Sensor Technology for High-End Coffee Machines

October 30, 2020, 64 minute read

Coffee Machine Sketch

Over a development period of three and a half years, the coffee machine manufacturer WMF worked in collaboration with Allengra on an ultrasonic flow sensor for its latest generation of fully automatic coffee machines. The micro-flow sensor is packed with smart technology.

Anyone who pulls into a service area for a short pit-stop to get things going again with a coffee, expects the highest quality drinks for the shortest waiting time possible. Coffee machines installed in gas station salesrooms are designed to brew over 250 cups of coffee daily. Their popularity stands out because of their user-friendly operation and the ability to swiftly prepare a wide range of coffee varieties. Whether it’s a morning pick-me-up or a midday refresher, these machines deliver convenience and flavor to busy clients.

When purchasing, the operators pay attention to cost-effectiveness and process reliability, as well to a simple cleaning process and reliable service from the manufacture.

In this highly competitive market, you can only survive with innovation and a constant listening ear to the wishes of your customers and end users. The flagship of the Geislingen-based coffee machine manufacturer is called the WMF 9000 S+ and was developed for the high-performance sector. An ingenious milk dispensing system offers four different consistencies for hot milk froth and up to three variants for adding cold milk froth as well as for hot & cold milk.

Small, precise, stable, fast response time, fast temperature measurement

An important part of the development process for the new coffee machine series was a smart flow sensor, which is able to measure reliably and with high accuracy cold & hot water.
The conditions in a coffee machine are not ideal for an average flow sensor, with a bursting pressure of up to 32 bar, temperatures of up to 130°C, withstand strong cleaning chemicals and demand of durable and suitable materials for contact with food; the sensor must therefore cover a wide range of technical properties in order to be properly used.

The most important criterion for WMF was the complete absence of moving parts in the flow sensor, therefore the impellers and vortex-based sensors failed from the start.

The design specifications for these compact coffee machine were quite rigorous: components needed to be compact, accurate, robust, responsive, capable of rapid temperature detection, and compliant with food and water safety standards. After an intensive search, WMF was unable to find a sensor market supplier who could fulfill their specific requirements. However, during their pursuit for the ideal measuring component for their premium model, WMF discovered Allengra GmbH; a company that specializes in creating and manufacturing ultrasonic flow sensors and had previously collaborated with a leading companies in the heating sector to develop a compact ultrasonic sensor for wall-mounted gas heaters, which was then produced on a large scale.

WMF sought the same level of flexibility and creativity that Allengra had demonstrated in past projects for the manufacturing of a flow sensor for their high-end automatic coffee machines. WMF's choice was determined by Allengra’s recognition that it was two years ahead of its competitors in this field.

Raul Junker, the founder of Allengra, noted that the project was a partnership from the outset, with WMF engineers contributing their expertise and support at every stage of development. The ultrasonic flow sensor we developed monitors the pump's flow rate over time, adjusting it as necessary to account for any changes in performance. This innovation means that the milk pump no longer requires factory calibration, as the sensor automatically adjusts it. It ensures a consistent milk volume, precise control, and early detection of an empty container to prompt refilling. Additionally, the sensor is capable of detecting air bubbles equipped with an alerting system.

Packed with smart technology

Ultrasonic sensors do not use mechanical counters. As a result, there is no wear of individual parts and the precision of the measurement is retained along with a very long lifetime. The high-precision time-to-digital chip, which forms the computing heart of the Allengra sensor, which is ideal for this application. With a response time of 50 ms, the sensor measures the smallest flow rates, down to 1 ml/sec. Compared to other measurement techniques, the ultrasonic sensor offers the advantage of a design that is free of empty spaces, a must for approval in the food industry.

WMF tested the sensor extensively for its purposes and among other things, it was discovered that the fast response time of the sensor was influenced by the ambient temperature. A fast and precise temperature measurement was necessary (response time of 100ms) to compensate for this effect.; Allengra implemented a sophisticated solution, a combination of the time-of-flight measurement of the ultrasonic signal and the values of the platinum temperature sensor. With this method, the temperature of the liquid is obtained immediately without being affected by the ambient temperature.

Allengra's flow sensor come equipped with certain basic elements that have already proven useful in other projects: The micro-flow sensor used for WMF is also packed with smart technology.

High precision, detection of the smallest flow rates

Metallic parts and liquids quickly form condensation, which can affect the accuracy of the sensor, therfore to improve its response time and temperature transfer, WMF and Allengra tested other different materials to suitably insulate the metal and prevent condensation.

"The entire development period was a collaboration at a very high technical level...We have gained a lot of new experience in the field of high-frequency ultrasonic measurement, which we will use for our next projects in the food industry, but also for new applications in the pharmaceutical, beverage, and automotive (fuel volume flow) sectors. Wherever high precision and detection of the smallest flow rates are important."

-says Raul Junker 

The Allengra micro-flow sensor is now in series production at WMF and is used in the WMF 1500 S+, WMF 5000 S+ and WMF 9000 S+ models. The sensor supports WMF in its efforts to have all beverage quality-relevant processes in its coffee machines "under control" for its customers - in this case, for example, to keep the dosing quantities and dispensing temperatures of the coffee specialties, as well as the milk foam consistency, constant during the entire operating time of the coffee machine.

Check out Allengra's products and request a quote from us today!

If you continue to use this site means you accept Terms and Conditions and Privacy Policy. We use cookies to ensure that we give you the best experience on our website.

Read privacy policy