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Smart sensors in the food industry

30 November 2023

The food industry presents challenging environments for components and, in particular, for the sensors used in process control applications. In addition, users’ expectations of sensor technology are continually increasing. These considerations mean that the future belongs to smart sensors that not only offer outstanding performance and reliability but also deliver substantial added value, says Andy Walker of ifm electronic.

Many processes in the food industry require accurate control of the temperature of fluids.
Many processes in the food industry require accurate control of the temperature of fluids.

Automation systems in the food manufacturing and processing sector depend on data from huge numbers of sensors. The most important parameters monitored by these sensors include pressure, temperature, flow and level. Many of the specifications for these sensors are the same as those in any other process industry but, in the food sector, hygienic design is often an additional and critical requirement. And in some cases, the sensors must also be suitable for use in hazardous areas.

Sensors with added value
Many sensor products are now available in hygienic versions designed specifically for food industry applications, and leading manufacturers of these sensors are increasingly focussing their development efforts on applying innovative technology to provide added value for users of their products.

A good example of these innovations is a new generation of level sensors that operate on the guided wave radar (GWR) principle. GWR sensors are installed vertically at the top of a tank and emit high frequency electromagnetic pulses that are guided downwards along a stainless-steel rod. These pulses are then reflected from the surface of the medium back towards the sensor. The transit time of the pulses is used to evaluate the distance to the surface and thus the level in the tank. 

This measuring technology provides important benefits over other types of level sensors. GWR sensors are unaffected by changing media (provided that the dielectric constant >5), changing temperature, gas blankets or vapours, or by build-up of product on the probe itself.  In addition, they can accurately and reliably measure liquid levels in many foaming applications.

The probes for the food-industry versions of these innovative sensors are made of high-grade stainless steel and all other components follow hygienic design principles to meet the requirements of EHEDG. Probes with different lengths are available and can be easily interchanged by the user to meet the needs of the application. The probes can also be cut to length if no suitable standard length is available. This modular design maximises versatility and reduces costs. The best of these sensors also has an IO-Link interface.

Another example of sensors that offer added value is provided by temperature sensors that incorporate two sensor elements with opposing temperature characteristics. The elements – Pt1000 and NTC thermistor – operate independently and are continuously monitored by a microprocessor within the sensor. This verifies that the measured temperature value is valid based on a user defined temperature differential or “drift” between the two sensors. If the internal drift is exceeded then it is signalled immediately via a separate diagnostic output. Both measured temperature values, the differential value as well as the diagnostic value, are available via IO-Link. 

The use of these sensors in temperature critical processes provides assurance of measurement, and therefore process performance, between calibration intervals and may therefore reduce requirements for costly calibration.

Communication via IO-Link
With the growing interest in and adoption of Industry 4.0, communication between devices and systems has never been more important. Communication at sensor level is the basis for comprehensive communication infrastructures that extend all the way up to corporate level and beyond. 

Type LR level sensors from ifm electronic operate to the guided wave radar principle which eliminates incorrect measurements due to foam and the build up of residues and deposits.
Type LR level sensors from ifm electronic operate to the guided wave radar principle which eliminates incorrect measurements due to foam and the build up of residues and deposits.

For many users of industrial automation systems, sensor level communication means IO-Link and latest generation of sensors use this digital protocol as well as providing conventional analogue interfaces such 4...20 mA. With IO-Link, interference on the connecting cable to the sensor has no effect on the accuracy of the measurement. This is a big benefit compared with analogue interfaces, where measurements can be severely affected by interference. Further, with IO-Link, multiple values from a single sensor can be transmitted simultaneously adding even more value to the user.

IO-Link also has benefits during maintenance and repair. Since sensors can be configured via IO-Link, should it become necessary to replace a sensor, the configuration data can be transferred directly to it. The time-consuming process of setting up the sensor on site is eliminated, which means that the time needed to put the plant back into service is significantly reduced. Users can even access self-diagnostic data from sensors that have an IO-Link interface, making the location of faulty devices faster and more certain. Once again, this helps to reduce plant downtime.

Data transmission to an ERP system
Another important aspect of the digital sensor communication is the transmission of sensor data to ERP and other high-level corporate systems. A convenient way of achieving this is to use an agent connectivity port, which is a software gateway that supports bidirectional communication for a wide range of different interfaces. This makes possible communication between ERP systems and devices at the field, control and process control levels. Implementations specifically designed for the capture and transmission of data from IO-Link sensors are available and, with these, data can be transmitted directly from sensors to the ERP system without the need for it to pass through a PLC.

This direct path for sensor data which bypasses the control level is referred to as "Y communication" because the data splits like the letter Y, flowing via one branch to the PLC and via the other branch to the ERP and other corporate systems. This solution opens up possibilities that would be hard to implement with conventional sensors and analogue interfaces. Data logging, condition-based maintenance and improvement of energy efficiency are just some of these.

The future belongs to smart sensors 
Smart sensors offer many advantages in food industry and can significantly reduce costs. Today many automation solutions still use analogue sensors, but the adoption of sensors with IO-Link interfaces is increasing rapidly, as more and more users become aware of the added value they provide.

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