Vibration monitoring: Key considerations

•  Identify the vibration level and frequency range that is to be measured. This is the first thing you need to establish before choosing your vibration monitoring system. Careful consideration must also be given to issues such as the temperature, humidity, and whether there are any corrosive chemicals present.  

•  Consider the working environment. Vibrations sensors are available for a wide range of sectors, including offshore, petrochemical, utilities, paper, marine, metals, water treatment, aerospace, pharmaceutical, automotive and beyond. For instance, in the paper industry high-IP-rated components are required for monitoring in wet areas, while in the coal and quarrying industries ATEX-certified sensors are needed for use in atmospheres containing potentially explosive gas. Further options are available for vibration monitoring at low speeds, where the signals generated by bearings are harder to detect.

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

•  Decide whether to use online or offline monitoring. Vibration monitoring offers the option of measuring output either online or offline. An online system is one that measures and analyses the output from sensors that interface directly with a PLC. An offline system is created by mounting sensors onto machinery and connecting them to a switch box; engineers can then use a hand-held data collector to collect readings.

•  Install close to the source of vibration. For the best results, accelerometers should be located as close as possible to the source of vibration.

•  Establish a network. Create a dedicated condition monitoring system, using a network of accelerometers positioned close to various machine parts – such as fans, motors and gearboxes – to improve operational efficiency and prevent problems long before they occur.

•  Establish the best possible stability. Accurate condition monitoring depends on stability, otherwise the readings from a poorly mounted accelerometer could be recording the instability of the sensor itself. You should therefore eliminate instability using spot mounting. Sensors should be mounted on a flat, smooth, unpainted surface, larger than the base of the accelerometer. The surface should also be free of grease and oil. When mounting a sensor there may be a choice between drilling, tapping or gluing, but make sure you understand and consider how these methods may affect the warranties on your equipment.

•  Train your operators. Any system is only as good as those who manage it. But with so many sensors in operation within modern engineering systems (in the paper industry there may be up to 600 sensors on each machine, primarily to monitor the vibration levels on the roller bearings) the problems associated with human error have to be addressed. Training in the use of condition monitoring components such as vibration sensors is now provided by organisations such as BINDT (British Institute of Non-Destructive Testing).

•  Use the information that vibration monitoring provides. Despite the exceptional capability of vibration monitoring systems, they cannot save a plant if the warnings are ignored. Yet warnings have been disregarded in order to continue production, with the eventual costs of unplanned downtime and major repairs far exceeding those that would have been caused by a short, planned period of preventative maintenance. So, do you perform simple maintenance there and then? Or do you ignore the warning, risking a more costly failure further down the line?

•  Consult an experienced provider. With so many variables to consider, you need professional advice. To achieve the best specification, it makes sense to work closely with a supplier that has a depth of industry experience and knowledge.