Expressing a number using the binary system requires the use of many more digits than in the decimal system. The many binary digits can be difficult to read; therefore other related numbering systems were developed.

The octal numbering system uses a base of 8. This number is used because 8 bits of data make up a byte of information. The…

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The hexadecimal, or “hex”, numbering systems is used in PLCs because a “word” of data is made of 16 data bits or two 8-bit bytes.

The hexadecimal system uses 16 as its base. It uses the numerals 0 through 9 and the letters A through F. A through F is used to represent the decimal numbers 10 through 15.

The benefits of using a hexadecimal…

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The binary system uses the number 2 as its base. This means, the only digits used in this system are 0 and 1. The binary system can be applied easily to PLCs.

For example, to distinguish between two voltage levels (5V and 0V), the two levels can be related to the binary digits 1 and 0 where the high voltage is 1 and the low voltage is 0.…

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Ladder Diagram (LD) is the most commonly used PLC programming language, which is the method that the user uses to communicate information to the PLC.

A ladder diagram is a diagram used to represent relay ladder logic control systems.

The diagram receives its name from the fact that it looks like a ladder because the power feed and return…

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A wiring diagram is a visual representation of an electrical circuit. It displays the components of a circuit as simplified shapes. It also illustrates the power and signal connections between the devices.

Wiring diagrams often give information about the relative position and arrangement of devices and terminals, in order to help in…

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The term “chassis” refers to a piece of hardware which has slots into which you can insert different types of modules.

The term “rack” is a unit of measurement that refers to 16 words of data (8 words of input and 8 words of output), with 16 bits if each of the words.

A rack is NOT a piece of hardware, although it is sometimes used improperly in this way.

One of the more common address schemes is the PLC-5 address format.

Using the example “O 0 : 0 1 / 00”, the below diagram illustrates how this format is organized.

O –> File Type (O=Output; I=Input)

0 –> File number

: –> File delimiter

0 –> Rack number

1 –> Group number (0-7); there are 8 groups in a rack

/ –> Bit delimiter

00 –> Terminal…

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The PLC memory system stores a large amount of information about the statuses of all the inputs and outputs. In order to keep track of this large amount of information, the PLC uses a system called addressing.

An address is a label or number that indicates where a certain piece of information is located. This number directs the PLC where to…

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Bit: This is an abbreviated term for “binary digit”. This is the smallest unit of information in the binary numbering system. It represents a choice between two possible and equally likely values. It is often used to represent an on/off or true/false state.

Word: This is a group of smaller units in the binary numbering system. This group is…

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Connecting a piece of equipment, electronics or person to the ground by a piece of conductive material.

This ensures that any electrical charges will flow through the object or person and into the ground, rather than remaining in the object or person and causing electrocution.

Overview of field wiring connection for an AC input module

In an AC input module, the field wires are connected to a terminal strip.

The wires are then connected from the terminal strip to the AC input card.

This allows for easier and faster trouble shooting when considering how difficult it is to see which wire connects to which location on…

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The following are the steps for Proper technique of installing and removing a modular I/O module.

1. Disconnect the terminal assembly

2. Remove the module from the rack

3. Install the new module

4. Reconnect the terminal assembly to the new module

Discrete Input/Output modules are the most common types of I/O interface modules. This type of device connects binary or “On/Off” inputs. <div>

On/Off inputs are devices that have only an “On” or “Off” setting, such as selector switches, pushbuttons and limit switches.

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In discrete modules, output controls are limited to devices such as…

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Explain the communication methods required for using remote I/O?

Do you know what a remote I/O network is?

It is a type of communications network that communicates with input/output devices that are located physically far away from the CPU of the PLC.

These were created by PLC manufacturers so that the devices could be controlled from…

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When using a remote I/O system, the two major considerations are speed and distance.

As the distance between the rack and the PLC increases, the speed of communication decreases. This varies depending on the type of cable you use.

Regardless, greater speed and distance will cost a higher price and it will not always be possible to have the…

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A remote Input/Output rack is one that is located away from the processor module. To communicate with each other, a specialized communications network is used.

Each remote rack must have a station number to distinguish itself from each other. The remote racks are connected to the local rack through a communications module and cables connect…

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A local Input/Output rack is one that is located within the same rack as the processor module.

The obvious benefits of this system are that it is simpler to install and troubleshoot, is less expensive and is well-suited for basic functions.

Like a car chassis, which is the frame that the rest of the car sits on, a PLC chassis is the rack on which the PLC processor and I/O modules sit.

Based on the definition you just learned of Modular I/O devices, what disadvantages do you think this type of device offers?

The two main disadvantages of the Modular I/O devices are that they are larger and more expensive than Fixed I/O devices.

The size can be a problem in environments, such as classrooms, that have limited space constraints.…

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Based on the definition you just learned of Modular I/O devices, what advantages do you think this type of device offers?

Modular I/O devices offer many advantages. The modular design allows for the installation of many I/O modules with increased application options.

Many devices allow for the installation of additional racks which gives…

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Based on the definition you just learned of Fixed I/O devices, what disadvantages do you think this type of device offers?

Fixed devices are often built with less memory than their modular counterparts. Because fixed devices are built already containing I/O components, they have a limited number of inputs and outputs that cannot be changed.

As…

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Based on the definition you just learned of Fixed I/O devices, what advantages do you think this type of device offers?

There are a few advantages to using a fixed I/O device with your PLC.

Fixed units are often smaller and are therefore more conducive to small classroom environments.

These units are also less expensive per unit than their…

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The I/O (Input/Output) section of the PLC is the part of the unit that all external devices are connected. The I/O section communicates between the I/O sections and the CPU to carry out programmed functions.

A typical PLC has several I/O sections that allow for a variety of functions to be controlled. We will distinguish between the input…

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Generally when the PLC is integrated into process control or automated control systems all the components work together to form a complete control system. <div>

The system is normally made up from a combination of PLCs, networks, I/O, software and terminals. Many sub systems are used with many terms describing them

Process Control:

It consists of…

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Many networking options exist with PLC’s. Included may be remote I/O, peer-to-peer, host computer communications, and LAN’s.

Any of these methods can be a cost effective method of communication for two or more PLC’s, computer, and other devices. List the key terms are required for student understanding of this topic

Networking:

Many…

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Interface is to communicate with other devices as in computers running programming software or collecting data. An example may be an operator entering a command into a PLC located in a remote location. The devices will communicate through a network interface.

Examples of inputs and outputs may include Networks, Operator Terminals,…

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1. How many situations or different types of signals are available for a discrete signal?

A. 2

B. 4

C. 1

D. 8

Answer = A

2. When using Discrete Signals ON/OFF, 1/0, and True/False all have the same meaning?

Answer = True

3. A pushbutton is an example of a discrete output? Is this statement True or False?

Answer = False (Pushbutton is…

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The PLC offers many advantages over conventional relay control.

The flexibility is much easier for a PLC because it is easy to change the program, rather than rewire a circuit with conventional relay control.

Reliability– the PLC takes the place of many wires and relays in a conventional relay system. Once a program is written it can be…

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Analog: Most analog inputs and outputs vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts.

A module generally occupies one slot in a plc chassis. The module creates an interface between the PLC processor and a foreign device that would otherwise have no way to connect to the processor.

An example of Analog is a (Example: Thermocouple/Temperature Sensor) in the field sending an Analog input signal to the PLC thru the input module,…

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Discrete is a signal sent either to the PLC (input) or from the PLC (output). The signal has two states (either ON or OFF). A Discrete I/O (I/O stands for Input/Output) device or module recognizes only ON/OFF signals.

Discrete is nothing but digital. It is the most common type of I/O module. This is a type of interface with input devices such…

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