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In this post, we compare the various I/O systems available from Rockwell Automation including 1756 ControlLogix I/O, 5069 Compact 5000 I/O, 1769 Compact I/O, 1734 POINT I/O, 1794 FLEX I/O, 1732 ArmorBlock I/O, 1719 Ex I/O, and 1715 Redundant I/O and talk about the questions you should ask when selecting an I/O system for an application.
After the PLC, I/O modules are the most important components in an automated system. Inputs allow the PLC to understand the state of the process that it is controlling, and output modules allow the PLC to influence the process that it is controlling.
But I/O selection is not a straightforward task. Most manufacturers, including Rockwell Automation, have many different I/O platforms to choose from.
In this post, I will explain the factors that can influence the selection of an I/O platform for an automated systems, introduce the various I/O platforms that are available from Rockwell Automation, and explain the key differences between these I/O platforms.
By the end of the post, you will know enough about the Rockwell Automation I/O platforms to make an informed decision about which I/O platform to use in automation projects and to justify that selection.
There are a lot of things to consider when choosing an I/O platform for an application. In fact, one of the reasons that manufacturers like Rockwell Automation have so many different I/O platforms available is that applications can have a broad range of requirements, some of which are conflicting.
In this section, we'll look at some of the factors that you might consider when selecting an I/O platform for a new application and what Rockwell Automation I/O families are suitable based on these factors.
The most basic question to consider when choosing an I/O platform for an application is where the I/O modules will be mounted.
If you plan to use local I/O then the choice of I/O modules is very simple because each Logix 5000 PLC uses a specific I/O platform for local I/O modules. With local I/O, expansion I/O modules are connected directly to the controller using an electrical backplane.
In general, local I/O is used for simple applications. These applications are usually small, standalone machines, or simple processes that have a limited number of I/O points.
Let's look at the local I/O platforms available from Rockwell Automation in more detail.
Every Logix 5000 PLC family uses a dedicated I/O platform for local expansion I/O. These local I/O modules are referred to as "chassis-based I/O modules". Surprisingly, they are called chassis-based I/O modules even in PLC systems that do not use a physical chassis, like the CompactLogix series of PLCs, which we learned about in this post. What chassis-based I/O really means is that there is a direct connection between the I/O module and the controller via an electrical backplane.
The main chassis-based I/O platforms for Logix 5000 PLCs are;
The only criteria to consider when selecting one of these platforms is the type of Logix 5000 controller being used in the application.
1756 ControlLogix I/O modules are used with the Logix 5000 ControlLogix PLC systems. Just like other components in the ControlLogix PLC system, ControlLogix I/O modules have a part number beginning with 1756. The 1756 ControlLogix I/O modules are designed to be installed in a ControlLogix chassis.
The ControlLogix PLC system is designed to tackle large, and complex applications. For this reason, the 1756 ControlLogix I/O modules are rich in features, and relatively expensive when compared to lower-end I/O platforms.
The 5069 Compact 5000 I/O platform is the latest addition to Rockwell Automation's line up of I/O platforms.
The 5069 Compact I/O platform is a high performance I/O platform. It is considered high performance because of the 200 microsecond update time, which enables high speed and precision in critical applications. These I/O modules also have other premium features making them a good choice for difficult applications.
Compact 5000 I/O modules are used as local expansion I/O for the high performance 5380 CompactLogix controllers and are recommended as the distributed I/O platform for the high performance 5580 ControlLogix controllers.
Finally, 1769 Compact I/O modules are used as local expansion I/O modules for 5370 CompactLogix controllers. These I/O modules are less expensive and less advanced than Compact 5000 I/O modules, making them a good choice for non-critical I/O applications with budget constraints.
Local I/O modules are very useful for standalone machines and simple processes. As applications become larger and more complex, it can be beneficial to use distributed I/O modules.
Distributed I/O modules are I/O modules that are mounted in a different chassis or rack than the controller. The distributed I/O modules communicate with the controller over an industrial network.
Distributed I/O modules are very useful when field devices are spread out over a large area. Since the I/O modules are installed close to the field devices, less wiring is required to connect the field devices to the I/O modules. To connect the I/O modules to the controller, you only need to run one network cable back to the electrical cabinet that houses the PLC. This reduction in wiring can massively reduce the installation cost associated with an automated system.
The chassis-based I/O modules that we have discussed up to now, can be used as distributed I/O modules. In distributed I/O applications, the modules are connected to a network adapter that communicates with the PLC over an industrial network.
As well as these chassis-based I/O modules, Rockwell Automation offers several other I/O platforms for distributed I/O applications. Let's look at those platforms in the next sections.
Traditionally, distributed I/O modules have always been mounted in electrical cabinets. These cabinets provide protection to the I/O modules from dust, damp, and generally harsh industrial environments.
More recently and in specific industries, there is a push to move automation products from being mounted in electrical cabinets to being mounted directly on machines. This trend is particularly noticeable in the automotive industry.
To mount an I/O module directly on a machine, it has to be designed differently from an I/O module that is to be mounted in a cabinet. By mounting I/O modules directly on the machine, wiring costs can be reduced dramatically - instead of pulling wires from the field devices to terminal blocks in the cabinet and on to the chassis based I/O, .you can place the I/O modules beside the field devices for easy connection. Field devices are connected to on-machine I/O modules using M12 screw in connectors which makes wiring mistakes almost impossible.
Of course, there are drawbacks to using on-machine I/O modules too. Because the I/O modules are ruggedized, they are more expensive when compared to chassis-based I/O modules. This makes sense because more material and coatings are used to ensure that on-machine I/O modules have adequate corrosion and water resistance to survive in tough environments.
The I/O platform that you use will be different depending on whether you plan to install I/O modules in-cabinet or on-machine. Let's start by looking at the in-cabinet distributed I/O platforms from Rockwell Automation.
The 1734 POINT I/O system is an in-cabinet distributed I/O system. It is designed as a modular system, which means that different types of I/O modules can be combined in one rack to provide the right combination of I/O for a given application. There are also many different types of I/O modules available for the POINT I/O system. This includes standard digital input and output modules, standard analog input and output modules, as well as specialty modules like IO-Link I/O modules.
POINT I/O modules are designed to have a small footprint. Each standard module is only 12mm wide, making it an ideal I/O system for space constrained applications.
This narrow width is only possible because POINT I/O modules are low density I/O modules. This means that each I/O module has a small number of input or output channels. Specifically, POINT I/O modules have between one and eight channels. Low density I/O modules can be useful in systems where you need a small number of many different types of I/O. For example, if you needed a few digital inputs, a few digital outputs, a few analog inputs, and one I/O Link connection, then the low density POINT I/O system would be a good choice.
Most low-density I/O applications are found in machine control. However, the POINT I/O system is occasionally used on small process skids with low I/O counts.
In larger process applications, there are many I/O channels required and an I/O system with higher I/O density is preferred. For those applications 1794 FLEX I/O can be a better choice.
Just like the POINT I/O platform, the FLEX I/O platform is a modular I/O platform that is suitable for distributed, in-cabinet applications. Unlike the POINT I/O platform, the FLEX I/O platform provides high I/O density I/O modules. A high density module is an I/O module with many channels to connect to many different field devices.
To achieve the high I/O density per module, FLEX I/O modules are much wider than POINT I/O modules. A typical FLEX I/O module is 94mm wide, and has up to 32 I/O channels per module.
Applications with a lot of field devices benefit from high density I/O modules. Typically, these applications are found in the process industry for process automation systems.
Unlike the FLEX I/O and POINT I/O systems, which are designed to be mounted in electrical panels, the 1732 ArmorBlock panels are designed to be mounted directly on machines.
To ensure that the connections on the I/O module are resistant to dust and water, there are no terminals on the ArmorBlock I/O modules. Instead, connections are made with screw-in M12 connectors. Typically, ArmorBlock I/O modules have connection points for power, network, and between 4 and 16 I/O channels.
On-machine I/O modules are usually daisy-chained together. This means that the modules are connected in series, with the power and network connection being passed from one module to the next. To accommodate daisy-chaining of devices, ArmorBlock I/O modules have two network and two power connection points - one is used to supply power and network to the device, and the other is used to pass power and network to the next I/O module in the chain.
There are many different ArmorBlock I/O modules available for different applications but most ArmorBlock I/O modules are IP67 and IP69K rated making them suitable for washdown environments. The modules are also coated to provide increased corrosion resistance.
Generally, distributed I/O systems are designed as modular or block I/O systems. When I was describing the FLEX I/O and POINT I/O families, I mentioned that they were modular I/O systems. In contrast, the ArmorBlock I/O system is, as the name implies, a block I/O system. So, what's the difference?
In a modular I/O system, the I/O module's electronics module, terminal blocks, and network interfaces are separate pieces. These pieces can be joined together to create the total I/O rack. You can see below, how a POINT I/O module is built up from 2 or 3 separate components.
Since you can effectively build your own I/O modules, a modular I/O system is a very flexible system that can be customized to meet an application's requirements exactly.
On the other hand, a block I/O system is one where the I/O module is a single piece. Obviously, a block I/O system is less flexible than a modular system since the I/O modules cannot be customized. However, since a block I/O modules are designed as a single piece, they can be ruggedized more easily than their modular counterparts. For this reason, on-machine I/O modules tend to have a block-style design.
Safety rated I/O modules must be used in systems that are deployed to protect people. These I/O modules are specially designed around safety standards and safety principles to reduce the risk of an undetected failure in the field devices. After being designed, these I/O modules are reviewed by third parties and rigorously tested to make sure that they work (and fail) safely and correctly. Only after this test and review process are I/O modules given a safety rating.
As you can imagine, safety rated I/O are more expensive than standard I/O modules, however it is mandatory to use safety rated I/O modules for safety applications.
Safety rated I/O modules are required for machine safety applications. Machine safety applications are generally applications where machines or processes are made safe by switching them off. For example, a lift that is dangerous while running, is generally not dangerous if stopped (so long as a brake is applied!). Machine safety products are designed to make sure that motors and other moving parts stop safely if there is ever an abnormal condition. Some common machine safety applications include monitoring the status of emergency stop buttons and safety light curtains, or activating the Safe Torque Off (STO) function of a drive. In these applications, safety rated input modules are used to monitor the status of the safety devices and safety rated output modules are used to activate the STO function of the drive.
Rockwell Automation does not have a dedicated I/O system for machine safety rated I/O. Instead, they offer a safety rated version of their standard I/O modules. You can recognize the safety rated version of I/O modules because the product name includes the word "Guard". For example, the safety rated I/O modules in the POINT I/O system is called POINT Guard I/O and the safety rated version of the ArmorBlock I/O system is called ArmorBlock Guard I/O. Visually, you can spot a safety rated I/O module, because the body is coloured red.
In some modular I/O systems, standard I/O modules and safety rated I/O modules can be connected on one rack using a standard network adapter to communicate with the controller.
Safety rated I/O is only safe when used in conjunction with safety rated controller. That means that all Guard I/O products must be used with GuardLogix controllers, Rockwell Automation's safety rated PLC family.
Intrinsically safe I/O modules are I/O modules that are designed to reduce the risk of explosion in explosive environments. This is another type of safety application that is commonly found in process industries.
Intrinsically safe I/O modules must be used in Hazardous Locations. Hazardous Locations are places where flammable gas or dust may be present. An obvious example of a hazardous location is a propane tank filling station, where flammable gas may be present in the environment. A less obvious example of a hazardous location is a saw mill. A saw mill is a hazardous location because saw dust is extremely flammable.
The most important feature of intrinsically safe I/O modules is that they are designed to minimize the risk of electrical sparking that could ignite the flammable gases or dust that is present in the hazardous location.
Hazardous locations are characterized by classes, and divisions (for North America), and Zones (for the rest of the world). Rockwell Automation's 1719 Ex I/O system, which is an intrinsically safe I/O system, can be used when connecting to field devices that are installed in hazardous locations rated Class 1, Division 1, or Zone 1. The I/O modules themselves can be mounted directly in Class 1, Division 2, or Zone 2 areas.
Some applications require specialty I/O modules which provide a specialty function like redundancy. These specialty modules are not available for every I/O system and so should be taken into consideration when choosing an I/O system for an application.
In the process industry, there are some applications where downtime is so critical, that redundancy of the I/O modules is required. In a redundant I/O system, all field devices are double wired to I/O modules. If one I/O module fails, then another I/O module can take over to keep the system running without stopping. These redundant systems are often called Fault Tolerant.
Certain I/O modules can also be replaced without interrupting the operation of the system. This capability is called High Availability.
In a Logix system, 1715 Redundant I/O modules are used when I/O redundancy is required.
In this post, we have learned some of the key things that you should consider when choosing an I/O system for a Logix application. We have also learned which Rockwell Automation I/O systems can be used for different applications.
Although I tried to be as accurate as possible in this post, I always recommend checking the detailed literature for an I/O system before making a final decision.
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