Guralp Systems CMG-3ESPCD - Manual (Page 28)

CMG-3ESPCD Digital Broadband Seismometer Calibrating the 3ESPCD
4 Calibrating the 3ESPCD
4.1 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 3ESPCD 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 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.)
4.1.1 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
MAN-C3E-0002 28 Issue B - November 2013