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Welcome to Issue #77     

 

Bonjou! (Louisiana Canjun slang for "Hello.") This issue comes to you from the French Quarter of New Orleans, Louisiana. While attending a conference this week, I was fortunate to witness the noise and revelry of a number of parades as that city goes into the full swing of Mardi Gras season. All that noise, along with the pleasant sounds from some very authentic jazz clubs, made for an easy acoustic theme for this month's newsletter.

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Tip of the Month: Consider Pre-Polarized Microphones

Consider saving cost with precision prepolarized -inch microphones, ICP preamplifiers and coaxial cable when replacing damaged microphones or growing your instrumentation stock. The low noise constant current microphone operation matches head to head with traditional condenser microphones, trading off only a few dB at the very high end of the operating amplitude range. Practically, this is only a consideration in extremely loud applications like military or aerospace, which can be typically handled with a less sensitive -inch prepolarized microphone cartridge. 

Technical Exchanges
Quick Links
PTB 
ISO TC 108 - Mechanical vibration, shock and condition monitoring
ISO TC 108/SC 3 - Use and calibration of vibration and shock measuring instruments
ISO TC 108/SC 6 - Vibration and shock generating systems
SAVE (Formerly SAVIAC)
Previous Newsletters
Harvard Uses Shaker to Simulate Bumblebee Vibration Frequency; Dynamic Calibration Seminars

Dynamic Sensors & Calibration #75
Accelerometers for Health & Usage Monitoring Systems; Shock Tubes & Dynamic Pressure Characterization 
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by Topic
PCB Group Companies
Why Is It Important to Calibrate My Microphones?
By Chad Walber, PCB Piezotronics
Regular (daily) calibration checks establish a record of the operation of your instrumentation; not just the sensor, but the entire measurement chain. This is important as cabling and other parts of the measurement chain may wear out, and a recent calibration check for comparison can help rule out a faulty sensor. Calibration also helps to establish the level of uncertainty associated with the measurements. It gives a historical account of the sensor's performance, and the...

Click to read full article 

 modalshop.com/calibration.asp?ID=918
KU Leuven Designs Alternative to 
Impedance Tube Testing 

Katholieke Universiteit Leuven's (KU Leuven) Department of Mechanical Engineering is working on an ongoing project designed to offer an alternative to impedance tube testing. The University's "Sound Box" research involves a concrete walled cavity with 12 1/2-in. prepolarized free-field condenser microphones and 1/2-in. prepolarized random-incidence condenser microphones. The microphones are placed both in and outside the cavity and uniaxial lightweight accelerometers are mounted to the test specimen to measure the vibration levels. Triax accelerometers are mounted on the rigid frame to assess mounting structure rigidity. One hundred lbf shakers, in combination with impedance heads, are used to investigate...

 
modalshop.com/calibration.asp?ID=919
Blast from the Past: 
What's Wrong With My Accelerometer?
[Adapted from PCB Piezotronics Technical Note 0401] 
A frequently asked question about measurements made with piezoelectric (PE) vibration sensors is related to the measurement parameters. After completing a test and evaluating data, the test engineer observes obvious signs of problems with his data, such as the decay in baseline voltage or drops in the coherence of forced response frequency response function (FRF) measurements. Many things can affect the data from a PE Accelerometer including...

                                       Click to read full article
modalshop.com/calibration.asp?ID=663
 

 

Thanks for joining us for another issue of "Dynamic Sensors & 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,

Mike Lally signature
Michael J. Lally
The Modal Shop, Inc.
A PCB Group Company