Engine Manufacturer Integrates Operator Interface

Natural gas fields provide energy to millions of homes and factories. Because the nearest gas fields are typically far from cities and towns, miles of pipelines make the connection. To push the gas from field to town requires an engine/compressor—the equipment that puts the gas under pressure and causes it to flow.

11/01/2004


Natural gas fields provide energy to millions of homes and factories. Because the nearest gas fields are typically far from cities and towns, miles of pipelines make the connection. To push the gas from field to town requires an engine/compressor—the equipment that puts the gas under pressure and causes it to flow.

Explaining the business of a natural gas operation, Cam Dowler, general manager at REM Technology Inc. (RTI) in Calgary, AB, Canada, says, "A natural gas operation must get the gas out of the ground as quickly as possible. That's because competitors often have drilled into the same natural gas field. Production is not limited by consumption, because we can put the extra gas in storage caverns. The operation that has the most productive and efficient engines wins." (REM is an abbreviation for Reciprocating Equipment Management.)

RTI develops engine/compressor control solutions for its Canadian-based parent, Spartan Controls Ltd., which has been serving the process controls industry for more than 35 years.

Engines cost $500,000 to $7 million, and can last 30 to 50 years, or more. Furthermore, the compressor can earn from $5,000 to $25,000 per hour for the user company. "But old controls cannot get as much production from each engine as we need today," Dowler says, "and now we monitor additional conditions, such as exhaust temperature and oil pressure, and shut down the engine automatically when necessary."

Cost of the equipment and length-of-service requirements make engine reliability extremely important to a natural gas operation. Tapping into that reliability, Dowler says, all boils down to how the operators interact with the engine.

"The interface unit must be rugged and reliable," he says. "The touchscreen must work with operators' big, greasy fingers. And some of these engines are two stories tall; you can feel the ground shaking 200 feet away and, of course, the vibration reaches the interface. In addition, the temperature in which these systems operate is essentially the same as it is outdoors, and Canada's winters can get extremely cold."

Interface performance

The newest engine controller from RTI is REMVue (Vue refers to the Xycom HMI screens on the controller). Design goals for REMVue were aggressive. Dowler notes, "We wanted an engine controller that was 30% more powerful and cost 30% less. Also, we needed at least a high-performance four-line by 80-character display."

A solid NEMA rating was required for the interface to operate in the application. Xycom's operator panels are rated NEMA 4 (Class 1 Division 2).

Because competitors required the use of a laptop PC to configure their controllers, Dowler says RTI wanted to incorporate all the configuration screens within the HMI. They did this by using Xycom's GLC (graphic logic controller).

"Of the 350 screens, the operator only uses about 15; the rest are for configuration and diagnostics," explains Dowler. "With built-in three-level password protection, operators and technicians access only what they need."

Adding to HMI needs, the compressed gas passing through gas field engines/compressors, often powers them. Using HMI screens, a system integrator can configure cylinder count, fuel type, air-fuel mixture, ignition timing, and precombustion, accommodating many engine types. The controller automatically compensates for the energy content in the fuel.

According to Dowler, REMVue end-users report annual fuel savings in the tens of thousands of dollars per engine—a sum that becomes even more significant considering that one facility can house as many as 25 engines.

Programming environment

Though Xycom's GLC handles control functions via ladder-logic programming, REMVue uses an embedded controller to implement and protect RTI's patented fuel-air control methods, and perform a dozen or more high-speed PID loops. Controller and HMI communicate via Modbus protocol on a 115 kbits/second serial link, using the GLC as the master.

John Demuth, engineering and operations manager at RTI, says, "In REMVue, we are using GP-Pro software, Xycom's Microsoft Windows-based development environment. This allows users to select a screen object and modify anything about it, including orientation and tags. GLC can run D-scripts that are similar to Basic. Local D-scripts run upon entry to a screen, and global D-scripts run in the background. We use scripts to do data collection and trending."

After exporting the tag names to Modbus variable names, the names were then put into CSV (comma-separated value) format and imported to the symbol table in GP-Pro, Demuth explains. "This gave us a one-to-one mapping," he says. "After placing a screen element, we use the drop-down menu and choose the symbol name. After that, we change the Modbus mapping by updating only the symbol table."

The data-logging feature acts as a historical data keeper, allowing the operator and field technicians to go back in time when they are troubleshooting an engine. In addition, GLC's graphing feature provides REMVue with trending capabilities.

Network connectivity

Each REMVue system operates as a stand-alone engine controller; connectivity helps in managing multiple units.

"REMVue can connect to the plant network via either the embedded controller or Xycom GLC," says Demuth. "A network server then communicates with each REMVue. We can even start and stop an engine remotely in this way, as well as monitor all data available at the HMI."

Xycom's server-based GP-Web application monitors GLC operator panels via the plant network, and then makes the data available to a PC client via a Web browser. No special programming is needed—just an initial, menu-driven configuration.






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