Geometrics, Inc. G-822/G-823 Magnetometer Manual
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on this cable is greater than 1 V p-p, coupling noise onto this cable by running it near an
electric motor may still reduce performance.
Temperature
The G-822A is designed to operate over an ambient temperature range of -35 to +50°C.
In an enclosed region it may be necessary to providing adequate cooling by free flowing
air. If the sensor and electronics are in an unconfined region, convection cooling is
generally adequate. The cesium lamp only needs to dissipate 3 to 4 watts of heat and
when operating in cold regions providing some insulation or baffling will help reduce the
sensor’s power consumption.
The G-822A requires a minimum warm up period of 15 minutes. In cold regions the
warm up period will be longer and, to avoid delay, we recommend that the sensor power
be left on overnight when ambient temperatures are expected to fall below -10°C.
5.0 OPERATION
The G-822A produces an analog output signal on the BNC connector of its sensor driver
module. Because this BNC connection also serves as the power input connection it is
necessary to decouple the power from the output signal. The circuit shown in Figure 11
shows a simple decoupling circuit. The output is the Larmor signal and it is a sinusoidal
wave with a peak-to peak amplitude of approximately 2.0 volts and a frequency that will
vary from 70kHz to 350kHz in accordance with the local magnetic field (Cesium oscillator
frequency is 3.498572 Hz per nT). This signal can be observed by attaching the output of
the signal decoupler to an oscilloscope. To be useful as a survey instrument the G-822A’s
Larmor signal must be converted into a digital data stream and this is done by attaching a
counter to the output of a the decoupler circuit.
Figure 11. Signal decoupler circuit
