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Advanced Diagnostics increase process visibility

Processes are increasing in complexity, while lead times continue to be cut. Plant operators, challenged to reduce maintenance costs, increase uptime and improve product quality, are finding diagnostics to be a critical part of the solution.

Emerson Process Management and customers like Mitsubishi Chemical therefore, continue to extend the applications of the Rosemount 3051S Series Scalable Pressure Transmitter’s Advanced Diagnostics capabilities.

According to Bill Zhou, senior product marketing engineer with Emerson Process Management’s Rosemount Division, the Advanced Diagnostics technology takes advantage of the HART digital protocol’s ability to carry diagnostic information in addition to the regular pressure value.

Advanced Diagnostics uses this capability to provide information like standard deviation, coefficient of variation and other background noise values. Advanced Diagnostics consists of two parts: Statistical Process Monitoring (SPM) and Power Advisory Diagnostics.

Useful information
SPM consists of a module built into the 3051S which learns and checks the process signal automatically, turning process noise and variation signatures into useful information about the dynamic process. Changes in these signatures indicate a significant change in the process, equipment, or transmitter installation will occur or has occurred.

“Traditional transmitters have certain types of diagnostics that tell you when the device has failed or certain elec tronics have gone bad,” said Zhou who is based in China. “SPM provides addi tional capabilities that we have added to the transmitter which allows it to look at issues that may be happening outside of the transmitter and in the process.”

Software plays a key part in SPM, by correlating changes in process noise as a way to detect process abnormalities. The software also filters the data to separate slow changes in the process from the process noise or variations of interest.

Meanwhile, Power Advisory Diagnostics detects and diagnoses electrical loop issues from the pressure transmitter back to the control system. “Power Advisory looks at the integrity of the electrical loop, checking from the terminal connection all the way back to the digital control system, or whatever is powering the transmitter,” explained Zhou.

Traditional pressure transmitters send outputs blindly, with no guarantee of the signal’s integrity as it travels through the wiring of the plant.

Common issues include corrosion build-up and water in housing from leaky conduits, both of which can skew the signal on the line.

“There are cases where the transmitter is sending out 4 mA, but the DCS is reading 12 mA, because analogue signals can be affected by phys ical changes in the environment,” Zhou told PACE magazine. “Power Advisory looks for these changes on the loop.”

Power Advisory Diagnostics works via a learning module within the trans mitter. When first installed, the module learns the baseline value of the electrical loop by recording the terminal voltage when the output is at 4mA and 20mA. By drawing a linear relationship from 4 mA to 20 mA outputs, the module calculates the loop resistance, the power supply value, and the amount of power being received by the transmitter.

During operations, the transmitter detects deviations of the terminal voltage from the linear relationship, indicating changes in resistance or the power supply value, which are possible symptoms for physical issues in the line, or a malfunctioning power supply.

The information provided by both parts of the Rosemount 3051S Advanced Diagnostics allow for increased visibility into processes and loops, opening the way for more advanced analysis and detection methods.

Advanced Diagnostics is based on high speed sensing hardware such as the 3051S pressure transmitter, combined with software. According to Mitsubishi Chemicals, the Rosemount 3051S updates 22 times per second, so SPM provides high resolution process profiles. Distributed control systems only update two times per second.

The proximity of the pressure trans mitters to the process allow them to quickly sense variations and events as they happen, allowing process engineers to have additional insight into real changing process conditions.

Power Advisory naturally offers the advantage of providing an integrity check on the signal from the transmitter.

Zhou says any HART system can use Advanced Diagnostics, including systems with HART cards, or systems with analogue I/O. The data can be pulled in as alerts or as SPM variables.

There are also possibilities for using Advanced Diagnostics with the WirelessHART protocol. Users can use the Smart Wireless THUM adapter on powered devices in order to transmit HART data. According to Zhou, this means a lot of existing installations can apply Advanced Diagnostics.

Extending applications
According to Zhou, Mitsubishi Chemical has been particularly innova tive in its use of the Advanced Diagnostics system. “They extracted the data that we provide as another HART output variable, put it into their own historian, and set their own limits.”

The system allowed the team at the Mitsubishi Chemical First Ethylene Plant, based in Kashima, Japan, to deter mine root cause in dP flow inaccuracies, verify if a pump issue was fixed, detect entrained air of pump inlet suction line, detect the partial blockage of two impulse lines, and sense strong winds.

At the 2010 Emerson User Exchange, Zhou and Takayuki Aoyama, instrument group leader at Mitsubishi Chemical, presented a session titled “How Process Insight Leads to Actionable Information at Mitsubishi Chemical”. In the presentation, Aoyama highlighted how Mitsubishi Chemical found new uses for the Rosemount 3051S Advanced Diagnostics functions.

In a part of the refinery process at the plant, a coke separator and filter is used for sludge removal. The nature of the task causes sediment to build up on remote seals with time, resulting in plug ging at the multiple measurement points and making it hard to monitor the process. Constant and frequent mainte nance was needed, but the technicians lacked the insight into when such actions would be needed.

Aoyama says Mitsubishi Chemical places a lot of focus on diagnostics and maintenance, as the plant does not often build new processes. They decided to take advantage of Advanced Diagnostics during system upgrades.

The team replaced the classic 4~20 mA capillary type transmitter being used in the sludge-removal process with the 3051S Advanced Diagnostics, gaining better insight into the process.

“When we installed the new tech nology, we didn’t want to use just critical analogue transmitters because they have less diagnostics than the HART protocol. The new diagnostics helped our facility reduce maintenance costs, and also we can prevent problems with the diagnostics functions,” Aoyama told PACE magazine.

Appropriate actions
The Standard Deviation graph generated by the 3051S SPM allowed operators to pinpoint the occurrence of a plug and take the appropriate actions to alleviate the condition.

3051S SPM was also used to detect the occurrence of a sticky valve in a heavy duty high pressure process. A recurring sticky valve on a reboiler made it difficult to control the temperature of a distillation column.

According to Aoyama, trending data provided by the 3051S SPM allowed detection of the sticky valve as early as 19 minutes in advance of the traditional method in the DCS.

Mitsubishi Chemical also ran a field trial on Power Advisory. Aging equip ment in the plant means some junction boxes in the field can be flooded, or be subject to moisture, resulting in corrosion. The 3051S was able to send an alert when the linear relationship between the terminal voltage and output current exceeded the threshold, or on detection of an abnormal situation.

Tests by interns found the transmitter could detect problems in the loops before the output is affected, allowing corrections to be made quickly.

Emerson Process Management says it has been listening very closely to its customers for the Advanced Diagnostics functions, working with end users who are early adopters of technology. “We’ve gotten a lot of feedback from Mitsubishi Chemical that has helped us to open our eyes to different applications with SPM,” Zhou said.

At the beginning of November 2010, Emerson Process Management announced an expanded Advanced HART Diagnostics Suite for the Rosemount 3051S Series of Instrumentation.

Dave Wehrs, vice president of pressure design and engineering for the Rosemount Division of Emerson Process Management, said, “The expanded capabilities of Advanced Diagnostics on the Rosemount 3051S gives plant personnel additional insight into their facilities, which they can use to make informed decisions.”

Aoyama says the experience of Mitsubishi Chemical holds many possi bilities for plant operators. “Some (plant problems) can be detected online with these diagnostic functions before malfunction occurs. It is possible to reduce maintenance costs and the number of problems,” said Aoyama.

At the Emerson Users Exchange, Aoyama also urged users to help improve the diagnostic functions, by sharing their experiences with vendors and other users.

[PACE magazine’s Isaac Leung attended the 2010 Emerson Global Users Exchange in San Antonio, Texas.]

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