Geometrics, Inc. G-822/G-823 Magnetometer Manual
14
existing installation is altered. It is also recommended that these items are checked
periodically as part of a scheduled platform or system safety check.
1.
Power check
a.
Minimum 24 Volts DC at electronics bottle. 28VDC recommended
b.
Maximum 33 Volts DC at electronics bottle
c.
Starting current 1 Ampere at 28 Volts
d.
Running current 0.3 to 0.6 Ampere at 28 Volts depending upon ambient
temperature
2.
Connector checks
a.
Dirt or corrosion
b.
Bent pins
c.
Back-shell tight
3.
Cable jacket check
a.
Kinks
b.
Abrasions
c.
Cuts
4.
Sensor orientation
a.
Use MagPick IGRF and CsAz to model sensor behavior
b.
Adjust sensor orientation and observe dead zones
c.
Return sensor to correct orientation for the survey area
5.
Field readings
a.
Reasonably close to MagPick IGRF model estimate
b.
Sample to sample noise less than 0.1 nT @ 10 Hz when not moving
6.
Larmor amplitude check and adjustment (Authorized Repair Facility only)
a.
Potentiometer on GSN board adjusted for 2.0 Volts Peak to Peak at
50,000 nT after 20 minute warm up
7.
Heater check and adjustment (Authorized Repair Facility only)
7.0 G-823A MAGNETOMETER
The addition of Geometrics CM-201 counter assembly board to the G-822A’s sensor driver
module transforms the instrument’s analog output signal into RS-232 digital data. With the
addition of the CM-201, the instrument is designated as the G-823A. The CM-201 counter
module is an integrated circuit that converts the cesium Larmor signal (70 kHz to 350 kHz)
into a numeric value indicating the magnetic field strength in nanotesla (20,000 nT to
100,000 nT). In addition there are 5 external 12 bit A/D channels and 1 internal A/D
channel that can be digitized and appended to the output data. This can be useful, for
instance, in digitizing an analog altimeter signal and incorporating it into the magnetometer
data stream. A Julian clock string can be enabled and added to the output data stream as
well. Finally there is an External Event pin that can be used for external trigger or event
marking.
