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Troubleshooting MODERN CONTROL SYSTEMS

Troubleshooting MODERN CONTROL SYSTEMS. A Presentation Provided By:. www.logictechnologies.com. Things You Need To Know About Control ProgramS. if. Regardless of the language used, all control programs are comprised of conditional statements and their intended results…

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Troubleshooting MODERN CONTROL SYSTEMS

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  1. Troubleshooting MODERN CONTROL SYSTEMS A Presentation Provided By: www.logictechnologies.com

  2. Things You Need To Know About Control ProgramS if • Regardless of the language used, all control programs are comprised of conditional statements and their intended results… • Programs do not change on their own. In effect, if the program worked yesterday, it will work the same today unless someone changed it! • In most cases you can determine the base-level control algorithms of control programs through simple deductive reasoning. A calm, rational approach to troubleshooting is required… • Always remember the program and its creator are your friends. Abusing either of them in a crisis situation will not help you… then while

  3. Things You Need To Know About Digital I/O Points • A controller’s I/O structure is monitored at the logic or buss level (typically 5VDC)… • In most modern I/O structures the signal level (110VAC, etc…) of digital inputs and outputs are optically-isolated from the system’s logic level… Typical AC Input Circuit Typical AC Output Circuit (General Instruments MID400 Circuit) (Motorola MOP3010 Circuit)

  4. Things You Need To Know About Analog I/O Points Typical Analog Input Circuit • A controller’s I/O structure utilizes AD (Analog to Digital) chips to evaluate analog input points… • A single AD chip is typically used to evaluate multiple analog input points (multiplexed and digitally stored based on a clock pulse)… • A controller’s I/O structure utilizes DA (Digital to Analog) chips to control analog output points… • In either case, analog values are converted to digital raw values (4-20mA 12 bit resolution = 0 to 4095 digital value)… • In either case, the program provides formulas to convert digital raw values to user-interface engineering units…

  5. Common Misconceptions That Occur During Troubleshooting Procedures # 1 – Failure to Utilize Control Bypass Resources • Hand-Off-Auto Switches for System Outputs • Software I/O Value Force Capabilities • Temporary Input Switching Configuration • Temporary Jumper Wires • Even Temporary Man-Power to Maintain Operations • Primary Point : • Control system issues do not necessarily equate to revenue losses…

  6. Common Misconceptions That Occur During Troubleshooting Procedures # 2 – Assuming Issues Are Software Related • Source Code Does Not Change Without Assistance… • If the code was correct yesterday, it is correct today… • 3 Valid Reasons for Assuming Software Issues: • Your system is based on AI (not likely!!!) • An unexpected value triggers an untested algorithm… • Someone recently made changes… • Primary Point : • Don’t waste time in critical situations pointing to your worst fear or chasing ghosts…

  7. Common Misconceptions That Occur During Troubleshooting Procedures # 3 – Becoming Overwhelmed by the Big Picture • All systems are comprised of simple area related control • algorithms… • Focus on the control algorithms related to the problem • area… • Primary Point : • Troubleshooting procedures should be focused on the problem area…

  8. Common Misconceptions That Occur During Troubleshooting Procedures # 4 – Failure to Utilize Troubleshooting Resources • Most Modern Control Systems Provide: • In-depth error/warning reporting capabilities… • I/O value display screens… • Real-time run statistic display screens… • Historical logging/analysis tools… • Primary Point : • Don’t forget about inherent troubleshooting tools and resources during crisis situations…

  9. 5 Essential Steps to Efficient Troubleshooting • Preparation • Step 1: Observation • Step 2: Defining the Problem Area • Step 3: Identifying Possible Causes • Step 4: Determine the Most Probable Cause • Step 5: Test and Repair • Follow-up

  10. 5 Essential Steps to Efficient Troubleshooting • Preparation: • Familiarize yourself with organizational safety rules… • Make sure you understand how the equipment was • intended to work… • Make sure you fully understand the problem at hand… • Make sure all equipment documents are available… • Attempt to find a safe and logical means of keeping the • equipment running during the troubleshooting • procedures…

  11. 5 Essential Steps to Efficient Troubleshooting • Step 1- Observation: • Do not assume that the problem report is factual. • Attempt to duplicate the issue prior to proceeding. • Look for signs of mechanical damage, overheating, • unusual sounds, etc… • Use all of your senses during observation… • The point here is simple, 99% of control system issues are related to mechanical failures or component breakdowns. Mechanical breakdowns provide clues which can be overlooked without thorough observation.

  12. 5 Essential Steps to Efficient Troubleshooting • Step 2- Define the Problem Area: • Use logic and reasoning to define the problem area(s). • Compile a list of probable causes based on your STEP 1 • observations. • Use the system schematics and your observations to • determine which portions of the circuit are operating • correctly.

  13. 5 Essential Steps to Efficient Troubleshooting • Step 3- Identifying Possible Causes: • Now that the problem area(s) have been identified, list • probable causes for the error. • List all possible causes, no matter how remote the • possibility is. • These steps typically require diagnosing each component • related to the non-functional portion of the errant circuit.

  14. 5 Essential Steps to Efficient Troubleshooting • Step 4- Determine the Most Probable Cause: • Prioritize the list of possible causes… • Look for components which burn out or have a tendency to wear out, i.e. mechanical switches, fuses, relay contacts. • Next, inspect coils, motors, transformers, and other devices with windings. All devices which generate heat are subject to malfunction. • Connections should be your third choice, especially screw type or bolted type. • Finally, you should look for defective wiring, insulation, etc... • Eliminate possible causes starting with the most • probable cause…

  15. 5 Essential Steps to Efficient Troubleshooting • Step 5- Test and Repair: • Use a digital volt meter (DVM) to test each possible cause • that you listed… • Repair or replace each component and/or wire found to • be defective prior to proceeding to the next possible • cause. • Make sure you test each possible cause on your list to • insure that the issue is not being caused by multiple fail • points..

  16. 5 Essential Steps to Efficient Troubleshooting • Follow-Up: • Disengage all temporary bypass procedures… • Attempt to determine the reason for the failure… • Did a component fail due to age? • Did the environment of the equipment cause excessive corrosion? • Are there wear points that caused the wiring to short out? • Did a component fail due to improper use? • Is there a design flaw that causes the same component to fail • repeatedly?

  17. Troubleshooting Decision Matrix • Steps required to use the matrix: • List the outputs that are not being controlled properly. • Think about the control algorithms associated with the errant outputs. • List the input values and points that would be required to properly control the errant outputs. • Use the force capabilities provided with your system to make sure that these errant outputs can physically be controlled. If not, your base source has probably been discovered. Use the information provided in section 7 below to resolve the issue. • Use a DVM to check the wiring and input values associated with the input points that you listed. Once again, if you discover erroneous or non-existent values, your base source has probably been discovered. Use the information provided in section 7 below to resolve the issue.

  18. The Matrix

  19. Step by Step Troubleshooting • Resolving Controller Related Issues: • Check the controller indicator lights (Manual Instructions)… • Check power supply levels… • If you have a backup, try replacing the controller… • Make sure all dipswitches and jumpers are set to match the unit being removed. • Contact the controller manufacturer’s technical support team… • Provide the support team with detailed information… • Repeat troubleshooting steps when asked to do so…

  20. Step by Step Troubleshooting • Resolving Communication and/or I/O Rack Issues : • Check all communication cable connections… • Check the communication device indicator lights… • Check power supply levels… • If the device in question is an I/O rack, check individual modules… • If you have a backup, try replacing the device in question… • Contact the equipment manufacturer’s technical support team…

  21. Step by Step Troubleshooting • Resolving Multi I/O Point Module Issues: • Use the software tools provided to make sure the module is being recognized… • Check for single point shorting issues… • Remove all connections then test the module as you reconnect each point… • If you have a backup module, try replacing it… • Contact the equipment manufacturer’s technical support team…

  22. Step by Step Troubleshooting • Resolving Digital Input Issues: • Check the values at the point when the input device changes state… • If the value changes but the software doesn’t reflect the change, the point is bad. • Check the values at the device when the input device changes state… • If the values are changing at the device but not at the point, the problem is wiring related. • If the values are not changing at the device, the device is bad.

  23. Step by Step Troubleshooting • Resolving Digital Output Issues: • Check the supply voltage for the output point… • If the value is errant or non-existent, you have probably found the source of the problem. • Use the force capabilities of the system to turn the output on and off while checking the values at the output point… • If the DVM is not displaying the appropriate values when the output is switched, the module is bad. • If the values are changing at the point but not the device, the problem is wiring related. • If the values are changing at the device but the device is not responding, the device being controlled is bad.

  24. Step by Step Troubleshooting • Resolving Analog Input Issues: • Check the power supply values for the input device… • Check the values at the point when the input device values should be changing… • If the values are changing but the software doesn’t reflect the change, the point is bad. • Check the values at the device when the input device values should be changing… • If the values are changing at the device but not at the point, the problem is wiring related. • If the values are not changing at the device, the device is bad.

  25. Step by Step Troubleshooting • Resolving Analog Output Issues: • Check the power supply levels for the output point… • If the value is errant or non-existent, you have probably found the source of the problem. • Use the output scaling capabilities of the system to change the values being supplied to the device… • If the changes are not being reflected at the point, the module is bad. • If the values are changing at the point but not the device, the problem is wiring related. • If the values are changing at the device but the device is not responding, the device being controlled is bad.

  26. THE END Thank you for your time and patience!

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