Monitoring and documenting ultrasonic frequency and power in-line on a batch-by-batch basis

Precision cleaning in fully-automated, ultrasonic multi-bath immersion systems is state of the art in high-purity industries such as the medical device sector, precision optics and the semiconductor supply industry, as well as when it comes to analysis, laser and vacuum technologies. Companies not only have to consistently meet extremely high cleanliness requirements, but they also have to record and document compliance with all validated process parameters for each batch of parts. While existing in-line measurement technology makes it possible to monitor parameters such as temperature, conductivity and pH value of the baths as well as the dwell time of the parts in the baths in an easy and reproducible manner, up to now there has been no way to automatically monitor ultrasonic frequency and power in-line. The current practice is to use test foils, which do not allow deviations to be detected with sufficient accuracy, or hydrophones. With these methods, ultrasonic frequency and power are measured manually. Since the measuring device is moved during the monitoring step, measurement results are not reproducible. In addition, the sensor must be immersed in the various baths, which can lead to contamination.

Reproducible, in-line batch monitoring with automatic analysis

Ecoclean GmbH’s newly developed Acoustic Performance Measurement (APM) system, on the other hand, is capable of monitoring the parameters of ultrasonic frequency and power in-line at each processing station and for each batch. Special directional microphones are used for this, which are placed in a fixed position at the edge of each tank, and directed towards the centre of the bath surface. Thus, measurements are carried out without any movement or contact, ensuring reproducible results and enabling them to be precisely assigned to the batch concerned. Analysis, evaluation and storage of the data are carried out by the software of the innovative measuring system.

Under identical conditions, the microphone records the sounds emitted by the cleaning medium under identical conditions for each batch. The measured ultrasonic frequency and power values are continuously transmitted to the system’s software, where they are evaluated by algorithms and compared with previously-defined and stored setpoint values of the part-specific cleaning program. Should there be any deviations, the system issues a warning or error message. To rule out the possibility of sounds from surrounding tanks falsifying the measurement results, the software detects and masks out any interfering signals.

All data and evaluations recorded during in-line monitoring by the APM are automatically transferred to the cleaning machine’s batch logging system, which comes as standard. This makes it easy to ensure and prove that the ultrasonically induced cavitation determined during validation of the cleaning process has been adhered to in production for each batch.

Alternatively: measurements at defined intervals

If ultrasonic parameters do not need to be recorded for each batch, the APM can also be used to monitor parameters at defined time intervals, such as once a shift, once a day or once a week. For this measurement strategy, a microphone is fixed-mounted to the automatic transport system (ATS), so that here, too, measurements are made without contact with the medium and their reproducibility is guaranteed. For this check, the ATS advances to the respective tank where it measures both the frequency and the sound power. When the software analyzes and evaluates the data, the values measured are compared with set parameters defined during validation of the cleaning process for the treatment station. The measurement results are archived automatically in the machine’s PLC, meaning that proof can also be supplied over a longer period of time. Compared to previous practice, even this application option of the new APM system offers far more reliable results and thus significantly higher process reliability .

Ecoclean’s innovative APM won second place at the FiT2clean Awards, which were presented for the first time by Fachverband industrielle Teilereinigung e.V. (FiT)  in 2022.

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