Leverage Wireless Communication for Vibration Monitoring

Transmitting vibration data through wireless networks makes continuous monitoring of rotating equipment more practical and cost effective.

According to Shuji Yamamoto of Yokogawa Electric Corp. (yokogawa.com, Tokyo), when people think of process manufacturing facilities, they tend to picture pipes, tanks, valves, and instrumentation. At the same time, however, they often tend to overlook how much rotating equipment there is and how critical it is to the overall operation (see Fig. 1 below). If, for example, a pump, compressor, or other device fails, it can have a serious effect on production. The fact that many pumps are configured in dual-redundant installations gives an indication of their importance.

Fig. 1. Process manufacturing facilities invariably have large populations of critical rotating equipment, such as these pumps, that can be subject to vibration problems. In addition to vibration inherent to such equipment, potentially harmful vibration can also be transmitted, to some degree, by way of piping and support structures from other machinery within a process unit.

As Yamamoto describes it, vibration, which has a variety of causes, is one of the greatest enemies of rotating equipment. “Consider,” he said, “a typical ANSI pump driven by a motor with a flexible coupling. If the two shafts aren’t truly on a common centerline, the coupling will compensate for the misalignment, but it will likely introduce vibration into the installation. Vibration creates detrimental forces within the ball bearings, causing premature wear, which further increases the overall vibration. Over a long enough period of time, the problem will compound until one or more of the bearings fail. The pump’s mechanical seals may also suffer damage and begin to leak. Before long, the installation must be shut down and overhauled.”

In addition to the vibration inherent with any rotating equipment, at least at some level, potentially harmful vibration can also be transmitted by way of piping and support structures from other machinery within the process unit. The good news is that, while vibration can’t be eliminated entirely, it can be measured and analyzed to guide corrective action.

Sensors are available to characterize and quantify the amount of vibration, and to capture characteristic patterns, often referred to as signatures. These monitoring systems typically use a piezo-electric sensor to create and transmit a signal proportional to measured vibration.

Vibration sensors have been available for many years, but older systems were costly to install, limiting their deployment to the most expensive and critical rotating equipment. For other installations, technicians have carried portable units on routine plant inspections and manually checked bearings, seals, and other critical points. According to Yamamoto, sophisticated portable systems can capture historical information and compare specific installations over time, but such rounds also can be time-consuming and, ultimately, costly. “Furthermore,” he noted, “in plants with minimal head counts, they can be delayed or skipped when more pressing tasks emerge.”

Advantages of continuous monitoring

Short of a catastrophic failure of some component, vibration problems don’t usually advance drastically in a brief period of time. This fact is usually cited to support the idea of periodic inspections. “Unfortunately,” Yamamoto explained, “vibration problems may increase slowly until they reach a critical point, and then the climb becomes much steeper toward failure, all of which can easily occur before the next scheduled manual inspection.”

Continuous monitoring, he continued, can detect those situations when the vibration curve begins to climb toward a failure point, informing maintenance technicians while there is still time to respond before a failure and outage. Software can spot those kinds of movements, and then sound alarms appropriate to the urgency of the situation and criticality of the equipment.

According to Yamamoto, economical vibration sensors have made permanent installations more practical for more pieces of equipment, but the costs of wiring a sensor haven’t decreased. In fact, in many situations, those costs have gone up. One of the biggest technological advances of the past decade has been the emergence of effective and practical wireless-instrumentation protocols, including ISA100 Wireless (see sidebar below), and sensors able to communicate using these protocols.

Launching a program

“Vibration monitoring program implementations are usually incremental,” Yamamoto said, “and involve working down a list of installations, beginning with the most critical. In this context, the term ‘critical’ takes different forms, the foremost of which typically involves the likelihood of production being interrupted due to a failure. If the process cannot run without a given pump and there is no spare ready to switch over, the pump is very critical, regardless of its capacity or cost.” Most plants, he noted, are aware of those installations, particularly if they have a history of problems.

Secondary and tertiary levels, though, can become more complex. Some companies select based on equipment cost. At the same time, other considerations, such as difficulty of repair or availability of spare parts, enter into the picture, but they are harder to quantify. Ultimately, it is important to include a variety of factors from different viewpoints when making such decisions.

“It is also important,” Yamamoto cautioned, “to select an appropriate asset-management platform to gather and process the data from the sensors around the plant. Once more information is available, questions emerge as to where it goes and how it should be used. Who should receive alarms? Maintenance? Control-room operators? If a highly critical installation is beginning to show signs of a problem, the control room may need to be informed if it necessary for operators to take action before the situation is turned over to maintenance for repair. An effective asset-management system can handle these sorts of situations.”

Bottom line

Yamamoto thinks process manufacturers can benefit substantially through the use economical vibration sensors combined with wireless networks. “Working together,” he said, “the two technologies provide critical information to operators and other plant personnel to warn of potential problems before the plant suffers damage or lost production. In some situations, the avoidance of a single outage saves enough money to pay for monitoring many pieces of equipment. This approach is highly flexible and scalable, allowing a facility to begin in one area, and then expand as needs and circumstances permit.”

SIDEBAR: Wireless Vibration Monitoring

Yokogawa has created a sensor and wireless transmitter system designed specifically for continuous monitoring of various types of rotating equipment used in process manufacturing facilities.

Fig 2. The Yokogawa wireless vibration-monitoring system consists of a piezo-electric vibration sensor connected to a host system by way of a wireless mesh network. The sensor can be mounted using a pedestal screwed to the equipment, i.e., target device, housing (in this case, a motor’s housing), usually near the bearings.

According to Yokogawa’s Shuji Yamamoto, the company’s piezo-electric acceleration sensor is compact and easy to install near equipment, i.e., the target device’s bearings (Fig. 2). A cable connects the sensor to a wireless communication module mounted in a convenient location, where there are no obstructions to interfere with the unit’s signal propagation.

How it works

The complete system is self-powered using a battery module in the communication module. With a one-minute data update rate, one set of batteries can run for as long as 10 years. The data is sent through the wireless network to the system gateway. If other ISA100 wireless field devices are already in use in the facility, the vibration monitors can become part of the same network, communicating with the gateway just like any other communication module or sensor.

The wireless vibration-monitoring system has all the specifications necessary to perform the functions required for condition monitoring (see “Main Specifications for Condition Monitoring” table). Data from the units installed throughout the plant can be directed to a control or monitoring system to inform operators and maintenance personnel as conditions change with the equipment being monitored.

TABLE: Main Specifications for Condition Monitoring

Methodology

Yokogawa’s piezo-electric vibration sensor is capable of measuring velocity and acceleration. The nature of the vibration and the type of equipment helps determine which analytical method is best when the primary objective is determining equipment condition. The rule-of-thumb suggests that where frequencies are low, velocity is the preferred measure, but when frequency increases, it’s better to measure acceleration.

Plant personnel determine reading frequency and what analytical techniques should be used for each installation. Ranges of what is considered tolerable vibration versus dangerous have been published by various sources, but the ultimate guidelines for a given piece of equipment in each plant may need to be established in cooperation with the equipment OEM.

“While the sensor can send a new reading as often as every 10 seconds,” Yamamoto said, “the need for such rapid refreshment is rare, and it comes at the cost of battery life. Switching to an update rate of once per minute can extend battery life significantly, while still providing more than enough data for most applications.”

If more sophisticated analysis is required, software packages are available from third-party vendors to look for patterns and identify sources of abnormal vibration. This type of work is done in the host system rather than the individual devices, and often combines signals from multiple sensors deployed around the equipment to pinpoint sources of trouble.

Shuji Yamamoto is a technical specialist in the Wireless Strategy Section of the Business Initiative Department, at Yokogawa Electric Corporation’s New Field Development Center, IA Platform Business Headquarters in Tokyo. For more information, visit yokogawa.com.