Critical machines are sometimes equipped with a bearing temperature monitoring system. Most of the time an alarm or a shutdown is triggered at a temperature 20F-30F above the normal operating temperature. When temperature has exceeded a preset absolute value due to lubrication malfunction, such as loss of oil, bearing cooling system failure, etc., the alarm would go off, but by that time it is likely too late and damage has been already done.
In addition to the above approach, a temperature rate of change (ROC) alarm has been introduced. It allows detection of an abnormal bearing operating condition Before the temperature reaches levels causing irreversible damage. In a nutshell, it works as follows. Temperature is continuously measured at a 30-second interval. Temperature gradient in time or ROC is then calculated and compared against a preset "ROC alarm" value. If all three consecutive gradients have exceeded the preset, an alarm is triggered. The three latest gradients are saved and continuously updated - the oldest one gets discarded and the latest one added if all three requirements are not met. Utilizing this approach, failure can be detected at an early stage of lubrication malfunction. (David Gluzman, Reliability Engineer)
We send $100 for each tip published. Submit your tip. |
