Sensor technology for high-end coffee machines

category: Food Industry

date: 2020-10-30

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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 with a short waiting time. Coffee machines for salesrooms at gas stations brew more than 250 cups a day. They are very easy to use and they prepare each of the many different varieties quickly. When purchasing, the operators of filling stations and service areas pay attention to cost-effectiveness and process reliability, as well as to a simple cleaning process and reliable service from the manufacturer.

Image on the right: The WMF 9000 S+ fully automatic coffee machine is an expert for milk in different new variants.

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 specially developed for the high-performance sector. An ingenious milk system offers four different consistencies for hot milk froth and up to three variants for adding cold milk froth as well as hot and cold milk.

Small, precise, stable, fast response time, fast temperature measurement
An important part of the development process of the new coffee machine series was a smart flow sensor that should be able to measure cold and hot water as well as milk reliably and with high accuracy. The conditions in a coffee machine are not ideal for a flow sensor. The bursting pressure is up to 32 bar, temperatures of up to 130°C with steam are not uncommon. The sensor must therefore cover a wide range of technical properties in order to be used here. It also has to permanently withstand chemicals used to clean the coffee machine. At the same time, its materials should be durable and suitable for contact with food.

The most important criterion for WMF was the complete absence of moving parts in the flow sensor. As a result, impellers and vortex-based sensors failed from the start. In addition, it was only allowed to take up little space in the compact coffee machine: including the electronics, a maximum of 70 mm x 30 mm with a G3/8'' pipe connection was provided. In summary, WMF's wish list read as follows: small, precise, stable, fast response time, fast temperature measurement and approved for food and drinking water. Despite an extensive search, WMF was initially unable to find a supplier on the sensor market who could meet these key data.

Flexibility and inventiveness
When researching the right measuring component for its high-end model, WMF came across Allengra GmbH, a specialist in the development and production of ultrasonic flow sensors. Together with a world market leader from the heating industry, Allengra had already developed a compact ultrasonic sensor for wall-mounted gas heaters and finally supplied this for large-scale production. For the development of a flow sensor for its fully automatic coffee machine, WMF wanted exactly this mixture of flexibility and inventive spirit, with which Allengra was already able to offer its customers the right solution in previous projects. The decision came with the realization that Allengra "is two years ahead of its competition," according to WMF.

“The project was a close collaboration from the start. The engineers at WMF brought their experience and support to every development step,” says Raul Junker, founder and owner of Allengra. The ultrasonic flow sensor monitors the flow rate of the pump over a certain period of time. If this changes due to the running-in behavior, it is readjusted. As a result, the milk-pump no longer needs to be calibrated at the factory.

The ultrasonic flow sensor does this automatically. The amount of milk should remain constant, be precisely controllable and an empty container should be recognized early enough to give a tip for refilling. The sensor also detects air bubbles and informs the system about them.

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 until the end of a very long service life. The high-precision time-to-digital chip, which forms the computing heart of the Allengra sensor, 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. 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. To do this, 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.
The flow sensors from Allengra are already 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. 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," is how Raul Junker sums it up.

“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.”

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.

Raul Junker summarizes: "WMF is a good example of how technological innovation - used for the benefit of the customer - can strengthen competitiveness and secure market leadership."

Publications in specialist media:
1. Ultrasonic flow measurement: brewed sensor for brewed coffee [30.10.2020]
2. Sensor technology for high-end coffee machines [03.12.2020]