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Troubleshooting

This page covers common issues encountered when using FG Sensors products, including sensors, the MAG-BOARD, the FGA Logger, and the DIY Gradiometer Kit.

Sensor Issues​

No output signal from the FG-3+​

  • Verify the supply voltage is 5 V and within the ±0.25 V tolerance
  • Check that the power cable polarity is correct — reversed polarity will damage the sensor
  • Measure the output pin with an oscilloscope or frequency counter to confirm signal presence
  • Replace the sensor if no output is detected with correct power applied

Unstable or noisy sensor readings​

  • Move the sensor away from power cables, motors, transformers, and electronic equipment
  • Avoid placing the sensor near ferromagnetic materials (iron, steel)
  • Use shielded cables between the sensor and electronics
  • Ensure the sensor mounting is mechanically stable — vibration can cause reading fluctuations
  • Check the supply voltage for ripple — use a linear regulated power supply if possible

FG-3C sensor outputs 0 V or 0 kHz​

  • A constant 0 V on the analog output or 0 Hz on the frequency output indicates a hardware fault
  • Check power supply polarity and voltage
  • Verify the SELECT jumper is configured correctly for the desired output mode (frequency or UART)
  • Contact FG Sensors support if the fault persists

FG-3C UART output not working​

  • Confirm the SELECT jumper has been modified to enable UART mode (see FG-3C documentation)
  • Verify the baud rate is set to 115200 bps on the receiving device
  • Check that only one side of the SELECT jumper is connected — both sides must not be bridged simultaneously

MAG-BOARD Issues​

Display shows no values or is blank​

  • Adjust the LCD contrast potentiometer on the MAG-BOARD until text becomes visible
  • Check the LCD connector is fully seated
  • Verify the LCD voltage jumper matches the display type (5 V or 3.3 V)

Gradiometer readings are unstable or constantly changing​

  • Perform sensor alignment and calibration as described in the Calibration guide
  • Check that both sensors are oriented in the same direction
  • Ensure the sensor cables are not near power cables or other interference sources
  • Keep the system away from metal objects during operation

NULL button has no effect​

  • Verify the button is wired to the correct pin on the MAG-BOARD
  • Check that firmware version 1.3 or later is installed (earlier versions may not support NULL)
  • Re-flash the firmware if necessary

Bluetooth connectivity issues​

  • Ensure the FG Sensors Android app is up to date
  • Restart Bluetooth on your phone and re-pair the device
  • Stay within 10 meters of the MAG-BOARD during connection
  • Re-flash the firmware if Bluetooth cannot be initialized

FGA Logger Issues​

Logger does not power on​

  • Check the power source — USB-C requires 5 V ±0.25 V, DB9 input accepts 6–35 V
  • Try a different USB-C cable or power adapter
  • Verify the DB9 connector polarity if using external power

SD card not recognized or logging does not start​

  • Ensure the SD card is formatted as FAT32
  • Use SD cards between 8 GB and 32 GB
  • Re-insert the SD card firmly and restart the logger
  • Try a different SD card if the issue persists

GPS not acquiring a fix​

  • Place the GPS antenna with a clear view of the sky — avoid indoor environments or obstructed locations
  • Allow up to 2–3 minutes for initial GPS acquisition (cold start)
  • Check that the SMA antenna connector is fully tightened
  • Verify the GPS lock LED is active — a blinking LED indicates signal searching

CSV data appears corrupted or truncated​

  • Do not remove the SD card while the logger is recording — always press Stop first
  • Check the SD card for errors using a PC file system checker
  • Replace the SD card if data corruption is recurring

Logger freezes during operation​

  • Update to the latest firmware version
  • Ensure the SD card write speed is sufficient for the configured logging rate
  • Reduce the logging rate in config.txt if issues persist at 10 Hz

Gradiometer System Issues​

Gradiometer detects nothing​

  • Verify both FG-3+ sensors are properly connected and powered
  • Check the sensor cable continuity
  • Confirm the gradient value (D) on the display — press NULL to zero it in a clean magnetic environment, then sweep the instrument over the target area

Gradiometer is too sensitive or too noisy​

  • Increase the sensor spacing for better gradient resolution
  • Use the "−" button to reduce sensitivity on the MAG-BOARD
  • Perform calibration in a magnetically clean environment away from metal structures

Calibration does not hold after restart​

  • Ensure calibration screws are properly tightened and secured with hot glue
  • Re-calibrate if the instrument has been mechanically disturbed or dropped

General Advice​

提示

If you are unable to resolve an issue using this guide, contact FG Sensors support at info@fgsensors.com or reach out via WhatsApp for direct technical assistance.

  • Always use a linear regulated power supply for sensitive magnetometer measurements
  • Keep sensors and electronics away from ferromagnetic objects and strong electromagnetic fields
  • For best results, perform measurements in an area free of buried metal infrastructure