Guralp Systems CMG-5T - Manual (Page 15)

Operator's Guide
The Ampl Cursors button will now be displaying a value,
which is the strength of the returning signal in counts
(doubled, if using a sine wave). Measure the other two signal
strengths in this manner.
Note that if you have used the Scale... option described above,
you will need to take the scale factor into account to produce
the correct number of counts. In the example, the MB
(calibration input) signal has been scaled by a factor of 40, so
the signal strength as measured by the Ampl Cursors must be
divided by 40 to yield the correct value.
8. Convert to volts using the µV/Bit values given on the digitizer's
calibration sheet for the various input ports, and compare the
returned signal with the input calibration signal (MB).
9. In the example, the following data are now known:
Input calibration signal strength (MB) 697,221 counts
Returning signal strength (Z3)
701,512 counts
The calibration sheets provide us with the remaining values
needed to calibrate the sensor:
Sensor acceleration response 0.254 V/ms -2
Equivalent accel. from 1V calibration 1.968 ms -2
Digitizer input port sensitivity 3.507212 µV/Bit
Calibration channel sensitivity 3.491621 µV/Bit
From these we calculate that the calibration signal is
producing 697,221 × 3.491621 = 2,434,431 µV (2.434 V). This
corresponds to an equivalent input acceleration of 2.434 ×
1.968 = 4.791 ms -2 .
The sensor's acceleration response is given as 0.254 V/ms -2, so
that an acceleration of 4.791 ms -2 will produce an output of
0.254 × 4.791 = 1.217 V (1,216,904 µV), which corresponds to
a count number at the digitizer's input port of
1,216,904 / 3. 507212 = 346,972 counts.
Because this calibration is being carried out with a
differential-output sensor, the count number observed at the
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