A serial device server is a simple piece of hardware that nonetheless makes a crucial bridge between the old and the new. The serial device server is an easy way to add Ethernet functionality to an RS-232, RS-422, or RS-485 line. On a scale this exemplifies interoperability, a concept that is becoming more and more crucial to understand as technology advances. Interoperability is a term that describes the ways in which manufacturers, engineers, and scientists connect different technologies to achieve their expanding goals. 

The next wave of automation isn't just about new software and hardware. It's also about integrating old and new technologies into a single system.

Today's industrial automation systems are increasingly becoming "integrated." They are combining products from different vendors, or even combining different types of products — such as programmable logic controllers (PLCs) with distributed control systems (DCSs), which were once separate systems.

Integration is Driven by Several Factors

Changing technology makes it more profitable than ever to integrate what were once discrete systems. The same technologies also make it easier to integrate those systems, especially to integrate legacy analog equipment with newer IT systems.

The availability of more powerful processors and more advanced software has made it possible for end users to take on more complex tasks without having to hire outside experts in system integration.

The integration of diverse systems is at the heart of what interoperability means, but I want to explain in more detail. To make systems interoperable is to create as many seamless access points between these systems as you can. Device servers are one kind of access point, but there are many other technologies that can make for more seamless integration between systems.

Serial communication is the oldest form of industrial data transfer, the form that has just recently been overtaken by the industrial Ethernet networks. What is to be done with the millions of serial devices on thousands of serial networks that are still fully functional? Invent a type easy to use, mostly plug and play equipment that allows the user to give Ethernet addresses to their legacy hardware.

Ex 1. tDS-700 PoE Device Servers add Ethernet Connectivity to a Pump Monitoring Station.

For a first example, we will stick to the humble device server. In the example pictured below, the tDS-700 series PoE device servers are connecting a local pump monitoring station to the Ethernet based control system at a natural gas plant. The serial devices they communicate with include DAQ modules, flow meters, and power meters. Usually these sensors and devices would be part of a discrete, local control network that would have to be constantly monitored, but these PoE-capable device servers help to centralize control and free up operators for more important tasks.

The key to this system is its transparency. The tDS-700 achieves this by creating a virtual COM port that sends data through the device server. With the Virtual COM port, the controller can be miles away and still behave as though the field device is connected directly to it. In large, complex systems like those in place at a gas plant, it’s vital to remove obstacles and make data interchange as smooth as possible.

Another key to how these device servers make the two systems interoperable is in the unique way that they reduce wiring. Each tDS-700 serial device server is PoE capable. This means that each device server can receive power and data through the same wire. Another advantage that Ethernet has over RS-485 or RS-232 is the option to deliver power over Ethernet. PoE reduces the mess and expense of extra power cables, simplifies cabling, and allows users to embed the PoE device servers in remote places, or even inside machines, where it would be impossible to place a power supply.

How it Works?

Ex 2. An Ethernet bridge between multiple serial networks.

Since this is a technical document, let’s dig in a little to see how these devices work. The tDS-700 series works by creating a virtual COM port that the controller uses to talk to the serial network as though it were directly connected. The virtual COM emulates a physical COM port on the host controller while the device server assigns TCP ports and IP addresses to route the data seamlessly between the two networks.

The server handles traffic on a first in, first out basis, storing the last queried value in its cache while waiting for a response from the controller. Besides a virtual COM port, the tDS-700 series can also be used to create a pair connection (as either a serial bridge or a serial tunnel) to route data over TCP/IP between two or more serial devices. (see diagram below) This is very useful when connecting mainframe computers, servers, or other serial devices that do not have Ethernet capability themselves. This is the most basic function of a device server, but more complex, programmable device servers can be used on networks with very heavy traffic or where operators want more security, more control, or a more customizable experience.

Device servers are just one of the many technologies that make it easier to integrate different systems. Device servers serve as a great, field level example of an easy way to connect two different networks. I want to take a second to zoom all the way out. At the software level, new technology has made it possible to acquire data and control vastly different processes from one common platform. And further, with the addition of cloud servers, operators anywhere in the world can access the same data as those in the control room.

In the last few years, IIoT platforms and technologies have changed the industrial automation landscape. IIoT platforms represent the peak of interoperability in 2022. In a sense, an IIoT platform is on the complete opposite end of the spectrum from device servers, in terms of its impact, while accomplishing the same broad goal. IIoT makes it possible to integrate vastly different systems with the latest technology. Crucially, IIoT enables engineers to put data from very system under their charge into one place. With all of the historical data these systems collect, factory management can dramatically increase operational efficiency. IIoT allows the user to look at the biggest possible picture and to find the gaps and slowdowns inside of it.

The question of interoperability has been a major concern for the IIoT community. It is important that all devices, systems and applications can "talk" to each other. While device servers and IIoT platforms may represent opposite extremes, they nevertheless exist on the same spectrum. They are radically different ways to increase interoperability between networks.

Essentially, device servers are used to connect industrial automation devices — such as PLCs, RTUs, sensors and actuators — to networks using Ethernet or serial protocols. Because these devices communicate over Ethernet/serial interfaces, they can be easily connected to any network type — whether it is an Ethernet local area network (LAN), a wide area network (WAN) or the Internet.

IIoT platforms use a concept known as middleware to connect different types of devices from different manufacturers together into one system. For example, if a sensor manufacturer uses a certain protocol for its sensors and another company uses a different protocol for its actuators, then middleware can be used to bridge these two protocols so that the two can communicate with each other in real time. IIoT represents the concept of interoperability at the largest possible scale. Serial device servers represent interoperability at the smallest scale. Both are methods for integrating very different networks. Both of these technologies represent a solution to the age old problem of adapting somewhat antiquated, but still useful, technology with the latest technology as it is reaching widespread adoption.

About ICP DAS USA

ICP DAS USA is a manufacturer of cutting edge industrial automation and control hardware and software. It offers a broad range of flexible and cost-effective total solutions for various industries, including energy and power, factory and machine, agriculture, aerospace, oil and gas, etc. Its products range from M2M and "Internet of Things" (IoT) controllers and protocol converters to remote data acquisition I/O modules, supporting a wide range of protocols.

Products Mentioned

The tDS-700 Series: A series of easy to use serial to Ethernet, PoE-ready device servers that add Ethernet connectivity to any RS-232, RS-422, or RS-485 network.  tDS-700 utilize virtual COM ports to add serial control to an Ethernet controller, or they use a serial bridge or tunnel to route data over TCP/IP between serial networks.

IoTStar:IoT software developed by ICP DAS USA for users to manage and control web based remote monitoring systems in industrial IoT applications. IoTstar can be installed on a private or public IoT cloud system and provides 3 major services for IIoT application: controller remote access, sensor data collection, and data visualization.