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Chapter 12 Troubleshooting with PLC Software

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Chapter 12 Troubleshooting with PLC Software

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    1. Chapter 12 Troubleshooting with PLC Software PLC Programming Software • Viewing PLC Programs • Debugging PLC Programs • Force Functions • Software “Help” Features

    2. The viewing screen contains multiple elements that allow a program to be viewed in a window. PLC programs are commonly referred to as a project. The PLC program or project contains all of the files—program files, data table files, and documentation—for a specific PLC. The first step in troubleshooting a PLC application is to view the program. See Figure 12-1. PLC programs are commonly referred to as a project. The PLC program or project contains all of the files—program files, data table files, and documentation—for a specific PLC. The first step in troubleshooting a PLC application is to view the program. See Figure 12-1.

    3. Programming software contains many features found in other Windows®-based software products. Because many of the viewing features found in Windows®-based programs are used in PLC programming software, technicians are generally familiar with most of the PLC software viewing features; for example, multiple windows can be open at the same time. The manipulation of the PLC programming windows is something that all technicians must thoroughly understand. See Figure 12-2. The common Windows® screen elements used in PLC programming software also include horizontal and vertical scroll bars, title bars, and project trees. Because many of the viewing features found in Windows®-based programs are used in PLC programming software, technicians are generally familiar with most of the PLC software viewing features; for example, multiple windows can be open at the same time. The manipulation of the PLC programming windows is something that all technicians must thoroughly understand. See Figure 12-2. The common Windows® screen elements used in PLC programming software also include horizontal and vertical scroll bars, title bars, and project trees.

    4. Programming software contains specific menus, toolbars, and windows that technicians must understand how to use. Programming software allows a technician to view all of the elements of a program, program files, data table files, and documentation. Various menus, toolbars, and windows are used to program, install, and troubleshoot a PLC using a PC. Technicians must understand the PC screen elements of programming software in order to perform tasks such as programming, installing, and troubleshooting PLCs. See Figure 12-3.Programming software allows a technician to view all of the elements of a program, program files, data table files, and documentation. Various menus, toolbars, and windows are used to program, install, and troubleshoot a PLC using a PC. Technicians must understand the PC screen elements of programming software in order to perform tasks such as programming, installing, and troubleshooting PLCs. See Figure 12-3.

    5. Programming software contains dialog boxes that allow the user to make choices and enter information. Some dialog boxes contain multiple pages. Another Windows® feature found in programming software is the dialog box. Dialog boxes are small windows that open to allow users to make choices and enter information. Dialog boxes are typically accessed from the menu bar. Dialog boxes contain check boxes, radio buttons, and text boxes for entering information. Some dialog boxes contain multiple pages, which are identified by tabs. Programming software dialog boxes are available for system communications, viewing properties, and system options. See Figure 12-4. Another Windows® feature found in programming software is the dialog box. Dialog boxes are small windows that open to allow users to make choices and enter information. Dialog boxes are typically accessed from the menu bar. Dialog boxes contain check boxes, radio buttons, and text boxes for entering information. Some dialog boxes contain multiple pages, which are identified by tabs. Programming software dialog boxes are available for system communications, viewing properties, and system options. See Figure 12-4.

    6. Many software debugging features can be accessed with the right mouse button. During debugging, changes are made to the program to optimize machine or process performance. See Figure 12-5. PLC programming software features include temporary end (TND) instructions and Cross Reference, Find All, and Goto Data Table functions.During debugging, changes are made to the program to optimize machine or process performance. See Figure 12-5. PLC programming software features include temporary end (TND) instructions and Cross Reference, Find All, and Goto Data Table functions.

    7. Temporary end instructions (TNDs) are useful when debugging programs, especially large programs that contain several different machines or processes. A temporary end (TND) instruction is an output instruction that is used to debug a PLC program. A rung containing a TND instruction is added to a program to stop the program from scanning a PLC. When the rung containing the TND instruction is true, the PLC processor stops scanning the rest of the program, updates the I/O with information that has been scanned, and continues scanning back at the beginning of the program (rung 0). See Figure 12-6. A temporary end (TND) instruction is an output instruction that is used to debug a PLC program. A rung containing a TND instruction is added to a program to stop the program from scanning a PLC. When the rung containing the TND instruction is true, the PLC processor stops scanning the rest of the program, updates the I/O with information that has been scanned, and continues scanning back at the beginning of the program (rung 0). See Figure 12-6.

    8. The Cross Reference function only provides a cross reference of all instructions with the same address. The results are displayed in the Cross Reference Report window. When debugging a PLC, it is often necessary to locate each instance of a particular address. The Cross Reference function searches the entire program (all program files) to locate each instance of a selected address, regardless of the instruction type. See Figure 12-7. When debugging a PLC, it is often necessary to locate each instance of a particular address. The Cross Reference function searches the entire program (all program files) to locate each instance of a selected address, regardless of the instruction type. See Figure 12-7.

    9. The Find All function provides a list of instructions with the same address regardless of the type of instruction. The results are displayed in the results window. The Find All function is similar to the Cross Reference function. The Find All function searches an entire program (all program files) and locates each instance of a selected address or symbol, regardless of the instruction type. See Figure 12-8.The Find All function is similar to the Cross Reference function. The Find All function searches an entire program (all program files) and locates each instance of a selected address or symbol, regardless of the instruction type. See Figure 12-8.

    10. The Goto Data Table function accesses the data table for the instruction selected. As part of the debugging process of a PLC and system, it is sometimes necessary to monitor the bit status of certain instructions. The Goto Data Table function displays the data table for the selected instruction. See Figure 12-9. The status of individual bits can be monitored, such as the presets and accumulated values of timers and counters. As part of the debugging process of a PLC and system, it is sometimes necessary to monitor the bit status of certain instructions. The Goto Data Table function displays the data table for the selected instruction. See Figure 12-9. The status of individual bits can be monitored, such as the presets and accumulated values of timers and counters.

    11. The menu options for the Force function depend on whether or not a force is already being applied. The Force function is used to gain access to a section of a machine or process for servicing. When troubleshooting, the Force function can simulate an energized input device to determine if the program is running properly and the output components are working. Forcing helps determine whether the actual input device is damaged or broken. A force can be left in place until the input device is repaired or replaced when an application is found to be safe. Forcing used during startup debugging verifies that the wiring to input devices and output components is in working order. See Figure 12-10.The Force function is used to gain access to a section of a machine or process for servicing. When troubleshooting, the Force function can simulate an energized input device to determine if the program is running properly and the output components are working. Forcing helps determine whether the actual input device is damaged or broken. A force can be left in place until the input device is repaired or replaced when an application is found to be safe. Forcing used during startup debugging verifies that the wiring to input devices and output components is in working order. See Figure 12-10.

    12. A forced input affects all input instructions with the same address. A single forced input can affect many instructions throughout a program. The input terminals of a PLC can be forced ON or OFF using programming software. When a force is applied to an input instruction, the programming software writes the force to the input data table. The force affects all instructions with the same address and program logic functions. An ON or OFF appears adjacent to all instances of the forced instructions with the same address. Also, any instruction that is true as a result of the force is highlighted. When a force is applied, the POWER, RUN, and FORCE processor status LEDs of the CPU light up. The LED for the forced input terminal does not light up. See Figure 12-11. The input terminals of a PLC can be forced ON or OFF using programming software. When a force is applied to an input instruction, the programming software writes the force to the input data table. The force affects all instructions with the same address and program logic functions. An ON or OFF appears adjacent to all instances of the forced instructions with the same address. Also, any instruction that is true as a result of the force is highlighted. When a force is applied, the POWER, RUN, and FORCE processor status LEDs of the CPU light up. The LED for the forced input terminal does not light up. See Figure 12-11.

    13. A forced output only affects the output instruction. Instructions with the same address as the forced output have an ON or OFF adjacent to them, but they are not affected. Although an ON or OFF appears adjacent to all addresses of the forced instruction, only the output component is affected. Also an output instruction is not highlighted when it is forced. When a force is applied, the POWER, RUN, and FORCE processor status LEDs of the CPU light up. The status LED for the forced output terminal also lights up. See Figure 12-12. Although an ON or OFF appears adjacent to all addresses of the forced instruction, only the output component is affected. Also an output instruction is not highlighted when it is forced. When a force is applied, the POWER, RUN, and FORCE processor status LEDs of the CPU light up. The status LED for the forced output terminal also lights up. See Figure 12-12.

    14. The Help Topics dialog box uses more than one method to locate information. Programming software contains several Help features. The Help features provide assistance to end users, PLC programmers, system integrators, and technicians. Help topics include addressing, communication configuration, instruction comments, and power supply loading. The Help features consist of a searchable index of topics, links to web sites maintained by the software manufacturer, and menus accessed by the F1 key. See Figure 12-13. All Help features can be used while a PLC is online or offline. Programming software contains several Help features. The Help features provide assistance to end users, PLC programmers, system integrators, and technicians. Help topics include addressing, communication configuration, instruction comments, and power supply loading. The Help features consist of a searchable index of topics, links to web sites maintained by the software manufacturer, and menus accessed by the F1 key. See Figure 12-13. All Help features can be used while a PLC is online or offline.

    15. The F1 key generates a window containing help information based on what dialog box, instruction, view, or window is selected. The F1 key is another Help feature found in programming software. The F1 key generates a window that displays help information similar to the searchable index of topics. When the F1 key is pressed, a window with help information is displayed for the dialog box, instruction, view, or window that has been selected. See Figure 12-14. The F1 key is another Help feature found in programming software. The F1 key generates a window that displays help information similar to the searchable index of topics. When the F1 key is pressed, a window with help information is displayed for the dialog box, instruction, view, or window that has been selected. See Figure 12-14.

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