34 n CONTROLS November/December 2024 www.drivesncontrols.com Understanding how remote I/Os work To navigate the world of industrial control and automation successfully, it’s important to have a good idea of what I/O or “input/output” means. Currently, there are two main types of I/O: 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 rst be familiar with I/O in general. Essentially, I/O simply refers to a device that transfers data to or from a computer or controller. Such devices play a critical role in the monitoring and utilisation of many critical devices and instruments in industrial control and automation. 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, this refers to an I/O device that operates in a remote location at a distance from a PLC. For example, the PLC may be in a safe space near a control room, while the I/O system is placed closer to the instrumentation being monitored and controlled, such as sensors and actuators. Remote I/O allows I/O technologies to be used more exibly. How remote I/O works For a remote I/O system to work, it relies on the PLC, which can process multiple points of data, including inputs and outputs. These devices are capable of reading and receiving data to and from the I/O sections of the PLC. Such sections may range from separate I/O cards such as digital input cards, to fully integrated sections that connect with the PLC’s hardware. The PLC – not the remote I/O system – is the device that reads and interprets the data. In addition, the PLC is also responsible for sending commands out, while the remote I/O simply acts as a pathway for data to reach 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 hardware and the PLC to send and receive information, some type of Ethernet protocol or other specialised transmission technology is typically used. Essentially, the remote I/O device will use an adapter module connected to the PLC backplane to speak to the PLC. It is important to consider the benets that remote I/O systems can provide. These include: n Less wiring Remote I/O can substantially reduce the amount of wiring that needs to be run . If a PLC cannot be close to the devices and instruments it is monitoring and controlling, a signicant amount of wiring is necessary. Locating the remote I/O away from the PLC and close to the devices and instruments, means that much less wiring is used. n More diverse hardware con guration options Due to the exibility that remote I/O provides, a wider variety of hardware congurations can be created. You will have more freedom to choose the set-up that works best for your network. n Facilitating communication in harsh environments In some cases, a PLC cannot be placed next to eld devices because of harsh environmental conditions. In cases 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. Potential disadvantages While remote I/O systems have the potential to save you a considerable amount of money by reducing wiring, hidden costs can emerge if you aren’t careful. For instance, users should know that when implementing remote I/O, they will need to congure all of the additional I/O modules. This can take a considerable amount of time in large systems if even one module is changed, requiring you to recongure all of the other modules as well. By being careful in how you implement the remote I/O modules, you can avoid unexpected headaches and costs. Another potential drawback is that all of the signals communicated in a remote I/O system rely on a single point of communication between the PLC and the remote I/O. If this becomes interrupted or lost, all of the data being received could be lost. In addition, you would also probably lose the ability to control the hardware. To minimise this risk, it is important to implement redundant communications channels in remote I/O systems. n Remote I/O systems can help to separate PLCs from challenging eld conditions. Henry Martel, a eld application engineer at Antaira Technologies, explains how they work and some precautions that users need to take. Managed switches, such as this eight-port Gigabit Ethernet device, oer a way of connecting devices such as PLCs, remote I/Os, sensors and other equipment, in industrial networks
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