Chapter 8 PLC Installations and Startup
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Transcript of Chapter 8 PLC Installations and Startup
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Chapter 8PLC Installations and Startup
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
Chapter 8 — PLC Installations and Startup
Installation issues that a technician must address include receiving a PLC, PLC enclosures, electrical noise, power supplies, safety, and wiring.
Chapter 8 — PLC Installations and Startup
When receiving a PLC and any associated hardware, there are several procedures that must be followed.
Chapter 8 — PLC Installations and Startup
An enclosure protects a PLC from the surrounding environment and protects technicians from contact with energized parts.
Chapter 8 — PLC Installations and Startup
PLCs can be mounted to a backpanel or to a DIN rail.
Chapter 8 — PLC Installations and Startup
Fans, cooling units, and/or solar shields are used to prevent excessive heat buildup inside PLC enclosures.
Chapter 8 — PLC Installations and Startup
Proper installation of a PLC in an enclosure should prevent most electromagnetic interference problems.
Chapter 8 — PLC Installations and Startup
PLCs have separate metal raceways (conduits) for voltage supply wires and signal wires.
Chapter 8 — PLC Installations and Startup
Ground lug connections must be tight and mechanically sound to guarantee a good electrical connection.
Chapter 8 — PLC Installations and Startup
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.
Chapter 8 — PLC Installations and Startup
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.
Chapter 8 — PLC Installations and Startup
Emergency stop buttons are wired to master control relays (MCRs) and are located on machinery and process equipment to protect equipment and personnel.
Chapter 8 — PLC Installations and Startup
Hold-up time is the length of time a PLC can tolerate a power loss without affecting operation.
Chapter 8 — PLC Installations and Startup
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.
Chapter 8 — PLC Installations and Startup
The three methods for terminating PLC wiring in an enclosure are direct, terminal strip, and interface module.
Chapter 8 — PLC Installations and Startup
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.
Chapter 8 — PLC Installations and Startup
Input and output modules are chosen according to the type of module and voltage level required for an application.
Chapter 8 — PLC Installations and Startup
PLC input and output modules are placed in a PLC chassis to ensure optimum performance and prevent noise-related problems.
Chapter 8 — PLC Installations and Startup
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.
Chapter 8 — PLC Installations and Startup
Technicians performing a PLC startup require specific startup items.
Chapter 8 — PLC Installations and Startup
Initial checks are visual tests performed by a technician before any power is applied to a PLC.
Chapter 8 — PLC Installations and Startup
Input section (or module) checks verify that input devices function properly and are wired to the correct PLC input terminal.
Chapter 8 — PLC Installations and Startup
Output section (or module) checks verify that all output devices function properly and are wired to the correct PLC output terminal.
Chapter 8 — PLC Installations and Startup
Program checks verify that a PLC program functions properly without the application or process that the PLC controls actually being run.
Chapter 8 — PLC Installations and Startup
A final check verifies that an application or process controlled by a PLC functions properly in RUN mode under actual conditions.