Tracking vibration levels to reduce downtime
13 September 2011
Vibration monitoring of rotating equipment can help to reduce costly down time due to maintenance requirements or to fix damaged machinery. CEE reports.
There is a growing demand for all companies to reduce and sustain low operating costs while maintaining quality and delivery standards. One area to benefit from this trend has been in monitoring the condition of rotating machinery by tracking vibration levels, because damaged machinery and unplanned shutdowns due to equipment failure can be hugely costly.
Maintenance engineers should already be aware of the benefits of monitoring vibration levels on industrial machinery. However, it is important that these benefits are recognised beyond the maintenance department. Chris Hansford, managing director at Hansford Sensors, explains why, using the experiences of one customer to demonstrate his points.
When one of the Air Handling Units (AHU’s) which powers the air conditioning at a pharmaceutical manufacturing facility failed the resulting high temperatures which were encountered inside the factory were in danger of adversely affecting the quality of production, as well as being uncomfortable for staff working on the production floor.
Because the implications of a high financial impact to the manufacturing facility were so high the situation needed to be quickly resolved. Unfortunately, due to health and safety legislation it was not possible to access the AHU, so the system could not be inspected on a regular basis by the facilities management team.
Luckily, the maintenance provider had heard of a method of monitoring the condition of rotating machinery by measuring the vibration levels. Further investigation resulted in Hansford Sensors being contacted to offer a possible solutions which could pre-warn the company of any future failures of the AHU system.
The first question that Hansford Sensors asked was about the construction of the the AHU system. In this instance, it used a combination of direct drive and a belt drive.
Chris Hansford explains why this is important: “Because the best sensor for this application has a limited field of vision there was a requirement to monitor each bearing with the sensor. In a machine with a belt drive, a sensor would need to be placed to monitor the motor on the drive end and non-drive end with one sensor on each journal bearing. For direct drives, only the motor itself can be monitored. In this instance, a belt drive is used, requiring a total of four sensors.”
There are also various techniques for measuring the output from a sensor including offline and online modes. Offline is the term used to describe the process for mounting the sensors on the machinery and connecting them to a switch box, which is fitted onto the outside of the AHU. This method requires an engineer to regularly take readings using a hand-held data collector. Alternatively, the on-line system can be used by interfacing the sensors directly to a PLC/BMS. This gives the ability to measure and analyse the output from each sensor.
The pharmaceutical company made the decision to use sensors that could be directly interfaced into the existing PLC/BMS and if there was a future requirement for a more sophisticated analysis, then a specialised vibration analysis solution could be introduced. The 4-20mA vibration sensors were subsequently installed and interfaced with the existing PLC/BMS system.
Chris Hansford conclude: “Following the installation of the sensors the maintenance provider was able to confirm that the condition of the AHU’s were being monitored and the company is now confident that there will not be a recurrence of the AHU and the problems that this causes to the production process.”
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