Understanding the Basics of Remote Input/Outputs

To navigate the world of industrial control and automation successfully, it’s important to have a strong comprehension of what I/O or "input/output" means. Currently, there are two primary types of input/output: local I/O and remote I/O. The latter is employed more frequently in industrial networking.
 
To understand what remote I/O is, you must first be familiar with I/O in general. Essentially, I/O simply refers to a device that transfers data to or from a computer. Such devices ultimately play a critical role in the monitoring and utilization of many critical devices and instruments in the industrial control and automation industry.
 
Now that you know what I/O means, let's talk about one of its primary subsets: remote I/O. Also known as distributed I/O, remote I/O refers to an input/output device that operates in a remote location at a distance from a programmable logic controller (PLC). For example, the PLC may be in a safe space closer to a control room, while the I/O system is placed closer to the actual instrumentation being monitored and controlled, such as sensors and actuators. Ultimately, remote I/O allows I/O technology to be utilized more flexibly.
 

How remote I/O works

For a remote I/O system to work, it relies on a programmable logic controller. The PLC can process multiple points of data, including inputs and outputs. As such, these devices are capable of reading and receiving data to and from the I/O sections of the PLC device.

Such sections may range from separate I/O cards like digital input cards to fully integrated sections that have been joined with the PLC’s hardware. In any case, the PLC is the device that reads and interprets the data, not the remote I/O system. In addition, the PLC is also responsible for sending commands out while the remote I/O simply acts as a pathway for the data to get to the PLC. Thus, in many I/O setups, the PLC will be in a separate location from the I/O cards or hardware.
 
Regardless of location, the PLC must be able to receive the data collected by the I/O hardware. To allow the remote I/O portion of the hardware and the PLC to send and receive substantial quantities of information, some type of Ethernet protocol or other specialized transmission technology is typically used. Essentially, the remote I/O device will use an adapter module connected to the backplane in the PLC rack to speak to the PLC.
 

Benefits of remote I/O

When it comes to understanding the basics of remote I/O, it’s important to address the benefits that such systems can provide. Here are some of the key advantages of remote I/O:

• Less Wiring: One of the main advantages of a remote I/O system is the ability to substantially reduce the amount of wiring that needs to be run. As you can imagine, locating an I/O close to a PLC in a situation where the PLC cannot be close to the devices and instruments being monitored and controlled, a significant amount of wiring is necessary. By having the option to locate the remote I/O away from the PLC and close to the devices and instruments, however, far less wiring is used.
• More Diverse Hardware Configuration Options: Due to the flexibility that a remote I/O setup provides, a greater variety of hardware configurations can be created. As such, you will have more freedom to choose the setup that works most advantageously for your specific network.
• Facilitating Communication in Harsh Environments: In some cases, a PLC simply can’t be placed next to the field devices that need to be monitored and controlled due to harsh environmental conditions.

 In instances of extreme temperatures, severe weather, strong vibration or other harsh conditions, the PLC can be placed in a safe space—often in or near a control room—while the I/O system is located more closely to the instrumentation. Ultimately, the remote I/O will help facilitate communication with the PLC from a safe distance.
 

Potential disadvantages of remote I/O systems

While remote I/O systems have the potential to save you a considerable amount of money by reducing wiring needs, certain hidden costs can emerge if you aren’t careful. For instance, users should know that when implementing remote I/O in a system, they will need to configure all the additional I/O modules. This can take a considerable amount of time in a large system when even one module in the system is changed. Thus, you must reconfigure all the other modules as well. By being mindful of how you plan on implementing the remote I/O modules in your system, you can avoid any unexpected headaches and costs. Other potential drawbacks you should be aware of are:

• Vulnerability: All the signals being communicated in a remote I/O system rely on a single point of communication between the PLC and the remote I/O portion of the hardware. If this point becomes interrupted or lost, all of the data being received could get lost. In addition, you would likely also lose the ability to control the hardware. To minimize this risk, it is important to implement redundant communication channels within a remote I/O system.
• Hidden costs: While remote I/O systems have the potential to save you a considerable amount of money by reducing wiring needs, certain hidden costs can emerge if you aren’t careful. For example, users should know that when implementing remote I/O in a system, they will need to configure all the additional I/O modules. This can take a considerable amount of time in a large system when even one module in the system is changed. Thus, you must reconfigure all the other modules as well. By being mindful of how you plan on implementing the remote I/O modules in your system, you can avoid any unexpected headaches and costs.