6calibration, 1 the calibration pack – Guralp Systems CMG-5TD User Manual
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Calibration
6
Calibration
6.1
The calibration pack
All Güralp sensors are fully calibrated before they leave the factory. Both
absolute and relative calibration calculations are carried out. The results are
given in the calibration pack supplied with each instrument:
Works Order : The Güralp factory order number including the instrument,
used internally to file details of the sensor's manufacture.
Serial Number : The serial number of the instrument
Date : The date the instrument was tested at the factory.
Tested By : The name of the testing engineer.
There follows a table showing important calibration information for he
instrument, which shows:
Acceleration Output (Differential) : The sensitivity to acceleration at 1 Hz, in
volts per ms
-2
. Because the CMG-5TD uses a balanced differential output to
connect to the digitiser, the signal strength as measured between the +ve and
–ve line will be twice the true sensitivity of the instrument. To remind you of
this, the sensitivity is given as 2 × (single-ended sensitivity).
Feedback Coil Constant : A constant describing the characteristics of the
feedback system. You will need this constant, given in amperes per ms
-2
, if
you want to perform your own calibration calculations (see below.)
Power Consumption : The average power consumption of the sensor during
testing, given in amperes and assuming a 12 V supply.
Calibration Resistor : The value of the resistor in the calibration circuit. You
will need this value if you want to perform your own calibration calculations
(see below.)
6.1.1 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
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Issue D - April 2013