4.4 Viscosity Control Technologies for the Controlled Application of Coating Materials

The control electronics and its associated DSP algorithms, which are used to run viscosity sensors, were adapted to a novel inline sensor technology. Next, a flow loop system was developed and set up to test the inline sensors under controlled conditions and to perform a complete characterization of the sensors. Once the flow-loop is extended by an automated thinner dosing, it becomes a fully automatic viscosity control system, which guarantees a constantly high coating quality and thus enables the user to make substantial savings in material, plant and working time.

Contributors: Partner(s): Funding: Duration: D. Fehr, U. Vögeli, A. Bariska, S. Hauri, N. Reinke Rheonics GmbH CTI 2016–2019

An control unit based on a DSP (Digital Signal Processor) was developed to evaluate the sensor signals of a new type of inline viscometer. The starting point was an electronic system from a previous project and its associated software. The analog front end and the algorithms were adapted to the new inline viscosity sensors. Figure 1: Characteristic decaying oscillation of a mechanical resonator for viscosity determination (top) and the associated spectrum from which the viscosity of the fluid can be deduced by determining the center frequency and bandwidth (bottom)). The underlying measuring principle can be described as follows: The electronics causes the mechanical resonator submerged in fluid to oscillate. The resonator’s resonant frequency and damping depend on the density and viscosity of the fluid. Figure 1 shows a typical oscillation waveform of the sensor, i.e. an exponentially decaying oscillation.

The DSP electronics determines the resonant frequency and damping based on the spectrum of the decay waveform, which is showed in in Figure 1, too. Parallel to the control electronics, a test system (flow loop) has been designed and implemented (Figure 2). It resembles a typical wet coating process: Conveying of coating material and thinner, a mixer, circulation with the inline viscosity sensor and a tap that simulates the application of the coating material. With the flow loop and the control electronics described above, the viscosity sensors can be tested and characterized under typical operating conditions. Furthermore, the system enables the development of an inline viscosity control system in which thinners are automatically mixed with the coating materials. With this technology a constant viscosity can be guaranteed in industrial coat-

ing plants.

Figure 1: Flow-loop test system.