Geometrics G-858 Caesium “Cs” Magnetometer MagMapper Walkmag


The G-858 MagMapper is a high-performance cesium magnetometer comprised of a belt-mounted console connected to a cesium sensor on a handheld counterbalanced staff.

Features & Benefits

Single or Dual Sensor Modes – Easily go from a single sensor survey to either a vertical or horizontal gradiometer survey.

Low Noise/High 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.

Easy-to-use Interface – Useable by inexperienced personnel.

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

Ultra-stable – No need to calibrate sensors.

Long Battery Life – Each battery pack allows for 6 hours of surveying with single sensor and 4 hours with gradiometer.

Optional Ergonomic Backpack & GPS – Upgrade to a complete survey system at any time. Provides more comfort during and after survey.

Optional Non-Magnetic Cart – Attach two or more sensors to our MagCart for large surveys looking for near- surface features.



Operating Principle: Self-oscillating split-beam Cesium Vapour (non-radio- active Cs-133) with automatic hemisphere switching.

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

Operating Zones: For highest signal-to-noise ratio, the sensor long axis should be oriented at 45°, ± 30 to the earth’s field but operation will continue through 45°, ± 35°. Sensor is automatic hemisphere switching.

Noise: < 0.008 nT/√Hzrms (SX (export) version: 0.02 nT/√Hzrms).

Heading Error: < 1.5 nT including backpack and GPS.

Gradient Tolerance: > 500 nT/in (>20,000 nT/m).

Temperature Drift: < 0.05 nT/°C.

Max Sample Rate: 10 Hz.

Data Storage: Non-volatile RAM with capacity for 8 to 12 hrs of magnetometer, time, event marks, field notes and XYZ or GPS locations.

Audio Output:

1. Audio tone of field variation; pitch and volume adjustable. (Search mode).
2. Audio pulse each 1 second (pace metronome).
3. Alarm for loss of signal, low battery or quality control setting exceeded.

Data Output: Three-wire RS-232 standard serial port, optional continuous real-time transmittal of data via RS-232 to PC. Total memory output transfer time less than 5 min at 115,200 baud.

Visual Output: 320 x 200 graphic liquid-crystal display, daylight-visible with selectable outputs for:

1. Display of up to 5 stacked profiles, real time or review mode. Survey grid showing boundaries and position.
2. All system set-up functions, e.g., memory status, data transfer, sample time.
3. All survey set-up functions, e.g., survey profile number and direction, station number or GPS data transfer protocol, line number.
4. Survey monitoring functions, e.g. total field, noise level, profile number or x-y coordinates.

Internal Clock: Resolution of 0.1 sec, drift: < 1 sec/day.

Power: 24 VDC rechargeable gel cell, 5hrs for Mag w/GPS.Magnetic effect less than 1.5 nT at 4 ft. Internal backup battery for clock and non-volatile RAM.

Operating Software:

1. Survey Modes: Search survey – Simple survey – Mapped survey, station or continuous – Base station
2. Data acquisition/display: Acquire and store data and survey functions. Display profiles, total field to 0.1 nT resolution, survey /map parameters and diagnostics.

Post-acquisition Software: MagMap software for installation on customer’s computer.

1. Data transfer and corrections:
a. Transfer of data from field Magnetometer, GPS, or Base station to PC.
b. Diurnal correction using base station data.
c. Processing the corrected data into ASCII values of X-Y-Z.

2. Data processing functions include spike editing, spline filtering, repositioning of X, Y, Z or GPS Lat/Long, conversion to UTM coordinates, profile and contour map plotting.


Sensor: DIA: 6 cm; L: 15 cm; Weight: 340 grams.

Backpack: 4.3kg.

Console: L: 28cm; W: 15cm; H: 8cm; Weight: 1.6kg. Magnetic effect less than 1 nT at 4 ft.


OperatingTemperature: -25°C to +50°C.

StorageTemperature: -35°C to +60°C.

Water Tight: Weatherproof in driving rain.

Shock: Survives a 3ft drop onto a hard surface.

Warranty: 1 year on G-858 and sensor, 1 year on accessories.

Other Models

G-858AP: Includes ergonomic backpack and Tallysman GPS.

Tallysman TW5341TM Specs:
  • Code and carrier phase tacking with 1Hz Position, velocity, time output.
  • SBAS capable and designed for harsh environments.
  • RS-232 compatible interface.

Size and Weight: DIA: 66.5mm; H: 21mm; Weight: 60 g .

Input Voltage: +9 to +16 VDC.

Power Consumption: 1.2W (typical).

Com Ports: 1RS-232 (optional 2 RS-232) at up to 19,200 baud.

Operating Temperature: -40°C to +85°C.

Position Accuracy: Single point L1 <2 m CEP; WAAS L1 <1 m CEP.

Data Rates: Measurements 1 Hz; Position 1 Hz.

Time to First Fix: Cold start 39 sec; warm start 34 sec; hot start 2.5 sec.

Signal Reacquisition: <1 sec typical.

Product Brochure

Product Brochure