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    PowerPoint® Presentation Chapter 11 Troubleshooting PLC Hardware PLC Hardware Problems • Power Supply Problems • Troubleshooting PLC Input Sections or Modules • Troubleshooting PLC Output Sections or Modules

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    Chapter 11 — Troubleshooting PLC Hardware PLCs are designed for use with all common supply voltages, such as 230 V, 208 V, 115 V, and 24 V.

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    Chapter 11 — Troubleshooting PLC Hardware When problems occur with PLC power supplies, input and/or output modules, or any system components, a check of the supplied power should be performed over time using a test instrument with a recording function.

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    Chapter 11 — Troubleshooting PLC Hardware Short circuits typically occur when conductor insulation is damaged, which allows a current-carrying conductor to come in contact with any grounded noncurrent-carrying metal parts. An overload is an overcurrent condition that occurs when circuit current...

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    Chapter 11 — Troubleshooting PLC Hardware Voltage measurements can be used to test fuses that are connected to a circuit.

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    Chapter 11 — Troubleshooting PLC Hardware Resistance measurements are used to test fuses that have been removed from a circuit.

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    Chapter 11 — Troubleshooting PLC Hardware Circuit breakers perform the same function as fuses and are basically tested the same way.

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    Chapter 11 — Troubleshooting PLC Hardware Control transformers are typically used to step down 115 VAC, 208 V, 230 V, or 460 V to 12 VAC or 24 VAC for control circuit use in a PLC enclosure.

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    Chapter 11 — Troubleshooting PLC Hardware When the power rating of a transformer is exceeded by placing too great a load on the transformer, the voltage on the secondary side will start to decrease and circuit problems will develop.

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    Chapter 11 — Troubleshooting PLC Hardware PLCs can have a single fixed voltage rating or a dual voltage rating. Dual voltage rated PLCs (115/230 VAC) have a selector switch (or movable links) to set the PLC to one of the possible voltage ratings.

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    Chapter 11 — Troubleshooting PLC Hardware Output power supplies of PLCs are typically used to supply voltage to input devices connected to the PLCs.

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    Chapter 11 — Troubleshooting PLC Hardware The listed current rating of a power supply must be accepted as the maximum amount of current that can safely be provided from a PLC output power supply.

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    Chapter 11 — Troubleshooting PLC Hardware When an input signal is sent to a PLC, the PLC conditions, filters, and optically isolates the signal.

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    Chapter 11 — Troubleshooting PLC Hardware When troubleshooting PLC input sections, programming diagrams and manufacturer troubleshooting charts indicate how input devices are connected and which output components are being controlled.

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    Chapter 11 — Troubleshooting PLC Hardware Testing input modules requires that power supplies and input devices be tested and that status lights of input modules and symbols on computer monitors be checked.

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    Chapter 11 — Troubleshooting PLC Hardware All input devices and the PLC program must operate correctly in order for an automated circuit to operate properly.

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    Chapter 11 — Troubleshooting PLC Hardware Proper heat sinking and cooling is required with solid-state devices to eliminate any potential heat problems.

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    Chapter 11 — Troubleshooting PLC Hardware The current that flows through an “open” solid-state switch is called leakage current. Leakage current can turn on the input circuitry of a PLC, affecting system operation.

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    Chapter 11 — Troubleshooting PLC Hardware Testing the leakage current of solid-state devices requires that the OFF state leakage current measurement be compared to the specified minimum operating current of the PLC input module.

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    Chapter 11 — Troubleshooting PLC Hardware Signals from the CPU of a PLC are sent through logic circuits to output section status lights and opto-isolation circuits before being sent to output terminals.

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    Chapter 11 — Troubleshooting PLC Hardware When troubleshooting PLC output sections, programming diagrams and manufacturer troubleshooting charts help the troubleshooter/technician understand how the input devices are connected and which output components are being controlled.

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    Chapter 11 — Troubleshooting PLC Hardware Testing output modules requires that power supplies and output components be tested and that status lights of output modules and symbols on computer monitors be checked.

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    Chapter 11 — Troubleshooting PLC Hardware All output components and the PLC program must operate correctly in order for an automated system to operate properly.

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