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Operator's Guide

The sensor transfer function

Most users of seismometers find it convenient to consider the sensor

as a “black box”, which produces an output signal V from a measured

input x. So long as the relationship between V and x is known, the

details of the internal mechanics and electronics can be disregarded.

This relationship, given in terms of the Laplace variable s, takes the

form

( V / x ) (s) = G × A × H (s)

In this equation

• G is the acceleration output sensitivity (gain constant) of the

instrument. This relates the actual output to the desired input

over the flat portion of the frequency response.

• A is a constant which is evaluated so that A × H (s) is

dimensionless and has a value of 1 over the flat portion of the

frequency response. In practice, it is possible to design a system

transfer function with a very wide-range flat frequency

response.

The normalising constant A is calculated at a normalising

frequency value fm = 1 Hz, with s = j fm, where j = √–1.

• H (s) is the transfer function of the sensor, which can be

expressed in factored form:

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Guralp-systems CMG-5T Manual do Utilizador Página 19