# John G. Webster (Editor) 's 30.Instrumentation and Measurement PDF By John G. Webster (Editor)

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The electrical intensity E in the gap can be expressed as E1 = (V1 − V2 )/h (31) so that the force of attraction may be found as F1 = kE 2 S/2h2 = k(V1 − V2 )2 S/2h2 (32) In the presence of acceleration, if V2 is adjusted to restrain the movable electrode to the null position, the expression relating acceleration and electrical potential may be given by a = F1 /m = k(V1 − V2 )2 S/2h2 m (33) The device so far described can measure acceleration in one direction only, and the output is quadratic, that is, √ (V1 − V2 ) = D a (34) ings are necessary.

They can easily be expressed as second-order differential equations, as explained in the frequency response section. However, during measurements, most accelerometers are affected by transverse vibrations and their sensitivity can play a major role in the accuracy of the measurements. The transverse, also known as cross-axis, sensitivity of an accelerometer is its response to acceleration in a plane perpendicular to the main accelerometer axis as shown in Fig. 15. The cross-axis sensitivity is normally expressed as a percentage of the main-axis sensitivity and should be as low as possible.

Quantitatively, the reverberation time is defined as the time required for the level of the sound to drop by 60 dB. The preceding discussion considered the effect of absorption on the propagation of sound in a definite direction. There are, however, many situations where sound is not expected to travel from one specified point to another, but rather to fill a volume of space with a uniform intensity. Such a sound field is called diffuse or reverberant, and is usually produced by multiple reflections.