If you increase the controller gain by the same factor that you increase reset time (e.g. double the gain and the reset time), how does it affect key performance indicators such as quality, yield, on-stream time, and environmental costs? If you make the valve and measurement faster, how does it affect these same KPI? If you want to improve a KPI, what is the priority of solutions?

The equations for the peak (Ex) and integrated error (Ei) in terms of controller settings, shown on slide 1 of EffectsLoopTuning&Dynamics-KPI.pdf, provide an answer to many of these questions if you embrace your inner geekness as advocated in the Control Talk Jan 2010 issue "The Future is Now"

Both equations were derived in Appendix A and B of Tuning and Control Loop Performance (scheduled to be back in print by Momentum Press, 2010). The derivation of the equation for the integrated error was included in Appendix C of New Directions in Bioprocess Measurement and Control (ISA, 2007) along with a unification of controller tuning rules. This unification, which showed how all the major tuning rules give basically the same result for a controller gain to minimize peak error, was personally satisfying but possibly not for people who are adamant about the relative merits of personal favorite tuning rules.

Since the integrated error is inversely proportional to the controller gain and proportional to the reset time, doubling the controller gain and reset time cancel each other out. However, doubling the controller gain halves the peak error since reset time doesn't appear in the equation of the peak error. Reset time has an effect on peak error but it is negligible unless the reset time is decreased to the point where it approaches the loop deadtime. This can happen for deadtime dominant systems, but the peak error here is basically the open loop (error with the controller in manual) as evident from the equations on slide 2 of EffectsLoopTuning&Dynamics-KPI.pdf.

Nearly all the process control literature focuses on integrated absolute error (IAE) as the measure of loop performance. The IAE is a good measure of product that is off-spec that can lead to reduce yield and the raw material or recycle processing to product cost ratio (euros per kg and dollars per lb). If the off-spec cannot be recycled or the feed rate cannot not be increased to compensate, there is also a loss in production rate. If the off-spec is not recoverable, there is an additional waste treatment cost.

What we usually don't take into account is the filtering effect of back mixed volumes as indicated by the equation on slide 3 of EffectsLoopTuning&Dynamics-KPI.pdf. For chemical and pharmaceutical plants and refineries, there are large volumes that provide significant attenuation of oscillations. However, in other process industries, various pathways of variability do not have significant filtering and culminate in the final product. These processes are also more vulnerable to interactions because there is no smoothing of effect of one loop's control valve movement on another loop's process variable. This changes the whole view on how you tune controllers. For systems with little back-mixing, controllers are tuned to limit the transfer of variability from the controlled variable (controller PV) to the manipulated variable (controller output) to prevent interactions and to provide a smooth response. The controllers are also tuned for coordination by enforcing a closed loop time constant (Lambda). For pulp and paper plants, nearly all of the variability expressed by the IAE ends up in the sheet since most of the processing is done in pipes and inline or unagitated equipment. Lambda tuning has been exceptionally successful in optimizing the transfer of variability and the coordination of loops. The same requirements could occur for plastics and textiles, since the IAE in the polymer lines and extruders shows up in the yarns and webs. However, these plants may have extensive blend tanks that average out the plus and minus fluctuations in product quality.

I ran into a process control improvement (PCI) study, where after an hour of discussion and investigation it became obvious a reduction in the considerable variability observed in each textile line had no value because the product coming out of the huge blend tank was always in spec and the variable speed pumps were maxed out. My decision to move on to better opportunities was not well received, so we stayed for 2 days to confirm there were no PCI opportunities (reducing the size or inventory in the existing tank or replacing the pumps were considered accounting or process design improvements).

When loops are oscillating across the split range point (common case due to valve stick-slip and installed valve characteristics), there can be a cross neutralization of acids and bases or a cross compensation of hot and cold heat transfer fluids that increases reagent and energy costs. Here the IAE is important but an integration of individual reagent and heat transfer fluids is a better indication.

If there are appreciable back mixed volumes whose residence time is much larger than the control loop period, the integrated error (Ei) where the plus and minus errors cancel out for a disturbance can be a better indication of the effect on product quality. Taking into account that the integrated error is also the IAE for an over-damped or critically damped response, we realize the simplification of the relationship of off-spec to an integrated error offers considerable understanding as to the effect of tuning settings.

This topic will roam on for 4 parts. In part 2, I discuss the effect of the peak error on onstream time and environmental costs. In part 3, I cover how measurement and valve dynamics impacts both types of errors and hence KPI. In part 4, I conclude with some rules of thumb on the priority of PCI solutions for various scenarios.

The figures in the attached VariableSpeedDriveRangeability.pdf and the following discussion is an excerpt from the ISA book The Essentials of Modern Measurements and Final Elements - A Guide to Design, Configuration, Installation, and Maintenance.

The 4 main practical reasons that variable speed drives (VSD) drives are not used as extensively as one might think for pump control are as follows [35].

1. Drives are generally not built just for pumps. They handle conveyors, extruders, etc. There are a lot of VSD menu choices and options not pertinent to pumping applications.

2. Users don't like the complexity of the VSD. The user must address setup, maintenance, and design issues. Special practices are needed to prevent EMI in instrument signals and from getting harmonics back into the power supply.

3. Someone needs to do the right calculations on dollars saved. Typically calculations don't take into account the drop in drive efficiency at low speeds. The duty cycle (amount of time speed is really turned down) is not known in advance. If there is a high static head, the energy savings of a drive disappear.

4. It is rare to compare a VSD and valve. There are generally no decision points in the project for this comparison.

Is a Valve or VSD Faster?

Exceptionally fast loops (e.g. furnace pressure, liquid pressure, and surge control) can ramp off-scale in milliseconds. These loops have essentially a zero process deadtime and may have a high process gain due to a narrow control range (e.g. fractional inches of water column for furnace pressures). These loops require DCS scan times of 0.05 to 0.1 seconds. Special fast scan rate digital controllers or analog controllers are needed. DCS scan time requirements of 0.2 seconds or less signify a VSD opportunity. A properly designed VSD has no measureable dead time while control valves and dampers take anywhere from 0.2 to 2.0 seconds to start to move. For example, an incinerator pressure and polymer pressure loop that could get into trouble in less than 0.1 second required a VSD and analog controller to stay within the desired control band [20][23][35].

The VSD has a negligible time delay unless a deadband or dead zone is introduced in the drive electronics to reduce reaction to process measurement noise or a low resolution input card is used. A control valve or damper has a deadtime that is proportional to the resolution limit (sticktion) or deadband (backlash) divided by the rate of change of the process controller output. For large or fast changes in signal this deadtime disappears.

A pneumatic actuator has a pre-stroke deadtime that is the time it takes for the actuator pressure to change enough to move the actuator shaft. For large actuators, the pre-stroke deadtime can be several seconds unless a booster is added.

The inertial time constant of liquid flow response is inversely proportional to flow. Consequently, the process lag at low flow rates and at the initial start of flow can be quite slow (e.g. 5 seconds) compared to the process lag at normal flows (e.g. 0.5 seconds). The comparison between VSD and control valve response should be at normal flows.

In a published comparison of the dynamic response of a control valve and a pump for flow control for a system with negligible static head, the integral times were about the same for the VSD and valve loops. However, the controller gain could be increased by over a factor of 6 for the VSD loop. As a result, the set point response was faster [38]. In this test the valve deadband was about 8% and there was no static head. In unpublished lab test results of control valves with low sticktion, low backlash, and a digital positioner and a VSD with a volts/hertz PWM drive for liquid flow control, the speed of response of the valve and VSD were similar.

Variable speed drives, control valves, and dampers have a velocity limited exponential response. The velocity limiting in a drive depends upon the available motor torque and the inertia of the motor rotor, the pump shaft, and the pump impeller. The exponential term is generally much smaller for a VSD than for a control valve or damper. On the other hand, the velocity limiting is slower for a VSD unless the actuator size is large and boosters are not used. Consequently, for small changes in signal, a well designed VSD is faster. Conversely, for large changes in signal, a small control valve is faster (see section on dynamics). This leads to the conflicting statements about whether a VSD or control valve is faster. Which final element is faster often depends upon the size of the change in signal.

VSD Best Practices

To summarize, a VSD is most likely to offer energy savings or better loop performance as a final element for the following types of applications:

• Loops that require 0.2 seconds or faster scan time
• Valves and dampers with 0.5% or more sticktion or backlash
• Large utility flows
• Integrating and runaway processes without a secondary flow loop
• Low static head processes requiring frequent turndown

A tachometer or inferential speed feedback signal should be sent to the process controller in the DCS that is sending the signal to the drive. The speed feedback should be used in a similar way to the position feedback from a digital positioner to prevent the process controller output from changing faster than the final element can respond. The use of the dynamic reset limit option for the loops in the DCS can automatically prevent the process controller from outrunning the final element response (see section on dynamics).

For best performance users should consider the following during the specification and implementation of variable speed drive systems:

• High resolution input cards
• Pump head well above static head
• On-off valves for isolation
• Design B TEFC motors with class F insulation and 1.15 service factor
• Larger motor frame size
• XPLE jacketed foil/braided or armored shielded cables
• Separate trays for instrumentation and VFD cables
• Inverter chokes and isolation transformers
• Ceramic bearing insulation
• Pulse width modulated inverters
• Properly set deadband and velocity limiting in the drive electronics
• Drive control strategy to meet rangeability and regulation requirements
• Dynamic reset limiting using inferential speed or tachometer feedback

VSD Response

The response of variable speed drives more closely resembles a pure ramp with no rounding or time delay provided a filter or deadband has not been added in the drive electronics to attenuate process noise in the process controller output signal. The ramp time in the VSD depends upon the size of the load compared to the available torque from the motor. In general, the ramp time of a VSD is longer than the stroking time of a control valve but is shorter than the stroking time of a large damper. Longer than necessary VSD ramp times may inadvertently be imposed in the drive electronics.

There is essentially no sticktion or backlash in variable speed drives for axial and centrifugal blowers, fans, and pumps but this does not necessarily mean there is no resolution limit or deadband in the VSD response.

Controller outputs invariably have fluctuations that originate from process or sensor noise and transmitter resolution limits. These fluctuations are not representative of the actual value of the process variable and are best ignored. These fluctuations are particularly large and fast for flow and pressure loops. A deadband is sometimes introduced in the VSD electronics to prevent changing the speed. The effect may be a true deadband where the desired speed does not change upon a change in direction until the change in signal is larger than the deadband setting. The effect here is similar to backlash in a control valve. In other cases, it may be a deadzone setting, in that the desired speed does not change until the accumulated change in signal since the last change in speed is larger than the deadzone setting. Here the effect is similar to a resolution limit.

If there is no deadzone setting, the resolution limit in a VSD is largely determined by the input card. Assuming there is no sign bit, the VSD resolution limit is simply 100% divided by 2 raised to the number of bits (n) of the input card. Unfortunately, VSD manufacturers did not understand the limit cycle that would result from the resolution limit and offered an 8 bit input card (0.4%) as the standard card. Higher resolution input cards (e.g. 12 bit and 16 bit) should be specified to make the VSD I/O resolution comparable to the DCS I/O resolution.

VSD Installed Gain

In a variable speed drive for liquid flow, the pump characteristic curve shifts with pump speed. Since there is no control valve, there is no valve drop and the flow is at the intersection of the pump curve and the system frictional loss curve.

For a negligible static head and an idealized pump, motor, and VSD, the change in flow with speed is linear. If the static head is negligible, the loss in pump efficiency and the increase in slip at low speed, cause a decrease in gain (sensitivity) at low speed. This loss of sensitivity is seen as a flattening at low speed in the plot of flow versus speed.

If we ignore the loss in pump efficiency and increase in slip, a pump curve that approaches the static head will show a sharp bend downward to zero flow at low speed. The plummet of the speed at low speed causes a significant increase in gain and a nosier flow at low speeds [46].

A flat pump curve will cause almost a quick open type of flow characteristic. The high gain (sensitivity) at low speed can cause cycling [46]. Operation on a relatively flat pump curve can occur from improper pump selection or over-sizing.

VSD Rangeability

For variable speed drives, estimating rangeability gets tricky. The decrease in process gain from speed slip offsets the increase in process gain as the pump discharge head approaches the static head. If there are no overheating or cogging problems as suggested is the case for a pump and valve system with a well designed open loop (volts/hertz) PWM drive, high resolution input card, and negligible static head, the rangeability is normally 40:1. When the pump head is operating near the static head, the minimum controllable flow is set by rapid changes in the static head and frictional loss. These rapid changes could be due to noise and sudden or large disturbances. The speed can not be turned down below the amplitude of these fast fluctuations.

The rangeability of a VSD could drop to 4:1 for the following systems:

(1) Older VSD technologies such as 6-step voltage (excessive slip at low speed)

(2) Systems with a high static head (flow plummets to zero at a low speed)

(3) Operation on the flat portion of the prime mover curve (cycling at low speed)

(4) Hot gases (motor overheats at a low speed)

There are a lot of ways of looking at rangeability. Nearly all of them lead to the wrong conclusion as to what type of valve is best for process control. Some of the absolute worse valves for control (e.g. on-off piping valves) have the highest stated rangeability.

Valve rangeability is particularly important for pH control, batch control, startup, and plant turndown (see Control Talk column "Downturn Turndown" in Control July 2009 issue)

From, a piping view point, a full bore ball valve might be thought to have the highest rangeability because when the valve wide open, the flow path is nearly an open unobstructed section of pipe. A conventional butterfly would not be far behind because the only obstruction is a disc that could be almost horizontal when wide open.

Another definition of valve rangeability I have heard is the maximum flow divided by the minimum flow where the actual flow characteristic deviates by some specified margin from the specified inherent flow characteristic. Based on this definition, a linear trim (linear inherent characteristic) is stated to have the best rangeability. This approach is bogus in that the installed characteristic will be different and the controller can compensate for a deviation in characteristic through reset action.

The largest controllable flow divided by the smallest controllable flow is the definition of valve rangeability from a control viewpoint. Just being able to pass a high flow for a given valve size or adherence to an inherent valve characteristic does not mean the valve has high rangeability for control. You need to look at the installed valve characteristic where the percent flow is plotted versus stroke. Note the plot uses percent flow so the magnitude of how much flow the valve passes is not the issue.

For liquid service, the ratio of the pressure drop of the valve wide open to the valve fully closed can be used to show the effect of pump and piping design on the installed characteristic. This valve drop ratio varies from 1.0 where the frictional loss from the piping is negligible (entire difference between pump discharge and destination pressure is available as a pressure drop across the valve) to a minimum of about 0.05 where the valve drop at wide open is about 5% of the system pressure drop for energy conservation (decreased pump head and hence size). Figures 7-47a through 7-47c in the attached ControlValveRangeability.pdf excerpt from the ISA book The Essentials of Modern Measurements and Final Elements - A Guide to Design, Configuration, Installation, and Maintenance show the effect of valve drop ratio on the installed characteristic for linear, equal percentage, and modified percentage inherent characteristic. These figures show that a linear trim distorts to an undesirable type of quick opening characteristic where there is a burst of flow near the closed position followed by a noticeably decreasing valve gain (valve sensitivity) above 30% open. Conversely, the equal percentage trim becomes more linear as the valve drop ratio decreases. The curves for the equal percentage trim shown in Figure 7- 47b are for a conservative rangeability parameter equal to 100 (R=100). Many valves designed for superior throttling service have a larger R that would lower all of the curves in Figure 7-47b near the closed position.

Some progress has been made in a more realistic assessment of valve rangeability based on changes in slope of the installed valve characteristic and hence changes in the valve gain (more commonly referred to as the process gain). The lowest controllable and highest controllable flow depends upon where the slope decreases to less than 1/4 of its maximum thereby putting a limit on the change in process gain of 4:1. Based on this criterion, a sliding stem valve has a better rangeability than a ball valve or the conventional disc butterfly as seen in Figures 7-48a through 7-48c in the excerpt.

Heat exchanger temperature and inline composition control loops often benefit from the increase in gain with stroke offered by an equal percentage characteristic because it helps compensate for the decrease in temperature or composition process gain as the flow through the valve increases. In fact there is theoretically an exact linearization possible for a valve drop ratio of 1.0, because the slope (valve gain) of the inherent equal percentage characteristic being proportional to flow exactly cancels out the process gain inversely proportional to flow.

For vessel level, pressure, and temperature control loops, the process gain is so small that the allowable controller gain is way above the controller gain used. Consequently, changes in valve gain have a negligible effect.

Flow loops have a linear process gain so the valve gain linearity affects tuning. The effect of this is minimized by the use of reset rather than gain action.

I have suggested for more than 20 years that a more absolute accounting of valve rangeability from a control perspective would be to take the stick-slip near the closed position and use this as the X coordinate and use the corresponding Y coordinate on the installed valve characteristic as the minimum controllable flow. You cannot control tighter than the limit cycle from the resolution limit near the closed position. Based on this criterion, valves with a minimum sticktion near the seat and a percentage type of characteristic would offer the best rangeability. Sliding stem valves with a percentage trim, a valve drop ratio of 0.25 or higher, low friction correctly tightened packing, diaphragm actuators, and digital positioners would have the best rangeability and the best dynamics. If the pressure drop allocated to the control valve is less than 10% of the system drop to save energy, the nonlinearity of the installed characteristic of most trims becomes potentially detrimental to loop tuning and performance.

I got on a roll listening to Bob Seger's "Roll."

In the process industry, what a control loop eventually manipulates in nearly all applications is a flow via a final control element such as a control valve, damper, or variable speed prime mover (pump, fan, or compressor). Dampers and variable speed prime movers are commonly found in utility systems. Peristaltic pumps are used in labs and positive displacement pumps are used for extremely low additive flows in plants. In instances, mass flow controllers (thermal mass flow meters with an integrated PI controller and valve) and remotely set pressure regulators are used. However, in production units, control valves are used as the final element in 95% or more of the loops.

Do we know for a change in controller output, did the valve actually move and if so when? Do we know when the control valve is the source of process variability? Do we know what makes a valve "Good" or Bad" in terms of its ability to do its job?

In valve selection and specification, a lot of effort is put into making sure the valve passes the required flows, has minimal leakage, no plugging, and has materials of construction and packing that withstands process composition and conditions. The dynamic response is often neglected possibly because response criteria and requirements are not well understood. Since most loops are digital, the question comes down to whether the change in controller output in a given scan results in a change in position of the internal trim (closure component such as a plug, ball, or disc). Of course most valves will eventually re-position, but the internal trim may not move until the total accumulated change in the controller output is large enough to

(1) Exceed the sensitivity of the positioner and actuator
(2) Change the pressure in the actuator enough to move its shaft
(3) Work through the play in shaft/stem linkages or connections (backlash)
(4) Break free the internal trim from packing, seating, and sealing friction (sticktion).

The result is a delay and a jump followed by a slow transition to a new position. The jump from sticktion causes a limit cycle in any PI or PID control loop. The deadband from backlash causes a limit cycle in any PI or PID control loop on an integrating process (e.g. level or batch temperature). The delayed and slow response adds pure and effective deadtime, respectively, to the loop.

The ultimate question is what should a user specify in terms of valve response? The table ControlValveResponseCriteria.pdf provides a summary of the parameters that makes a valve rated "Great", "Good", "Fair", "Poor", and "Bad". For most loops where process variable deviations of 0.5% are tolerable, a "Fair" valve will suffice. For loops where tighter control is needed (e.g. column, crystallizer, evaporator, or reactor temperature), a "Good" valve is needed. For loops with high process gains (e.g. pH), a "Great" valve is required to prevent self-inflicted oscillations from limit cycles being larger than the allowable deviation around set point (pHControlValveSizeandResolution.pdf). For tight control in loops with extremely fast dynamics (e.g. polymer pressure and incinerator pressure) a "Great" valve or a special variable speed drive may be needed (see "Analog Control Holdouts" on this website).

The ISA-75.25.01-2000 (R2006) draft standard "The Test Procedure for Control Valve Response Measurement from Step Inputs" and ISA-TR75.25.02-2000 (R2006) draft technical report "Control Valve Response Measurement from Step Inputs", use the time to reach 86% of the final response as a major criteria. This assumes the step input size is larger than the valve resolution and deadband for steps in the same direction and reverse direction, respectively. This 86% response time for small steps can be estimated as the sum of the pre-stroke deadtime and secondary lag time plus twice the primary lag time. For example, the 86% response time of a "Good" valve would be about 1.3 seconds for a 0.5% step (0.2 sec + 0.1 sec + 2*0.5 sec). For large step sizes encountered in surge and vessel pressure control systems, the 86% response time can be estimated as the sum of the pre-stroke deadtime and secondary lag time plus the stroking time to reach 86% of the step size. For example, the 86% response time of a "Good" valve would be about 2.45 seconds for a 50% step (0.2 sec + 0.1 sec + 0.86*0.5*5 sec). Note that the actuator size, pneumatic connections, and accessory (e.g. booster, positioner, and solenoid valve) flow coefficient determines the pres-stroke deadtime and stroking time, The pre-stroke and stroking values are based solely on actuator shaft movement and are determined by the manufacturer for tests of an actuator not connected to a valve. The sensitivity of the actuator and positioner is the minimum change in signal that causes a change in shaft position within a reasonable time frame (e.g. 10 seconds). Diaphragm actuators and digital positioners have the best sensitivity. Rack and pinion actuators and spool positioners have the worst sensitivity. Pneumatic positioners and scotch-yoke actuators are also bad news. The deadband from backlash in stem and shaft connections and the resolution from friction in packing, seats, and seals are determined after the actuator shaft moves. For practical purposes, the sensitivity of the actuator and positioner can be combined with the resolution limit of the valve for a total resolution of the package.

I have been particularly sensitized to valve response due to working on pH, furnace pressure, and compressor control. To add insult to injury, a proliferation of piping valves with piston actuators and spool positioners developed as a result of the emphasis on tight shutoff and low cost rather than response. These on-off valves posing as throttling valves created a problem for all types of loops. The idea was if the on-off valve worked well for sequencing and safety systems and was already in the piping spec, why not slap on a positioner and make it a throttling valve. Often the process variability from valve limit cycles was attributed to unknown process disturbances since there was no readback of actual closure component position.

This blog is getting long so I will just close with some figures on valve dynamics (ControlValveDynamics.pdf) from my new book The Essentials of Modern Measurements and Final Elements - A Guide to Design, Configuration, Installation, and Maintenance.

In upcoming entries we will seek to sort fact from fiction and hopefully provide some insight on valve rangeability and variable speed drive dynamics and rangeability.

I will be doing the presentation McMillanISABostonExceptionalOpportunities.pdf next week at the Boston ISA section meeting. I will be giving out 10 free copies of my book The Funnier Side of Retirement for Engineers and People of the Technical Persuasion to balance out the serious stuff.

When?
Tuesday, October 20, 2009
6:00 - 7:00 Reception and registration
7:00 - 8:00 Dinner
8:00 - 9:00 Presentation

Where?
Best Western, Waltham, MA
380 Winter Street, Waltham, Massachusetts, 02451-8700, US
Phone: 781/890-7800 Fax: 781/890-4937

I spent the first 7 years of my career in instrument design and construction. After being responsible for the calibration, installation, and commissioning of instruments for a half dozen plants in the 1970s, I became painfully aware that the actual performance of the measurements and control valves was largely unknown. These were the days before the advent of smart instrumentation. We didn't know the effect of stiction and backlash on valve position or the effect of impulse line, process and ambient conditions on sensors. We didn't know what was the installed accuracy of measurement or if a valve or measurement had a timely and sensitive response. We shifted set points and just shook our heads when the material and energy balances did not close. Since we were mostly interested in capacity we just pushed on to make more product. Operating efficiency and turndown were not as much an issue, which was fortunate because we didn't have the spectrum and accuracy of instruments for knowing process performance. The time I spent in the 1980s working on pH, furnace pressure, and compressor surge loops were the ultimate test of sensor and valve sensitivity and speed. My perspective on the importance of the field devices was solidified in the 1990s, when I was part of a corporate wide process control improvement program, most of the opportunities involved tuning loops and adding feedforward control and loops for fed-batch operation. A lot of great ideas went by the "way side" because of missing or imprecise measurements and unresponsive valves.

An important point is that if you don't have the capability of determining actual capability and benefits of the automation system, projects will seek the lowest cost alternatives. A classic example of capital cost superseding performance was the proliferation of rotary piping valves that were posed as throttling valves by the addition of spool type positioners to modulate a piston actuator, linkages, and stem connections fundamentally designed for on-off service. The leakage specs and price were attractive. Deadband and resolution limit were not considered. Since the valve specification didn't require the valve actually move in response to the small changes in signal commonly incurred in a control loop and there was no position feedback measurement either locally or remotely, the user did not know the real price paid. Aggravated by noisy flow measurements with poor turndown, increased process variability was attributed to mysterious sources. Without online loop metrics, there was little recognition of the deterioration in loop performance. Since the normal practice of testing whether a valve worked was to make 25% or larger changes in signal, instrument technicians and engineers where unaware that the valve did not respond to the small changes in controller output each scan. Putting a smart positioner on a piping valve with the feedback measurement of actuator shaft rather than ball or disk stem position in a rotary piping valve only added to the confusion. The actuator shaft would move in response to the positioner but the ball or disk did not due to extensive seal friction, ball or disk shaft windup, and backlash in the connection and linkages. It was only after actual tests in the flow labs of control valve manufactures was the true cost of these valve recognized. The publication of the lab test results and the subsequent ISA standards developed on valve step testing, the availability of position feedback as a secondary process variable on digital signals, and the analysis of resolution (e.g. stick-slip) and deadband (e.g. backlash) lead to an increased awareness and hence dramatic improvement in valve dynamics.

Today we have smart transmitters and control valves with a rangeability, resolution, and sensitivity that is an order of magnitude better than the typical fare of the last century. A combination of embedded intelligence and new sensor, transmitter, valve, and positioner technology have resulted in dramatic improvements. Combined with the ability to have additional process variables, diagnostics, and alerts reported to the control room by digital signals and the mobility afforded by wireless communication, we can increase the spectrum and flexibility of the field automation system including finding the optimum locations for process analysis and control. Doors will open for online data analytics, process performance metrics (e.g. energy, quality, and yield) and increased opportunities for basic and advanced control improvements to address the increasing needs of process efficiency, flexibility, and rangeability. My recent Control Talk column "Downturn Turndown" digs into the increased importance of sensor and valve performance with of course a top ten list to cap it off.

Recently it was realized that research and development could greatly benefit from the advanced performance, intelligence, and historization of smart industrial automations systems. The future is best exemplified by the lab optimized industrial distributed control system with industrial pH, dissolved oxygen, pressure, temperature, and mass flow measurements for bench top and pilot plant bioreactors that was pioneered by Broadley-James Corporation. The portability and reduced installation cost of wireless instrumentation increase the already significant advantages of moving advanced industrial automation system capability upstream in the commercialization process.

The foundation of a process automation system is the measurements and final elements. If you don't get these right not much else matters. Measurements provide the only window into the process and final elements provide the only means of affecting the process. The height of the pyramid consisting of increasingly more advanced layers of process analysis and control depends upon the integrity and breadth of the foundation. The goal of the book I just finished is to create a foundation where the sky is the limit for automation. The book royalties go to the Center for Energy and Environmental Resources at the University of Texas where tests are being conducted on the use of wireless conductivity, flow, pH, pressure, and temperature measurements for carbon dioxide capture research.

The new book titled Essentials of Modern Measurements and Final Elements makes no assumptions other than the reader has some technical background. In Chapter 1 Modern Measurement Fundamentals, special care has been taken to explain technical terms and concepts on the use and performance of measurements in the process industry. There is a special emphasis on the advances in wireless instrumentation and communication. Chapters 2 through 6 focuses on the details needed for the best implementation of specific types of measurements that would be used on automation upgrade and new plant projects today in the process industry. Chapter 7 on Final Element Fundamentals follows an approach similar to Chapter 1 in assuming no industrial experience so the material on control valves, dampers, guide vanes, and variable speed drives is beneficial to students and new employees. Chapter 8 gets into the details on the types of control valves that are used in 95% of the applications in the chemical and petrochemical industry. The book concludes with the latest details on WirelessHART automation systems in Chapter 9. The questions at the end of each chapter are designed to stimulate the thought process involved for a successful application.