Does a Manufacturer's Nominal Spec Matter?
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One of our "Dynamic Sensors and Calibration"  newsletter readers recently sent me an email about a concern they encountered with some pre-owned 'Brand X' accelerometers which they purchased from an e-commerce website.
The reader explained that the sensors performed "fine" in the lab, but that the recent re-calibration certificate provided to them by TMS showed that although the sensors' frequency response was fine, the reference sensitivity was out of tolerance from the manufacturer's stated maximum deviation from nominal. Here is the discussion that followed:
modalshop.com/calibration.asp?ID=819
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Technology Fundamentals of Microphone Types
Excerpted from, "The Microphone Handbook"
by PCB Piezotronics
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When an object vibrates in the presence of air, the air molecules at the surface will begin to vibrate, which in turn vibrates the molecules adjacent to them. This vibration will travel through the air as oscillating pressure at frequencies and amplitudes determined by the original sound source. The human ear transforms these pressure oscillations, or sound, into electrical signals that are interpreted by our brains as music, speech, noise, etc. Microphones are designed, like the human ear, to transform pressure oscillations into electrical signals. These signals can be recorded and analyzed to tell us information about the original source of vibration or the nature of the path the sound took from the source to the microphone.
 This is exhibited in testing of noise reducing materials. Sound pressure must be analyzed in the design stages to not only protect the materials around it, but also to protect the mechanism designed to perceive it, the human ear. Like the human ear, microphones are designed to measure a very large range of amplitudes typically measured in decibels (dB), and wide ranges of frequencies measured in hertz (Hz). Microphones measure sound pressure. There are a few different designs for microphones...
Click to read full article
modalshop.com/calibration.asp?ID=820
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Blast From The Past:
Primary vs Secondary Calibration
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 The question often asked is, "When (or even why) do I need primary calibration?" Metrologists are also curious to know, "What does it cost?"
The short answer to "who needs it?," is that primary calibration (as covered in ISO16063-11) is the standardized means to obtain the absolute minimum in uncertainty. But to fully answer this question, one needs to first consider the reasons for calibration. This discussion answers the question from the angle of uncertainties, costs and throughput rates.
Click to read full article
modalshop.com/calibration.asp?ID=201
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Thanks for joining us for another issue of Dynamic Sensor & Calibration Tips. As always, please, speak up and let us know what you like. We appreciate all feedback: positive, critical or otherwise. Take care!
Sincerely,
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 Michael J. Lally A PCB Group Company
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