinitum about how wonderful the candidate was or how positively flawless the [...] Read the full text.