Maximizing Machine Uptime With Vibration Sensors

Sensors Insights by Chris Hansford

Vibration is a common problem in machines across applications, sometimes resulting from misalignment of rotating equipment due to poor installation, sometimes the consequence of natural wear and tear. However, it is increasingly possible to reliably identify sources of wear with the use of vibration monitoring equipment.

As machinery has become more complex there has been a corresponding growth in the need for sophisticated vibration sensors that can maximize the performance of many engineering processes. Today's designers and engineers have not only succeeded in providing devices of exceptional accuracy and reliability but also in packaging that functionality in a variety of resilient enclosures to enable its use within a wide range of applications.

The efficiency of vibration sensors has driven demand in a number of ways. As well as offering enhanced efficiency and increased performance, these devices also enable operators to satisfy the ever-more robust regulations imposed regarding health and safety, which have made the use of sensors in non-safe areas a prime requisite. As a result, vibration sensors have become an increasingly essential fixture in modern engineering.

A recent report from market forecasters BCC Research illustrates this. BCC predict that the market for sensors is expected to increase to £50.7 billion in 2014, reaching £74.1 billion by 2019, at a compound annual growth rate (CAGR) of 7.9%.

Market demand for sensors will be fuelled by conditions such as increases in motor vehicle and machinery production and government regulations, say BCC. Meanwhile, a number of sources have attributed the growth to the maturity of many sensor markets and improved fabrication techniques. This, according to these claims, has led to increased sensing abilities at lower costs, and this also will help increase market growth.

A major reason for this growth even within challenging economic circumstances is the fact that, more than ever, efficiency is the driver of all business decision-making, and the driver of efficiency is sensing. This explains why emerging markets such as Asia are developing fast for the market-leading suppliers of vibration sensors. At the moment, the numbers in terms of sales are relatively low but there is massive potential to increase sales over the coming decades. It's also true to say that, as Process Magazine suggests, the proven effectiveness of techniques such as vibration monitoring and the subsequent rise in sales has caused sensor costs to fall. So what should businesses do to harness the power of sensors and vibration monitoring?

To discover how much can be saved by using vibration monitoring, you need to evaluate plant performance. If the plant is running at, say, 60% of its maximum performance capability, you need to ask what are the causes. If your investigation reveals that the plant is running at reduced potential largely as the result of machine failure then there is a strong argument for employing vibration monitoring. This will provide an early warning system that allows engineers to perform preventative maintenance and keep the line running smoothly. Machine failure can have a massively detrimental effect on manufacturing operations such as automotive where the product is funneled through one production line. For example, if the rolling road fails in an automotive plant and there is a massive bottleneck, the whole line is held up. However, with vibration monitoring, downtime can be prevented.

One reason why vibration monitoring is so vital today is that in this challenging economic climate there is sometimes less new plant construction and more focus on maintaining and enhancing the efficiency of an existing plant. There's also the possibility that facilities may be running machinery that is 'out of condition' because the plant is not running at full capacity and sitting idle for longer periods than normal. Both of these symptoms of the current economic crises make vibration monitoring perhaps an even greater priority than ever.

Condition monitoring has proved to be so cost-effective across industry because machines that have begun to exhibit defects are at greater risk of failure than those without defects, and are therefore more likely to generate unwelcome downtime costs. This may sound rather obvious but it is also true to say that historically - and even currently, despite the range of condition monitoring options available - there has been a widespread belief that it is cheaper to continue running worn equipment rather than replace it and, so the (flawed) thinking follows, wring more life out of the soon-to-be replaced parts. However, hard experience in the industrial environment shows that this is often proved dramatically wrong.

Condition monitoring is cost-effective across industry, preventing failures before they happen.
Condition monitoring is cost-effective across industry, preventing failures before they happen.

To install and use vibration sensors to their fullest potential, engineers first need to understand how they operate. Vibration sensors, which measure a quantity of acceleration and are therefore a type of accelerometer, typically contain a piezoelectric crystal element bonded to a mass. When the accelerometer is subject to an accelerative force, the mass compresses the crystal, causing it to produce an electrical signal that is proportional to the level of force applied. The signal is then amplified and conditioned using inbuilt electronics that create an output signal, which is suitable for use by higher level data acquisition or control systems. Output data from accelerometers mounted in key locations can either be read periodically using sophisticated hand-held data collectors, for immediate analysis or subsequent downloading to a PC, or routed via switch boxes to a centralized or higher level system for continuous monitoring.

There are two main categories of vibration sensor, or accelerometer: AC accelerometers and 4 mA to 20 mA accelerometers. AC accelerometers are typically used with data collectors for monitoring the condition of higher value assets, while 4 mA to 20 mA components are commonly used with PLCs to measure lower value assets, such as motors, fans and pumps.

Condition monitoring depends on stability; a poorly mounted accelerometer may give readings that relate not only to a change in conditions but also to the instability of the sensor itself. Accelerometers should therefore be mounted as close as possible to the source of vibration onto a surface than has been made free from grease and oil. The surface should be smooth, unpainted, and larger than the base of the accelerometer itself. It should also be flat and this may require the creation of a flat surface using spot facing tools to eliminate instability. A good spot facing kit will provide all the necessary tools needed to accurately mount a vibration sensor onto the rotating machine, including a tapping drill, taps, tap wrench and a spot facing tool. These kits are now available to allow for different mounting threads, including ¼, M6 and M8. Correct mounting of the sensor is vital to ensure true readings and, where possible, mounting a sensor via a drilled and tapped hole directly to the machine housing will give the best results. However, if the housing is not flat, a spot facing installation kit allows creation of a flat surface.

A vibration monitoring system with a variety of components.
A vibration monitoring system with a variety of components.

The development of vibration monitoring equipment has been driven primarily by the changing needs of its customers around the world. Among the industrialized economies in recent years there has been a steady move from reactive to predictive maintenance. This is now evolving into a far more strategic approach that is effectively process-wide; encompassing every stage in the production process in a bid to maximize uptime and productivity, while reducing operating costs, and sensors are an essential part of this process.

About the Author
Chris Hansford is the Managing Director of Hansford Sensors. He is a qualified Electro-Mechanical Engineer with over 30 years of experience in the vibration monitoring industry. At the start of his career, Chris was employed as a Design Engineer by a company that provides condition monitoring services to the power sector. From there he became involved in the formation of a sensor manufacturing company and continued to run the business for 20 years as Managing Director. In 2006, Chris moved on to set-up Hansford Sensors Ltd, manufacturing accelerometers and ancillary equipment.


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