Geometrics Inc. G-882 Cesium Marine Magnetometer Page
At the right edge of the screen are two normalized scales for the analog data.
One scale is for unipolar analog channels [0-100%],and the other is for bipolar
channels [ 50%].
4.5.4 Depth Cal
This program is intended for use only if you purchased logging software other
than MagLog-Lite or MagLog from Geometrics that might allow calibration
of the depth sensor by determining a bias and scale factor. For additional
automatic depth calibration, see Depth Calibration using MagLog-Lite or
MagLog™ in section 4.5.5 of this manual.
The Depthcal.exe program provides BIAS and SCALE values for entry into
logging software to calibrate the depth sensor. This program was installed in
C:\GEOUTIL on your hard drive when you installed the Utility software.
DepthCal is an independent program (you may need to exit the logging
software to use it) that will lead you through an experiment with your G−882 to
derive the BIAS and SCALE values. To execute, at the DOS prompt in
C:\GEOUTIL, type DEPTHCAL and press the Enter key. The questions that
you answer will guide you through a simple experiment and then calculate the
BIAS and SCALE values.
Bias and Scale Factors Explanation and Calculation:
The depth transducer provides full scale readings of '9999' regardless of
whatever there range may be.
The DepthCal program supplied on the Magnetometer CD under Utilities may
be used to calculate the bias and scale factors for the depth transducer as
explained below.
The DepthCal program assumes that the logging software has initial settings of
zero bias with a scale factor of 1.000. What this means is that the logging
software should output zero meters when the serial data stream has "0000" in
the appropriate analog channel and 128 meters when it has '0128', 5000
meters when '5000' and 9999 meters when '9999' (full scale).
The depth channel does not put out exactly zero volts at zero depth. Nor does
a change of one digit '0001' equal one meter. And it varies from unit to unit due
to differing sensor full scale values that may have been installed per the
customer's system requirements. To correct for this, logging software may
allow the user to input a bias (offset) value and a scale factor to transform the
incoming device data such that the display readings that correspond to the
device's actual reading. DepthCal can be used to avoid having to do the math
required to obtain the bias and scale factors as shown in the example below.
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