Sensor Technology


In-house sensor secures competitive advantages


The number and variety of standard sensors appears enormous, and yet factors such as measurement methods, sizes, performance and


interfaces mean that many compromises have to be made in specific applications. Swiss company BELIMO Automation AG, the world's leading specialist in actuator, valve and sensor solutions for HVAC systems, has chosen an alternative that requires no compromises – and commissioned a


customised sensor solution S


o what prompted the company to commission the development of a customised, application-specific sensor solution? "Having our own sensor frees us from the dependencies and compromises associated with the integration of standard sensors. Standard sensors might seem cost-effective at first glance, but they present considerable risks – especially for specialists such as Belimo. If a major buyer requests changes, for example, manufacturers often respond by modifying specifications and models. This forces us to invest a great deal of time and money in modifying our applications, or we pay for sensor features that we do not need. The situation is similar when it comes to availability. Operating our own sensor production facilities tailored precisely to our needs and requirements not only gives us plenty of freedom but also secures competitive advantages for us," explains Andreas Marty, head of Product Management for Europe, Room & Systems Solutions, at BELIMO Automation AG, Hinwil, Switzerland. Most people never see Belimo


products, and yet they play a crucial role. To guarantee energy-efficient operation as well as adequate ventilation and air- conditioning, modern buildings feature highly complex, precision-regulated


32 November 2018


variable-air-volume (VAV) ventilation systems. Belimo supplies damper manufacturers with the necessary volumetric flow controllers. These and other specialty products generate worldwide sales of more than €490 million for the Swiss company.


Compact control unit Belimo's core product in the single-room range is the VAV-Compact D3, a neatly packaged electronic unit that combines measurement, regulation and control functions. The VAV-Compact D3 is mounted from the outside on a special air damper. Pressure differences are measured by a differential pressure sensor in the duct segment (a constriction or flow element). The device uses the pressure difference to calculate the current volumetric flow rate, compares it with the target value and uses the motor to reposition the damper blade. Information is transmitted to fan controllers, maintenance systems and monitoring systems via digital interfaces connected to various bus systems. "This application imposes very specific


requirements on the sensor. The most important factor is that the unit is installed in the building, amid the labyrinthine network of ventilation ducts. This requires a sensor solution that is extremely stable over long periods, fully calibrated and suitable for all installation positions. Stability over long periods is important for the accurate, long-term reproducibility of measurements as well


Components in Electronics


as resistance to dirt. It is also essential that the sensor and electronics form a compact module that can be easily installed in our housings without taking up too much space," says Andreas Marty.


MEMS differential pressure sensor including microprocessor A team of developers from First Sensor in Weissensee, Berlin, has worked with Belimo on a range of sensors and electronics. It was a project that took almost four years from the initial discussions to series production at First Sensor, but that has now given Belimo a lasting edge over the competition.


The customised First Sensor solution is a flow-based MEMS pressure sensor that connects to the ventilation duct with two robust pressure hoses. The flow channel in the sensor is extremely narrow. As a result, the small quantity of air flowing through protects the sensor unit from contamination. The calorimetric measurement principle employed by the sensor involves a heating element that creates a temperature profile in the medium which is displaced by the air flow. This results in temperature differences at upstream and downstream


thermopiles, which are measured in the form of electrical voltage and serve as a means of calculating pressure differences at the sensor. Yet that is not all from the Berlin-based sensor specialists. The electronic assembly with which the sensor is installed features a microprocessor for linearisation and temperature compensation for the signal/pressure curve, including purpose- built electronics and firmware. The entire assembly is produced and calibrated at the First Sensor factory.


www.first-sensor.com www.cieonline.co.uk


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