FEATURE
SENSORS & SENSING SYSTEMS
The fuTure belongs To smarT sensors Smart sensors offer many
advantages to the food industry.
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. Andy Walker of ifm electronic comments
S
ensors are used throughout the food manufacturing and processing sector to monitor important parameters such as
pressure, temperature, flow and level. Despite often having the same specifications as sensors used in other process industries, these also need to have an hygienic design and, in some cases, be suitable for use in hazardous areas. In addition to offering hygienic solutions,
leading sensor manufacturers are increasingly focussing on applying innovative technology to provide added value to their products. One example 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. Of benefit, 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. They can also accurately and reliably measure liquid levels in many foaming applications. The probes for the food-industry versions of
these 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. These can even be cut to length if necessary. Some also have an IO-Link interface. Added value is also 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 calibration requirements.
Io-lInk CommunICaTIon
Growing adoption of Industry 4.0 means 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. For many users of industrial automation
systems, sensor level communication means IO-Link – and the 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; and it is even possible to access self-diagnostic data from sensors that have an IO-Link interface, making the location of faulty devices faster and more certain. Also important in digital sensor communication
is the transmission of sensor data to ERP and other high-level corporate systems. A
10 DESIGN SOLUTIONS NOVEMBER 2021
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.
ifm electronic T: 020 8213 1111
www.ifm.com/uk
Sensors are essential for the automation of many processes in the food industry
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