Capturing far-flung data
Advancements in RTU technologies help optimize data acquisition and control.
The use of remote terminal units (RTUs) began in the U.S. oil and gas industry in the 1980s, and has expanded to utilities, environmental protection, heating networks, water conservancy, and long-distance pipelines.
Microprocessor-controller RTUs have evolved to help industrial organizations effectively deal with large distributed operations. Tightly integrated with supervisory control and data acquisition (SCADA) systems, they provide new insights into the production potential of distributed assets through efficient remote monitoring, diagnostic, and asset management capabilities.
This discussion will take a look at recent advancements in RTU technology, which optimize data acquisition and control capabilities in a wide range of industry applications.
Remote data monitoring is required in a host of industrial settings, including oil and gas, power, wastewater, and environmental monitoring. The common element is monitoring a variety of items that are spread over a large geographical area. A large number of RTUs installed in remote and/or hazardous locations may be used to log data and alarms from sensing or metering devices and send this information to a SCADA system in a central control room. The RTU may also receive data from the central station for process execution.
The term SCADA usually refers to centralized systems which monitor and control entire sites, or complexes of systems spread out over large areas. One useful definition is that SCADA handles things outside the plant fence, while a DCS (distributed control system) controls more densely packed items in a plant or process unit.
An RTU operates by scanning its inputs—usually at a fairly fast rate. It may also do some processing such as change-of-state processing, time stamping of changes, and storage of data awaiting polling from the SCADA master. Some RTUs have the ability to initiate reporting to the SCADA master while others rely on the SCADA master to poll the RTU and request changes. The RTU may even handle alarm processing, particularly on degraded or low-bandwidth networks with slow update rates where SCADA-only alarming could miss a significant event.
The data acquisition functions of an RTU in a SCADA system can be quite diverse. The device is designed to read both analog measurements and digital status data. It contains setup software to connect data input streams to data output streams, define communication protocols, and troubleshoot installation problems.
In many industrial applications, data acquisition begins at the RTU level and includes meter readings and equipment status reports that are communicated to the SCADA system as required. Data is then compiled and formatted in such a way that a control room operator or pipeline controller using the HMI (human-machine interface) can make supervisory decisions to adjust or override normal controls. With large quantities of RTUs performing a similar monitoring and control function, tabular summaries are the norm. This differs from a DCS where process-orientated displays are common. In addition, data may be supplied to a historian to allow trending and other analytical auditing.
There are two basic types of RTUs on the market. One is a single board RTU, which is compact and contains all I/O on a single board. The other is a modular RTU, which has a separate CPU module and can have other modules added—normally by plugging into a common backplane.
Today’s RTUs feature more versatile programmability and broader communication and protocol support. They also add greater flexibility to remote control applications. For this reason, RTUs are now widely used in mission-critical industrial automation environments. For example, rapidly developing “green” industries, such as solar power plants, wind power plants, and smart buildings, are new applications for RTUs.
RTUs are gaining popularity for a variety of reasons:
- In a competitive business environment, enterprises have an ever-greater need for information. Some measurements were previously given up because they were scattered and the cost to collect data was too high. In the era of “big data,” data collection is increasingly viewed as an operational priority.
- As business and production operations expand in size, they can span wide geographical areas, making localized support an expensive exercise. Central management requires remote data collection even in the most dispersed enterprises.
- Enterprises that may have discontinued remote data collection because of high investment requirements are finding it advantageous to implement today’s less expensive smart RTU systems.
- Emerging 3G and 4G networks, along with new types of wireless instrumentation, have resulted in RTU signal transmission methods which are both reliable and cost-effective.
- Affordable photovoltaic technology and improved batteries, combined with new low-power RTUs, makes it possible to place RTUs in locations not previously considered economical.
There have been significant developments in recent years in RTU hardware and software technologies. These developments have enabled more choices in the instrumentation that can be put into the field and the data that can be brought back to the control room. While conventional RTUs are based on proprietary operating systems and architectures, the newest instruments have adapted embedded system technology, resulting in products that are more cost-effective and extremely flexible.
RTU designs have advanced to offer enhanced communications, database, and signal transmission capabilities. The devices feature low power consumption and serve as bridge points to sensor networks, as well as access points to mobile users in the field. They also respond to users’ queries and collect data from specific sensors.
Modern RTUs go a step further by combining advanced features for automation, monitoring, and telemetry in a single unit. They are often equipped with Internet protocol (IP) and Web capabilities allowing users to access site information by mobile phone, tablet, or laptop, with Web pages served via the Internet or intranet, e-mail, and text messaging (See Fig. 1).
The new breed of RTUs is designed to help industrial companies oversee and maintain large distributed operations encompassing hundreds or even thousands of remote production assets. These operations involve complex remote automation and control applications.
Integration of RTUs with SCADA systems allows users to realize the production potential of distributed assets through efficient remote monitoring, diagnostic, and asset management capabilities. Some products are designed to optimize these applications through built-in, onboard smart I/O such as HART, with integration of field device management for interrogating instrument data and diagnostics as well as running methods like valve signatures—all via the RTU.
Suppliers have also made significant strides in improving the overall user experience with RTUs. For example, incorporating removable, plug-in terminal blocks—which simplify wiring and shorten the time required for cabinet assembly—eases installation and configuration requirements.
Additional improvements include modular designs for future expansions and bulk replication capabilities. Robust batch configuration tools allow a user to copy the configuration from one template to multiple RTUs, as well as create multiple RTUs in one task. Unique RTU parameters can then be updated from a single page across all copies.
The days of putting personnel in cars and trucks at a drop of a hat to travel to remote sites is coming to an end. It is not only an expensive exercise, but also an unsafe one—and that is just the trip to the site. The traditional RTU strengths of data logging and good sub-system communications with local devices alongside the newer smart device integration with HART is enabling better fault modeling, both direct on the RTUs and at central locations. This means better decisions can be made about the actual health of the remote asset, possibly delaying a site visit for maintenance to a future, previously scheduled trip.