Magnetometer

DSES is building a SAM III (Sensitive Amateur Magnetometer). It was developed by Stuart Wier and others for SARA, this fluxgate magnetometer can detect magnetic storms and variations from auroras.

SAMIII is an Induction Coil Magnetometer, as described below.

🧭 1. Types of Magnetometers

a. Fluxgate Magnetometers

  • Common in professional and educational setups.
  • Measure the direction and strength of magnetic fields using a ferromagnetic core driven by an AC signal.
  • DIY designs often use op-amps, ferrite cores, and differential amplifiers.
  • Example project: SAM (Sensitive Amateur Magnetometer) from the Society of Amateur Radio Astronomers (SARA).

b. Induction Coil Magnetometers (Search-Coil Type)

  • Detect variations (not absolute levels) in the magnetic field—useful for observing geomagnetic pulsations or Schumann resonances.
  • Simpler construction: a large coil of wire and an amplifier.
  • Often used in Radio JOVE and other low-frequency radio science projects.

c. Hall Effect Magnetometers

  • Use Hall-effect sensors (like the popular Honeywell SS495A) to measure magnetic flux directly.
  • Easy to interface with microcontrollers (Arduino, Raspberry Pi).
  • Limited sensitivity compared to fluxgate or proton precession types, but good for educational purposes.

d. Proton Precession Magnetometers

  • Based on nuclear magnetic resonance; very sensitive and can measure the absolute field strength (~50,000 nT range).
  • DIY builds require precise timing electronics and are more complex, but instructions are available in amateur geophysics forums.

What is SAM / SARA SAM (Sensitive Amateur Magnetometer / Simple Aurora Monitor)

Specifications & architecture

From the SAM-III construction manual and descriptions:

ParameterTypical / approximate value
Magnetic induction (field) measurement range± 50,000 nT (i.e. ±50 microtesla) UNH Earth, Oceans, and Space Institute+1
Resolution~1 to 2 nT UNH Earth, Oceans, and Space Institute+1
Number of sensors supported1, 2, or 3 (i.e. you can choose to deploy only a subset of axes) UNH Earth, Oceans, and Space Institute
Microcontroller / electronicsUses a PIC16F877 microprocessor (or variant) for signal processing, control, and data output UNH Earth, Oceans, and Space Institute
Display / user interfaceBacklit 4×20 LCD, with keyboard (buttons) for mode, calibration, etc. UNH Earth, Oceans, and Space Institute+1
Data interfaceSerial (EIA-232) interface output as ASCII text / logging UNH Earth, Oceans, and Space Institute+2FG sensors+2
Alarm / analog outputProvides analog output proportional to K-index (configurable 0 to +5 V, or –2.5 to +2.5 V) and a relay for K-index threshold alarm UNH Earth, Oceans, and Space Institute+1
Real-time clockSupports RTC with battery backup UNH Earth, Oceans, and Space Institute
Power12 V DC, with current draw ~60 to 100 mA (depending on how many sensors are active) UNH Earth, Oceans, and Space Institute+1
Physical / mechanicalThe controller + display + enclosure are ~200 × 112 × 64 mm (nominal) in suggested form factor UNH Earth, Oceans, and Space Institute+1
Sensor typeThe sensors are fluxgate magnetometer sensors (from Speake & Co, commonly used type) UNH Earth, Oceans, and Space Institute+2FG sensors+2

Notes / caveats:

  • The sensors are sensitive and subject to environmental influences. In the manual, it’s stressed that tiny movements or nearby metallic objects will alter readings. UNH Earth, Oceans, and Space Institute+1
  • Sensor cable layout and wiring are important to reduce crosstalk (signals from one axis coupling into others) and noise. One mitigation is to convert unbalanced sensor outputs into differential (balanced) signals for transmission over twisted pair cables (e.g. TIA-422 style) to reduce interference. Society of Amateur Radio Astronomers+1
  • The SAM-III is designed in kit / DIY format; you or an organization assemble the boards, mount sensors, and do calibration. UNH Earth, Oceans, and Space Institute+2Steve’s Open Lab+2
  • Temperature effects: the sensors are temperature-sensitive; the SAM-III does not inherently include temperature compensation (beyond perhaps relative compensation) in many versions. UNH Earth, Oceans, and Space Institute

Uses and roles / network / projects

The SAM / SARA SAM (SAM-III) is not just a standalone instrument — it participates in networked or distributed measurement and has roles in educational and citizen science.

  • The Space Weather Underground (SWUG) project is one such network / initiative using SAM-III magnetometers deployed across schools, amateur networks, etc. The idea is to build distributed magnetometer coverage to observe ionospheric currents, magnetic disturbances, and auroral phenomena. scientia.global
    • In SWUG, schools build or deploy SAM-III units, mount the sensors properly (e.g. in PVC tubes underground to stabilize temperature and orientation), and then feed data to a central site. scientia.global
    • In one test, SAM-III units spaced ~20 km apart detected a magnetic disturbance in concert, showing that even these “amateur” instruments can pick up real geophysical signals. scientia.global
    • The SWUG design calls for sampling intervals on the order of every 2 seconds (though SAM-III could do faster) in this deployment mode, to manage reliability and noise. scientia.global
    • To ensure synchronization across widely distributed units, GPS time stamping is used (or recommended) because the onboard RTC can drift by up to a second per day. scientia.global
    • Placement considerations: the magnetometers must avoid magnetic interference (from power lines, infrastructure), so remote or “quiet” sites are preferred. scientia.global
  • Aside from SWUG, SAM-III is used by aurora photographers, radio amateurs, and magnetism enthusiasts to sense geomagnetic storms, monitor K-index, generate alerts, or integrate with other propagation / aurora prediction tools. FG sensors+2Society of Amateur Radio Astronomers+2
  • Some amateur radio astronomy / SARA conferences report work on mitigating sensor crosstalk, calibrating, and improving the SAM-III in field conditions. Society of Amateur Radio Astronomers
  • As a lower-cost alternative to expensive professional geomagnetic observatories, SAM-III enables broader spatial coverage and “many more measurement points” even if each point has lower absolute precision. The philosophy is that more low-cost sensors can sometimes outperform fewer super-high precision ones in terms of capturing large-scale phenomena. scientia.global+2FG sensors+2

Strengths, limitations, and what to watch out for

Strengths

  • Affordability / accessibility — The SAM-III is much cheaper than professional geomagnetic observatory systems, yet good enough for many space weather / ionospheric phenomena. scientia.global+2FG sensors+2
  • DIY / kit format — Users can build it themselves, facilitating learning, customization, repairability. Steve’s Open Lab+2UNH Earth, Oceans, and Space Institute+2
  • 3-axis capability — Having full vector measurements (X, Y, Z) is very useful for interpreting complex geomagnetic phenomena. UNH Earth, Oceans, and Space Institute+1
  • Networking potential — Because many units can be deployed, spatial and temporal correlation of events is possible (e.g. by SWUG) to infer propagation speeds, direction of currents, etc. scientia.global
  • Alarms and real-time outputs — The system has outputs to trigger alarms or feed to external systems (analog, relay) based on magnetic activity thresholds. UNH Earth, Oceans, and Space Institute+1

Limitations / challenges

  • Sensor noise / environmental interference — Nearby metallic objects, currents, infrastructure, and even cable layout can disturb measurements. Users must carefully site sensors. UNH Earth, Oceans, and Space Institute+1
  • Crosstalk between axes — Because multiple sensor signals are carried, interfering coupling is a risk. Good design (balanced transmission, shielding) is needed. Society of Amateur Radio Astronomers+1
  • Temperature sensitivity — Without built-in advanced compensation, measurement drift or bias may occur with temperature variation. UNH Earth, Oceans, and Space Institute
  • Time accuracy / synchronization — The internal clocks (RTC) drift, so especially in networked arrays, GPS time stamping or periodic correction is necessary for high-quality inter-station correlation. scientia.global
  • Resolution / dynamic range tradeoff — Because it’s designed for amateur / semi-professional use, there are limits on how fine-scale or high-frequency phenomena it can resolve compared to top-tier instruments. E.g. very high frequency or extremely low amplitude variations might be beyond its sensitivity.
  • Maintenance / calibration — As a kit instrument, long-term stability, recalibration, and repair are user responsibilities.

Example deployment & use case

One illustrative use is from the SWUG project:

  • Schools build or receive SAM-III units, mount the sensors in PVC “trees” or structures to ensure stable orientation and thermal isolation, install them underground (or in thermally stable environment) to avoid freezing / overheating. scientia.global
  • A solar panel + battery powers the system autonomously. scientia.global
  • The sensor reads magnetic field values at, e.g., every 2 seconds, tags each measurement with a GPS-derived timestamp, and transmits to a local Raspberry Pi or data logger at the site. scientia.global
  • The data from many distributed sites are aggregated to map how geomagnetic disturbances propagate in time and space, infer ionospheric current behavior, and correlate with solar / space weather events. scientia.global
  • The project also offers educational opportunity: students build, install, monitor, analyze magnetometer data, correlate with aurora / radio propagation phenomena, etc. scientia.global+1

In one demonstration, SAM-III devices spaced ~20 km apart detected concurrently a magnetic disturbance lasting ~1 hour. This suggests that even “amateur-grade” systems can detect meaningful geophysical signals when properly deployed and synchronized. scientia.global