The Schaeffler Industrial Aftermarket is presenting the lubricating grease sensor FAG GreaseCheck as a highlight at this year's Husum WindEnergy trade fair. Analysing the grease in ongoing operation can prevent damage from occurring to the rolling elements in good time and permits a shift to lubrication which is driven by requirements and not according to defined time periods. Initial uses of this sensor by leading manufacturers of wind turbines and large wind farm operators have shown that substantial cost savings and time economies can be achieved with this method for critical turbines which are very difficult to access. In addition, it is beneficial to the environment and resources and a higher degree of turbine utilisation is achieved.

> >A question of correct lubrication
Around 90 percent of all rolling bearings are lubricated with grease. If the lubricating grease is depleted or contaminated, then rolling bearing damage is inevitable. Monitoring the condition of the grease whilst the turbine is in operation is an important safety factor for the operator of the turbine, if this is to be prevented. As the only method previously available for determining the actual condition of the grease involved conducting elaborate sampling operations and costly, time-intensive laboratory measurements, the option usually taken was to overgrease the rolling bearing intentionally. However, increased churning work and the resulting increase in bearing temperature can also have a detrimental effect on rolling bearing function. As a result of the online monitoring system provided with the FAG GreaseCheck, the user is informed about the condition of the grease at all times and is only then required to intervene if the physical properties of the grease are no longer adequate to provide reliable lubrication. In every case however, this takes place long before any damage to the rolling bearings and potential turbine failures can occur as a result of inadequate lubrication.

&&>FAG GreaseCheck - small sensor with intelligent electronic evaluation system
The sensor head, which measures just five millimetres in diameter, is embedded directly in the lubricant. Four parameters can be detected with the aid of the optical infrared reflection method: Water content, cloudiness, thermal or mechanical wear and temperature. An intelligent electronic evaluation system generates an analog signal from these, which informs the user about the condition of the grease both rapidly and simply. If a threshold value is set, a direct indication of whether the grease condition is good or poor can be provided by a signal. This allows suitable action to be taken immediately, right up to an emergency shutdown, in response to any changes in grease condition that may suddenly occur.

&&>Use, installation and introduction to the market
The FAG GreaseCheck can be used for FAG Arcanol lubricants, as well as other greases available on the market following prior calibration. This method offers significant cost-saving potential, particularly for wind turbines which are critical to production and very difficult to access. Downtimes, as well as costs for lubricants, maintenance and replacement parts, can be reduced and the degree of turbine utilisation is increased. The current applications of this sensor in wind turbines confirm these approaches. The sensor is installed with assistance from Schaeffler's application engineers, as the optimal installation location varies from application to application and must be accurately determined. In the large-size bearings of wind turbines for example, the FAG GreaseCheck should be fitted in close proximity to the load zone of the bearing. A number of the rolling bearing housings supplied by Schaeffler will come equipped with an appropriate fixture for optional positioning of the sensor in future. This option will be available on the market from the second quarter of 2013, once the final field tests have been completed.