Guralp Systems CMG-3T - Manual (Page 20)

CMG-3T
3 Calibrating the 3T
3.1 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 3T 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 m/s². 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
m/s², 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.)
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