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Chapter 10Troubleshooting Principles and Test
Instruments
Chapter 10Troubleshooting Principles and Test
Instruments
Troubleshooting • Troubleshooting Methods • Measurement Precautions • Meter Abbreviations, Symbols, and Ratings • Troubleshooting with Test
Instruments
Chapter 10 — Troubleshooting Principles and Test Instruments
PLCs provide a centralized location for input device and output component wiring. PLCs are the logical place to start the troubleshooting process.
Chapter 10 — Troubleshooting Principles and Test Instruments
Troubleshooting by knowledge and experience is improved when standard maintenance practices are followed.
Chapter 10 — Troubleshooting Principles and Test Instruments
Facility (plant) procedures are specific to the system or process used by an individual company.
Chapter 10 — Troubleshooting Principles and Test Instruments
Manufacturer procedures vary from facility procedures in that manufacturer procedures are shorter and generally refer to a specific piece of equipment or part.
Chapter 10 — Troubleshooting Principles and Test Instruments
PLC status indicator lights (LEDs) provide a visual display of operating conditions.
Chapter 10 — Troubleshooting Principles and Test Instruments
Flowcharts use symbols and interconnecting lines to provide a troubleshooter with a logical path to problem solving.
Chapter 10 — Troubleshooting Principles and Test Instruments
PLC Error codes indicate problems such as memory errors, processor and software incompatibility, power failure, an empty address slot in a rack, or a module being inserted while the power is ON.
Chapter 10 — Troubleshooting Principles and Test Instruments
The user’s manual for a test instrument details specifications and features, proper operating procedures, safety precautions, warnings, and allowed applications.
Chapter 10 — Troubleshooting Principles and Test Instruments
Several precautions must be taken when using test instruments on a PLC-controlled system.
Chapter 10 — Troubleshooting Principles and Test Instruments
Abbreviations are used individually or in combination with prefixes.
Chapter 10 — Troubleshooting Principles and Test Instruments
Symbols provide quick recognition and interpretation regardless of the language spoken.
Chapter 10 — Troubleshooting Principles and Test Instruments
Test instruments are used to measure electrical quantities. A technician should be able to recognize both the unit of measurement and the abbreviation used to represent the quantity.
Chapter 10 — Troubleshooting Principles and Test Instruments
The IEC 1010 standard classifies the applications in which test instruments and meters can be used into four overvoltage installation categories.
Chapter 10 — Troubleshooting Principles and Test Instruments
Test lights provide a visual indication when voltage is present in non PLC circuits but do not indicate the amount of voltage.
Chapter 10 — Troubleshooting Principles and Test Instruments
Voltage testers indicate the approximate voltage amount and type of voltage (AC or DC) in a circuit.
Chapter 10 — Troubleshooting Principles and Test Instruments
A specific procedure is followed when using a voltage tester to take measurements.
Chapter 10 — Troubleshooting Principles and Test Instruments
DMMs are portable test instruments that measure two or more electrical properties and display the measured properties as numerical values.
Chapter 10 — Troubleshooting Principles and Test Instruments
When the voltage is DC at the test point, the two measured values will be the same, but one will have a negative (–) reading and the other a positive (+) reading.
Chapter 10 — Troubleshooting Principles and Test Instruments
When the two measured voltage values do not indicate a DC voltage, the meter should be set to measure AC and the measurements should be retaken.
Chapter 10 — Troubleshooting Principles and Test Instruments
A true-rms DMM must be used when taking AC voltage measurements in a PLC circuit or system.
Chapter 10 — Troubleshooting Principles and Test Instruments
PLC input devices are typically powered by DC voltages such as 24 VDC.
Chapter 10 — Troubleshooting Principles and Test Instruments
Continuity testers are simple test instruments that test de-energized circuits or components for a complete path for current.
Chapter 10 — Troubleshooting Principles and Test Instruments
A continuity test can be used to check the operation of a photoelectric switch.
Chapter 10 — Troubleshooting Principles and Test Instruments
Ohmmeters measure the amount of resistance (in ohms) in de-energized circuits, devices, or components.
Chapter 10 — Troubleshooting Principles and Test Instruments
Technicians must always verify that circuits, devices, or components do not have voltage before taking any resistance measurements.
Chapter 10 — Troubleshooting Principles and Test Instruments
Current measurements are typically measured using clamp-on ammeters or multimeters with clamp-on current probe accessories. In low-current applications, in-line ammeters can be used.
Chapter 10 — Troubleshooting Principles and Test Instruments
Current measurements are taken using standard procedures.
Chapter 10 — Troubleshooting Principles and Test Instruments
Current measurements for both AC and DC can be taken with in-line ammeters.
Chapter 10 — Troubleshooting Principles and Test Instruments
Noncontact temperature instruments measure heat by measuring the infrared energy emitted by a material.
Chapter 10 — Troubleshooting Principles and Test Instruments
Infrared temperature measurements prevent problems by locating unwanted heat in electrical equipment enclosures before the heat can cause PLC or equipment failure.
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