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A Resonant Rolling Sphere Viscometer Using Magnetic Actuation and Readout
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ScienceDirect Procedia Engineering 168 (2016) 670 – 674
30th Eurosensors Conference, EUROSENSORS 2016
A resonant rolling sphere viscometer using magnetic actuation and readout S. Clara*, B. Antensteiner, W. Hilber, B. Jakoby Institute for Microelectronics and Microsensors Johannes Kepler University Linz, AUSTRIA
Abstract We present a viscosity measurement principle based on a metallic sphere rolling on a plane on a circular trajectory. The sphere is magnetically positioned and driven using a permanent magnet and four actuation coils placed below the rolling surface. This measurement principle is particularly suited for the characterization of thin fluid films and therefore also for cases where small sample volumes are available. We describe our prototype setup consisting of three parts: the probing body (sphere), the actuation part, and the readout part. For the readout two differential transformer arrangements are used, yielding a total of required five coils: one pair of readout coils for one direction and another pair perpendicular to it for the orthogonal direction. The fifth coil is used as primary coil in the differential transformer readout setup where the aforementioned coil pairs act as secondary coils. In this contribution we describe the sensor setup, outline the actuation and readout process and present first measurements. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing the organizing committee of the 30th Eurosensors Conference. Peer-review under responsibility of the committee of the 30th Eurosensors Conference Keywords: viscosity, resonant, rotatory oscillations, magnetically actuated
1. Introduction Viscosity sensors are used in chemical industry to monitor and control production processes [1]. Inline viscosity measurements increase the sample rate and optimize the process output [2]. Miniaturized resonant viscosity sensors offer accuracy and speed at low cost (see [3], [4] and [5]).
* Corresponding author. Tel.: +43 732 2468-6250; fax: +43 732 2468-6252. E-mail address: [email protected]
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference
doi:10.1016/j.proeng.2016.11.244
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
Recently presented resonant viscosity sensors [3] often need mechanical or electrical connections and/or wires for actuation and readout into the measurement camber. In many cases these elements interact with the sample liquid which can cause problems if the sample liquid is a solvent or corrosive. In our approach we avoid any direct contact of the sensor system with the fluid to be measured except for the sphere and the bearing surface. Both the actuation (Fig. 1 and Fig. 2) and the readout (Fig. 3) are working electromagnetically which avoids spurious effects as almost all liquids show a relative permeability of approximately one. The choice of the sphere as sensitive part is due to the comparability to standard laboratory viscometers such as the falling or the rolling sphere viscometer [6]. In the following we present the sensor setup and describe its working principle, we outline the actuation and readout of the sensor and present first measurement results. 2. Setup The mechanical parts of the sensor setup shown in Fig. 1 - Fig. 3 are manufactured using Vacoflux 50 steel (high permeability) for the magnetic circuit, stainless steel for the rolling surface (slightly ferromagnetic) and stainless steel (strongly ferromagnetic) for the sphere. A silicon-wafer was placed on the rolling surface to obtain a better surface flatness. The most important parts for the resonance characteristics of the sensor setup discussed below are the permanent magnet, which provides the restoring forces acting on the sphere, and the sphere itself with its magnetic properties, size and mass. For the actuation and the readout several coils are used (see Fig. 1 and Fig. 3), their working principle is explained below.
Fig. 1: Sensor prototype, consisting of the sphere, the rolling surface, a permanent magnet, four actuation coils and the readout coils shown in Fig. 2.
Fig. 2: Top view of the setup showing the sphere on the rolling surface. Parts of the actuation coils can be seen under the rolling surface.
Mathematically the system can be described as a spring mass oscillator where the restoring force acting on the sphere is generated by the permanent magnet placed below the rolling surface. For large deflection amplitudes this force is nonlinearly dependent on the position of the sphere. 3. Actuation, Readout and Signal processing The actuation part of the sensor setup consists of five actuation coils (see Fig. 1) mounted below the rolling surface. The first one is placed in the center of the setup and can be used to superimpose the magnetic field of the permanent magnet which provides the restoring force acting on the sphere. A change of this field leads to a shift of the resonance frequency. The other four actuation coils are placed around the center coil. For the stimulation of the sphere, the geometrically opposing actuation coils are actuated differentially. The phase shift between two adjacent coil currents is 90° so that a circulating field is generated. This field superimposes the constant field of the permanent magnet and leads to an alternating force acting on the sphere. The latter starts to perform rolling movements on a circular path. For the analyses of the resonance characteristics the deflection in x-direction is used.
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S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
Note that the restoring force of the permanent magnet is nonlinearly dependent on the distance of the sphere from the center therefore a strong Duffing effect [7] can be seen for larger actuation current amplitudes resulting in larger deflections and therefore larger radii of the circular motion. The readout is based on the differential transformer principle. Fig. 3 shows the bottom of the rolling surface including the permanent magnet and the readout coils. The circularly shaped coil in the center is the primary coil of the transformer. This coil is actuated with a sinusoidal signal with constant amplitude of 15 mA at 10 kHz. The rectangularly shaped coils below the primary coil are the secondary coils. For the readout of the sphere position in xor y-direction, two of these coils are connected differentially. Depending on the position of the sphere, the amplitude of the induced voltage (due to the change of the magnetic field generated by the primary coil) is modulated. Fig. 4 shows the amplified differential signal in x-direction. This signal can be divided into three parts: the induced modulated voltage of the primary coil (10 kHz), the induced voltage due to the moving sphere modulating the magnetic field of the permanent magnet (12 Hz) and a non-modulated offset voltage due to fabrication asymmetry (10 kHz). Note if the setup is totally symmetric and the sphere is placed in the middle no induced differential voltage is measured. For the calculation of the sphere position only the modulated 10 kHz signal is of interest. By demodulating it using a lock-in principle, the sphere position can be calculated.
Fig. 3: Rolling surface (upside down) containing the four readout coils (rectangular shape), the primary coil (round shape) and the permanent magnet in the center.
Fig. 4: Amplified measurement signal of the induced differential voltage. Clearly visible is also the induced voltage due to the moving sphere modulating the magnetic field of the permanent magnet.
4. Measurements We measured the frequency response of the system for different viscous fluids. For this we deposited 10 µl of viscosity standard oil on the sphere and actuated it with constant current amplitude. Due to the viscosity of the oil the movement of the sphere is damped and the radius of the circular path is influenced. A higher viscosity leads to a higher damping and to a smaller radius. The measured sphere position was plotted versus the actuation frequency. Fig. 5 shows three resonance curves for different viscosity standard oils. In a next step a second order model was fitted to the measurement points and the resonance frequency fr and the quality factor Q were extracted. Table 1. Measurement results. Nominal viscosity K
Resonance frequency fr
Quality factor Q
14.50 mPas
43.0 Hz
8.47
39.58 mPas
42.8 Hz
5.62
70.65 mPas
42.8 Hz
3.36
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
A closer look on the measurement curves shows two spurious effects. The red curve shows deviations from the theoretical model, due to contaminations and scratches on the surface. For the blue curve the actuation radius is already very large so that the magnetic restoring force is nonlinear.
Fig. 5: Measured resonance curve giving the output of the differential transformer setup (corresponding to the sphere’s deflection) for different actuation frequencies. 10 µl of viscosity standard oil where dropped on the sphere to serve as liquid to be investigated.
5. Conclusion We presented a viscosity measurement principle based on a rolling sphere. The sphere is placed on a flat surface and positioned magnetically. It is actuated by four electromagnetic coils to perform circular movements. For the position readout a differential transformer principle is used, a primary coil generates a sinusoidal magnetic field with a frequency of 10 kHz, leading to a modulated induced voltage, depending on the position of the sphere, in the secondary coils. The frequency response of the system is measured and the quality-factor Q is calculated. This factor is related to the viscosity of the fluid. The sensor system has some drawbacks: the magnetic coupling is nonlinear and influences the results for larger deflection radii of the sphere. This problem can be solved by measuring at a constant radius by controlling the actuation currents accordingly. The second problem is related to contaminations. Although the surface quality of the rolling surface and the sphere are very high, even small particles influence the rolling characteristics of the sphere leading to measurement errors. In a next step the tunability of the system will be investigated. To do so, the shift of the resonance frequency due to a constant current in the center actuation coil will be examined. Also the possibility of an active linearization of the magnetic spring constant by applying a current to the center actuation coil (dependent on the sphere position) is of interest. Acknowledgements Financial support was provided by the Austrian research funding association (FFG) under the scope of the COMET program within the research project “Industrial Methods for Process Analytical Chemistry - From Measurement Technologies to Information Systems (imPACts)” (contract # 843546), and the Austrian COMET Program (Linz Center of Mechatronics). References [1] [2]
A Nahm, Steven H., „Use of dielectric spectroscopy for real-time in-situ reaction monitoring “, JCT Research, 2006 , 10.1007/s11998-0060021-6 P. Kroll, P. Sagmeister, W. Reichelt, L. Neutsch, T. Klein, and C. Herwig, “Ex situ online monitoring: application, challenges and opportunities for biopharmaceuticals processes,” Pharmaceutical Bioprocessing, vol. 2, no. 3, pp. 285–300, Jun. 2014.
673
674
[3]
[4] [5] [6] [7]
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
B. Jakoby, R. Beigelbeck, F. Keplinger, F. Lucklum, A. Niedermayer, E.K. Reichel, C. Riesch, T. Voglhuber-Brunnmaier, B. Weiss, "Miniaturized sensors for the viscosity and density of liquids-performance and issues," Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on , vol.57, no.1, pp.111,120, Jan. 2010 Antlinger, H., Clara, S., Beigelbeck, R., Cerimovic, S., Keplinger, F., & Jakoby, B. (2012). Sensing the characteristic acoustic impedance of a fluid utilizing acoustic pressure waves. Sensors and Actuators A: Physical, 186, 94-99. Heinisch, Martin, et al. "Tunable resonators in the low khz range for viscosity sensing." Sensors and Actuators A: Physical 186 (2012): 111117. L. D. Landau and E. M. Lifshitz, “Fluid Mechanics”, Pergamon, Press, London, UK, 1959. I. Kovacic and M.J. Brennan, “The Duffing Equation: Nonlinear Oscillators and their Behaviour”, John Wiley & Sons, 2011.
ScienceDirect Procedia Engineering 168 (2016) 670 – 674
30th Eurosensors Conference, EUROSENSORS 2016
A resonant rolling sphere viscometer using magnetic actuation and readout S. Clara*, B. Antensteiner, W. Hilber, B. Jakoby Institute for Microelectronics and Microsensors Johannes Kepler University Linz, AUSTRIA
Abstract We present a viscosity measurement principle based on a metallic sphere rolling on a plane on a circular trajectory. The sphere is magnetically positioned and driven using a permanent magnet and four actuation coils placed below the rolling surface. This measurement principle is particularly suited for the characterization of thin fluid films and therefore also for cases where small sample volumes are available. We describe our prototype setup consisting of three parts: the probing body (sphere), the actuation part, and the readout part. For the readout two differential transformer arrangements are used, yielding a total of required five coils: one pair of readout coils for one direction and another pair perpendicular to it for the orthogonal direction. The fifth coil is used as primary coil in the differential transformer readout setup where the aforementioned coil pairs act as secondary coils. In this contribution we describe the sensor setup, outline the actuation and readout process and present first measurements. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing the organizing committee of the 30th Eurosensors Conference. Peer-review under responsibility of the committee of the 30th Eurosensors Conference Keywords: viscosity, resonant, rotatory oscillations, magnetically actuated
1. Introduction Viscosity sensors are used in chemical industry to monitor and control production processes [1]. Inline viscosity measurements increase the sample rate and optimize the process output [2]. Miniaturized resonant viscosity sensors offer accuracy and speed at low cost (see [3], [4] and [5]).
* Corresponding author. Tel.: +43 732 2468-6250; fax: +43 732 2468-6252. E-mail address: [email protected]
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 30th Eurosensors Conference
doi:10.1016/j.proeng.2016.11.244
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
Recently presented resonant viscosity sensors [3] often need mechanical or electrical connections and/or wires for actuation and readout into the measurement camber. In many cases these elements interact with the sample liquid which can cause problems if the sample liquid is a solvent or corrosive. In our approach we avoid any direct contact of the sensor system with the fluid to be measured except for the sphere and the bearing surface. Both the actuation (Fig. 1 and Fig. 2) and the readout (Fig. 3) are working electromagnetically which avoids spurious effects as almost all liquids show a relative permeability of approximately one. The choice of the sphere as sensitive part is due to the comparability to standard laboratory viscometers such as the falling or the rolling sphere viscometer [6]. In the following we present the sensor setup and describe its working principle, we outline the actuation and readout of the sensor and present first measurement results. 2. Setup The mechanical parts of the sensor setup shown in Fig. 1 - Fig. 3 are manufactured using Vacoflux 50 steel (high permeability) for the magnetic circuit, stainless steel for the rolling surface (slightly ferromagnetic) and stainless steel (strongly ferromagnetic) for the sphere. A silicon-wafer was placed on the rolling surface to obtain a better surface flatness. The most important parts for the resonance characteristics of the sensor setup discussed below are the permanent magnet, which provides the restoring forces acting on the sphere, and the sphere itself with its magnetic properties, size and mass. For the actuation and the readout several coils are used (see Fig. 1 and Fig. 3), their working principle is explained below.
Fig. 1: Sensor prototype, consisting of the sphere, the rolling surface, a permanent magnet, four actuation coils and the readout coils shown in Fig. 2.
Fig. 2: Top view of the setup showing the sphere on the rolling surface. Parts of the actuation coils can be seen under the rolling surface.
Mathematically the system can be described as a spring mass oscillator where the restoring force acting on the sphere is generated by the permanent magnet placed below the rolling surface. For large deflection amplitudes this force is nonlinearly dependent on the position of the sphere. 3. Actuation, Readout and Signal processing The actuation part of the sensor setup consists of five actuation coils (see Fig. 1) mounted below the rolling surface. The first one is placed in the center of the setup and can be used to superimpose the magnetic field of the permanent magnet which provides the restoring force acting on the sphere. A change of this field leads to a shift of the resonance frequency. The other four actuation coils are placed around the center coil. For the stimulation of the sphere, the geometrically opposing actuation coils are actuated differentially. The phase shift between two adjacent coil currents is 90° so that a circulating field is generated. This field superimposes the constant field of the permanent magnet and leads to an alternating force acting on the sphere. The latter starts to perform rolling movements on a circular path. For the analyses of the resonance characteristics the deflection in x-direction is used.
671
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S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
Note that the restoring force of the permanent magnet is nonlinearly dependent on the distance of the sphere from the center therefore a strong Duffing effect [7] can be seen for larger actuation current amplitudes resulting in larger deflections and therefore larger radii of the circular motion. The readout is based on the differential transformer principle. Fig. 3 shows the bottom of the rolling surface including the permanent magnet and the readout coils. The circularly shaped coil in the center is the primary coil of the transformer. This coil is actuated with a sinusoidal signal with constant amplitude of 15 mA at 10 kHz. The rectangularly shaped coils below the primary coil are the secondary coils. For the readout of the sphere position in xor y-direction, two of these coils are connected differentially. Depending on the position of the sphere, the amplitude of the induced voltage (due to the change of the magnetic field generated by the primary coil) is modulated. Fig. 4 shows the amplified differential signal in x-direction. This signal can be divided into three parts: the induced modulated voltage of the primary coil (10 kHz), the induced voltage due to the moving sphere modulating the magnetic field of the permanent magnet (12 Hz) and a non-modulated offset voltage due to fabrication asymmetry (10 kHz). Note if the setup is totally symmetric and the sphere is placed in the middle no induced differential voltage is measured. For the calculation of the sphere position only the modulated 10 kHz signal is of interest. By demodulating it using a lock-in principle, the sphere position can be calculated.
Fig. 3: Rolling surface (upside down) containing the four readout coils (rectangular shape), the primary coil (round shape) and the permanent magnet in the center.
Fig. 4: Amplified measurement signal of the induced differential voltage. Clearly visible is also the induced voltage due to the moving sphere modulating the magnetic field of the permanent magnet.
4. Measurements We measured the frequency response of the system for different viscous fluids. For this we deposited 10 µl of viscosity standard oil on the sphere and actuated it with constant current amplitude. Due to the viscosity of the oil the movement of the sphere is damped and the radius of the circular path is influenced. A higher viscosity leads to a higher damping and to a smaller radius. The measured sphere position was plotted versus the actuation frequency. Fig. 5 shows three resonance curves for different viscosity standard oils. In a next step a second order model was fitted to the measurement points and the resonance frequency fr and the quality factor Q were extracted. Table 1. Measurement results. Nominal viscosity K
Resonance frequency fr
Quality factor Q
14.50 mPas
43.0 Hz
8.47
39.58 mPas
42.8 Hz
5.62
70.65 mPas
42.8 Hz
3.36
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
A closer look on the measurement curves shows two spurious effects. The red curve shows deviations from the theoretical model, due to contaminations and scratches on the surface. For the blue curve the actuation radius is already very large so that the magnetic restoring force is nonlinear.
Fig. 5: Measured resonance curve giving the output of the differential transformer setup (corresponding to the sphere’s deflection) for different actuation frequencies. 10 µl of viscosity standard oil where dropped on the sphere to serve as liquid to be investigated.
5. Conclusion We presented a viscosity measurement principle based on a rolling sphere. The sphere is placed on a flat surface and positioned magnetically. It is actuated by four electromagnetic coils to perform circular movements. For the position readout a differential transformer principle is used, a primary coil generates a sinusoidal magnetic field with a frequency of 10 kHz, leading to a modulated induced voltage, depending on the position of the sphere, in the secondary coils. The frequency response of the system is measured and the quality-factor Q is calculated. This factor is related to the viscosity of the fluid. The sensor system has some drawbacks: the magnetic coupling is nonlinear and influences the results for larger deflection radii of the sphere. This problem can be solved by measuring at a constant radius by controlling the actuation currents accordingly. The second problem is related to contaminations. Although the surface quality of the rolling surface and the sphere are very high, even small particles influence the rolling characteristics of the sphere leading to measurement errors. In a next step the tunability of the system will be investigated. To do so, the shift of the resonance frequency due to a constant current in the center actuation coil will be examined. Also the possibility of an active linearization of the magnetic spring constant by applying a current to the center actuation coil (dependent on the sphere position) is of interest. Acknowledgements Financial support was provided by the Austrian research funding association (FFG) under the scope of the COMET program within the research project “Industrial Methods for Process Analytical Chemistry - From Measurement Technologies to Information Systems (imPACts)” (contract # 843546), and the Austrian COMET Program (Linz Center of Mechatronics). References [1] [2]
A Nahm, Steven H., „Use of dielectric spectroscopy for real-time in-situ reaction monitoring “, JCT Research, 2006 , 10.1007/s11998-0060021-6 P. Kroll, P. Sagmeister, W. Reichelt, L. Neutsch, T. Klein, and C. Herwig, “Ex situ online monitoring: application, challenges and opportunities for biopharmaceuticals processes,” Pharmaceutical Bioprocessing, vol. 2, no. 3, pp. 285–300, Jun. 2014.
673
674
[3]
[4] [5] [6] [7]
S. Clara et al. / Procedia Engineering 168 (2016) 670 – 674
B. Jakoby, R. Beigelbeck, F. Keplinger, F. Lucklum, A. Niedermayer, E.K. Reichel, C. Riesch, T. Voglhuber-Brunnmaier, B. Weiss, "Miniaturized sensors for the viscosity and density of liquids-performance and issues," Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on , vol.57, no.1, pp.111,120, Jan. 2010 Antlinger, H., Clara, S., Beigelbeck, R., Cerimovic, S., Keplinger, F., & Jakoby, B. (2012). Sensing the characteristic acoustic impedance of a fluid utilizing acoustic pressure waves. Sensors and Actuators A: Physical, 186, 94-99. Heinisch, Martin, et al. "Tunable resonators in the low khz range for viscosity sensing." Sensors and Actuators A: Physical 186 (2012): 111117. L. D. Landau and E. M. Lifshitz, “Fluid Mechanics”, Pergamon, Press, London, UK, 1959. I. Kovacic and M.J. Brennan, “The Duffing Equation: Nonlinear Oscillators and their Behaviour”, John Wiley & Sons, 2011.