Guralp-systems CMG-40T Instrukcja Użytkownika Pobierz pdf (Strona 24)

CMG-40T

Poles and zeroes

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:

In this equation z

are the roots of the numerator polynomial, giving the

zeros of the transfer function, and p

are the roots of the denominator

polynomial giving the poles of the transfer function.

In the calibration pack, G is the sensitivity given for each component on the first

page, whilst the roots z

and p

, together with the normalising factor A, are

given in the Poles and Zeros table. The poles and zeros given are measured

directly at Güralp Systems' factory using a spectrum analyser. Transfer

functions for the vertical and horizontal sensors may be provided separately.

24 Issue A

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 34 35

Brak uwag

Guralp-systems CMG-40T Instrukcja Użytkownika Strona 24