Development of a quartz crystal sensor system to monitor local soil removal during cleaning in closed food processing lines

Closed production lines are often cleaned by oversized cleaning in place (CIP) procedures designed according to worst-case scenarios. This study presents an inline sensor system for monitoring the local cleaning process of swellable food soils based on the inverted piezo electrical effect. The sensor uses quartz crystals to detect soil layers on its surface. A network analyser induces an AC voltage into the quartz and in return measures the resulting resonance parameters. The resonance of the quartz differs with its mass. Hence, any adhering soil layer influences the measured signal. First tests with the sensor were performed in a flow channel test rig. Therefore, the quartz was coated with a model soil and afterwards cleaned in the channel. As a reference, an established camera sensor monitored the cleaning process. Starch was used as model soil. The tests showed that the sensor is able to detect the soil removal from its surface and that the signal correlates with reference data from the camera sensor. Furthermore, it was possible to observe an influence of the operating parameters, such as fluid temperature or cleaning agent, on the sensor signal, what needs to be compensated by calibration and smart data processing in further studies.