How to Reduce the Effects of Audible Noise From an Ultrasonic Cleaner

There are many advantages to an ultrasonic cleaner over other traditional cleaning technologies. Among these are faster cleaning times, better quality of cleaning, and ease of use. At the same time, ultrasonic cleaner technology differs a lot from these older methods. There are many characteristics unique to this technology, covering maintenance, handling and operation. An unavoidable aspect of ultrasonic cleaning is its production of ultrasonic waves. Ultrasonic waves themselves, by design and definition, have a higher pitch than audible for human ears. While this is true of the core transducer unit that effects the cleaning, the device as a whole does have a tendency to produce some audible sound waves.
During operation, the ultrasonic transducer-generator subunit generates purely ultrasonic waves. However, the construction of the complete device causes an element of mechanical coupling or interaction between the transducer-generator unit and various other parts. Typical components of the cleaner that have such vibrational interaction are the cleaning tank, enclosures and lids. This side effect of ultrasonic cleaner operation induces a variant of sympathetic resonance – activating some natural frequencies – where these resonance frequencies are in fact subharmonics.
These subharmonics are frequencies that can range from halves to quarters, as opposed to harmonics that are multiples of the base frequency. Take for example an ultrasonic cleaner with a 40 KHz transducer. The vibrational interaction will produce subharmonics such as half or 20 KHz, and a quarter or 10 KHz sound frequency. The loudness and relative intensity of these subharmonics depend on the specific mechanical design of the overall cleaner components, and the particular transducer frequency in use.
Since these audible subharmonics depend only on predetermined design and frequency, their direct online control is not possible. Indirect mechanical and precautionary methods are necessary to alleviate the problems arising from these unavoidable audible sounds. There are clear health and safety guidelines that stipulate the acceptable intensity for operating personnel.
For ultrasonic cleaners where the audible sound levels are fairly low, the primary precaution is to ensure that operating personnel stay a certain distance away from the unit. For additional reduction in audible sound intensity, use either or both of tight-fitting sound-insulating lids and complete device covers, depending on the uncovered cleaners’ sound levels. When proximity to the cleaner is necessary, the operator must wear special sound-reducing ear covers. For certain larger cleaners, the sound levels can be quite loud and unpleasant. In that case, we suggest exiting the enclosed room during operation. For additional precaution, see that you switch off the equipment immediately after the cleaning cycle completes.
The audible sound from the ultrasonic cleaner can occasionally provide a useful remote indication of faulty operation or operating mode. If the unit gives off abnormal sounds, immediately shut it off and get it looked at by maintenance staff. The pitch of the sound can detect the degassing mode remotely. During degassing, the pitch stays high, and on completion of degassing, it alters to a steady, relatively lower pitch.

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