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Precise measurement of shock phenomena
Applications where precise measurements are needed
In the present flight and missile
weight have become very important
large safety factors cannot be built
Therefore, accurate information is
nature of shock phenomena that are during
the operation of the system.
The shocks which are encountered and are of interest
can vary from less that one 'g' to many thousands
of 'g' with durations of from a few microseconds
to 100 millliseconds or more. This very wide
dynamic range makes it very difficult to have a single
measuring system that will cover the entire
range. The transducer best suited to this requirement
is the piezoelectric accelerometer because of
its wide dynamic range and its high natural frequency.
In order to accurately measure the shock phenomenon,
a transducer, amplification and signal conditioning
system, and readout device must be used.
System
Each component of the measuring
system will in some degree distort the shock pulse
being measured. The transducer, in general, is the
limiting part of the system. The pizzoelectric
accelerometer is many times better than other types
of transducers which are presently available because
of its wide dynamic range and high resonant frequency,
and is often better than electronic systems
chosen without due care.
A voltage amplifier should be chosen to have high
input resistance and sufficiently wide frequency
response to that the error introduced is held to a
minimum. A charge amplifier is ideal for shock
measurement because it eliminates the low frequency
transfer function caused by the transducer capacity
and amplifier input resistance. If a filter is used,
it should be of the constant time delay type so that
phase distortion is not introduced.
Finally the readout device should be chosen to give
the desired type of readout.
To determine the total error which will be introduced
by the system a calculation can be made to
determine the error caused by each section of the
system and then adding all of the errors together to
get the total.
Due to the complexity of working with second
order gransfer functions, wherever possible an
approximation should be made using a first order
function.
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