Calibrating the 3TB
5 Calibrating the 3TB
5.1 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 each component
of the instrument,
VERTICAL, NORTH/SOUTH,
and
EAST/WEST.
Each row details:
•
Velocity Output (Differential) :
The sensitivity of each component to velocity
at 1 Hz, in volts per m/s. Because the 3TB uses balanced differential outputs,
the signal strength as measured between the +ve and –ve lines will be twice
the true sensitivity of the instrument. To remind you of this, the sensitivities
are given as 2 × (single-ended sensitivity) in each case.
•
Mass Position Output :
The sensitivity of the mass position outputs to
acceleration, in volts per ms
-2
. These outputs are single-ended and referenced
to signal ground.
•
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 Volt 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.)
5.1.1 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.
50
Issue G - November 2019
