Perform a “background” test. This can show that the vibration present during the bump test is due to the user’s impacting of the structure. In some cases vibration from nearby equipment can transmit through foundations into the equipment being tested. Simply collect data while the machine is off and no impacting is being done on the structure; then compare these to the data collected during operation and impacting.
- Check the accelerometer. The accelerometer placed onto a machine’s measurement position can skew results unless operators take care. Follow these basic guidelines: the magnet should be firmly screwed onto the accelerometer (any looseness between the magnet and accelerometer will corrupt the reading); the accelerometer should be gently slid onto the measurement position (slamming the transducer onto the machine may cause data overload); the magnet should be in firm contact with the machine’s surface (any movement will be falsely recorded as vibration data); and operators should avoid knocking or disturbing the accelerometer while taking the measurement.
Using any of these techniques, situations may arise where the analysis data can’t clearly identify the cause of a problem. In these cases, outside expertise or a working partnership with a knowledgeable supplier can prove invaluable.
Confirm the lubricant is correct. Critical machinery can benefit from tags placed at grease points identifying the proper lubricant to be analyzed and, if necessary, replaced after analysis.
Scott Brady is director of marketing for SKF Condition Monitoring, San Diego, Calif. E-mail him at firstname.lastname@example.org.
- Sample properly. The possible introduction of a contaminant during the sampling process is the most likely cause of invalid analysis results. When taking lubricant samples from storage tanks or equipment in service, workers should adhere to proper sampling techniques.
- Document the results. Detailed documentation makes sharing of test results more widely easier and, in the process, may telegraph useful information for other parts of an operation. Over time, it enables meaningful comparisons based on prior history to help solve current problems.