In the case of the flow sensors we have been able to cut the development times in half through the use of cutting edge, scientifically founded simulation and testing methods.

In cooperation with the University RWTH Aachen, our developers have advanced CFD simulation (computational fluid dynamics) methods to new levels. CFD simulation enables the flow behavior of the heating water in the flow sensor to be cal-culated as a function of its geometry, the flow velocity and the temperature. The re-sults of the CFD simulation are then checked experimentally using particle image velocimetry (PIV methods). This involves using a special laser technique to make the water flow visible with high resolution. It is then filmed and compared with the calcula-tions. On the basis of these observations we are now able determine which specific minor modifications to the geometry must be made in order to achieve reproducible largely linear characteristic curves for our flow sensors. On top of that, the character-istic curves for vertical and horizontal operation are nearly identical. That means that measurements made with Engelmann magnetic inductive heat meters are just as independent of the mounting position as ultrasonic heat meters.

During the development we also paid attention to keeping the design practical for manufacturing. The flow sensors consist of only a few parts, which can be easily dis-tinguished and assembled. The non-magnetic impeller scanning is free of feedback and has a high level of resistance to interference. Each individual flow sensor is tested and calibrated (100% testing). On a computer-ized test bench the flow sensors are fully automatically pre-warmed and flushed, then measured at three flow rates. The volume measurements are checked against high-precision scales. The pulse values of the individual sensors are stored in a central database from which they can be retrieved later upon assembly of the complete heat meters.

For the development of our calculators we employ modern development tools such as PISPICE (numerical simulation) and MathCAD (symbolic and numerical circuit calculation). The results of these methods are extremely energy-saving, high-precision calculating counters.

In order to guarantee a superior level of reliability we produce our electronic assem-blies ourselves on an SMD technology assembly line specifically configured for our products. The line consists of a fully-automatic screen printing machine, a highly flexible six-head pick-and-place chip mounter and a four-zone reflow soldering oven. The screen printer applies the soldering paste with a tolerance of a few micrometers on the printed circuit boards, the results being 100% checked by a 3-D camera Then the circuit boards are assembled at a rate of 13,500 components per hour. The connections, the positions and the dimensions of all components are constantly checked by camera recognition. An optimized temperature profile ensures an extremely gentle soldering of the components in the reflow oven. Like the flow sensors, all of the electronic assemblies are tested and calibrated (100% testing). The measurement values are stored in the central database.

Our temperature sensor production line carries out the soldering, sealing of the tube and labelling of the sensors on processing equipment designed in-house. All of the temperature sensors are measured at three temperatures in precisely accurate thermostatic baths. This procedure also includes the storage of all measurement values in the central database.

Finally, when the heat meters are assembled, the individual characteristic curves of the temperature sensors and the flow sensors are retrieved from the database and programmed into the calculators. This exact electronic matching is the final step in the creation of the highly precise Engelmann heat meter.