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Loop checking a technicians guide pdf

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of instrumentation. An instrument technician must have known loop checking. Imran Nawaz Mehthal. caite.info Loop Checking: A Technician's Guide (ISA TECHNICIAN SERIES) [Harley M. Jeffery] on caite.info *FREE* shipping on qualifying offers. In today's. Research Triangle Park, NC (September ) - ISA recently announced the release of "Loop Checking: A Technician's Guide" by Harley M.


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This technician's guide defines loop checking in the broader scope of control loop performance in addition to the more traditional terms of the plant startup. The chapters of Loop Checking: A Technician's Guide are arranged to follow a typical .. Because of the scope of this manual, we will not cover the receiving. caite.info - Ebook download as PDF File .pdf), Text File .txt) or read book online.

Mel England. Measurement and Control Basics. Simulation 5. Department of Commerce recognizes Phoenix Contact for investment in the United States Ian Steff, deputy assistant secretary for manufacturing at the U. Why are smart field devices transmitters and valves desirable for a loop performance program?

This guide discusses general methods and practices that can be applied across many processes and industries. Some of the topics included are: More information about this resource can be found at www. Based in Research Triangle Park, North Carolina, ISA develops standards; certifies industry professionals; provides education and training; publishes books and technical articles; and hosts the largest conference and exhibition for automation professionals in the Western Hemisphere.

Did you Enjoy this Article? Check out our free e-newsletters to read more great articles. Subscribe Now. Back to top Posted in: Indonesia to serve as partner country Roughly 6, exhibitors from around the world presented solutions for the future of manufacturing and energy supply, including more than OSI to help Fayetteville, North Carolina enhance Outage Management System OMS This project will provide technology for the tracking and prediction of outages and service disruptions, in addition to supporting real-time Bentley Systems announces Dr.

Nabil Abou-Rahme as chief research officer A chartered engineer, Dr. If your plant has just one control system. Deadtime and noise introduced by measurement installation location can really hurt the loop performance the typical controller.

Of course. In addition to the controller performance enemies of deadtime and noise mentioned previously. Other Loop Types In addition to feedback control. The valve receives the most attention in the loop check because it receives an electrical signal from the controller i. Friction from seals and packing. Proper valve sizing and selection of valve characteristic can help linearize the flow response to controller output changes — again very important to how the PID can perform.

Technicians guide pdf checking a loop

Once the technician checks the control strategy to verify that the expected output to the final control element is produced. It continues through installation and start-up and into the ongoing plant operation. On-off Valves. Vendor literature and application papers are good sources of information as are a variety of industry publications e.

Further discussed in Chapter 2. In addition. This verification testing prior to start-up is known as the factory acceptance test FAT which. Loop Checking Some think of loop checking as a process to confirm that the components of the loop are wired correctly and is typically something done prior to start-up. This process starts when the instruments are received at the plant site.

The block diagram in Figure illustrates the components of this expanded loop checking process. In some plants. There are several excellent resources that go into more depth on each of the elements of the loop.

ISA Releases 'Loop Checking: A Technician's Guide'

Such smart digital technology makes it possible to access and use new types of information that were not available from the analog 4-tomA transmitter and valve. Software packages store the extensive data for analysis.

As a result. Close control to the level set point is desired because of process equipment safety issues. This is achieved by controlling the feedwater inlet flow. Subsequent chapters of this guide will discuss the impact of smart technology on the various phases of loop checking. These include concerns over water carryover into steam lines resulting from high drum levels and the potential for boiler tube damage as a result of low water levels.

By combining feedback. This example assumes a pneumatic-operated. The control strategy involves the following loop types: All controller algorithms are proportional-integral-derivative PID. These guidelines are based on the philosophy that control systems should minimize product variability and improve the overall efficiency of an.

Final Control Element. The feedwater and steam flows utilize orifice plates to develop a differential pressure that is proportional to the square of the flow.

Pdf loop guide a checking technicians

The drum level transmitter reads a differential pressure signal between the water and steam in the drum and an ambient water column. Control System. This closed loop control of the feedwater flow in a cascade system allows the feedwater flow loop to correct for any disturbances in the feedwater flow before those disturbances affect the drum level.

This signal is then used as the set point for the feedwater flow loop. Loop Checking 11 Measurement. For the purposes of this example. Variability can be defined as two times the standard deviation divided by the mean. In Figure This section briefly discusses a few of these measurements that have been used in process control applications. Keeping Score How do we know when a loop is performing well?

Some people have mentioned the following as performance measurements Ref. Loop Checking 13 Standard Deviation Sigma. Consider the following example: Figure shows data on a recorder from a flow loop transmitter while the loop is in MANUAL with random disturbances causing the flow to vary.

As sort of an industry benchmark. See Figure for a representation. By using commercially available spreadsheet tools or loop analysis software. Ps ol2slddo T i m e seconds You would hope that by placing the loop to automatic and repeating the test in Figure that the calculated variability would be reduced. Sigma of TABLE OYO Very l j o o d Less than 2. The table below suggests a variability range for key loops in your process as a rule of thumb.

Harris Index. The following examples are from vendor information describing their evaluation techniques: Variability Index. Loop Checking 15 In addition.. Variability index is not fooled by noise or load disturbances i.. The Harris Index looks at the error signal. The larger the value. It is simply the Harris Index. If the variability index is A variability index of zero 0. Larger numbers might be considered worse. The Harris Index calculation results in a number between 1 and infinity.

The Harris measures the ratio between the error variance and the variance achievable by a minimum variance controller. A value of 1 is perfection or minimum variance control. With the IAE for each case. These classifications were refined through extensive validation and industry feedback to reflect controller performance relative to practical expectations for each measurement type.

The more nonlinearities and deadtime that creep into a loop. Loop Nonlinearities and Deadtime — The Bad Guys By far the most widely used control algorithm in process control loops is the proportional — integral. The index uses a process model combined with current and optimal PID tuning values.

Based on performance demographics of twenty-six thousand PID controllers collected over the last two years across a large cross sample of continuous process industries.

The simulation provides the data to calculate the integrated absolute error IAE between the set point and process variable for each case. The index can be found by simulating the response of the control loop to a load upset with both sets of tuning values. The ExperTune index is: This metric will catch those loops that have been de-tuned. The throttling control valve absorbs the difference between the two pressures. To help minimize these problems. Control valve sizing and selection can also play a large part in the overall loop linearity.

As mentioned previously. In general. Notice the difference in the pump and system B curve shown in Figure Loop Checking 17 In fact. For the pump and system curve A where the throttling pressure drop across the valve decreases as flow increases.

Notice that only a small part from about a 20 to 40 degree opening provides a linear response with a process gain that is within a desired range called the EnTech Gain Specification.

Even though you know the inherent valve characteristic. Control devices valves. Table gives a summary of the different types of control valves and approximate control ranges.

Process transport delay should be minimized. These guidelines are based on the philosophy that control systems should minimize product variability and improve the overall efficiency of an operation. Imagine trying to tune the loop for a butterfly valve that has to operate near 70 degrees open for one product and 30 degrees for another—probably job security for your loop tuning people. Dead time or time delay as seen by the control loop should be minimized wherever possible.

We recommend the following guidelines: There are workarounds such as output signal characterization to ease some of the installed curve nonlinearities or gain scheduling in your controller but spending the time and money to install the correct size and style valve will provide the best solution for the loop checking performance. This means that a measurement devices should be located as close as practically possible to the control device without effecting their measurement characteristics.

Industrial Process Control Fisher Controls. Sheldon G. Only linear control algorithms should be used. The outer loop of a cascaded loop structure should be tuned five to ten times slower than the inner loop. Their speed of response should be reasonable for the application.

The less critical loop of a set of interacting loops should be tuned five to ten times slower than the more critical loop. Process gains in the range of 0. Measurement and Control Basics.

Filtering of the control loop measurement should be kept to a minimum. Thomas A. Process areas should be tuned in a coordinated manner to minimize loop interaction and disturbances to processes that rely on the ratioing of ingredients or raw materials.

The control loop should be tuned using nonoscillatory tuning techniques. Control loop nonlinearities such as control dead bands. What are the basic elements of the control loop? Which loop element would be most susceptible to long-term performance degradation and thus a candidate for specific device monitoring?

Nancy J. ISA — The Instrumentation. When does the loop checking process start? When does it end? EnTech Performance Group. ITT-Goulds Pumps. Gregory K. Willy K. Advanced Control Unleashed.

Loop Checking Guide

Terrence L. John A. Loop Checking 23 5. The typical plant can realize the best return on investment by which of the following programs? Centrifugal Pump Fundamentals — System Curves. The control system technician? The process engineer? Process Control for Engineers. Emerson Process Management.

QUIZ 1. Michael W. CPC VI. Figure in Chapter 1 shows that this testing occurs prior to the commissioning and start-up phase. With fast-changing technology and variety of control system approaches to loop implementation e. As a side benefit. Usually there are more resources and time to fix things at FAT versus at start-up and certainly less pressure.

The main objectives are to verify that the system is setup correctly and will operate as expected from both the hardware and configuration software points of view before it ships to the site.

Some plants opt for a repeat of the FAT at site with the hardware and field wiring installed. As with any plan. The overall checkout time is usually quite a bit faster than the hard-wired method.

The methods for loop check in the FAT can differ depending on the complexity of the checkout desired. Outputs are tested in a similar manner for observation and check. This can be the hardware specification sheets. This method does not usually cover complex control strategies. It also provides the team with some training on troubleshooting the new system with the knowledgeable vendor present.

Loop Checking 27 2. Although this next test is duplicated when the system is in place see the next section on loop checking. A similar procedure is used with outputs by driving the output channel from the operator workstation and verifying with a meter and diagnostics that the proper value is set. Depending on team size and level. Listing each BOM item for check- off is typical. Some companies have spent time to track FAT deficiencies over several projects to use in quality improvement processes Ref.

The following is an example of the test plan topics that you might use as a starting point for your hardware FAT plan the example assumes you are using a digital control system but it could also be used for DCSs. Section 1 — Introduction 1. This may just be a simple statement that you want to verify the system hardware against the contract document or add any general statements about additional tests. Section 2 — Test Method Instructions 2. Check for labels and loose wires.

Verify wiring to breakers. Same for DC powered devices. Loop Checking 29 Section 4 — System Components 4. Measure voltages at the devices to verify proper voltage levels per vendor specs. Section 5 — Grounding and Wire Shielding 5. Test redundant power design by shutting down primary then secondary AC feeds and DC supplies to verify the system continues to function as desired.

A detailed plan with procedures and checklists will help assure a successful acceptance test and a smoother start-up. Any loop interlocks. With diagnostics or test configurations. Focusing on the control loop. The set point. The raw input to the loop is checked along with any calculations or modifications to the signal such as square root.

Using control system diagnostics. It is interesting to note that a company tracking deficiencies in loop checks found the most problems with the configuration aspects of the operator interface piece of loop checks Ref.

After this test procedure is completed and accepted. For example: Many organizations spend significant resources defining configuration standards so that using proven methods that are copied from project to project with the associated testing and documentation can reduce project costs.

Test any redundancy features such as controllers and communication networks to verify proper switchover. For this guide. The loop test areas are shown in Figure and described in the following subsections. Checkout Flow Chart. As a general rule. The PC-based simulation packages also provide for process dynamics such as level. Loops can then be placed in automatic and overall control strategies can be checked in conditions that closely follow actual plant conditions.

Fixed sequence and batch control guidelines are outside the scope of this guide. Example testing forms have been included in the process control example at the end of the chapter. On-Off Devices 4. By completing these checks prior to shipment to the site. Plant personnel have said that simulation testing is very valuable.

Checklists and Discrepancy Forms Technicians can develop checklists to keep track of the items in the preceding list during the testing. Simulations will give plant personnel and the implementation team the means to verify the accuracy of the logic that is spelled out in the process descriptions and to verify that the control logic performs the actions as designed.

Forms for noting discrepancies should also be maintained. Mass balance models can also be written for the individual process units in which the control logic performs ingredient additions and product transfers from a vessel or vessels. The simulation software can also be used to model complex chemical reactions and process thermodynamics if technicians cannot verify the proper operation of process logic without them.

Since the SAT occurs after the system is installed at the plant and field wiring is connected. In fact. Documentation The required documentation includes: The following specifics will be added to the plan checklists. Feedwater control: With the loop in manual. The technician will use the control system operator interface screens to check indications and control actions.

Inputs and outputs: Using the simulation program. The simulation program can be used to verify that the proper output channel is changing to the desired value. The technician should note alarm points and also verify that they indicate on the operator interface. Loop Checking 41 The drum level control strategy test plan will verify: The technician should indicate on a checklist when items are completed.

Steam flow feedforward: The technician should make changes in steam flow and verify that the feedwater flow set point flows the steam flow and that drum level maintains the set point. The technician should place the loop in automatic and make set point changes. He or she will also perform a first- principles simulation of the steam drum.

The following four test methods will be used: The technician will use a simulator system to manually force all inputs and monitor outputs. Drum level control: Test Methods. In particular. Test Plan 3. Tables through are examples of the test flowchart check areas.

Simulation 5. Operator Displays 4. Design Review and Documentation 1. Loop Checking B Output is set. C The current output is C indicated by a bargraph and a numeric display. Cole, Wayne E. How can smart instruments help in the acceptance testing? Since this test resembles the factory acceptance test FAT described in the previous chapter.

It is desirable to gain a listing of.

254624490-Loop-Checking-Technicians-Guide.pdf

Since the process is not yet running. Note that we are discussing just the control loop here. Our review in this chapter is based on a new installation. Appropriate power and grounding checks have been performed. As the start-up date approaches. It is assumed that field measurement and control devices or transmitters and valves for our example have been received.

Several scenarios for loop checking may be possible at start-up. Radios for communicating between team members are essential. The plan should take the physical location of the installed instruments into account so an efficient route can be determined for the field personnel. The traditional instruments are 4-tomA DC-based devices. Smart Instruments use a digital communications protocol that is transmitted on the individual 4—20 mA wires e. As noted previously.

Note that the plan should clearly specify any signal characterization required. Many a troubleshooter. The control system team member should be aware of these applications and verify the proper signal is received at the system.

Everyone on the checkout team should understand his or her role. Plant standards can help here. This will enable them to know what is expected at the operator level. He or she should also note any comments on a checkout form.

Note that some implementation teams prefer to check the transmitter output by actually simulating the process signal rather than just verifying. Loop Checking 49 communications with multiple instruments on a communication cable e. Be sure to verify that the screw terminals have been tightened after checkout! Experience has shown that loose terminals cause more problems than anything else. At the transmitter end. Once the field person is ready. Any alarms on the signal are also verified while the signal is stepped through the range.

Such characterization may cause the operator interface reading to differ from the signal being introduced at the field device. There should be a pause at each step to confirm that the display is showing the correct value.. He or she should verify the location. The technician at the control system should have located the display where the transmitter variable is displayed there may be several displays.

Traditional Instruments Non-smart Starting with the process measurement.

The technician should be aware and note on the checkout form any input signal characterization during this check. The checkout team member at the control system operator interface is then informed that the transmitter is ready to be checked. If satisfied that the transmitter and control system are performing as expected. During each step pause. The completion of this check now gives confidence to the team members that when the start-up occurs. Technicians check the control valve in much the same way as the transmitter: This procedure is then repeated for each loop in the control system.

Smart Instruments Smart field devices make the loop checkout more efficient. After establishing that the operation and display are satisfactory.

A veteran of a recent large job informed the author that tens of thousands of dollars in time and equipment had been spent only to find one bad transmitter and two with an incorrect range. Note that this step test is not an adequate indication of valve performance. The person at the control system should have located the valve on the display.

This box would also be a good way to check transmitter calibration. The procedure is the same: After checking for instrument tubing crimps. This is a real time saver when you need to verify ranges and tag names while also looking for possible problems— such as incorrectly entered high damping values.

As mentioned earlier. A technician uploads field device configuration parameters into the software database so they can be verified against spec sheets. It can also note any diagnostics problems with the field device and fix them prior to start-up. In the actual field situation for a new installation most implement- ation teams make the trip to the field devices in order to verify that the right instrument has been mounted and that installation details are correct.

Control system team member: Locate the feedwater loop on Display YY and access the loop faceplate on the display. Feedwater Loop Field team member: Proceed to the ground floor location of the feedwater flow transmitter. Record the values from the display and faceplate on the loop check form they should be Loop Checking 53 For example.

Record the values from the display and faceplate on the loop check form they should be — Locate the steam flow on Display YY and access the indicator faceplate on the display. Record the values from the display and faceplate on the loop check form they should be 0- kpph. Note each step on the loop check form along with any comments made by the field team member on installation or other discrepancies. Control System team member: Locate the drum level loop on Display YY and access the loop faceplate on the display.

Steam Flow Transmitter Field team member: Proceed to the top floor location of the steam flow transmitter downstream of the drum steam line to the process. Drum Level Transmitter Field team member: Proceed to the top floor location of the drum level transmitter near the boiler drum. Be sure to pause with each step and ask for verification from the field team member. Field team member: Proceed to the feedwater valve. Using the software package. All these activities are documented in the smart instrument software package for future reference.

Some plants have estimated time savings of around 30 minutes per loop using these smart instruments. One Instrument per Form Date of Checkout: The Instrumentation. Instrument Loop Diagrams. Updated with 20 New Specification Forms in Instrumentation Symbols and Identification. What is the main objective of the loop check at start-up? What are some of the advantages of smart instrumentation?

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What key observation can the field team member make during loop checks? General Considerations. Periodic testing to verify performance may just require a subset of the steps outlined below. These procedures can also be used to troubleshoot problem loops. This will also help point out possible improvements. Interview Key Personnel Interviews with operations. Engineering should also be consulted for their observations. The technician should have access to loop sheets.

With a good knowledge of the history and operating problems. These figures will come in handy. What does the operator say the reasons are? How long has the loop not been in auto? Does Operations Supervision believe it is performing to their expectations? What is the expected performance of this loop?

Most control systems have a process historian software package that can be used to help you evaluate and understand past performance.

If not. Compare all inputs and resolve any plant differences on expectations. This information is the basis for the next step in planning.

Turn test results into meaningful information about loop performance and make recommendations for improvement. Look for signal characterizations in the control system program that can affect the output signal to the valve. This will help you decide the variables to analyze during your test. Knowing the number of open loop controller in manual bump tests. It is not unusual for control implementers to have configured the strategies in ways that will affect how the loop will react. Loop Checking 61 recommendations on improving loop performance.

The process control engineer can supply control strategy drawings and write-ups so you can understand the control objectives. Loop Check Planning A loop performance check test plan will get the most out of time spent testing the loop. Your plan should now have a list of variables you want to monitor and test. Verify that the valve characteristic is adequate for the application and installation. The maintenance input to planning is usually part of your job as instrument technician.

Based on your knowledge of the process. It is a worthwhile effort to evaluate the different analysis packages with your performance team in order to select one that is right for your plant. With some critical loops. Depending on loop dynamics. Summarize and present all of the above information to the operators. Although this electronic method introduces some communication delays. Be sure they know you just intend to make very small changes starting at 0. Sometimes it can be a little disturbing to the operator when you ask if you can get into the wiring cabinets.

Standards such as OPC OLE for Process Control allow a fairly easy method of electronically sharing data directly between the control system and your data analysis package more on this in the next chapter. In summary. With some of the more recent control system architectures. Bringing a couple boxes of doughnuts in the control room seems to help this process. Digital cameras can record your installation see Figure and provide a means to enhance your report.

What mode is the loop in? What is the output to the valve? What is the transmitter reading? Time and money constraints enter in. Look for piping layout. The Walk-through Having reviewed the documentation and drawings and set your plan. What condition are the devices in? What is the valve supply air pressure? Any air leaks?

Can you hear any cavitation? Are there straight runs of pipe before and after the measurement and valve? Are transmitter impulse lines correctly installed? Will the location of the devices introduce undesired deadtime? Record the transmitter and valve vendor model numbers and nameplate data on your Loop Inspection Data sheet see typical sheet in Figure It may be beneficial to perform the walk-through prior to the actual loop check test if time and costs permit.

Look for any sources of disturbances on your loop such as multiple users on a header. Record control system loop tuning parameters on your Loop Inspection Datasheet. Most plants have unexpected problems or production constraints that could cloud any data you gather.

Checking pdf technicians guide loop a

This would give you an opportunity to digest the installation information. This should verify the impressions from your homework reviewing the documentation prior to visiting the plant site. Example Loop Inspection Data Form.

It is a good idea to put a small sign on the test area that includes names. An old wire spool can act as your workbench with an empty bucket from the trash can as your chair.

Set up your data-recording device to the control system input and output terminals for the valve and transmitter. Plenty of extension cord with ground fault circuit interruption is a good idea. The folding hand truck with table top in Figure This lets plant personnel know testing is in progress and who to contact in case there is a need to perform maintenance or to troubleshoot in that area. Although sometimes the resistor may be easy to access. Clip onto Voltage Signals at the Resistor Other times the voltage is not as easy to access.

Clip-on with Insulation Piercing Connectors Another alternative when no standard voltage is available.. It is very easy to dial in a high damping value that will cover the true process dynamics. Look for transmitter damping times. Loop Checking 69 Also. All help when you are trying to make sense of the data in the analysis phase. Other smart. This gives a feel for the disturbances that the controller will see and provides a comparison with the loop in automatic.

One possible alternative would be to configure spare analog output channels in the control system to drive 4—mA current outputs representative of the signals of interest that could then be recorded. There are several vendors that include performance and analysis features in their digital bus-based system. The data. Ask the operator to make some set. Coriolis meters can access flow density and temperature as well as the mass flow. Collect some data while the controller is in manual mode.

Needless to say. Include anything you think is important about the circumstances surrounding the test run — product names. Set up your recording device to collect the process variable and the output from the control system see Figure The bumps will also give you a feel for the general condition of the control valve or other final control element such as a damper. Figure shows a set point change to the process and the interaction between these boiler loops. You now have a baseline of loop performance that you can compare against after any recommendations you make are implemented.

Time Series Data Figure shows a typical time series graph of the data with statistics displayed. A cycle is noticeable in the data so that. This will give you a couple of valuable pieces of information about the loop. You may want to make some overnight data runs to get longer collection periods in addition to the shorter runs.

Like the as-found data gathering test. This will also help you to identify different period cycles that the process may be experiencing and give you an idea of any loop interactions that may be occurring.

Turn the process back over to the operator and let things settle out before starting the next bump test. The time in between bumps will depend on the process response time. The example in Figure shows the loop output to the final control element in the upper half of the graph and the corresponding. Time Series Data probably need to be sitting with the operator as you run this test since you will need to advise him when to go to manual if approved by the operator and when to make the bump changes in the output.

After the operator places the loop to manual. A valve in good shape should respond to these small bumps. You should be looking at the transmitter variable to determine how many of these steps it takes for the process to respond. Let it settle out before making the next bump remember. Make several steps in this direction. As previously mentioned, and with reference to the next chapter, some newer control systems are implementing these loop performance features as an integral part of the system even automating the bump test , which greatly eases the time and effort of setup and testing.

Reporting and storing for future comparison your benchmark data and findings is an important consideration for working. As-found Data Collection Analysis Your data collection tool or analysis software such as a spreadsheet can help you pull out meaningful information from the raw data. There are a number of statistical techniques that have been used in process control for evaluating and setting benchmarks.

You will need to work with your process improvement team to decide which are right for your plant. And, since a lot of loops are interacting with other loops in the unit operation, driving out the cycles will not only reduce the variability in the loop of interest but can improve the other loops that interact. Other data analysis techniques, such as histograms which show the statistical distribution of the data points over their range and around the mean or average value , and correlation analysis which shows the degree to which the variability of a signal has a purely random characteristic or the degree to which 2 signals show a relationship with each other , can also help analyze the data to find variability sources.

Bump Test Analysis As previously mentioned, analyzing the bump test will allow us to calculate the process dynamics or how fast the process responds and how much , which is the critical data needed in tuning the loop.

Also, the bump tests reveal how well the final control element is responding. There are many resources that discuss loop tuning, process models, and the math involved see Ref. Temperature loops, due to thermowell installations, are sometimes classified as 2nd Order. The calculations made for this type loop are:.

Integrating Process Dynamics. Set reset integral. Lambda tuning gets its name from the Greek letter. Lambda tuning is based on a model of the process to be tuned. By making step changes bumps to the output of the controller while in manual. Controller gain. Rate derivative. The key activity in the Lambda tuning method is the bump test and the resulting data previously shown.

Without going into much of the theory see Ref. As previously discussed in Chapter 1. Appendix A on page contains a very good discussion of loop tuning with background on loop basics. You can now apply the Lambda tuning rules to the bump test data. In Figure bump test. The process example later in this chapter shows how this method can be applied.

Depending on your loop tuning strategy.

Pdf loop checking guide a technicians

Other things you might see are unequal changes in process variable from equal bumps. Here are a couple of rules of thumb: For interacting loops. By adjusting the Lambda value. Confidence in your bump test parameters. Loop Checking 77 2. Controller gain proportional. Start with a Lambda of 3 times the open loop time constant. Some vendors provide more integrated loop testing and reporting in their products. We have seen several approaches to this task.

Reporting your results to your team members. He or she will begin filling out the Loop Inspection data sheet see typical data sheet on page 64 to keep track of the information.

Next Step Following the Summary Meeting. Depending on the severity of the service conditions. The technician will also pull the loop sheets to get an idea of where the wiring is terminated. By adding financial data to the report such as costs. This is covered in the next chapter. Loop Checking 79 implement the recommendations for the problems you find during the loop check. Repeat the Loop Check testing to establish and document the results for variability.

This is now your updated. The powerhouse superintendent echoes these thoughts but places a dollar. Interviews Next. It looks as though there have been some minor tuning changes made since start-up. The technician mentions that he or she would like to do some testing to establish performance and set loop tuning by moving the feedwater valve in manual.

The feedwater transmitter and orifice plate are upstream of the valve. The control valve is a sliding stem type with a spring and diaphragm actuator and smart digital valve controller for positioning. For this example. The actual feedwater valve position would be another good choice to ensure the valve is performing correctly during actual service. Performing the Test The Walk-through As the technician walks around the boiler.

With a typical boiler feedwater flow pump head and system loss curve. The control engineer says the control strategy checked out okay in simulation at FAT. The technician records all this information on the Loop Inspection Data form. Planning the test The variables that the technician needs to monitor are the drum level.

The impulse lines meet our plant installation standards. As previously mentioned. Loop Checking 81 figure on the cost of unscheduled downtime by having to run the more expensive backup package boiler. Mechanical integrity looks good. Since this is a smart valve. If no major problems are found. With the feedwater loop in cascade mode. The drum level and feedwater loops are in Auto and Cascade.

Be sure to record while the steam flow load changes to see the effect on drum level variability. Setting up for the Test With the above complete and the list of test variables in hand. This will give the technician data to analyze for fast and slow cycling of the data. With the drum level and feedwater loops in manual. Tune the drum level loop to desired performance.