The Role of Seismic Sensors in Predictive Maintenance

The credibility of a predictive maintenance program centers around, not only detecting problems, but finding their root cause. It does absolutely no good to say that a bearing is at its initial stage of failure, and it still has ten years left of life. Every rolling element bearing (REB) installed is at its initial stage of failure when it’s initially installed. Despite marketing information to the contrary, rolling element bearings are not “frictionless” bearings. The grease or oil employed to lubricate the bearings helps to reduce the friction within the bearings, however, over time, the bearing will start to degrade due to normal wear and tear. The methodology employed when using seismic sensors or transmitters in a predictive maintenance program should ensure that when a bearing issue is identified, and the bearing is removed, one can see damage with your naked eye, not just with a microscope. Seismic sensors and transmitters can monitor and protect a number of critical assets at the plant, including compressors, pumps, motors, turbines, and gearboxes. If you want to cut back on your repair costs and downtime, the key is to find a manufacturer who understands how your machinery works and how it can be properly monitored. We'll look at how different sensors and transmitters function and why your entire operation depends on having smarter devices that provide actionable information.

Monitoring Solutions

In industrial plants, solutions can be difficult to assess, due to physical constraints, environmental applications, and potential fault frequencies of interest. Whether the machinery is in a hazardous area, or in a remote difficult-to-access location, operators are often working in an environment where the best solution can be difficult to implement. When we’re discussing using seismic sensors or transmitters to monitor REB machines, we can take advantage of the frequency regions that will give us the most information.

For example, let’s look at a motor pump combination or a motor fan combination. Depending upon the asset, you may not be able to get direct vibration transmission from the rotor to the casing due to the physical constraints of the machine. Most designers have created paths where the vibration measurement device mounting location has a direct transmission path from the rotor to the casing. Sometimes in cases where you do not have a direct transmission path, you must create one. One may have to remove a portion of the fan cover to get to the location where direct transmission can be received. It’s important to watch out for mounting locations that have air gaps between the casing and the vibration measuring device mounting location. In cases where direct transmission is not attained, it’s possible to measure values that are in error, either vibration signals that are too low or that are too high depending upon how the vibration signal is either attenuated or amplified by the mounting location.

It's important that the vibration measuring device, whether it be a sensor going to a monitoring system, like the Metrix SW5580, or a transmitter providing a 4-20 mA output that the solution is suited for the environment in which it is mounted. If the sensor is going to be subjected to water, it needs to be rated for a water application, usually NEMA 4X or IP67/IP68. If the sensor or transmitter is located in a hazardous area, it should be rated for that hazardous area application. The ambient temperature of the mounting location also needs to be considered, most seismic vibration sensors or transmitters, can accurately measure from -40°C (-40°F) to 100°C (212°F).

When monitoring and protecting REB machines, it’s important to measure the frequency ranges of interest. Those include the rotor related region, which extends from ¼X to 3X (X being the rotor speed / frequency) and the bearing related region, which extends from one to six times the ball pass frequency outer race. With the 5580 or SW5580 two channel monitor, it’s possible to monitor the rotor related region integrated velocity on Channel 1 and the bearing related region using acceleration on Channel 2 with a single accelerometer located on the casing of the bearing housing.

What's more, smart monitoring solutions can be configured for accuracy to avoid false trips. A system that sends out spurious alarms will not be trusted; it will inevitably leave staff wondering if they really need to take action in the event of an alarm. Choosing monitoring solutions that can be configured according to your needs can reduce or eliminate false trips.

Types of Seismic Vibration Instrumentation

Accelerometers, velocity sensors, signal conditioners, and transmitters can all be used to measure the vibration of both support structures, as well as rotating and reciprocating machinery. From piping to housings, this equipment can be vital for both predictive and preventive maintenance. The more information you receive from the sensors and transmitters, the easier it is to predict patterns of normal and abnormal behavior. It's common for machinery to start showing signs of wear without anyone in the plant being any the wiser without proper vibration monitoring.

Seismic monitoring systems have been especially valuable to machinery that has rolling-element bearings because they transmit vibration from the shaft through the bearing directly to the casing. For instance, in a power plant or refinery, seismic sensors could be used for most of the motor pump and motor fan combinations. When you have the right instrumentation, the severity of any abnormal activity can be recognized and then reported to the appropriate parties.

Predictive Maintenance

All rotating and reciprocating machines, as they operate, even if they’re maintained properly, are going to wear with time. The predictive maintenance goal of a seismic sensor or transmitter is to allow staff the opportunity to understand the rate of wear so proactive actions can be taken. Equipment failures can occur at any time for many reasons, but all too often, the failure comes as a surprise even when it shouldn't. Due to improved training, better maintenance, better machines, and increased knowledge of machine failure modes, machinery failure is not as common as it used to be. It's more common for machinery to show early warning signs of wear and fatigue, and for operators to take action to properly plan maintenance. When you have enough information coming from your vibration sensors and transmitters, the time and money savings for implementing a predictive maintenance program using vibration sensors and transmitters can be truly eye-opening.

At Metrix, our seismic sensors and transmitters have been carefully designed with operators and maintenance personnel in mind, and this is true across industries. With every iteration of the product, we ask ourselves what would make it more valuable to the customer. If you need to test and adjust different settings or subdue the alert mode during the machinery startup to avoid a resonance peak, we make it possible.

By thinking of nearly every aspect that could affect setup, our equipment is used in some of the most profitable enterprises in the world. We know that the real world is very different from a testing facility, particularly when it comes to the placement and the operating conditions of each site. If you're looking for successful implantations of all your seismic vibration monitoring equipment, contact us today. We can work with you to determine which products to use and how they can be installed and maintained.