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Sascha Mäuselein, Oliver Mack P B T Silicon load cells Investigations of new silicon load cells with thin-film strain gauges SIM MWG11 – Load Cells Tests.

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Presentation on theme: "Sascha Mäuselein, Oliver Mack P B T Silicon load cells Investigations of new silicon load cells with thin-film strain gauges SIM MWG11 – Load Cells Tests."— Presentation transcript:

1 Sascha Mäuselein, Oliver Mack P B T Silicon load cells Investigations of new silicon load cells with thin-film strain gauges SIM MWG11 – Load Cells Tests by OIML R60 Buenos Aires, June 3010

2 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 2/19 Table of contents Introduction Mechanical spring made of silicon Investigations (I) Application of strain gauges Investigations (II) -> characteristic line -> time depending effects Evaluation according to OIML R60 Applications

3 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 3/19 Introduction Dominant sensor technologies in weighing instruments: Electromagnetic force compensation load cells Very high precision Complex technology Limited load range Strain gauge load cells Most common Maximum number of verification intervals: 6000 Limiting factors to step up the precision:  time depending effects  hysteresis

4 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 4/19 Introduction Single crystalline material (silicon) for the mechanical spring - High purity - Ideal elastic properties - Less mechanical after effects Thin film strain gauges - Direct connection - Less creep effects - High reproducibility Sensor with - High reproducibility - Low time depending effects - Good sensor properties - High potential to improve the properties by digital compensation Sputtering technique Crystal growth procedure

5 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 5/19 Spring made of single crystalline silicon Aspects of design:  Nominal load  Thin film application  Material properties of Si double bending beam geometry Numerical simulations to optimise the geometry parameters the orientation of Si within the spring Mechanical spring made of silicon

6 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 6/19 Investigations (I) – Experimental setup Schematic arrangement of the experimental setup Deformation measurements Fizeau Interferometer 3-D topology data of the surface ->Tipping effects can be calculated and corrected Loading Dead loads Wire and pulley to switch the load force Application of strain gauges in a later step Before:Investigation of the mechanical spring -> Time dependent deformation after load change

7 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 7/19 Investigations (I) – Experimental setup Picture of the experimental setup Pulley Interferometer Wire Si spring Masses Clamping

8 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 8/19 Investigations (I) – Results Surface topology as function of the positions x and y for different load steps Deflection sensitivity s u = nm/g Position of thin places

9 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 9/19 Investigations (I) – Results Normalised deflection u y,n as function of the time for loading and unloading Loading: Influence of pulley Unloading: No detectable creep behaviour Not suitable Mechanical after effect: ≤ 2·10 -5 Low time depending effects of silicon spring are verified

10 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 10/19 Application of thin film strain gauges Si load cell with thin film strain gauges Layer composition of the SGs - Connection of four strain gauges to a full bridge - Analysis by precision amplifier

11 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 11/19 Investigations (II) Load depending investigations of the sensor signal - Reproducibility - Hysteresis - Linearity Time depending investigations of the sensor signal - Creep

12 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 12/19 Investigations (II) – Experimental setup Picture of the experimental setup Clamping Connection of SGs Si load cell Chain masses Temperature measurement Humidity measurement Piece of hardwood

13 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 13/19 Investigations (II) – Reproducibility Relative repeatability error b as function of the load L By a factor of 10 better than the requirements for class 00 Classes according to ISO 376:

14 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 14/19 Investigations (II) – Hysteresis Relative reversibility error u as function of the load L About a factor of 10 better than the requirements for class 00 Classes according to ISO 376:

15 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 15/19 Investigations (II) – Linearity Relative interpolation error I as function of the load L Requirements for class 1 are kept Classes according to ISO 376:

16 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 16/19 Investigations (II) – Creep Relative creep C while loading as function of the time t Relative creep C while unloading as function of the time t Relative creep < 2∙10 -5 After 7 minutes: No creep detectable Relative creep < 2∙10 -5

17 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 17/19 Investigations (II) – Results Meaningful improvement by digital compensation is possible Reproducibility ++ + o 2∙10 -5 Hysteresis Linearity Creep 9∙ ∙ ∙10 -5 Next step: - Digital compensation of data concerning linearity and temperature - Evaluation of data according to OIML R60

18 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 18/19 Evaluation – OIML R60 Load cell error E LC as function of the load L Precision weighing instrument

19 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 19/19 Fields of application Load cells for precision measurements Transfer standard Thank you for your attention

20 Sascha Mäuselein, Oliver Mack P B T Silicon load cells 20/19 SiliziumAluminiumStahl (Ck67) Dichte in g/cm 3 2,332,707,85 Elastizitätsmodul in N/m 2 (13-18) · · ·10 7 Therm. Ausdehnungsk. in 1/K(2,3-2,6) ·10 -6 (23-25) · ·10 -6 Zugbruchfestigkeit in N/m 2 (5-20) ·10 7 (7-19) ·10 7 (53-160) ·10 7


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