Transducers – “A lifetime of quality”

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At Brüel & Kjær, transducers are a core part of our business. They have been for more than50 years – almost a lifetime! The quality of our transducers is world-renowned. It is the result of our unique experience and knowledge, backed up by meticulous testing and quality control.

Experience, Knowledge and Innovation

Our experience and knowledge, acquired over more than 60 years, are inseparable – they go arm-in-arm. At Brüel& Kjær, we don’t just design and manufacture transducers. We are in the business of innovation and always have been. Many of our employees are world renowned experts, frequently speaking at conferences, presenting papers at seminars, and advising on new Standards. However, our expertise doesn’t only come from within; it also comes from working closely together with our customers and suppliers.

Initial Development

Bin Liu is a Transducer Development Engineer. Bin has a Ph.D. and the subject of her dissertation was “Transducers for Sound and Vibration – Finite Element Method Based Design”.

Bin explains, “Brüel & Kjær has a huge database of transducer design data. Through verification of the FEM (finite element model) with the tested parameters of transducers, the ‘quality’ of our mathematical models constantly increases, and less prototypes are needed.

“Based on our customers’ requirements and our own product development plans, we decide upon the parameters of a new transducer. We probably have the industry’s broadest range of transducers, and it’s still growing. So, we normally make modifications to an existing type and change dimensions, materials, etc. As an example, our new Miniature Triaxial DeltaTron® Accelerometer Type 4524 is an improvement to the popular OrthoShear® design. This makes it more rugged, and reliable, and ensures even more consistent production quality and adherence to specification.”

Bin continues, “First, we make a FEM model. Using ANSYS software, we can animate the3D geometry picture of the model and obtain its specification. We then make adjustments to the design until it conforms to the requirements, and we define a final predictive specification”.

Prototype Testing and Verification

Jens Ole Gullov is a Project Manager and is responsible for Brüel & Kjær’s transducer R&D department. Jens has a M.Sc. in Electrical Engineering – Semiconductor Physics.

Jens explains, “Following verification of the mathematical model, the next step is to construct between 10 and 20 prototypes. These are hand made in our production department under the supervision of R&D”.

The parameters of each prototype are thoroughly verified against the FEM model and the requirement specification. In addition, further tests are made including:

  • Environmental testing – heat, humidity, etc.
  • EMC (electromagnetic compatibility)
  • Base bending
  • Destructive testing

Jens continues, “There are many external inputs that can create measurement errors in an accelerometer and thus affect the accuracy of the measurement. Therefore, it is extremely important to know how sensitive each type of accelerometer is to these external parameters.

“The sensitivity to unwanted external sources can only be accurately determined using advanced testing techniques and at Brüel & Kjær we have developed our own testing equipment using the latest advanced technology”

Pilot Production
 
The valuable manufacturing experience gained during manufacture of the prototypes is used in the design of the production tooling. Typical pilot production quantities are from 20 to 50units.

Jens says, “The pilot production batch is made without R&D or engineering supervision. This ensures that production takes place in the normal manufacturing routine. At this stage, the accelerometers are tested to their basic calibration parameters. If we experience problems, we investigate the cause, re-engineer, and make a new pilot production quantity”.

Jens admits, “Of course this can result in a delay in bringing a new type to market but quality is always our most important focus”.

Verification of Pilot Production

For a new type of accelerometer to be released for production, it must pass two levels:

  1. The production department can manufacture the accelerometer without incurring problems
  2. The pilot production accelerometers fully comply with the complete product specifications
    In addition, the pilot production batch is placed in quarantine and subjected to a further series of tests including EMC, climatic testing, base bending, shock, etc.

The results of these tests are placed in a verification report. This is frequently used when advising customers and helping them to determine the correct transducer for a specific testing requirement.

Jens concludes, “When testing, we try to prove that what we do is not good enough. But if the pilot production quantity is verified according to our exacting standards, then it’s released for normal production”.

Production – Test, Test and Test Again!
 
Klaus Seest Jørgensen is Brüel & Kjær’s Quality Assurance Manager. He has a Master’s degree in Electronics from The Technical University of Denmark, and joined Brüel & Kjær in 1993. Klaus’ initial tasks were to develop and implement a common quality assurance system, and to obtain ISO 9001 accreditation for Brüel & Kjær on a global basis.

Klaus says, “In this ever more technical world, our customers demand transducers that enable them to make precise and totally accurate measurements. All our transducers are thoroughly tested, often in the harshest environmental conditions, and extremely high standards are met in all levels of production quality. This is reflected in our status as an ISO 9001 certified company”.

Before the production of a transducer starts, all component parts, whether from sub-suppliers or manufactured within Brüel & Kjær, are subjected to rigorous inspection. This takes the form of physical and dimensional inspection, and conformity to specifications. Using ultrasound, the component parts are cleaned in a demineralised water and soap solution. They are dried using compressed air and placed in an oven to remove any traces of humidity. A special process is used to clean electronic components.

How Often Do We Do It?

Depending on the type, each transducer is subjected to between five and ten test functions during its manufacture. Here are some examples:

Sensitivity and Frequency Response

The sensitivity of each accelerometer is tested during the manufacturing process. With some accelerometer types, the sensitivity can be fine-tuned during production. A 5-channelPULSE Type 3560 B data acquisition system is used, connected to Vibration Exciter Type4809. The vibration exciter is driven by the PULSE system’s built-in generator.

Transverse Sensitivity

During the manufacturing process, 100%testing is carried out to check the transverse sensitivity. Again, a compact and rugged 5-channel PULSE Type 3560 B front-end is connected to a shaker which is excited with a10 Hz sine-wave from the generator in PULSE.

Clinically Clean

Before an accelerometer is finally sealed, the level of cleanliness is checked in a specially developed test setup. By exposure to heat and high humidity, a check on the bias voltage will show the presence of any contamination.

Klaus continues, “During 2004, the delivered quality of Brüel & Kjær accelerometers was 99.6%. For instance, there might be an incorrect number entered on the calibration sheet. Although the quality level is very high, we constantly strive for improvement”.

Final Calibration

After the production process is completed, the key parameters of every accelerometer are tested to check that it is within specification. The first tests are carried out in the production area, followed by further testing in the calibration laboratory.

Jørgen Moth Monrad is Manager, Service Coordination & Support and has worked for Brüel & Kjær for 27 years. He is responsible for the Service Centre in Denmark, including the calibration laboratory.

Jørgen says, “We use a new Vibration Transducer Calibration System Type 3629 for final calibration. An individual calibration chart is issued and, at this stage, if the accelerometer is a TEDS type, the TEDS information is programmed into the built-in chip”.

If specified at the time of purchase, a new accelerometer can be supplied with Accredited Initial Calibration (CAI).

Legislation

It is not only our customers’ demands that must be satisfied – legislation also sets exacting standards. This often means documented results that are traceable to known sources, such as a national calibration laboratory. Brüel & Kjær’s transducer calibration service provides:

  • Calibration of vibration transducers to international standards
  • Calibration to meet ISO 9000 requirements
  • Calibration according to ISO 5347
  • Calibrations are traceable to National Institute of Standards and Technology(NIST), USA and Physikalisch-Technische Bundesanstalt (PTB)
  • Certificate of calibration specifying all test and instrument details
  • All calibration test procedures fully comply with European Norm EN 45001

Primary Accredited Calibration

Brüel & Kjær operates The Danish Primary Laboratory of Acoustics (DPLA). It offers primary accredited calibration of vibration transducers which serve as Reference Standards and Working Standards for measurement laboratories and other users within the field of vibration.

Many customers return transducers to us on a regular basis for calibration. Using Vibration Transducer Calibration System Type 3629, either Accredited Calibration (CAF) or Traceable Calibration (CTF) can be specified. The calibration turnaround time is normally seven working days.

We Make a Difference!

Our customers demand accelerometers that enable them to make precise and totally accurate measurements. It is Brüel & Kjær’s attention to testing and quality control at all stages of the development and production process, backed up by our lifetime of experience that makes all the difference! 

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