As you can imagine with a large proportion of engineering activities, choosing the incorrect tool may have serious implications on the results of your measurements. The information contained below is to help visitors make a more information decision on an accelerometer sensor which is most appropriate for their requirements.
In general, there are two widely known types of accelerometers:
An AC-Responsive accelerometer means that the output is AC coupled. Essentially this means an AC coupled device cannot be used to fully measure static acceleration such as gravity and constant centrifugal acceleration meaning that it is only suitable for measuring dynamic events.
A DC-Responsive accelerometer means the output is DC coupled, meaning that this can respond down to zero Hertz (Hz). This ultimately means that it can be used to measure static, as well as dynamic acceleration. It is important to note however that measuring static acceleration is not the only reason a DC-response accelerometer should be selected.
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A large proportion of vibration studies that are made, require the knowledge of displacement, velocity and most importantly acceleration. These three elements helps engineers seek in designing of validating a structure / project. Most of the time, the g value provides good reference, however the other two (velocity and displacement) are two key variables that are also needed in most design calculations. To derive velocity and displacement from the output of acceleration, the signal from the accelerometer is not only integrated, by doubly integrated respectively in both analog and digital domains.
This is where an AC-response accelerometer may run into some trouble due to the output of this device never being able to track the peak of the half-since input due to the intrinsic limitation imposed by its RC time constant. Here's a quick picture to illustrate the problem;
At the end of the half-sine pule, it's important to note that the output of the AC coupled accelerometer will produce an undershoot (more commonly known as an offset) for the very same reason. The red tracing line in the graph above depicts the output of an AC coupled device following a long duration half-sine input.
This example is a commonly occurring trouble shooting problem that we hear from clients across a wide range of industries.