INITIAL DEVELOPMENT

Brüel SKjaer has a huge database of transducer design data. Through verification

of the finite element model (FEM) with the tested parameters of transducers, the 'quality' of mathematical models constantly increases, and fewer prototypes are needed. Based on our customers' requirements and our own product development plans, we decide upon the parameters of a new transducer. Brüel&Kjaer probably has 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. First, we make a FEM. This takes one to three days, depending on its complexity. Using ANSYS software, we can animate the 3D geometry of the model. We then make adjustments to the design until it conforms to the requirements, and define a final predictive specification.

PROTOTYPE TESTING AND VERIFICATION

Following verification of the mathematical model, the next step is to construct several prototypes. Based on the FEM, we make between 10 and 20. These are hand made in our production department under the supervision of R&D. The parameters of each prototype are tested and verified against the FEM and the requirement specification. In addition, further tests are made including:

* Environmental testing EMC

* Base bending

* Destructive testing

MEASUREMENT ACCURACY

There are many external factors that can create measurement errors in an accelerometer and thus affect its output and the accuracy of the measurement. Therefore, it is important to know how sensitive each type of accelerometer is to these factors. This can only be accurately determined using advanced testing techniques and we have developed our own testing equipment using the latest advanced technology. Once known, the effects of these extraneous inputs enable the correct type of accelerometer to be selected for specific testing applications. For instance, you can select a transducer with low sensitivity in the areas which are of greatest importance. Alternatively, the measurement results can be corrected to allow for these external factors, but either way, it is crucial to be fully aware of their influence.

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 50 units. 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 batch.

VERIFICATION OF PILOT PRODUCTION

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

* The production department can manufacture the accelerometer without incurring problems

* 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.

TEST, TEST AND TEST AGAINl

All Brüel&Kjær 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 components, whether from subsuppliers or manufactured within Brüel & Kjaer, are subjected to rigorous inspection. This takes the form of physical and dimensional inspection, and conformity to specifications. Using ultrasound, the components 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. Depending on the type, each transducer is subjected to between five and ten tests 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 adjusted during production. For instance, the sensitivity of charge accelerometers can be varied by adding or removing masses. The sensitivity of DeltaTron® types can be adjusted by changing capacitance.

Transverse Sensitivity

During the manufacturing process, 100% testing is carried out to check the transverse sensitivity.

Clinically Clean

Before an accelerometer is finally sealed, the level of cleanliness is checked in a specially developed test setup. Up to 24 accelerometers are screwed into the lid of a container using their connector threads. By exposure to heat and high humidity, a check on the bias voltage will show the presence of any contamination.

PROOF OF QUALITY

During 2007, the delivered quality of Brüel & Kjaer accelerometers was 99.5%. In only five instances out of every 1000 deliveries, was something not as it should have been. For instance, there might be an error in functionality or an incorrect number entered on the calibration sheet. These extremely high levels of reliability and quality are only achieved by our meticulous attention to testing during the development and manufacturing process.

R.S. 110 at www.SandVlnfo.com

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