TMS Square sensor & calibration tips                                                                                      Your one-stop sound & vibration shop
Dear Scott,

Welcome to our third issue -
The goal of this monthly communication is to provide technical information and tips about the calibration and use of dynamic sensors in vibration, pressure and force.  The information is provided by the PCB Group of companies, as well as industry experts from research, government and academia.  Technical information is presented in a short, easy to read format and will contain liberal links to further information should you desire a deeper dive into the technology.  
Tip of the Month

Mounting Irregular-Shaped Triaxial Accelerometers

Certain accelerometers - commonly triaxial units - are packaged in a non-symmetric fashion, often with an off-center through-hole mount.  These accelerometers can be the most challenging to calibrate because the sensing element is not aligned with the sensor's center of gravity or its intended mounting configuration.  In order to get acceptable results, the unit often needs to be mounted as a best compromise between these.  In other words, if the triax is mounted with its through-hole and a large amount of the sensor is consequently offset on the reference, a significant amount of transverse motion can be induced causing "glitches" in the calibration frequency response.  For this case, the calibration technician may be required to adhesively mount the unit, avoiding the use of the more convenient through-hole threaded mount, and perform trial and error with adhesive mounting to produce the best calibration results.
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Newsletter Archive
May 2007 - Basics of Accelerometer Function; How Standards Link Together
June 2007 - Shear, Compression, Flexure; ISO 16063 Overview
Accelerometer Transduction Types...
...Piezoelectric, Piezoresistive and Capacitive
Inside an AccelerometerAccelerometers are transducers that generate an electrical signal output as a result of a mechanical acceleration input to the unit.  The most common type of accelerometer operates by the piezoelectric effect.  Piezoelectric (PE) accelerometers are generally classified in two groups - low impedance voltage mode (for example, PCB Piezotronics trademarked ICP) or charge mode.  Other types of accelerometer transduction methods include piezoresistive (PR), based upon strain gage technology, and variable capacitive (VC).
Click here for the rest of this article describing the basic technology of PE, PR and VC sensors.
Overview of ISO-16063-11...
Primary Laser Calibration...Accelerometer Calibration via Laser Interferometry Method 
Primary accelerometer calibration is at the root of traceability for virtually every accelerometer calibration chain in the world: commercial, government, military, academic or vendor.  Acceleration calibration via laser interferometery is a primary method because it is an absolute method comparing the measured vibration from a sensor under test to a constant of nature - the wavelength of laser light. 
As always, your satisfaction is at the pinnacle of our work.  If you have questions that you would like answered, please contact us and we'll be glad to help out.  Your question may even be featured in a future month...
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Michael J. Lally
The Modal Shop
A PCB Group Company