Geometrics G-822A, Руководство по эксплуатации

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Geometrics, Inc. G-822/G-823 Magnetometer Manual
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7.4 Power-up Initialization
By default all counters will wake up thinking that they are counter #0 and begin to output
data at the default 10 hertz rate. This data will appear as commands to any subsequent
counters and will cause a brief period of chaos until each counter figures out where they
stand in the daisy chain. Thus there will be some garbled transmissions to the logging PC
upon power-up or reset.
8.0 G-823B MAGNETOMETER
The model G-823B magnetometer is a variant of the G-823A intended for use as a high-
performance base-station instrument. This model has the same dimensions and
performance as the G-823A with the exception of its heading error. G-823B heading
error is typically in the range of from 2nT to 3nT. Heading errors specifications are not
normally supplied with the G-823B. As with the G-823A, the G-823B is shipped with a
25ft external signal/power interface cable, a power/data junction box, and an RS-232 data
cable. These components are used to connect the magnetometer to the user’s 30VDC
power source and logging computer.
When used as a base station, Julian date/time are available for recording and the standard
sensitivities and measurement rates of the CM-201 counter apply. In this application the
D/A converters installed in the CM-201 can be used to convert such other parameter (e.g.
barometric altitude) and include these values in the data stream. Recording rates from
once each 10 seconds to 100 times per second may be selected.
The 25ft power/data cable included with G-823B will permit the logging computer to be
located far enough from the sensor to avoid interference. Base-station data will also be
more noise free if the sensor is positioned in a spot where the gradients are relative low.
Such a spot may be located by casual surveying of the area selected for the base station
site and identifying the spot with the most uniform field. Selecting this spot will also
make a reoccupation of the spot easier (e.g. for base-station recordings used for block-
leveling regional survey data).
We recommend a base-station installation that places the sensor approximately 5ft (1.5m)
above the ground in order to reduce motion-induced noise. Motion noise will be
proportional to both the amount of sensor motion and the size of the local gradient.
Positioning the sensor off the ground will reduce the strength of short wave-length
gradients arising for the soil or from disturbed outcrop. It is also important to provide a
ridged support structure so as to keep wind induced motion to a minimum. Figure 14
shows a base station installation that uses a kit supplied by Geometrics for this purpose.