| Tip of the
Month |
|
Use of a daily
verification accelerometer
We
recommend using a precision quartz
accelerometer, like the PCB Model 353B03, as a
dedicated,
stable verification accelerometer. Keep
this unit under tight control and use it to validate your system
performance on a daily basis. This process also provides you
with reliable data for evaluating any uncertainties or drift in your
system
measurements. |
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| Seismic accelerometer... |
|
...for low frequency measurements
 Piezoelectric
accelerometers are well suited for seismic vibrations studies. They are completely self
contained and self generating from an inertial frame of
reference. This
eliminates the challenges with relative vibration found in
optical/laser methods, as well as dual ended attachment coil based
methods, such as LVDT's.
The second most common challenge with seismic measurements is
the low excitation levels of seismic events. In terms of acceleration,
the g level falls off in an inverse square
relationship for a constant displacement as frequency
decreases, thus seismic events typically exhibit small acceleration
levels.
(http://www.modalshop.com/test_calibration.asp?ID=212) |
| Uncertain about your
calibration? |
 One of the most commonly
debated issues among calibration professionals and often least
understood by sensor users is the concept of measurement
uncertainties.
To
the novice user, the manufacturer's stated calibration is simply
accepted as gospel. However, a
closer inspection of the calibration certificate reveals that the
calibration lab is actually providing an INTERVAL, within which the
value for the device is "certain" to lie and typically includes a
statistical probability distribution statement. This
omnipresent and expected interval is typically expressed in a
tolerance term of plus or minus some level of
percent...
aka
uncertainty.
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| We appreciate your
interest and are glad to be providing regular information to help
you in your dynamic testing and calibration needs. If you have
any questions you would like answered or have a topic you would like
to see covered, please contact us and we'll be glad to help
out. Your question may even be featured in a future
newsletter...
Sincerely, |
|
Michael J. Lally The Modal Shop
A PCB Group Company | |
