Smarter RS-485 Remote I/O Devices

Even before the RS-485 standard was approved by the Electronic Industries Alliance (EIA) in 1998[1], RS-485 based I/O devices had been used in industrial automation and mission-critical data acquisition applications due to the communication standard’s ability to reliably transmit signals across long distances without succumbing to electrical noise.

In light of all the new technologies becoming available, it may be tempting to predict that RS-485 data acquisition devices will eventually be replaced by newer and faster alternatives like Ethernet I/O. However, RS-485 based remote I/O devices remain some of the most commonly used data acquisition devices in both commercial and industrial applications today despite their physical limitations and maintenance difficulties.

Traditional Limitations of RS-485 Remote I/O Devices
Although RS-485 data acquisition devices remain popular in the field of automation, a number of practical limitations and time-consuming maintenance problems persist. System integrators tasked with choosing between RS-485 and Ethernet I/O devices for their data acquisition networks often cite the following issues for turning away from RS-485.

Physical Limitations
Although RS-485 data acquisition devices can be used to build multi-point communications networks, the standard architecture is limited to 32 drivers and up to 32 receivers on a single (2-wire) bus. Furthermore, RS-485 data acquisition devices have no intrinsic method of avoiding data packet collisions. As a result, only one node in the entire network can transmit data to the bus at any given time, and all other nodes must wait in receiving status. If two or more nodes transmit data to the bus at the same time, all transmissions will fail.

Troublesome Troubleshooting
The process of configuring or updating RS-485 data acquisition devices can be excruciatingly time-consuming because engineers must adjust each communication parameter one by one. Replacing RS-485 devices or expanding an existing RS-485 network usually requires an engineer to bring a personal computer to various field sites to configure parameters or upgrade firmware for each field device. In a network comprised of hundreds of devices spaced up to 4,000 feet apart from each other, one can only imagine the hassle and cost of hiring an engineer to haul a personal computer from one field device to the next.

When Simple Serial Communication is Sufficient
Despite the traditional shortcomings discussed above, many system integrators continue to choose RS-485 I/O devices over faster Ethernet based alternatives due to the former’s simple design, ease of control, and low cost of deployment and maintenance. In addition, RS-485 can establish peer-to-peer communications between devices up to 4,000 feet (1,220 meters) apart before repeaters are needed, whereas Ethernet switches and I/O devices are limited to only 328 feet (100 meters) before repeaters are required to re-amplify communication signals.

Exploring New Ideas for RS-485 Data Acquisition Devices
A smarter RS-485 data acquisition device should not only be equipped with all the basic benefits of RS-485 communication, but also address the standard’s traditional limitations. Although not much can be done about the standard’s physical limitations, innovative device manufacturers can still find ways to improve upon the tried and true foundation of RS-485 serial communications.

Software Configuration Interface for Easier Maintenance
Instead of manually turning hundreds of dials and switches across an expansive field site, using software to configure all the RS-485 devices on the network would greatly reduce deployment and maintenance effort. This software should enable quick access to all the RS-485 data acquisition devices’ status information and settings in a user-friendly graphic interface. In addition, the software configuration tool should also provide an easy method for updating firmware remotely for all the data acquisition devices on the RS-485 network.


 Software Configuration Interface for Easier Maintenance

The ideal software configuration tool would also allow users to set up their RS-485 data acquisition device’s communication parameters from a remote location. So, instead of turning hundreds of dials to configure COM ports and device IDs during initial setup for all the data acquisition devices on the same RS-485 network, simply configure and duplicate the baud rate and mode for each network device through the graphical user interface. Converting manual hardware configuration to user-friendly software configuration will not only ease the effort of maintenance engineers, but also simplify the process of upgrading traditional device configurations and firmware.

“Plug and Chug” Deployment and Maintenance by USB
Although RS-485 is a relatively simple technology, RS-485 networks are not necessarily easy to maintain. In particular, companies are still required to train a specialized engineer who must carry a personal computer to the field site when remote access is insufficient. A simpler way to troubleshoot and repair field devices when field visits are necessary would not only allow system integrators to reduce labor costs, but also alleviate the maintenance effort of field engineers.

One solution is to add a USB port to the serial data acquisition device. This would serve as an alternative method for upgrading and configuring RS-485 remote I/O communication devices and firmware if remote maintenance was not feasible. All the engineer needs to do is upload the configurations onto a USB drive, bring the USB drive to the field site, plug it into the field device’s USB port, and all the configurations and firmware updates will upload to the field device automatically.


Dual RS-485 Ports for Backup and Redundancy 
Even though packet loss and transmission failures are common issues encountered by RS-485 networks, these problems can be easily prevented. System integrators for mission-critical applications generally deploy some type of backup system or redundant network to ensure that devices operate continuously without failing. If an RS-485 data acquisition device were equipped with dual RS-485 ports, system integrators could easily set up dual wiring or dual computer redundancy to back up their network.

For wiring redundancy, when the central computer detects that one of the RS-485 connections is not responding, it can quickly switch over to the other RS-485 line to guarantee continuous communication between the field sensor and the central computer. Alternatively, the additional RS-485 connection on the I/O device could connect field devices to a secondary computer on a local network to provide system operators with a secure backup in case the primary system goes down.


Although dual RS-485 ports are nothing new, an additional RS-485 port enables maintenance engineers to test or repair an I/O device more quickly when one of the RS-485 ports is damaged. So even though RS-485 remote I/O devices are already considered a low-cost technology, the addition of dual RS-485 ports can help system integrators save even more down the road without compromising on reliability.

ioLogik R1200 series: The Next Chapter in the Legacy of RS-485 Data Acquisition DevicesRS-485 serial devices like Moxa’s ioLogik R1200 series RS-485 remote I/O devices not only provide all the basic benefits of RS-485 communication, but also address the common limitations of traditional RS-485 remote I/O devices. In particular, time-consuming maintenance can be greatly reduced by introducing user-friendly improvements like the ioLogik R1200 series’ communication configuration via ioSearch software, uploading configurations or firmware via USB, dual RS-485 ports, and built-in repeater. These are all practical solutions that can help enterprises around the world integrate RS-485 I/O devices into an existing network, ease maintenance effort, reduce costs, and generate business growth at the same time.

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