Chapter 8 PLC Installations and Startup

1. Chapter 8PLC Installations and Startup PLC Installations • Receiving a PLC • PLC Enclosures • Electrical Noise • PLC Power Supplies • PLC Installation Safety • PLC Wiring • PLC Startup • Initial PLC Checks • Input Section Checks • Output Section Checks • Program Checks • Final Checks

2. Installation issues that a technician must address include receiving a PLC, PLC enclosures, electrical noise, power supplies, safety, and wiring.

3. When receiving a PLC and any associated hardware, there are several procedures that must be followed.

4. An enclosure protects a PLC from the surrounding environment and protects technicians from contact with energized parts.

5. PLCs can be mounted to a backpanel or to a DIN rail.

6. Fans, cooling units, and/or solar shields are used to prevent excessive heat buildup inside PLC enclosures.

7. Proper installation of a PLC in an enclosure should prevent most electromagnetic interference problems.

8. PLCs have separate metal raceways (conduits) for voltage supply wires and signal wires.

9. Ground lug connections must be tight and mechanically sound to guarantee a good electrical connection.

10. The twisting of conductors and the shield/drain wire provide enhanced noise reduction. The shield/drain wire is only grounded at one end (the PLC end) when connected to analog input devices.

11. PLC power supplies, input devices, output components, and related items use a common power source to avoid ground loops and mismatched hot and neutral phases and to ensure all items are powered up and powered down together.

12. Emergency stop buttons are wired to master control relays (MCRs) and are located on machinery and process equipment to protect equipment and personnel.

13. Hold-up time is the length of time a PLC can tolerate a power loss without affecting operation.

14. In order to prevent noise-related problems, conductors of different voltage levels and signal types must be separated as much as possible and must not be tywrapped together.

15. The three methods for terminating PLC wiring in an enclosure are direct, terminal strip, and interface module.

16. When input devices and output components are connected to an interface module, a prefabricated cable must be used to connect the interface module to the PLC.

17. Input and output modules are chosen according to the type of module and voltage level required for an application.

18. PLC input and output modules are placed in a PLC chassis to ensure optimum performance and prevent noise-related problems.

19. A sourcing PLC input or output has the negative (–) polarity connected to the field device, while a sinking PLC input or output has the positive (+) polarity connected to the field device.

20. Technicians performing a PLC startup require specific startup items.

21. Initial checks are visual tests performed by a technician before any power is applied to a PLC.

22. Input section (or module) checks verify that input devices function properly and are wired to the correct PLC input terminal.

23. Output section (or module) checks verify that all output devices function properly and are wired to the correct PLC output terminal.

24. Program checks verify that a PLC program functions properly without the application or process that the PLC controls actually being run.

25. A final check verifies that an application or process controlled by a PLC functions properly in RUN mode under actual conditions.