The smaller the physical size, think of etching ultra-thin lines in semiconductor lithography, the greater – and the more attractive – the mechatronics challenge for DEMCON. Take how to measure a small flow of mass, for example. In commonly used thermal measuring principles, the medium’s other properties, such as density and thermal conductivity, can distort the measurements and therefore cause the precision of the measured values to be uncertain. The Coriolis measuring principle does not have this drawback. While the Coriolis principle has been known for a long time, no reliable instrument for measuring small flows was as yet available.
In collaboration with Bronkhorst®, producer of precise flowmeters, and building onto the research conducted by the University of Twente, DEMCON has developed a compact flowmeter that works on the basis of the Coriolis measuring principle. A rotational vibration is applied to a curved thin tube (< 1 mm diameter) for this purpose. The medium (fluid or gas) flowing through the tube generates Coriolis forces that cause a small change in the shape of the vibrational motion. The magnitude of the mass flowing through the tube follows directly from the measurement of this change, while the medium’s other properties do not have any distorting effect.
The challenge inherent in small flows primarily relates to the flow’s laminar character, with a more unfavourable scaling across the flow rate than turbulent flow, and to the sensitivity to disruption due to actuation, measurement and external vibrations. DECOM incorporated the necessary innovations into the design to address these issues. For example, the vibrating tube is shaped such that it is possible to suspend it as a slack tube that allows for the desired motion. In addition, innovations were applied to effect the contactless excitation of the vibration, the contactless measurement of the movements and the signal processing. In terms of precision, the signal-noise ratio of the sensors and the amplifiers is a limiting factor. This is why the measurement is translated into a phase difference or a time difference. This way an accurate clock is sufficient.
DEMCON completed the entire development process in close cooperation with Bronkhorst®, ranging from the initial proof-of-principle to a production-ready instrument, in terms of the mechanical construction, as well as the electronics and embedded software. Furthermore, DEMCON played an important role in the set up of the production process for the instrument’s core. This included special tools for accurately bending the thin tube and for soldering inside a mould. The market has since enthusiastically embraced the mini Coriolis. All reasons for the partners to further scale up together to produce devices for measuring larger as well as still smaller flows.