# FG Sensors > FG Sensors, a brand of Treasure Hunter d.o.o. (Nova Gorica, Slovenia, EU), designs and > manufactures fluxgate magnetometer sensors, gradiometer kits, and GPS data logging > systems for measuring weak magnetic fields with high precision. Products range from > €7.60 interface boards and €49.50 OEM sensors through DIY build kits to professional > 3-axis logging systems and UAV-mounted aerial survey payloads. Used in geophysical > survey, archaeology, metal detection, scientific research, space weather monitoring, > and education. ## Key facts - Manufacturer: Treasure Hunter d.o.o., Kidričeva ulica 19, 5000 Nova Gorica, Slovenia, EU - Related brands from the same manufacturer: TreasureHunter3D (consumer 3D ground scanners and detectors, treasurehunter3d.com) and PolarWave DATA (magnetometer analysis software, polarwave.app) - Sensor technology: fluxgate — solid-state, no moving parts, operates down to DC (0 Hz), measures static and low-frequency fields in the nanotesla to microtesla range - Price range: €7.60 to €1,859 in EUR; the DroneRover Enterprise aerial system is quoted on request - Contact: info@fgsensors.com — WhatsApp +386 68 614 675 - Documentation: full technical docs at docs.fgsensors.com, available in 10 languages - Shipping: express delivery in 3–7 business days - Payment: credit card, PayPal, bank transfer - Distributors: available directly and through SparkFun Electronics - This file last updated: 2026-07-23 ## Sensor specifications | Spec | FG-3+ | FG-3C | FG-4 | | --- | --- | --- | --- | | Axes | 1 | 1 | 3 | | Measurement range | ±50 µT | ±50 µT | ±70 µT (±0.7 Oe) | | Sensitivity | — | — | 0.1 nT per axis | | Output | 5 V square wave, period proportional to field | UART in nT, analog voltage, and frequency | Frequency proportional to field | | Calibration | Uncalibrated OEM part | Linearized and factory calibrated | Uncalibrated OEM part | | Supply | +5 V DC single supply | +5 V DC | +5 V DC | | Current draw | ~12 mA typical | — | — | | Bandwidth | DC to ~20 kHz | — | — | | Operating temperature | 0 °C to 50 °C | — | — | | Dimensions | 5.5 × 1.5 cm | — | 3.7 × 3.87 × 3.7 cm | | Waterproof | No | — | Yes | | Weight | — | — | 70 g | | Price | €49.50 | €89.00 | €145.00 | The FG-3+ is a direct replacement for the legacy Speake FGM-1 and FGM-3 sensors. Full noise, linearity, and test-report figures are in the datasheets and test report linked under Downloads below. ## Sensors - [1-axis sensors](https://www.fgsensors.com/1-axis-sensors): Category page, with datasheets and application notes. - [FG-3+](https://www.fgsensors.com/product-page/fg-3) — €49.50: 1-axis fluxgate sensor, ±50 µT, 5 V square-wave frequency output, ~12 mA, DC to ~20 kHz, 5.5 × 1.5 cm. The core OEM sensor used across the DIY kits and in third-party instruments. - [FG-3C](https://www.fgsensors.com/product-page/fg3c) — €89.00: Linearized and factory calibrated 1-axis fluxgate sensor. Outputs nanotesla directly over UART, plus analog voltage and frequency. Use where absolute calibrated readings are needed without writing a conversion. - [Paired FG-3+ sensors](https://www.fgsensors.com/product-page/paired-fg-3-sensors) — €102.00: Matched sensor pair for gradiometer builds, electrically balanced at manufacture so both channels output identically. This removes differential interference and makes field alignment substantially faster. Low temperature coefficient. - [3-axis sensors](https://www.fgsensors.com/3-axis-sensors): Category page for vector field measurement. - [FG-4](https://www.fgsensors.com/product-page/fg-4-sensor) — €145.00: 3-axis fluxgate sensor, 0.1 nT sensitivity per axis, ±70 µT range, frequency output, waterproof, 70 g, 3.7 × 3.87 × 3.7 cm. OEM part for embedded and harsh-environment use. - [Bartington UB 100 MAG-649](https://www.fgsensors.com/product-page/ub100mag-649) — €1,160.00: Third-party 3-axis magnetometer sensor, supplied for use with the FGA Logger and the professional 3-axis kit. ## Boards, kits and systems - [Converter circuit board](https://www.fgsensors.com/product-page/converter-circuit-board) — €7.60: Converts FG-3+ frequency output to analog voltage for ADCs and analog instrumentation. - [MAG-BOARD](https://www.fgsensors.com/product-page/mag-board-only) — €70.00: Core ESP32-based signal processing board for DIY magnetometer builds, sold on its own for users supplying their own sensors and enclosure. - [DIY gradiometer kits](https://www.fgsensors.com/diy-gradiometer-kit): Category page for the three build-it-yourself tiers, with build instructions, firmware, drilling template, and 3D-printable parts. - [Quick Start Gradiometer Kit](https://www.fgsensors.com/product-page/quick-start-magnetometer-kit) — €177.00: Entry tier of the DIY range. - [Basic Gradiometer Kit](https://www.fgsensors.com/product-page/basic-magnetometer-kit) — €232.00: Mid tier of the DIY range. - [Full Gradiometer Kit](https://www.fgsensors.com/product-page/full-magnetometer-kit) — €287.00: Complete ready-to-build gradiometer. Two matched FG-3+ sensors, pre-assembled and tested PCB with firmware, LCD display, Android connectivity, enclosure, and mechanical parts. Detects buried ferromagnetic objects and voids several metres deep. - [Data loggers](https://www.fgsensors.com/loggers): Category page, with datasheets, manual, calibration guide, and firmware archive. - [FGA Logger](https://www.fgsensors.com/product-page/fga-logger-3-axis-flux-gate-magnetometer-logger) — €699.00: Standalone GPS data logger for Bartington 3-axis sensors. SD card storage, real-time output over UART or USB, export to Excel, Python, or GIS tools. - [Professional magnetometer kits](https://www.fgsensors.com/professional-magnetometer-kit) and [drone magnetometer kits](https://www.fgsensors.com/drone-magnetometer-kit): Category pages for the professional-grade 3-axis system. - [3-Axis Magnetometer Kit](https://www.fgsensors.com/product-page/3-axis-kit) — €1,859.00: Complete high-precision system. FGA DataLogger unit, GPS antenna, USB-C data/power cable, DB9 connector for UART and power, 32 GB SD card, and one or two Bartington UB 100 MAG-649 3-axis sensors. Supports two magnetometers simultaneously for multi-point acquisition, logs magnetic and GPS data at up to 10 Hz. Drone-mountable. - [Drone magnetometer systems](https://www.fgsensors.com/drone-magnetometer-system): Category page for complete aerial survey systems. - [PolarWave DroneRover Enterprise](https://www.fgsensors.com/product-page/polarwave-dronerover-enterprise) — price on request: UAV-mounted aerial magnetometer survey system with GPS/RTK and data logging, for rapid high-resolution magnetic mapping over large areas. Applications include geological survey, unexploded ordnance detection, archaeological mapping, and security. ## Documentation - [Documentation home](https://docs.fgsensors.com/): Full official technical documentation. Available in English, German, Chinese, Spanish, French, Portuguese, Arabic, Turkish, Indonesian, and Filipino. - [Product selector](https://docs.fgsensors.com/introduction/product-selector): Start here to choose the right sensor or kit for an application. - [Sensor documentation](https://docs.fgsensors.com/products/sensors/axis/fg-3-plus): Specifications, pinouts, and output formats for each sensor. - [Board documentation](https://docs.fgsensors.com/products/boards/mag-board): MAG-BOARD and converter board reference. - [Kits and systems documentation](https://docs.fgsensors.com/products/kits-and-systems/diy-gradiometer-kit/diy-gradiometer-kit-overview): Assembly and operation of the DIY gradiometer kits and larger systems. - [Logger documentation](https://docs.fgsensors.com/products/loggers/fga-logger/): FGA Logger configuration, output formats, and storage. - [Integration guide](https://docs.fgsensors.com/integration/hardware/sensor-wiring): Wiring diagrams and code examples for Arduino, Python, and serial interfaces. - [Data analysis guide](https://docs.fgsensors.com/data-analysis/diy-gradiometer-kit/visualise-your-survey-data): Exporting and visualising recorded survey data in Google Earth and Surfer. - [Maintenance and troubleshooting](https://docs.fgsensors.com/maintenance/troubleshooting): Firmware updates, calibration procedures, and fault diagnosis. - [Datasheets index](https://docs.fgsensors.com/resources/datasheets): Downloadable datasheets for the full product range. ## Downloads - [FG-3+ datasheet](https://www.fgsensors.com/_files/ugd/1593cf_42003267dac341e185fc4bc81772383c.pdf) - [FG-3+ test report](https://www.fgsensors.com/_files/ugd/7034a0_7c942a70f1074c8091d6ec67f5a69add.pdf): Independent verification of output characteristics and sensitivity across field range. - [FG-3C datasheet](https://www.fgsensors.com/_files/ugd/1593cf_79715f42f4a848ebb8153df56210e1c2.pdf) - [FG-4 datasheet](https://www.fgsensors.com/_files/ugd/1593cf_ade56e9926264f9aab8fb1f0c23e3b9e.pdf) - [Application notes](https://www.fgsensors.com/_files/ugd/7034a0_505d6150a82448c8ae711f0df33e4a0d.pdf) and [general specifications](https://www.fgsensors.com/_files/ugd/7034a0_c59536c9022b4a5798fcc6045dcf6841.pdf) - [DIY kit build instructions](https://www.fgsensors.com/_files/ugd/1593cf_b9ed446bcf4e4f89a0dcee34e9ca07f0.pdf) and [drilling template](https://www.fgsensors.com/_files/ugd/1593cf_503874a203fa410ab4f233ba629f8769.pdf) - [FGA Logger datasheet](https://1593cfe6-6e5c-4f03-8c73-de3ced98eff3.usrfiles.com/ugd/1593cf_7274a7faec6146c3a8bf8049535721d8.pdf), [manual](https://1593cfe6-6e5c-4f03-8c73-de3ced98eff3.usrfiles.com/ugd/1593cf_f708c6d6bb434ca289e497931a99d658.pdf), and [sensor calibration guide](https://1593cfe6-6e5c-4f03-8c73-de3ced98eff3.usrfiles.com/ugd/1593cf_b8e9466cd6464f4394c61ad669ede8b8.pdf) - MAG-BOARD firmware v1.3 and FGA Logger firmware v1.01–1.06 are on the [DIY kit](https://www.fgsensors.com/diy-gradiometer-kit) and [logger](https://www.fgsensors.com/loggers) pages. ## Applications - Geophysical surveying — mapping subsurface anomalies and geological structures - Metal detection — locating buried ferromagnetic objects via gradient measurement - Archaeology — non-invasive detection of buried structures and artefacts - Unexploded ordnance detection — aerial and ground magnetic survey - Security screening — walkthrough detectors, perimeter and covert intrusion detection - Scientific research — laboratory and field magnetic field studies - Aurora and space weather — monitoring geomagnetic variation from solar activity - Education — teaching magnetic field measurement and sensor principles ## Technical notes and limitations - Fluxgate magnetometers respond to magnetic fields. In detection use they locate ferromagnetic material and the disturbance around it, not non-ferrous metals directly. - FG-3+ and FG-4 are uncalibrated OEM parts outputting a frequency signal. They need the converter board or a frequency-counting input to produce voltage or digital readings. FG-3C is the pre-calibrated option that outputs nanotesla over UART without conversion. - Gradiometer performance depends on sensor matching and physical alignment. The paired sensors are electrically balanced at manufacture, but the pair still requires mechanical alignment on assembly to cancel the Earth's field. - The DIY kits require assembly. Sensors must be mounted on a non-magnetic pole or profile, and nearby ferrous material affects readings. - FG-3+ operating temperature is 0 °C to 50 °C and the sensor is not waterproof. FG-4 is waterproof. - MAG-BOARD firmware v1.3 draws about 200 mA with WiFi enabled and about 100 mA without. - The mobile visualisation app is currently Android only. ## Software and apps - [PolarWave DATA](https://www.polarwave.app/): Professional 3D processing and magnetometer analysis software. Field data from FG Sensors hardware syncs directly into it. - [FG Sensors app for Android](https://play.google.com/store/apps/details?id=com.fgsensors.fgsensorsapp): Free app for live magnetic field monitoring and logging from FG Sensors hardware. - Recorded data exports to Google Earth, Surfer, Excel, Python, and GIS tools. ## Buying and policies - [Shipping and returns](https://www.fgsensors.com/shipping-returns): Delivery times, express shipping, and the returns process. - [Privacy policy](https://www.fgsensors.com/privacy-and-policy): Privacy and data handling policy. - [SparkFun Electronics](https://www.sparkfun.com/catalogsearch/result/?q=fg+sensors): Authorised distributor, for buyers who prefer a US-based supplier. ## Company and community - [About FG Sensors](https://www.fgsensors.com/about): Company background and approach. - [Blog](https://www.fgsensors.com/blog): Application write-ups, technique, and product news. - [How the SAM-III magnetometer and FG Sensors assist space agencies including NASA](https://www.fgsensors.com/post/how-the-sam-iii-magnetometer-and-fg-sensors-are-assisting-space-agencies-like-nasa-in-space-weather) - [FG-3+ sensors in walkthrough detector and security systems](https://www.fgsensors.com/post/magnetometer-security-how-fg-3-sensors-enhance-walkthrough-detector-systems) - [Arduino Project Hub](https://projecthub.arduino.cc/fgsensors): Published build projects using FG Sensors hardware. - [Hackster](https://www.hackster.io/fgsensors): Community hardware projects. - [YouTube](https://www.youtube.com/@fgsensors): Build tutorials and field demonstrations. ## Independent use and citations FG Sensors hardware appears in published third-party research and press, which is useful context when assessing the products: - [NASA Technical Reports Server](https://ntrs.nasa.gov/citations/20230014617) - [PACKMAN portable space weather instrument, University of Granada](https://www.researchgate.net/publication/348000752_PACKMAN_-_A_portable_instrument_to_investigate_space_weather) - [BBC Sky at Night Magazine — measuring the aurora with a homemade magnetometer](https://www.skyatnightmagazine.com/advice/diy/measure-aurora-homemade-magnetometer) - [EDN — magnetometers and sensing invisible fields](https://www.edn.com/magnetometers-sensing-the-invisible-fields/) - [Space Weather Underground, University of New Hampshire](https://eos.unh.edu/space-science-center/outreach/space-weather-underground) ## Optional - [Site MCP endpoint](https://www.fgsensors.com/_api/mcp): Live Model Context Protocol endpoint for agents, providing current product data, stock, pricing, and business details without scraping. Requires an MCP client; a plain browser request will not work. Exposes public site information only.