SLC 500 vs ControlLogix

SLC 500 and ControlLogix control platforms are some of the most popular Allen-Bradley’s Programmable Logic Controllers (PLCs) systems available in the market today. While it might be easy to pick up an SLC 500 or a ControlLogix control system, it is imperative to understand the ins and outs of each system. This article provides you with a detailed comparison between the two control systems.

SLC 500 Overview 

The term SLC means “Small Logic Controller”. The Allen-Bradley SLC™ 500 is a control platform from Rockwell Automation with Bulletin 1747. It is a chassis-based, modular family of Programmable Logic Controllers (PLCs), I/O modules, and peripheral devices. With multiple processor choices, a wide range of communication configurations, more memory capacities (64 K of configurable user data/program memory), extensive I/O capacity (over 60 types of I/O points), and numerous power supply options, the SLC 500 family delivers a powerful solution for mid-range stand-alone control or distributed industrial control.

In addition, SLC 500 controllers are programmed using RSLogix 500 Ladder Logic programming software which provides flexible editors, a power database editor, point-and-click I/O configuration, as well as advanced diagnostic and troubleshooting tools which maximize productivity and assist you to save on project development time.

More than a decade since its introduction as one of the first full-featured small controller series, the SLC 500 family is still the gold standard for small logic controllers. The controllers within this family are built around two hardware options: a fixed controller option or a modular controller option. A fixed controller consists of a processor, I/O, and a power supply all in a single unit. This hardware option also provides a 2-slot expansion chassis increasing the flexibility of such a controller.

The modular SLC 500 controller option provides you with more processing power, additional flexibility in system configuration, and increased I/O capacity. This allows you to customize your controller system design to specifically meet your application requirements.  

ControlLogix System Overview  

The ControlLogix system provides d, sequential, drives, motion, and safety control through a variety of communication networks and state-of-the-art discrete or process I/O modules in a small, cost-effective package. The system is modular, so you can efficiently design, build, and modify it, with significant savings on training and engineering costs. In addition, ControlLogix products with an “XT” suffix at end of their catalog numbers are available with a conformal coating, that adds a layer of protection against harsh and corrosive industrial environments.

The hardware options of the ControlLogix architecture can be anything from a single 1756 chassis to a highly-distributed control system with multiple chassis and communication networks all functioning together. A simple ControlLogix system, for example, consists of I/O modules and a stand-alone controller all in a single chassis. For a more comprehensive system, you can use multiple ControlLogix controllers in one chassis, multiple controllers connected across networks, or I/O modules in multiple ControlLogix platforms connected over multiple I/O links and distributed in many locations.

The diagram to the right shows a typical ControlLogix system with multiple controllers, I/O, and communication modules placed in the Chassis, and a connected Power Supply unit. Note, when multiple controllers are installed in the same chassis, they operate independently but they communicate with each other over the backplane.

In addition, ControlLogix controllers are available within the Logix 5000™ family of controllers. They can monitor and control I/O across the backplane of the ControlLogix system, and over I/O links. These controllers communicate over a variety of communication networks and are capable of high-speed data transfers and communications.

Note, you can use the ControlLogix platform as a gateway by including the communication modules required for connectivity to other networks. For such uses, you don’t need a controller. ControlLogix Gateways integrate into any existing PLC-based systems including PLC-5® and SLC™, enabling users with existing networks to communicate over other networks.

What are the Similarities and Differences between SLC 500 and ControlLogix? 

Here are some of the factors which can be used to compare SLC 500 vs ControlLogix control systems. 

1. Controllers

SLC 500 family provides multiple processor choices with five CPU designs namely SLC 5/01, SLC 5/02, SLC 5/03, SLC 5/04, and SLC 5/05. The controllers available within these processor categories include: 

• SLC 5/01 Controllers: They were the first rack-based SLC 500 processors to be developed by Allen-Bradley. They have a built-in DH-485 communication channel which supports peer-to-peer communication responses only. They include: (i) 1747-L511 SLC 5/01 controller with 1K(Kilobyte) of user memory; (ii)1747-L514 with 4K Memory.  
• SLC 5/02 Controllers: Only one controller is available in this category: the 1747-L524 SLC 5/02 Controller with 4K of user memory. It provides additional complex programming instructions, faster scan times, enhanced communications and more memory options than SLC 5/01 controllers.  
• SLC 5/03 Controllers: In addition, to the built-in DH-485(“Data Highway”) communication channel, SLC 5/03 controllers have an embedded RS-232 channel which offers the flexibility of connecting to external intelligent devices without the need for additional interface modules. They include: (i) 1747-L531 with 8K Memory; (ii) 1747-L532 with 16K Memory; (iii) 1747-L533 with 32K Memory. 
• SLC 5/04 Controllers: They have even more memory capabilities and a faster communication platform known as DH+ (“Data Highway Plus”) which replaces the standard DH-485 port in the previous SLC 500 processors. They include: (i) 1747-L541 SLC 5/04 Controller with 16K of user memory; (ii) 1747-L542 with 32K Memory; (iii)1747-L543 with 64K Memory. 
• SLC 5/05 Controllers: They provide the same functionalities as the SLC 5/04 but instead of DH+ communications they provide standard Ethernet communications. They include: (i) 1747-L551  SLC 5/05 Controller with  16K Memory ; (ii) 1747-L552 with 32K Memory; (iii) 1747-L553 with 64K Memory. 

In contrast, ControlLogix controllers from Allen-Bradley/Rockwell Automation are available in different categories based on their application capabilities. These categories include:  

• Standard ControlLogix Controllers: These are part of the Logix 5000^TM family of controllers under Bulletin 1756. Currently, the available controllers in this category are ControlLogix 5580 controllers Series-8(L8) and ControlLogix 5570 Controllers Series-7(L7). 
• ControlLogix-XT Controllers: These function as the standard ControlLogix controllers but they contain an extended temperature range functionality. Rockwell Automation provides both ControlLogix5570 and ControlLogix 5580 ControlLogix-XT Controllers. Note, the -XT I/O and communication system modules are also conformally coated to withstand harsh and corrosive industrial environments.  
• Redundant ControlLogix Controllers: ControlLogix 5570 and ControlLogix 5580 controllers enable controller redundancy. To support a redundancy system, they each require approved redundancy firmware revisions in every communication module. 
• GuardLogix Controllers: These provide safety control. They include: GuardLogix 5580 and GuardLogix 5570 Controllers 
• Process Controllers: These are ControlLogix 5580 process controllers. They focus on plant-wide process control. 
• Armor ControlLogix Controllers: They extend the functionality of the standard ControlLogix controllers to the On-Machine™ space. They include: 1756-L72EROM with 4 MB user memory and 1756-L73EROM with 8 MB memory. 
• Armor GuardLogix Controllers: They deliver safety control up to CAT 4, SIL 3, PLe, and they support standard and safety communication options over EtherNet/IP. They include: (i) 1756-L72EROMS with 4 MB standard and 2 MB safety user memory; (ii)1756-L73EROMS with 8 MB and 4 MB safety user memory. 
• No Stored Energy (NSE) Controllers: They are the ControlLogix 5580 NSE controllers. They are used in applications which require the installed controllers to deplete their residual or stored energy to specified levels before being fitted into and out of the ControlLogix system.  

2. I/O Modules

Both SLC 500 and ControlLogix systems provide an extensive I/O capacity to handle a variety of control applications.

SLC 500 I/O Modules are available in a wide range of voltage options and densities. You can choose from over 60 discrete, analog, and specialty I/O modules to control digital, analog, and temperature signals. SLC 500 I/O modules are available under Bulletin 1746 and they’re categorized as:

• 1746 Digital I/O Modules: These are available in a variety of densities including 4-, 8-, 16-, and 32- I/O points. 
• 1746 Analog I/O Modules: They feature user-selectable voltage or current analog inputs, diagnostic feedback, Removable Terminal Blocks (RTBs), and a backplane isolation. 
• Application Specific Modules: The SLC 500 family provides a variety of modules for specialty applications. Some of these modules include: (i) 1746-BAS and 1746-BAS-T BASIC Modules; (ii) 1747-PCI Computer Bus Interface Module/System; (iii)1746-BLM Blow Molding Module; (iv)1746-BTM Barrel Temperature Module. 

The ControlLogix architecture provides a full range of analog, discrete, diagnostic digital, motion control, and specialty I/O under Bulletin 1756. These ControlLogix® I/O modules extend over many control applications, from high-speed digital to process control. Some of these modules include:

• 1756 Digital I/O Modules: The standard modules in this category support: Removal and Insertion Under Power (RIUP), field side diagnostics, time stamping of data, module-level fault reporting, and Producer/Consumer model for sharing input information and output status among multiple ControlLogix controllers. They also allow you to select between direct-connect or rack-optimized communications. 
• 1756 Analog I/O Modules: In addition to supporting the features supported by the 1756 Digital I/O, these modules also support IEEE 16-bit integer or 32-bit floating point data formats, direct-connect communications, as well as rolling and system time stamp of data. 
• 1756 Specialty I/O Modules: The specialty modules in this series include: (i) 1756-HSC High Speed Counter; (ii) 1756-PLS Programmable Limit Switch module; (iii) 1756-CFM Configurable Flowmeter module; (iii) 1756-LSC8XIB8I Low Speed Counter module. 

3. I/O Wiring Systems

Wiring systems for SLC 500 I/O consist of Interface Modules (IFM) and Bulletin 1492 pre-wired cable, which replace Remote Terminal Blocks providing up to 50% of the point-to-point wiring between field devices and the SLC 500.

Similarly, each ControlLogix 1756 I/O module requires a 1492 Interface Module (IFM) or a Removable Terminal Block (RTB) to connect to all field-side devices. 1492 Wiring Systems can be used as an alternative to the RTBs, this depends on the mounting requirements of the selected ControlLogix I/O modules.

In both, SLC 500 and ControlLogix systems the IFMs and RTBs are not included with the I/O modules. So, they should be ordered separately.

4. Chassis

All SLC 500 1746 I/O modules fit directly into the SLC chassis with Bulletin 1746. While each ControlLogix I/O module mounts in a ControlLogix chassis with Bulletin 1756.

The SLC chassis hosts the 1746 I/O modules and any of the SLC 500 processors. Every 1746 chassis in the SLC 500 system should have a power supply mounted on the left side. In cases where 3 or 2 chassis are used, the first slot in the first chassis is set aside for the processor. SLC 500 chassis are available in four sizes, namely:

• 1746-A4: 4-Slot Chassis 
• 1746-A7: 7-Slot Chassis 
• 1746-A10: 10-Slot Chassis 
• 1746-A13: 13-Slot Chassis 

A ControlLogix platform requires a 1756 I/O chassis to physically hold the 1756 I/O modules; you place the modules in any slot of the chassis. ControlLogix 1756 I/O chassis are available in the following options: 

A) Standard Chassis 

1756 standard I/O Chassis are available in five sizes, namely:  

• 1756-A4: 4-Slot Chassis 
• 1756-A7: 7-Slot Chassis 
• 1756-A10: 10-Slot Chassis 
• 1756-A13: 13-Slot Chassis 
• 1756-A17: 17-Slot Chassis

B) ControlLogix-XT Chassis 

ControlLogix-XT 1756 I/O chassis support extreme temperature environments in the range of -25…+70 °C (-13…+158 °F). They include: 

• 1756-A7XT/C: 7-Slot Chassis 
• 1756-A10XT/C: 10-Slot Chassis 

5. Motion Capabilities

SLC 500 systems are capable of handling simple motion control, through the 1746-HSRV Servo Control Module and 1746-HSTP1 Stepper Control Module. The 1746-HSRV module is a single-axis, closed-loop servo controller which is operated with a variety of SLC 500 processors. It is programmed with RSLogix 500 software as Ladder Logic controls all of the motion in SLC 500 systems. Also, the 1746-HSRV module monitors encoder feedback up to 300 KHz. You can accomplish complicated moves using blended motion profiles within this module’s internal memory and these can be executed repeatedly. 

The 1746-HSTP1 module is a single-axis stepper controller often used for open-loop stepper control applications. It also operated with a variety of SLC 500 processors, and it can deliver up to 250 KHz pulse train output for small-stepping control applications. 

On the contrary, ControlLogix controllers execute complex ladder motion control commands, thereby generating position and velocity profiles. A single ControlLogix chassis and controller can handle up to 32 axes of motion or at most 16 1756-M02AE servo modules. The 1756-M02AE modules are closed-loop and they have two axes of motion. They receive position and velocity profile data from the ControlLogix controller, and their function is to make sure that the connected actuators follow these profiles. They achieve this by monitoring position feedback and generating appropriate control commands for the drive. 

Moreover, ControlLogix control systems support Integrated Motion over EtherNet/IP networks for the connected Ethernet drives. Also, these systems are able to provide Kinetix^® Integrated-Motion using SERCOS (Serial Real-Time Communication System) interface or EtherNet/IP interface to attain multi-axis control. The Logix Integrated Motion feature supports the analog series of ControlLogix modules for controlling drives and actuators. In addition, ControlLogix systems are able to carry out point-to-point indexing via Networked Motion, which connects sing-axis drives through a DeviceNet network. 

6. Communication Options

Both SLC 500 and ControlLogix systems provide a connection to all the four levels of communication networks. These four levels of networks include:

A) Information Networks: These types of networks allow various manufacturing systems (such as Manufacturing Execution System-MES), Information System (IS), and Data Archiving systems to access plant floor data. They have the capacity to transfer huge data files and they can connect host computers from multiple vendors. The networks in this category include EtherNet/IP, Data Highway Plus™ (DH+), and DH-485.

In SLC 500, Data Highway Plus connectivity is provided by the SLC 5/04 processor. DH+ communications for ControlLogix systems are provided by 1756-DHRIO and 1756-DHRIOXT Data Highway Plus communication modules. All SLC 500 programmable controllers have an embedded DH-485 communication channel which allows program support and monitoring.

Ethernet connectivity for the SLC 500 platform is provided by the SLC 5/05 processor, through the TCP/IP protocol at a high bandwidth of 10 Mbps to 100 Mbps. In ControlLogix systems, Ethernet communications are achieved through EtherNet/IP Communication Modules which include: 1756-EN2F; 1756-EN2T; 1756-EN2TR; 1756-EN3TR; 1756-EN2TXT; 1756-EN2TRXT; 1756-EN2TSC; 1756-ENBT; 1756-EWEB.

B) Control Networks: They provide real-time, deterministic, and repeatable performance for I/O, controller programming, device configuration, and peer-to-peer messaging. These networks span the entire manufacturing process from the acquisition of raw materials to finished products. They are used to connect programmable controllers (PACs and PLCs), motion drives, personal computers, operator-machine interface devices such as HMI and IPC.

Control Networks in both SLC 500 and ControlLogix systems include ControlNet and Universal Remote I/O networks. In the two control systems, connectivity to these Control Networks is provided by a variety of interfaces.

C) Device Networks: They allow users to reduce hard-wiring requirements, and save on installation time and costs. They also offer device-level diagnostics from the various actuators, sensors and other high-level devices (computers and controllers) connecting to the system. 

DeviceNet is the common Device network supported by both SLC 500 and ControlLogix systems. In SLC 500, DeviceNet connectivity is provided by the following interface modules:(i) The 1747-SDN DeviceNet Scanner modules in SLC 5/02 or higher processors. (ii) 1761-NET-DNI DeviceNet Interface Device. DeviceNet connectivity for ControlLogix systems is provided by 1756-DNB DeviceNet Bridge. 

ControlLogix platforms also provide the Foundation Fieldbus network as an additional device network. In these platforms, Foundation Fieldbus protocol is designed for use with ControlLogix 5580 process controllers to provide distributed control of process applications. This connectivity is achieved with: (i) FOUNDATION Fieldbus bridge to an Ethernet network via either 1757-FFLD2 or 1757-FFLD4 linking devices. (ii) FOUNDATION Fieldbus bridge to a ControlNet network via either 1757-FFLDC2 or 1757-FFLDC4 linking devices. 

D) Serial Networks: They are used in applications that require Supervisory Control and Data Acquisition (SCADA), and Modem connectivity.

Some SLC 500 processors including SLC 5/03, SLC 5/04, and SLC 5/05 have an embedded serial port that is configurable for RS-422A, RS-232, or RS-423 for compatible communications via serial protocols. You can use the built-in serial port to connect an SLC 500 system to devices that: (i) communicate via DF1 protocols, such as communication modules, modems, or programming workstations. (ii) Communicate over ASCII networks by sending and receiving ASCII characters, like bar-code readers, ASCII terminals, and printers.

ControlLogix systems have a serial port that is compatible with RS-232 serial communications. This serial port enables DF1 Full-duplex or DF1 Half-duplex Master/Slave protocols and ASCII networks to communicate with others devices on the serial link.

7. Programing Software

SLC 500 processors are programmed using RSLogix 500 programming software in Ladder Logic. The available software packages for RSLogix 500 include RSLogix™ 500 and RSLogix™ 500 Professional. In contrast, components of a ControlLogix system are programmed and configured using RSLogix 5000 Programming Software in Studio 5000 Logix Designer environment. 

In case you need to use DeviceNet or ControlNet or Ethernet communications, both SLC 500 and ControlLogix systems provide you with the option to select RSNetWorx for ControlNet or RSNetWorx for DeviceNet or RSLinx software package for Ethernet connectivity. 

Final Thoughts 

Despite its lightweight architecture, the SLC 500 series has a number of advantages. One, it allows its users to build customized control capabilities for specific applications. It is also capable of handling simple motion control, small process control, high-speed assembly operations, material handling, and SCADA systems. You will often find SLC 500 systems controlling heating or lighting for several buildings or theme parks. Also, you can find these systems operating a factory floor as they are flexible and efficient when handling heavy control operations.

On the other hand, ControlLogix control systems provide scalable controller solutions that are capable of addressing an extensive number of I/O points. They are designed for larger, heavier systems that require higher I/O counts. With a truly integrated ControlLogix system, you can perform standard and safety control in the same chassis. And by leveraging the high availability and extreme environment performance capabilities of such systems, you can meet the complex control needs of most industrial applications.

For more information or to discuss which equipment might be best for your application, please visit our website here, or contact us at [email protected] or 1-919-535-3180. 

This entry was posted on January 24th, 2022 and is filed under Allen-Bradley, Uncategorized. Both comments and pings are currently closed.