PLC Chapter 1

Identify the appropriate comparison of the single-ended, multitask, and control management types of PLC applications.

A single-ended application involves one PLC controlling one process, and a multitask application involves one PLC controlling several processes, whereas a control management application involves one PLC controlling several others.

What do the numbers represent with reference to the process control PLC ladder logic diagram in the given figure?

Addresses

Fixed I/O PLC's

Fixed Input and Output. A small PLC that comes in one package with no separate, removable units. Lack of flexibility.

Human Machine Interface (HMI)

PLC software that allows the user to monitor and control the process.

What provides rules for combining the instructions so that they produce the desired actions?

Programming Language

Programming language

Provides rules for combining the instructions so that they produce the desired actions.

What is relay ladder logic?

Relay ladder logic (RLL) is the most common programming language used to communicate with PLCs and was developed to mimic relay logic.

Modular I/O PLC's

Expandable Input and Output. It is divided into compartments into which modules can be plugged. Thus increasing your options and flexibility.

When do the pressure switch contacts close?

When the pressure reaches the preset value

When do the temperature switch contacts close?

When the temperature reaches the preset value

Relay system is changed by changing the __________ , whereas PLC system is changed by changing the _______

Wiring and Program

Identify the differences between open and proprietary PLC architecture.

- An open-architecture uses off-the-shelf components that conform to approved standards, whereas a proprietary architecture uses custom components that deny the approved standards. - An open-architecture design is easy to connect to devices and programs made by other manufacturers, whereas a proprietary architecture is difficult to connect to another manufacturer's system.

Identify the tasks in addition to relay switching operations that PLCs are capable of performing.

- Counting analog signals - Calculating analog signals - Comparing analog signals - Processing of analog signals

Identify the statements that describe how the I/O modules connect to the processor in a modular-type PLC configuration.

- The I/O modules plug into a rack. -When a module is slid into the rack, it makes a connection with a series of contacts called the backplane. -The PLC processor is also connected to the backplane and, therefore, can communicate with all modules in the rack.

Identify the criteria by which PLCs are categorized.

-Functionality -Physical size -Number of inputs and outputs -Cost

What two conditions will provide a continuous path from left to right across the rung with reference to the process control PLC ladder logic diagram in the given figure?

-If contacts I/1 and I/2 are closed -If contact I/3 is closed

—(\)—

A "not" coil, energized whenever its rung is open.

—[\]—

A "not" contact, closed whenever its corresponding coil or input which controls it is not energized.

HW Question. What is a programmable logic controller (PLC)?

A PLC is a specialized computer used to control machines and process.

What does the instruction set for a particular PLC refer to?

A list of different types of instructions supported.

—( )—

A regular coil, energized whenever its rung is closed.

—[ ]—

A regular contact, closed whenever its corresponding coil or input which controls it is energized.

Programmable Logic Controller (PLC)

Industrial grade computer that is capable of being programmed to perform certain functions

What are the three basic components of a PLC?

Input and Output Module CPU Power Supply

What is the I/O module do?

Input: Devices and transducers which are entrusted with taking in information about the physical world to the PLC Output: Devices called actuators convert the electrical signal of the PLC to a physical movement for instance a valve solenoid stoke or a motor contactor.

Program

Is a user developed series of instructions that direct PLC to execute actions.

Identify the main function of processor module (CPU).

It accepts input data from sensing devices, executes the stored user program from memory, and sends appropriate output commands to control devices.

What is the CPU?

It is the brain of the PLC. A typical processor consist of a microprocessor for implementing logic and controlling the communications among the modules. The processor requires memory for storing user program instructions, numerical values and I/O device status

What field device is the number I/2 in the given figure identified with?

Temperature switch

Identify the appropriate difference between the PLC and PC with regard to execution of program.

Unlike personal computers, PLCs execute a single program in a sequential order, while computers execute several programs or tasks simultaneously in any order.

Identify the appropriate comparison of the PLC and PC with regard to physical hardware differences.

Unlike personal computers, the PLC comes with its program language built into its memory and has no permanently attached keyboard, CD drive, or monitor.

Identify the appropriate difference between the PLC and PC with regard to method of programming.

Unlike personal computers, the PLC is programmed in relay ladder logic or other easily learned languages.