Inline monitoring of ultrasonic through innovative APM solution

In high-purity industries, all process parameters must be recorded and documented batch by batch during component cleaning. The development of APM (Acoustic Performance Measurement) has provided a new solution to the previously problematic inline measurement of ultrasonic frequency and power in fully automated immersion cleaning systems.

Precision cleaning in fully automated ultrasonic multi-bath immersion systems is state of the art in high-purity industries such as medical technology, precision optics, the semiconductor supply industry, and analysis, laser and vacuum technology. Companies not only have to meet extremely high cleanliness requirements in a stable manner, but also have to record and document compliance with all validated process parameters for each batch. While this can be easily and reproducibly achieved for parameters such as temperature, conductivity and pH value of the baths as well as dwell time of the parts in the baths using existing inline measurement technology, the monitoring of ultrasonic frequency and power could not be automated inline until now. It is usually done either with test foils, with which deviations cannot be detected with sufficient accuracy, or with hydrophones. In this alternative, measurements of ultrasonic frequency and power are performed manually. Since the measuring device is moved in the process, the measurement results are not reproducible. In addition, the sensor must be immersed in the media of the individual baths, which can lead to contamination.

In contrast, Ecoclean GmbH's newly developed Acoustic Performance Measurement (APM) system allows the ultrasonic frequency and power parameters to be monitored inline at each treatment station and for each batch. The monitoring is carried out with special directional microphones, which are placed stationary at the respective pool edge and aligned with the center of the bath surface. The measurements are thus carried out without movement or contact, ensuring that the results are reproducible and can be precisely assigned to the respective batch. Analysis, evaluation and storage of the data are performed by the software of the innovative measuring system.

The microphone records the sound image emitted by the medium under identical conditions for each batch. The values determined for ultrasonic frequency and power are continuously transmitted to the software of the measuring solution, evaluated by algorithms and compared with the previously defined and stored target values of the part-specific cleaning program. In the event of deviations, the system issues a warning or error message. To rule out the possibility of sound noise from surrounding basins falsifying the measurement result, the software is able to detect and mask out interfering signals. All data and evaluations recorded during inline monitoring with the APM are automatically transferred to the standard batch logging of the cleaning system. This makes it easy to ensure and prove for each batch that the ultrasonically induced cavitation from the cleaning validation was adhered to in production.

If the task does not require batchwise recording of the ultrasonic parameters, the APM also enables monitoring at defined time intervals, for example per shift, day or once a week. With this measurement strategy, a microphone is permanently installed on the transport machine so that the measurement is also carried out without contact with the medium and its reproducibility is guaranteed. For the control, the machine travels to the respective basin and determines the frequency as well as the sound power. When the data is analyzed and evaluated by the software, the measured actual values are compared with the target parameters defined in the cleaning validation for the treatment station. The archiving of the measurement results takes place automatically in the plant control system, so that here, too, proof can be provided over a longer period of time. Even this application variant of the new APM system enables significantly more reliable results and thus significantly improved process reliability compared to previous practice.

Ecoclean's innovative APM system took second place in the FiT2clean Award, which was first presented by the Fachverband industrielle Teilereinigung e.V. (FiT) in 2022. (OM-1/23)