Calibrating the 3TB
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
f
m
= 1 Hz, with
s
=
j
f
m, where
j
= √–1.
•
H
(
s
) is the transfer function of the sensor, which can be expressed in factored
form:
In this equation
z
n
are the roots of the numerator polynomial, giving the zeros
of the transfer function, and
p
m
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
n
and
p
m
, 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.
51
Issue G - November 2019
