What are the Allen Bradley PLC Families?

This post introduces the different Allen Bradley PLCs that are available to use in automation projects. Allen Bradley is a hardware brand from Rockwell Automation, one of the world’s most popular PLC manufacturers.

After reading this post, you will be able to;

• List the different Allen Bradley controller families,
• Talk about the features of each controller family,
• Explain the positioning of each controller family relative to each other

Let’s start with an overview of the different Allen Bradley PLC families.

Allen Bradley PLC Families

The contemporary Allen Bradley PLC families in the Rockwell Automation controller portfolio are:

The Micro800 Controller Family

The Micro800 controller family is a range of low cost controllers that are designed to control simple machines.

The Logix 5000 Controller Family

The Logix 5000 controller family includes CompactLogix and ControlLogix controllers.

CompactLogix are controllers that are designed to control medium-sized machines with some axes of motion.

ControlLogix controllers are advanced controllers that are designed to control production lines or large processes.

AADvance and Trusted Platforms

AADvance and Trusted are Process Safety platforms that are not used for standard control.

They are not in the scope of this post but, since they are mentioned in Rockwell Automation’s controller literature, I thought I would mention them for completeness.

Now that we know what the contemporary Allen Bradley PLC families are, let’s look in detail at each family.

Before we move on, I want to point out that the PLC families that I have mentioned are the contemporary PLC families from Rockwell Automation. There are older PLC families like MicroLogix, SLC, and PLC-5 that are not mentioned because they are largely being phased out and obsoleted.

The Micro800 PLC Family

Allen Bradley Micro800 PLCs are low-cost PLCs that are designed to control small, standalone machines. The family is made up of small PLCs that are available in different form factors with different combinations of embedded IO points, networking options, and capabilities to address different project requirements.

All PLCs in the Micro800 family are programmed with the same software package, called Connected Components Workbench and all Micro800 PLCs (excluding the Micro810 PLC) can be extended with plug-in modules. These plug-in modules let machine builders add capabilities to a PLC to meet the requirements of a project.

Connected Components Workbench

Connected Components Workbench, or CCW, is the software used to configure and program Micro800 PLCs. Connected Components Workbench is also used to program and configure other devices like PanelView800 HMIs, PowerFlex drives, and GuardMaster configurable safety relays.

Plug-In Modules

The Micro800 PLC family can be extended using plug-in modules. These modules plug into the front of the Micro800 controllers to extend the functionality of a PLC without impacting the footprint of the controller.

Plug-in modules enable machine builders to buy just enough control for an application. They can be used to add additional I/O to a controller, add communication capabilities to a control, or add specialty functionality like a real-time clock to a controller.

Plug-in modules are compatible with all Micro800 controllers excluding the Micro810 controller.

Expansion I/O

Micro850 and Micro870 controllers can be extended with 2085 expansion I/O modules. 2085 expansion I/O modules are local I/O modules that extend the I/O capacity of Micro850 and Micro870 controllers.

These I/O modules are more advanced, higher density, and more expensive than plug-in I/O modules but are very useful for machines with many I/O points.

2085 expansion I/O modules are only compatible with Micro850 and Micro870 PLCs.

Micro810 PLCs

As I have already mentioned in the previous sections, the Micro810 PLC is a black sheep in the Micro800 family.

The Micro810 PLC is designed to be a replacement for smart relays. It combines high current relay outputs with the programming capabilities of a micro PLC.

Since it is designed for simple relay applications, it cannot be extended with plug-in modules or expansion I/O.

The image above shows a Micro810 with and without an option plug-in LCD screen installed. This screen can be used to visualize the status of the PLC and to configure the controller.

Sample Code

Micro800 PLCs support the concept of User Defined Function Blocks (abbreviated to UDFB).

These are blocks of code that a user can create to execute a specific function, making it easy to reuse code in and across projects.

Rockwell Automation provides a set of UDFBs for common functions like communicating via Modbus or MQTT communication protocols or interfacing with specific hardware. These UDFBs can be downloaded from Rockwell Automation’s website and imported into Connected Components Workbench projects to reduce the development time of a project.

Micro800 Summary

Micro800 PLCs are low-cost PLCs that can be extended with plug-in and expansion modules to provide just enough control for an application.

One of the big advantages of using Micro800 PLCs is that the engineering software is free to download and use and the same software that is used to program Micro800 PLCs is used to develop applications for PanelView800 HMIs and configure component class drives.

The easy-to-use software combined with Rockwell Automation’s sample code library is designed to help machine builders easily develop software to control simple machines in a cost-effective way.

Logix 5000 Controller Portfolio Overview

The Micro800 PLC family is designed to tackle micro-sized and small-sized applications.

In contrast, the Logix 5000 PLC family is positions above the Micro800 family. Logix 5000 controllers are designed to be scalable to meet an applications requirements with controllers available that are suitable for small applications to very large automation applications with tens of thousands of I/O points and many axes of motion.

Logix 5000 controllers are the flagship Rockwell Automation PLC family and are at the core of Rockwell Automation’s Integrated Architecture portfolio of products.

Integrated Architecture is a portfolio of tightly integrated control products. The products in the Integrated Architecture portfolio include Logix 5000 controllers, I/O systems, servo drives, variable frequency drives, and HMIs.

The main benefits of Logix 5000 controllers are;

Multi-Discipline Control

Logix 5000 controllers are multi-discipline controllers. This means that a single controller can be used for discrete, process, motion, and safety control.

Traditionally, this would have required different controllers for each discipline. Each controller would be programmed with a different software package and engineering hours would be spent integrating the controllers into a single system.

By using Logix 5000 controllers, manufacturers can have simpler controls architectures and lower maintenance costs.

Scalable

Logix 5000 controllers are designed to be scalable to tackle any application.

Since there are a wide range of Logix 5000 controllers available with different capabilities, Logix 5000 controllers can be used for small to large systems.

EtherNet/IP

Logix 5000 controllers use EtherNet/IP as their primary communication protocol. EtherNet/IP is a real-time control network that utilizes standard, unmodified Ethernet and Internet protocol.

Unlike some other industrial communication protocols, EtherNet/IP is “IT Ready”. This means that data from the control system can be sent to IT networks for collection and analysis. EtherNet/IP enables manufacturers to turn data into actionable information by collecting it from where it is created.

Logix 5000 Portfolio

The Logix 5000 controller portfolio is made up of two families of controllers called ControlLogix and CompactLogix.

ControlLogix

The ControlLogix PLC family is designed for larger more complex applications. ControlLogix systems tend to have higher IO counts, more axes of motion, and complex requirements like redundancy.

CompactLogix

CompactLogix controllers are targeted at small to medium-sized applications. CompactLogix PLC systems tend to have a smaller footprint since the power supply and Ethernet ports are embedded and there is no physical chassis.

GuardLogix and Compact GuardLogix

In the world of Allen Bradley, the term “Guard” means a safety-rated version. There are safety-rated versions of ControlLogix and CompactLogix controllers. a GuardLogix controller does everything that a non-safety rated controller does plus enables safety-rated control. Safety-rated control is required for safety applications.

Armor CompactLogix and Armor GuardLogix

The term “Armor” is used for on-machine version of products. In an on-machine version of a product, the enclosure is modified so that it can be mounted directly on a machine instead of in a panel.

There are on-machine versions of both standard and safety-rated Logix 5000 controllers.

Studio 5000 Logix Designer

All Logix 5000 controllers are programmed in Studio 5000 Logix Designer. Studio 5000 is a design environment that includes tools to architect systems, create a database of reusable application code, emulate Logix controllers, and program PanelView 5000 HMIs.

Now that we know about the Logix 5000 controllers on a high-level, let’s look in more detail at CompactLogix and ControlLogix PLC systems.

The CompactLogix PLC System

The CompactLogix PLC system is a modular PLC system that is positioned above the Micro800 PLC system and below the ControlLogix PLC system.

In the image above, you can see an example of a CompactLogix PLC system. In this image, the controller is on the left and several I/O modules are connected to the PLC on the right.

As you can see, the CompactLogix PLC system is a rackless system. That means that it does not use a physical chassis to connect the module together. Instead, the modules are connected together using a connector on the right of the controller and each module.

In newer models of CompactLogix PLC, EtherNet/IP network communications are embedded in the controller. The controller’s Ethernet ports are typically located on the bottom of the controller.

Projects can be downloaded to the controller using the Ethernet connection or the USB port located on the front of the controller.

All CompactLogix PLCs also have an SD card which is installed behind a small door on the front of the controller. This SD card is used to back up the controls program. If a controller fails, the SD card can be moved to a new controller to get a line up and running as quickly as possible.

CompactLogix part numbers start with 1769 or 5069.

Product Selection Information

There are many different models of CompactLogix PLC available to use in projects. This let’s users select the most cost-effective solution to meet the needs of their application but makes product selection a bit complicated.

Some things to think about when selecting a CompactLogix PLC for an application are:

Memory

How much memory is required for the application?

Connected Devices

How many devices will be connected to the PLC over an industrial network?

Motion Control

Does the application require integrated motion? In other words, will the PLC have to control one or more servo drives.

Integrated Safety

Does the application require integrated safety? In other words, will the PLC monitor and control safety devices?

Preferred I/O

Is there a preferred I/O system? Different CompactLogix PLCs use different I/O platforms.

Controller Positioning

This graph shows the relative positioning of the different types of CompactLogix controllers.

As you move to the right of the graph, controllers have more user memory available, can control more axes of motion, and support more I/O modules.

As you can see from the picture, different CompactLogix PLCs use different I/O cards.

CompactLogix 5370 L1 controllers use 1734 POINT I/O modules for local I/O.

CompactLogix 5370 L2 and L3 controllers use 1769 Compact I/O modules for local I/O.

Finally CompactLogix 5380 controllers use Compact 5000 High Performance I/O for local I/O.

To make it easy to understand the differences between the various CompactLogix PLC families and select the right hardware for an application, Rockwell Automation publish a CompactLogix Selection Guide. This guide provides more details about the specific functionality of each product line and catalog number.

The ControlLogix PLC System

Now that we've discussed the CompactLogix controllers, let's move on to the ControlLogix platform.

ControlLogix is a chassis-based controller that requires some type of communications and I/O. Modules that provide this functionality are installed into a chassis, like the one shown here.

And here's what it looks like once the modules are installed into the chassis.

The power supply is on the left.

A controller can be installed in any slot in the chassis and multiple controllers can be installed in a single rack. This image shows two installed.

Some of the newest ControlLogix controllers have an EtherNet/IP communication port built in, but it is more common for the communications to be on a separate, dedicated module that is connected to the controller via the chassis backplane.

I/O for the system can be in the local chassis or it can be distributed I/O that is connected to the controller via a control network, such as EtherNet/IP.

There are also modules that provide other specific functions, such as redundancy for highly critical applications and Model Predictive Control for advanced tuning of process applications.

Most Rockwell Automation products intended to be installed as modules in a ControlLogix rack have catalog numbers that start with 1756, including the controllers, the communications cards, and the local I/O.

ControlLogix controller model names start with 55 followed by a number indicating the model generation and a fourth digit indicating the specific model. Examples include 5573 and 5585.

ControlLogix-XT

Many ControlLogix and GuardLogix models have a specialized version called -XT for extreme environments.

The primary technical differences are a wider temperature range and improved protection against corrosive environments. Notice that the chassis includes larger spacing between the modules for improved airflow. This is just one of many design modifications to achieve the wider temperature range.

The improved protection against corrosive environments is achieved by conformal coating of the electronics.

Network and I/O Modules

There are many 1756 network and I/O modules.

These can be installed in chassis with or without a ControlLogix controller. If there is no controller in a given chassis, that chassis would typically be remote I/O for a Logix controller connected via a network.

There are network modules available for many common automation networks.

There is a wide variety of types of I/O modules to meet many different application requirements.

here are specialty modules for dedicated functions, such as a Compute Module which is basically an industrial computer in the rack, a Model Predictive Control module for advanced process applications, and a network security module.

There are even third party modules that provide functionality not covered by the Rockwell Automation product line.

Relative Positioning of Allen Bradley Controllers

Now that each of the lead products have been discussed, this image reiterates how they're positioned relative to each other.

The Micro800 is an entry level controller platform with free software designed for OEMs with significant price sensitivity.

CompactLogix and ControlLogix are a common platform with a common design software. This software is called Logix Designer and it is part of the Studio 5000 design environment. There is very little overlap between the target applications for the Micro800 family and the Logix controller family.

CompactLogix is a collection of related products. They are sometimes referred to as "Mid-range" and are typically targeted at standard machines, although some newer controllers in this family are high performance and quite capable of advanced applications.

While there is some capability overlap, ControlLogix is generally positioned above CompactLogix. It has more network options and specialty functionality. Some functions that are often required for Process applications are only available in the ControlLogix platform, such as redundancy.

Summary of Older Controller Platforms

Now that the modern Allen Bradley PLC families have been defined and summarized, let’s get a brief overview of some older controller platforms. These products are either older or already obsolete, but they each have a very large install base.

The MicroLogix was the previous generation of micro controller and it is very popular with OEMs. Some MicroLogix models have been obsolesced but others are still selling well and fully supported.

The MicroLogix shares programming software with another product called the SLC, short for Small Logic Controller. You will often here the product called "SLICK". It was designed for applications similar to what would be covered by CompactLogix today. Like the MicroLogix, some SLC models are still sold and supported today, while a larger part of the product line has been obsolesced.

The PLC-5 was introduced in the mid-1980s and only recently made obsolete. It is one of the most successful products in the history of the automation industry and helped to firmly established Alien-Bradley as the leading PLC brand. It still enjoys a huge install base.

Rockwell Automation strongly encourages anyone still using PLC-5 controllers to migrate to the ControlLogix platform. There are hardware products to help ease the transition, service offerings to handle the work, and commercial programs to make the transition more viable for companies.

Wrap Up

After reading this post, you should be able to:

• List the different Allen Bradley PLC families,
• Identify and describe each Allen Bradley PLC family,
• Understand the positioning of the different PLC families relative to each othe