Very High Frequency Calibration of Laser Vibrometer up to 350 khz

Transcription

1 Very High Frequency Calibration of Laser Vibrometer up to 350 khz Requirements, Solutions and Traceability Dr. Martin Brucke, Frank Schulz There is simply no substitute for knowing what you re doing Jeff Case

2 Introduction Who needs a well defined vibration excitation in the frequency range up to 50 khz and above? APMP 4th TCAUV Workshop, Viet Nam 11/2/2016 4

3 Introduction 2008 First request from MEMS manufacturer for a test system for the frequency range > 20 khz Unexpected reaction of a gyro MEMS regarding high-frequency events in a car body (e.g. stone hits car body) Case and circuit board of the control unit was obviously no sufficient mechanical low-pass filter How can this be simulated in experiments to improve the control unit and/or MEMS? SE-09 high-frequency exciter with VCS 403 vibration controller for the frequency range 5 Hz to 50 khz 5

4 Introduction Who needs a well defined vibration excitation in the frequency range up to 50 khz and above? Research/Development related to MEMS Devices (Sensors, Actuators, ) Vibration properties of MEMS Structures are key technical data Contactless measurement is the only choice Source: Polytec GmbH APMP 4th TCAUV Workshop, Viet Nam 11/2/2016 6

5 Introduction Who needs a well defined vibration excitation in the frequency range up to 50 khz and above? Research/Development of Hard Disk Drives (see above) Ultrasonic applications (technical, medical) Laser Vibrometer measurements in the frequency range > 20 khz APMP 4th TCAUV Workshop, Viet Nam 11/2/2016 7

6 Introduction How can we excite a DUT precisely in an arbitrary direction up to 50 khz? First solution for arbitrary excitation: L-shaped aluminum adapter Resonances in the adapter lead to high cross motion (>1000 % of main excitation) Even materials like Beryllium do not shift these resonances above 10 khz Mechanical adapter is no feasible solution 8

7 Introduction From SE-09 to SE-11 Based on standard SE-09 Armature No air-bearing Grinding of lateral surfaces to create mounting surfaces for DUT 3 gluing areas (32 x 20 mm) Very low cross motion up to 45 khz 9

8 From 20 khz to 200 khz Performance Improvement APMP 4th TCAUV Workshop, Viet Nam 11/2/

9 From 50 khz to 200 khz Improvement of Armature Bigger Armature with 4 lateral surfaces (30 x 30 mm) Optimization with FEM leads to improved modal properties APMP 4th TCAUV Workshop, Viet Nam 11/2/

10 From 50 khz to 200 khz SE-11 B max. acceleration: 400 m/s² Frequency range: 1 khz to 50 khz (100 khz) Cross Motion < 10 % (1 50 khz) Robust, wear resistant ceramic armature 12

11 From 50 khz to 200 khz Application example PCB with soldered DUT How to attach the PCB? Gluing techniques: mounting wax, rapid bonding glue (cyanoacrylate, HBM X60) Different properties regarding: connection stiffness vs. removability Many experiments and a lot of experience are necessary 13

12 From 50 khz to 200 khz SPEKTRA SE-16 max. acceleration: 200 m/s² Frequency range: 1 khz to 100 khz (200 khz) Cross Motion < 10% (1 100 khz) Robust, wear resistant ceramic armature Armature Dimensions 15 mm x 15 mm Operation above 100 khz 200 khz possible with a special power amplifier Higher cross motion at certain frequencies has to be considered 15

13 Excitation of bigger DUT up to 50 khz SPEKTRA Piezo-Cube Multi-Axes Excitation 17

14 Reference Sensors and Traceability Appropriate Reference Sensors APMP 4th TCAUV Workshop, Viet Nam 11/2/

15 Reference Sensors and Traceability PE-Accelerometer Internal reference accelerometer in SE-11 Resonance frequency > 70 khz can be used up to 50 khz Miniature PE-accelerometers mounted at piezo-cube exciter can be used up to 40 khz? 19

16 Reference Sensors and Traceability Example: Miniature PE-Accelerometer Seemingly high cross motion measured with accelerometer at frequencies > 40 khz Laser vibrometer measures no cross motion of the shaker A PE-accelerometer can show unexpected behavior due to resonances in the sensor element that is not published by the manufacturer Careful characterization in the high-frequency range required 20

17 Reference Sensors and Traceability PE-Accelerometer Internal reference accelerometer in SE-11 Resonance frequency > 70 khz can be used up to 50 khz Miniature PE-accelerometers mounted at piezo-cube exciter can be used up to 40 khz? For the frequency range above 50 khz the use of a laser vibrometer is recommended 21

18 Reference Sensors and Traceability Laser Vibrometer Non-contact measurement Laser vibrometer offers wide bandwidth (350 khz) Reference point can also be on the DUT Lowest acceleration amplitudes at high frequencies are limited by signal-to-noise ratio of laser vibrometer output 22

19 Reference Sensors and Traceability Example Laser Vibrometer SE-16 shaker Excitation 100 khz, 2.4 m/s² Laser sensitivity (2 mm/s/v) Velocity about 4 µm/s Output signal about 2 mv If low acceleration amplitudes are required, the vibration controller must offer special filter techniques for the laser signal to cope with low signal-to-noise ratio Shaker khz and low acceleration amplitude; Spectrum of laser vibrometer output measured with VCS 403 and activated VCS tracking bandpass APMP 4th TCAUV Workshop, Viet Nam 11/2/

20 Reference Sensors and Traceability And what about traceability? APMP 4th TCAUV Workshop, Viet Nam 11/2/

21 Reference Sensors and Traceability Traceable calibration of reference accelerometers ISO , section 9, Method 3: Sine approximation method This method is applicable to sensitivity magnitude and/or phase calibration in the frequency range 1 Hz to 10 khz Note 2 mentions that with an appropriate technique calibration at high vibration frequencies (e.g. 20 khz) is possible. Currently NMI offer traceability of reference accelerometers up to 20 khz Is there a NMI that offers traceability >20 khz?? 25

22 Reference Sensors and Traceability Traceable calibration of reference laser vibrometer ISO is a newer standard In section a note mentions that Method 3 in the homodyne or heterodyne interferometer version provides calibrations in the frequency range 0.4 Hz to 50 khz or wider. In Reference [26], the applicability of method 3 has been demonstrated at frequencies up to 347 khz. Request from NMI customers for calibration systems up to 350 khz according to ISO

23 Reference Sensors and Traceability Systems Schematic Reference Laser Vibrometer PC A D PE-Actuator A D HW - Driver CS18 - VHF Power Amplifier APMP 4th TCAUV Workshop, Viet Nam 11/2/

24 Reference Sensors and Traceability Frequency response of ADC Determined with high class DVM Correction function in CS18 Software Noise of Laser Vibrometers approximately 0,15 mm/s (dependent on reflection) High vibration amplitude is needed Positioning of Laser points PE-Actuator has from its principle a non even displacement APMP 4th TCAUV Workshop, Viet Nam 11/2/

25 Reference Sensors and Traceability CS18P VHF System for laser vibrometer calibration up from 5 Hz to 350 khz APMP 4th TCAUV Workshop, Viet Nam 11/2/

26 Reference Sensors and Traceability Microscope camera for exact positioning of laser beams required APMP 4th TCAUV Workshop, Viet Nam 11/2/

27 Reference Sensors and Traceability What about traceability of this system? Reference laser vibrometer is traceable up to 20 khz only Above 20 khz only a specification from Polytec is available Unknown measurement uncertainty of reference laser vibrometer > 50 khz No traceability to a National Standard above 20 khz available? 31

28 Conclusion There are industry applications that require a well defined vibration excitation in the frequency range > 50 khz There are technical solutions available to provide this excitation But there is currently no traceable calibration of reference transducers or laser vibrometers for this high frequency range available. 32

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