Serving up smart sensors

AUTOMATION SYSTEMS in the food manufacturing sector depend on data from huge numbers of sensors that monitor parameters like pressure, temperature, flow and level. The specifications for these sensors are similar to those in any process industry but hygienic design is often an additional and critical requirement. Many sensors are now available in hygienic versions for food industry applications, and manufacturers are increasingly focussing development efforts on providing added value for users.

A good example is new level sensors that use guided wave radar (GWR). Installed vertically at the top of a tank, these sensors emit high-frequency electromagnetic pulses that are guided downwards along a stainless-steel rod. The pulses are 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.

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 measure liquid levels in many foaming applications. Food-industry versions follow hygienic design principles to meet the requirements of EHEDG and the best types feature an IO-Link interface.

Another example of added value is provided by temperature sensors with two sensor elements that have opposing temperature characteristics. The elements – Pt1000 and NTC thermistor – are continuously monitored by a microprocessor within the sensor. This verifies that the measured temperature is valid based on a user-defined maximum temperature “drift” between the two sensors. If the maximum drift is exceeded, this is signalled via a diagnostic output. All measured temperature values are available via IO-Link. These new sensors provide assurance of accuracy between calibrations, which may mean that costly calibration is needed less often.

Communication via IO-Link

The adoption of Industry 4.0 concepts means that communication between devices and systems is increasingly important. And communication at sensor level is the basis for communication infrastructures extending to corporate level and beyond.

For many users of industrial automation system, sensor-level communication means IO-Link and the latest sensors support this protocol as well as providing conventional analogue interfaces. With IO-Link, electrical interference has no effect on the accuracy of the measurement and multiple values from a single sensor can be transmitted simultaneously, adding even more value for the user.

There are also benefits during maintenance and repair. Sensors can be configured via IO-Link, so if it is necessary to fit a replacement, configuration data can be sent directly to it. Time-consuming setting up is eliminated, so the plant can be put back into service more quickly. Users can even access sensor self-diagnostic data via IO-Link, which makes it fast and easy to locate faulty devices fast and certain.

Data transmission to ERP

Another important aspect of sensor communication is the transmission of data to ERP systems. Agent connectivity ports – software gateways that support bidirectional communication for a wide range of interfaces – provide a convenient solution. They allow communication between ERP systems and devices at the field, control and process control levels. Implementations specifically designed to capture and transmit data from IO-Link sensors are available and, with these, data can be sent directly from sensors to the ERP system without passing through a PLC.

This direct path for sensor data 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 to the ERP system. This solution opens up possibilities, such as condition-based maintenance, that would be hard to implement with conventional sensors.

Andy Walker is product sales manager at IFM Electronic

www.ifm.com/gb/en