Non-contact sensors in the food industry

What food factories will look like in the future can never be 100% predicted. However, we can take it for granted that sensors will play an important role. Simply because the path taken in the field of automation is simply not possible without sensors. For the food industry, there is logically a focus on non-contact sensors so that the chance of food contamination is not possible.

Sensors generate various types of data as input for the control system of production lines in the food industry. For example, they measure pressure and temperature, as well as presence or color. The measured values are used by the control system or control algorithm to monitor process steps, ensure safety or simply as a trigger to initiate a next process step.

Contact versus non-contact sensors

Precisely because hygiene is one of the main concerns in the food industry, there is a preference for the use of so-called non-contact sensors. As the name suggests, the part of the sensor that actually performs the measurement makes no contact with the product or medium. This is in contrast to classical sensors where there is often a mechanical interaction between the sensor and the object. We know this, for example, from strain gauges, thermocouples, pressure sensors and sensors that respond to touch. 

A major advantage of contact sensors is their relatively high reliability. A disadvantage is that the very contact causes wear, which reduces accuracy and ultimately reliability. Perhaps even more important for the automated food industry is the fact that a suitable contact sensor does not exist for all quantities. The speed of moving objects, for example, is difficult to detect, and quantities such as "color" and "gloss" also become a tricky story. For this reason, developments in so-called non-contact sensors have been rapid and today's machine builder can choose from a wide range of high-tech non-contact sensors. Measuring elements whose operation is based on, for example, a changing magnetic or electric field, sound waves, light rays or laser beams. Highly accurate, wear-free and hygienic.

Vision

Sensors ideally suited for the food industry are vision sensors. In fact, nothing more than a camera that takes images, but combined with special software that analyzes the images and - possibly in cooperation with AI - draws a conclusion. Vision sensors are available from simple versions to integrated into highly sophisticated vision systems. 

For example, a simple sensor "sees" whether or not there is specific information on a label and switches based on that information. More sophisticated systems are used for quality control, among other things, and are capable of comparing recorded images with a reference image at lightning speed. A good example is quality control of pre-packaged grapes. A vision system using artificial intelligence (AI) checks each tray that passes the camera for mold, cracks (leaks), color, moisture and shaped fruit, among other things. The time span between assessment by the AI and the "approve or reject" decision is only 0.3 seconds, making it possible to check up to ninety trays per minute.

Changing field

Sensors that operate on the basis of a (changing) electric field are the inductive and capacitive sensors. Sensors that respond to a changing magnetic field have a similar effect. Within the food industry, these types of sensors can be used, for example, to check that there are no metal particles in the food. 

Finally, we mention infrared sensors. These components are sensitive to heat radiation and can emit it (active sensors) or only capture it (passive sensors). Within the food industry, they can be used to quickly detect heat differences in the food itself. These potentially indicate errors or can monitor a process.

In all cases, the data generated by the sensors can be used to make immediate decisions, but also to collect and build a history. For example, to check in retrospect whether processes went well or to observe certain trends.