Geometrics G-823 Caesium “Cs” Vapour Magnetometer

The G-823A includes the proven high-performance G-822A cesium sensor with the ultra-small sized CM-201 Larmor counter. The CM-201 counter also includes Julian time/date, a provision to accept an external sync pulse, and six A/D converters for digitising and recording signal amplitude, radar/barometric altimeter, EM or other analog data.

The system has two outputs: the standard Larmor sine wave superimposed on 28 VDC power or the Larmor signal counted, converted into nT and output as serial data for recording by any standard computer.


Airborne and Vehicle Applications with Multi-Sensor Array Capability – Versatility is the name of the game! This instrument can be used in fixed wing, helicopter or in land applications to fit any surveyor’s needs

Highest Sensitivity – Pick up the smallest changes in magnetic field

Fast Sampling – Save money and time on large-scale surveys; detect the smallest objects

Low AC Field Interference – Survey next to power lines when necessary

Very Low Heading Error – Get very clean, repeatable measurements without fear of instrument noise impacting the data

Rugged and Reliable – Weatherproof, Survives three-foot drop onto hard surface

Ultra-stable – No need to calibrate sensors

Export Version Available – Use anywhere in the world without need for an export license (except embargoed countries). See specifications



Operating Principle: Self-oscillating split-beam Cesium vapour (non-radioactive).

Operating Range: 20,000 to 100,000 nT.

Operating Zones: The earth’s field vector should be at an angle greater than 10° from the sensor’s equator and greater than 10° from the sensor’s long axis. Automatic hemisphere switching.

Noise: <0.004 nT/√Hzrms. (SX (exportversion: <0.02 nT/√Hzrms).

Hz Heading Error: ± 0.15 nT over entire 360° equatorial and polar spins.

Max Sample Rate: 20 Hz.

Output: Cycle of Larmor frequency = 3.498572 Hz/nT, RS-232 data at 9600 baud, concatenated data streams from up to 6 sensors.

Power: 24 to 32 VDC, 0.75A at power-on and 0.5A thereafter.


Sensor: DIA: 60 mm; L: 146 mm; Weight: 0.45 kg  – any orientation in 177mm diameter stinger.

Sensor Electronics: DIA: 63 mm; L: 279 mm; 1.36 kg (2.5×11 in; 48 oz).


Sensor to electronics: Standard 2.77m with connector on electronics end. Other lengths available from 0.75 m to 3.75 m at 1 m increments. Lengths approximate due to cable variations.

Electronics to Junction Box: RS-232 to Computer, standard 8m, 60m max. Larmor to external counter with coupler over Coax, standard 10m, 50m max.


Operating Temperature: -35°C to +50°C.

Storage Temperature: -45°C to +70°C.

Altitude: Up to 9,000m.

Weatherproof: O-Ring sealed for operation in the rain and/or 100% humidity.

GradientTolerance: 500nT/in.

Temperature Drift: <0.05 nT/ oC.


Standard: Power/RS-232 multi-conductor cable (electronics to power/ data junction box with 9 pin RS-232 connector and power lugs), lengths to be specified, spare O-Rings, operation manual and carrying case.


Logging Software: MagLog (Logs GPS and Mag, shows track plot, mag profile, other data).

Accessories: Birds, Stingers, Wingtips, Avionics, GPS, Gamma Ray, Logging Computer.


G-823B: Enjoys all of the same specifications and performance as the G-823A, with the exception of a confirmed/tested heading error specification.

G-823AWL: The Larmor output capability is removed for installations that don’t utilise an external counter. “B”version also available in this model.

G-823AWL-SX: The SX designates that this model is our “Special Export” version which has a reduced sensitivity specification of 0.02nT/√Hzrms. This model does not require an export license prior to shipping.

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