Predictive Maintenance Widens Its Acceptance

By Frank J. Bartos, Control Engineering July 1, 1999

Predictive maintenance is the most sophisticated of industrial maintenance and asset management techniques. It’s an evolving, forward-looking method that combines hardware elements–for sensing and collecting information about equipment operation–with software elements for analyzing and managing the data. Actually, predictive maintenance employs a collection of nondestructive methods to do its work; for example, vibration analysis, oil wear particle analysis, infrared thermography, various electric motor circuit analyses, motor parameter monitoring, etc.

Predictive, more than preventive Sophisticated numeric analyses then go on to estimate machine health and predict remaining life of equipment, using historical as well as operational data. This brings two benefits. Users can maximize the useful life of machinery and plan realistic, cost-effective equipment change or maintenance schedules. In this way, predictive maintenance is a step ahead of preventive maintenance.

Preventive maintenance also works with comprehensive historical databases and can shift plant downtime to noncritical periods. However, such maintenance efforts are inherently conservative. Equipment is indeed replaced ahead of its failure (or that of the connected process), but replacement is often premature or unnecessary at the time performed.

Historically, predictive maintenance systems appealed to the more critical machinery in a processing plant or manufacturing facility because of risks to the business and high initial cost of these maintenance systems. And ‘critical equipment’ often–though not always–meant large, costly machinery, such as turbines, generators, and very large electric motors.

Today, the cost of predictive maintenance systems is trending down. As a result, predictive methods will find wider application with more types of industrial equipment receiving the benefits.

More about suppliers, products Numerous suppliers exist in the fields of predictive and preventive maintenance. Product and system offerings likewise are on the rise. Here’s an expansion of products and companies beyond that covered in the main article.

Besides rotordynamic products (see main article), Bently Nevada (Minden, Nev.) offers tools for thermodynamic assessment of machinery. Its Performance Manager 2000 (PM2000)–an integrated mechanical and aero/thermal condition software–fits this category. PM2000 uses Microsoft Windows NT and 95 operating systems, as is the case for all the company’s software.

Among members of Bently’s 3500 Series Machinery Protection System family is 3500/92 Ethernet Communications Gateway, which enables 3500 Series devices for TCP/IP Ethernet communications over the user’s dedicated machinery information network or a shared plant LAN. The gateway talks to distributed control systems, machine control systems, PLCs, and other plant computers via Modbus/TCP (Modbus over Ethernet) protocol, according to Bently Nevada.

Machine critical parameters such as oil pressures, temperatures, and flows are often available from a transmitter as a proportional voltage or current (i.e., 4-20 mA). These measurements can be used to protect machinery and provide critical indication to operators. Process Variable Monitor 3500/62 incorporates such measurements into the 3500 system as a simplified integrated machinery protection platform for all critical parameters.

TDIX, Bently’s main communications processor, has been enhanced with TDXnet for faster information handling via Ethernet. With TDXnet Ethernet extension, the communications processor works fast enough in conjunction with Data Manager 2000 software to support real-time viewing of data during machine start-up or coast-down conditions. Downloads to and from DM2000 are said to be 20 times faster with TDXnet.

Bently Balance, a software product for complex balancing of rotating equipment in the field or at a test stand, is one of Bently Nevada’s newest products, with availability set for 3Q99. It will feature sophisticated tools for balancing single- or multiple-rotor systems, and a highly graphical user interface to allow, among other things, ‘what if’ viewing of predicted rotor system response for different balance weight placements, says the company.

Bently Nevada provides global technology to protect and manage rotating and reciprocating machinery. Application areas include turbines, generators, large electric motors, etc., but, as noted in the main article, these methods are starting to reach down to smaller and more varied machines.

National Instruments (NI, Austin, Tex.) provides computer-based instrumentation and software tools used in machine-condition monitoring. NI emphasizes the positive role of PC-based systems for predictive and preventive maintenance applications.

‘With its increasing power and connectivity, the PC provides the platform of choice for predictive maintenance operations. In fact, PCs revolutionize how industrial measurements are connected to existing and future automation systems,’ comments Ryan McDonald, NI’s automation software marketing manager.

Instrumentation for machine monitoring continues to evolve. One example mentioned by National Instruments is the use of new fiber-optic sensors for continuous measurement of combustion pressure in large-bore stationary engines. Here, PCs meet several challenges of integrating new sensors with existing, older engine monitors and controls. PCs also simplify data acquisition from networked sites.

Liberty Technologies (Conshohocken, Pa.), a division of Crane Nuclear Inc., supplies nondestructive evaluation systems/services, condition monitoring, and diagnostics to optimize equipment and plant performance. Its proprietary products monitor condition and performance by gathering and interpreting operating data on valves, turbines, engines, compressors, motors, motor-driven equipment, pumps, and fans. Advanced diagnostic technologies plus comprehensive software analysis permit plant operators to avoid unplanned downtime, improve asset usage, and increase plant safety.

Valve testing equipment comprise a major solution area at Liberty. A product example here is ValveVision, a portable instrument that tests process control valves for performance without the need for costly disassembly. ValveVision accurately measures friction forces between the valve stem and packing, along with seating and unseating forces of the valve. The instrument interfaces to a PC by means of the serial port or the PCMCIA slot.

Motor management solutions represent another Liberty Technologies product sector. Offerings include both permanently mounted and portable devices. Motor Performance Tracker, an on-line device mounted at the motor control center, continuously monitors performance and efficiency of critical ac motors and predicts potential failures. The ‘tracker’ continuously samples motor condition, performance, and power quality, while making 40 diagnostic checks. Motor data are easily downloaded to analysis software for trending and reporting. Motor Performance Analyzer is a compact, portable field instrument that provides electrical and mechanical performance analysis of large three-phase motors while they operate.

Importance of motors Electric motors represent a huge installed base of equipment in industry. Monitoring motor health maximizes productivity of the processes and machines they run and protects users’ motor investments, as well.

Rockwell Automation/Reliance Electric’s (Greenville, S.C.) IQ Intelligent motor with PreAlert technology is an example of just how far technology has come in the area of monitoring machinery health. Major components of the motor, such as electrical windings, bearings, and rotor can be ‘electronically inspected’ using embedded sensors, logic, and onboard microprocessors of IQ PreAlert technology. It provides reliable early warning to incipient motor failure via software. IQ PreAlert (Control Engineering, Nov. `97, p. 7; March ’98, p. 96) is available for ac induction motors of 2 to 500 hp (1.5-375 kW). Data storage and retrieval comply with the format of MIMOSA relational data schema (see MIMOSA online item and sidebar in main article).

However, motors are destined for larger roles in predictive maintenance. The next generation of intelligent products will likely provide prognostic as well as diagnostic information. With emerging condition monitoring methods, the motor itself can become a ‘sensor,’ monitoring the connected process, not just the motor.

IQ Intelligent motor is still exploring its market boundaries. For example, Richard Schaefer, customer service manager for Rockwell Automation’s Athens Motor Plant, (Athens, Ga.), mentions pump maintenance as a promising application of IQ PreAlert technology.

Today, Rockwell Automation/Reliance is working closely with universities and a leading pump manufacturer to develop the next generation of intelligent motor/pump system. ‘Key to this activity is development of advanced algorithms to analyze the collected data based upon known equipment design characteristics. This integration of inherent machine design criteria and actual operational data will unlock the door to understanding operating conditions of a complex system,’ says Mr. Schaefer.

Another notable condition monitoring system for all sizes of ac motors is MotorStatus from Computational Systems Inc. (CSI), a division of Emerson Electric (St. Louis, Mo.). The self-contained version of MotorStatus mounts to the motor to collect and store information on motor operational and cumulative effects. Associated software displays conditions and trends by comparison to preset thresholds. Alarms alert the user if limits are reached or if deeper diagnostics are needed. This product version was covered in the main article.

An embedded version of MotorStatus is coming with a launch date slated for April 2000. This version is intended for ac motors in the 40-200 hp (30-150 kW) range working in severe, corrosive process industry environments. The new MotorStatus product is a joint technology of CSI and U.S. Electrical Motors. It will be embedded in USEM motors for North American markets and in motors from Leroy Somer for European markets. USEM and Leroy-Somer are also divisions of Emerson Electric Co.

Recent improvements to EMPATH (Electric Motor Performance Analysis and Trending Hardware) system from Framatome Technologies Inc. (FTI, Lynchburg, Va.) include remote unattended monitoring capability for motor testing and a triggering feature that determines if the motor is operating prior to data collection. Remote monitoring applies both to motors that run only occasionally and for continuous assessment of critical motors.

FTI says these improvements have helped to increase sales of EMPATH systems. In 1998, EMPATH system customers included The Boeing Co. (its ninth EMPATH purchase), Eli Lilly Pharmaceuticals, Taiwan Power, and Florida Power & Light with two sales for use in nuclear generating stations.

FTI is a leading provider of products and services to U.S. industry including commercial nuclear utilities, the U.S. Department of Energy, and other industries. It supplies a variety of advanced engineering, inspection, diagnostic and repair, and chemistry and waste-processing services, as well as advanced robotics, and I&C systems. FTI is part of Framatome S.A., of Paris, France.

Maintenance briefs PdMA Corp. (Tampa, Fla.) supplies portable electric motor test equipment, as well as predictive maintenance programs and related training tools. Products encompass static and dynamic testers that can analyze motor and circuit conditions. Typical areas evaluated include rotor, stator, air gap, power circuit, motor efficiency, and incoming power quality. Data can be analyzed immediately or recalled later for trend analysis.

GE Industrial Systems, Large Motors Div. (Peterborough, Ont. Canada) incorporates a rotor monitoring system into its large motor and generator products. Called Rotector II, the system protects against catastrophic overheating failure of the large rotors due to excessive starts or improper operation. It also provides rotor ground-fault protection. Rotector II monitors selected rotor temperatures directly via an onboard transmitter that communicates by wireless telemetry to a motor-mounted interface/receiver module. This module then sends the data (via a serial link) to a remote-mounted GE Fanuc Series 90/30 PLC used for processing and data analysis. Rotector II is compatible with GE induction motors and synchronous motors and generators.

ECC Inc., Power Modules Div. (Rockford, Ill.) provides a related technology that monitors ac motor power consumption as an indicator of the condition in the drive train, attached equipment, and the process upstream of the motor. A microcontroller-based power sensor/watt transducer module comprises the core of Power Modules’ Load and Process Monitor system. Motor power rather current is monitored as a more realistic measure of motor loading (or torque). The modular system is said to be sufficiently sensitive to indicate changes in flow, pressure, viscosity, etc.–without intruding into the process. For example, it can indicate open/shut condition of valves, presence of fluid or material for dry run or cavitation protection in pumps, wear condition of machine tools, etc.

For more information, enter the following Reader Service Numbers:

Bently Nevada

ECC Inc., Power Modules Div.

Emerson Electric/CSI

Framatome Technologies

GE Industrial Systems, Large Motors Div.

Liberty Technologies

National Instruments

PdMA Corp.

Rockwell Automation/Reliance Electric