How to improve process control using RTU's

Here, Matthew Hawkridge, Chief Technology Officer, answers questions about Remote Telemetry Units and why they help improve security, productivity, safety and operations.


Where are RTUs used in process industries? 

Remote telemetry units (RTU) are widely used in the industrial sector for process automation and control as part of a supervisory control and data acquisition (SCADA) system. Effectively, RTU’s are mini-computers that collect data locally, act upon it immediately, and report securely to the central control room, whilst maintaining a local historical store as an additional backup.

Although RTUs were traditionally used to monitor and control remote field devices, they are now routinely specified for industrial processes as engineering, operations and planning teams gain a better understanding of their benefits. In these applications, the RTU connects to a plant control room or SCADA, providing a low latency response to changing process conditions as well as performing data filtering. They ensure that only key, critical information is passed securely via the narrow communications links, minimising data throughput but maximising useful information received.

How are RTUs different to sensors and PLCs?

RTUs, the field part of a SCADA system, are used to translate the physical world into digital and then send this data for storing, trending, analyse and action. Sensors are simpler devices, which means they are not designed to interpret protocol communication on their own like RTUs. That’s why RTU’s play a crucial role in digitising the inputs from sensors into protocol format and transmitting them to SCADA. The SCADA then issues control commands back to the RTU which in turn transmits electrical signals to control relays.

The move to ‘digitization’ in industrial processes means that, historically, sensors were used to collect information. However, as good as sensors are at improving efficiency and assisting the move to automation, they only offer a partial solution. RTU’s are specifically designed to address these limitations - gathering data locally, analysing it, acting upon it, and reporting the resulting information to the control centre.

The main difference between an RTU and PLC is that the former is highly suitable for assets spread over wide geographic areas because they use wireless communication. PLCs can be better suited to local controls, although there is now much overlap in functionality between the two and cost effectiveness of latest RTU’s mean they are often used for ‘near’ location assets, too.

What are the advantages of an RTU over a PLC?

The single biggest advantage of an RTU compared to a PLC is that the environmental robustness of the former makes it the stand-out choice for demanding industrial and manufacturing applications.

That means RTU’s can be used in localities with extreme climatic temperatures and/or remote locations that are off the power grid. For instance, Kingfisher RTU’s have been selected as high availability process controllers with extensive communications capabilities for sites with temperatures ranging from -40C to +85C.  Their resilient and secure nature, combined with independent communications links, redundant power supplies and redundant process controllers make them an extremely robust solution in these applications.

Again, RTUs can perform autonomous control in real time and then report to SCADA that it has everything under control. Engineers at the SCADA interface can ‘supervise’ the operations by setting new KPIs (Set Points) or updating instructions (open/close this, start/stop that, for example) for RTUs to then act upon and manage locally.

How can RTU’s help improve efficiency?

RTU’s operate in a similar way to PLCs. Both are controllers that can have multiple different types of I/O, different communications modules, and programming of processes. This allows them to act without operator intervention in a wide range of process control situations.

However, if there is a communications breakdown or a failure of AC power, the RTU will continue to operate and maintain site control. In these situations, algorithms in the RTU allow it to act autonomously, keeping the production process running. Data extracted from assets can be stored in the cloud, analysed using customized embedded algorithms and data analytics to identify problems before they cause equipment down time.

With the RTU acting as the site co-ordinator and maintaining a full history of events, engineers have a better understanding of the site conditions both in a live environment and historically.

The key features needed in an RTU are security and resilience to the site environment, an ability to operate with minimal drain on local power resources and the processing power to perform local control algorithms autonomously. It is also beneficial to have extensive diagnostics capability and a low MTTR (Mean Time To Repair) to reduce the time required for engineer to spend on site, improving both efficiency and personnel safety.

A challenge in remote areas is power supply, which is the reason why the RTU should incorporate intelligent management of power consumption as well as battery or solar power sources.

What are the benefits of ‘information’ gathered by RTUs?

Information gathered, analysed and interpreted by RTU’s provide the operator with the tools to improve efficiency, safety and maintenance costs. Achieving these goals requires RTU’s to collect additional data points from a vast range of equipment. For instance, new data points may replace manual dips tests to verify the accuracy of primary level sensors, track product density to ensure that the right product is in the right vessel or monitor product temperatures, inert gas blanket supply and pump vibration.

There are benefits for engineers overseeing remote sites that are vulnerable to theft and vandalism, too. Deploying a suite of RTUs for the monitoring of equipment ensures a cost-effective and safe way to protect physical assets at these locations. The opportunity list is virtually endless.

Are RTU’s cyber secure?

Until relatively recently, industrial networks were isolated from IT networks however, now they are deeply interconnected and as such need to be robust against cyberattacks. As a result, RTUs need to incorporate a range of security measures such as: Firewall SSL (Authentication & encryption), HTTP, FTPS & SFTP, SMTPS and open VPN. Auditing should be carried out regularly according to IEC 62443 4 2 and ISO 27019.

Can RTU's facilitate IIoT?

There has been a significant improvement in RTU processing power and memory recently, which means they are capable of running and storing data in the most challenging of applications. This increased processing power is helping facilitate Industrial Internet of Things (IIoT). A significant area of opportunity is the ability of IIoT to create smart assets, even those that are part way through their lifecycle. For example, deploying RTU’s with latest processing power on an old asset can turn it into ‘smart’ asset. This helps engineers to make the most of their aging equipment and reduce lifecycle costs.

This article was featured on Process & Control Today.